Formation of the Yandangshan volcanic–plutonic ...

Lithos 266–267 (2016) 287–308

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Formation of the Yandangshan volcanic–plutonic complex (SE China) by melt extraction and crystal accumulation Li-Li Yan a,b, Zhen-Yu He b,⁎, Bor-ming Jahn c, Zhi-Dan Zhao a a b c

School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Department of Geosciences, National Taiwan University, Taipei 106, Taiwan

a r t i c l e

i n f o

Article history: Received 9 June 2016 Accepted 22 October 2016 Available online 29 October 2016 Keywords: Volcanic–plutonic complex Magmatic differentiation Zircon Hf–O isotopes Yandangshan caldera SE China

a b s t r a c t The association of volcanic and shallow plutonic rocks in caldera may provide important clues to the geochemical evolution of silicic magma systems. The Yandangshan caldera is a typical example of late Mesozoic volcanic– plutonic complex in SE China. It is composed of a series of rhyolitic extrusives and subvolcanic intrusions of porphyritic quartz syenites. In this work, we conducted petrological and geochemical studies, as well as zircon dating, on the coexisting volcanic and plutonic rocks from the Yandangshan caldera. The results of SHRIMP and LA-ICP-MS zircon U–Pb dating revealed that the crystallization of the rhyolitic extrusives and subvolcanic intrusions was contemporaneous within analytical errors and in a short period (104–98 Ma). Geochemically, the volcanic rocks are characterized by high Rb/Sr and Rb/Ba ratios and depletion in Ba, Sr, P, Eu and Ti, while the shallow plutons show high K, Ba, Al, Fe and low Rb/Sr and Rb/Ba ratios with insignificant negative Eu anomalies. The volcanic and plutonic rocks have a similar range of zircon Hf isotopic compositions (εHf(t) = −10.0 to +1.5) and TDM2 model ages of 2.10–1.23 Ga. They also have comparable whole-rock Sr and Nd isotopic compositions ((87Sr/86Sr)i = 0.7084–0.7090; εNd(t) = −7.8 to −6.5) and zircon oxygen isotopic compositions (δ18O mainly = 4.5 to 6.0‰). We argue that the volcanic–plutonic complex of the Yandangshan caldera was formed by reworking of Paleoproterozoic lower crusts in the eastern Cathaysia block, and that the complex could be linked by fractional crystallization and crystal accumulation in a shallow magma chamber. The volcanic rocks represent the highly fractionated end-member, whereas the subvolcanic intrusions of porphyritic quartz syenites could be the residual crystal mushes. This case study could have a general implication for the genetic relationship between volcanic and shallow plutonic rocks in calderas. © 2016 Elsevier B.V. All rights reserved.

1. Introduction The genetic relationship between silicic plutonic and volcanic rocks has long been debated, but it is fundamental to complete understanding of the geochemical evolution of silicic magma systems (Glazner et al., 2015; Lundstrom and Glazner, 2016; Ustiyev, 1965). Some authors considered plutonic rocks to be compositionally equivalent to associated volcanic rocks, and further argued that the plutonic and volcanic rocks formed by different processes; that is, large caldera-forming ignimbrite eruptions formed by rapid magmatic input, whereas large plutons were constructed incrementally over millions of years in response to lower thermal flux (Annen, 2009; de Silva and Gosnold, 2007; Glazner et al., 2004, 2015; Reubi and Blundy, 2009). By contrast, other workers proposed that volcanic rocks are produced by extraction of fractionated melt from crystal mushes, and plutons represent cumulates left behind ⁎ Corresponding author at: Institute of Geology, CAGS 26, Baiwanzhuang Road, Beijing 100037, China. E-mail address: [email protected] (Z.-Y. He).

http://dx.doi.org/10.1016/j.lithos.2016.10.029 0024-4937/© 2016 Elsevier B.V. All rights reserved.

after eruption of volcanic magma (Bachmann and Bergantz, 2004; Bachmann et al., 2007; Eichelberger et al., 2006). This hypothesis predicts silicic volcanic rocks to have a more pronounced crystal fractionation signature than their plutonic equivalents. In addition to the two hypotheses above, some authors considered that the genetic relationship between granitic and volcanic rocks varies according to the primary magma type (S- or I-type) (Kemp et al., 2008; Wyborn and Chappell, 1986). However, there is a general consensus that shallow plutons in large silicic calderas have a genetic link with the coexisting volcanic rocks. This is supported by field observations, similar ages and comparable or complementary compositions (Bachmann et al., 2007; Glazner et al., 2004; Lipman, 1984, 2007; Ustiyev, 1965). The eruptions commonly partially evacuate the magma chamber, leaving behind the remnants of magma chamber as associated shallow plutons (Lipman, 1984, 2007; Smith and Bailey, 1966). Multiple collapse and erosion of calderas give rise to a continuum of volcanic–plutonic rock connections in the upper-crust, which record multi-stage histories of magma accumulation, fractionation, mixing, replenishment and solidification (Cole

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et al., 2014; Lipman, 1984, 2007). Therefore, the relationship between caldera volcanism and related shallow plutonism is important for the understanding of the nature and evolution of the mid- to upper crustal magma system (e.g., Lundstrom and Glazner, 2016; Müller et al., 2005; Tappa et al., 2011; Zimmerer and McIntosh, 2012). Intensive Cretaceous volcanisms are widespread along the coastal area of SE China, which constitute a great portion of the Mesozoic Circum-Pacific magmatic belt and are believed to have been produced in response to the subduction of the paleo-Pacific plate (Fig. 1; Chen et al., 2008a, 2008b; He and Xu, 2012; Jahn, 1974; Zhou et al., 2006). Shallow intra-caldera plutons exposed in deeply eroded volcanic fields and associated volcanic rocks, together with some coeval large granitic plutons, constitute a large-scale volcanic–plutonic complex belt extending about 2000 km and 400 km wide in SE China (Wang et al., 2000; Zhou et al., 2006). Previous studies suggested that the volcanic rocks and subvolcanic plutons within a caldera were co-magmatic, and their compositional difference was interpreted to result from progressively deeper tapping of a stratified magma chamber, with highSiO2 magma at the top and low-SiO2 magma at depth (Wang et al., 2000; Xing et al., 2008). This is similar to the model proposed by Smith and Bailey (1966) and Lipman (1984), i.e., rhyolitic magma erupted from an upper level, while the non-erupted magma frozen as intra-caldera plutons. However, detailed assessment of the relationship between volcanic and shallow plutonic rocks has only received minimal attention. The Yandangshan caldera is characterized by voluminous rhyolitic rocks in association with porphyritic quartz syenites. This provides the best example of the late Mesozoic volcanic–plutonic complex in SE China. In this study, we conducted petrographic study, zircon U–Pb– Hf–O isotope analyses and whole-rock geochemical and Sr–Nd isotopic analyses of the Yandangshan volcanic–plutonic complex. We used the data to constrain their crystallization ages, nature of the magma sources

and magmatic differentiation, and finally assess the genetic relationship between the volcanic and plutonic rocks. 2. Geological background The South China Craton comprises two major Precambrian continental blocks: the Yangtze block in the northwest and the Cathaysia block in the southeast. The two blocks are sutured by the Neoproterozoic Jiangnan Orogen (Fig. 1; Chen and Jahn, 1998; Wang et al., 2013; Zhao, 2015). The Cathaysia block may be further divided into an interior (western Cathaysia) and a coastal (eastern Cathaysia) tectonic units with different crustal development (see Chen and Jahn, 1998; Xu et al., 2007; Yu et al., 2012). Precambrian granites and highgrade metamorphic rocks in the eastern Cathaysia occur widely in the Wuyishan area (southern Zhejiang and northwestern Fujian Provinces) with intrusive ages or original depositional ages of Paleoproterozoic to Neoproterozoic, which are intruded by early Paleozoic and late Mesozoic granites, or covered by Paleozoic sediments and late Mesozoic volcanic rocks (Chen and Jahn, 1998; Yu et al., 2012). The Cretaceous volcanic–plutonic complex belt in SE China is mainly located in the eastern Cathaysia block (Chen et al., 2008a; Jahn, 1974; Xing et al., 2008; Zhou et al., 2006). The volcanic rocks are exposed widely with a total area about 90,000 km2, which is almost twice that of the coeval intrusive rocks (Fig. 1; Chen et al., 2008a, 2008b; Zhou et al., 2006). The volcanic rocks were traditionally divided into the lower and upper volcanic series, separated by a ubiquitous regional unconformity (He and Xu, 2012; Lapierre et al., 1997; Liu et al., 2012). The lower volcanic series contains mainly rhyolitic and dacitic rocks with sporadic andesite and basalt. They were emplaced from 140 to 110 Ma. The upper series comprises predominant rhyolite and minor basalt. They were emplaced during 110–85 Ma (Chen et al., 2008a, 2008b; He and Xu, 2012; Lapierre et al., 1997; Liu et al., 2012).

Fig. 1. Simplified geological map of SE China showing the distribution of Late Mesozoic granite-volcanic rocks (modified from Zhou et al., 2006).

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second volcanic unit is approximately 500 m thick, composed mainly of rhyolite with porphyritic massive, perlitic or flow-banded structures (Fig. 3b). In some places, it contains distinctive zones rich in spherulites and lithophysae (Fig. 3c and d), which are interpreted to be hightemperature crystallization domains of silica-rich lava and welded ignimbrites (Breitkreuz, 2013). Minor rhyolitic welded crystal tuff and autobrecciated rhyolite were locally observed. The third volcanic unit, about 380 m-thick, is dominated by rhyolitic lapilli tuff and interlayered rhyolite (Fig. 3e). The fourth volcanic unit is dominated by rhyolitic welded crystal-vitric tuff with a thickness over 300 m and it crops out in the innermost of the caldera. The rock has a distinctive appearance of well-developed columnar jointing and eutaxitic texture (Fig. 3f and g). Dark mafic enclaves with ellipsoidal and banded form are locally observed (Fig. 3g). In the NE side of the caldera, the fourth volcanic unit is cut by subparallel basic dykes (Fig. 3f). Porphyritic quartz syenite is emplaced in the center of the caldera, exposed as three individual intrusive bodies, i.e., Luochuan, Shanqiaotou and Baigangjian bodies, with exposed areas of 18, 27 and 10 km2,

The Yandangshan caldera is situated in the famous Yandangshan Geopark of Zhejiang Province. This caldera is bounded by inferred ring-faults with a diameter of ca. 25 km (Fig. 2a). The northern part has an angular unconformity or fault contact with early Cretaceous volcanic complexes, while the eastern part cuts older volcanic domes. The volcanic–plutonic complex is composed of four volcanic lithofacies units and several syenitic subvolcanic intrusions (Fig. 2a; Feng et al., 1997; He et al., 2009; Yu et al., 2008). Each volcanic unit represents a main eruption event followed by a period of caldera collapse. The volcanic units, from the first to the fourth unit, are annularly distributed from exterior to interior and vertically distributed from base to top (Fig. 2b and c). The eruption products are mainly pyroclastic and lava flows. Some lava domes or dykes were also developed at the edge or the center of the caldera along the ring fault. The first volcanic unit comprises pyroclastic-flow deposits in the SE and NE parts of the caldera, with a thickness of ~360 m. The dominant rock type is rhyolitic welded crystal-lapilli tuff, which typically displays well-developed eutaxitic texture (Fig. 3a). Minor agglomeratic breccia crops out locally. The

120°50´E

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(a)

Ky 2 Ky

Ky

28°27´N

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Ky

1

Yangtan K1g

Ky

1

4

Dianling

Ky 4

Xiyuan Ky

Q

4

Nange

Luochuan

Xiaao

Ky

Shanqiaotou

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Ky

Ky 2

Ky 3

(b)

Zhuangwu

Hesheng

4

Baigangjian Ky

Fangdong Ky

4

Ky 0

2

Ky 28°20´N Ky 1 Ky

2 km

Ky 3

4 The second volcanic unit Ky

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The third volcanic unit

Porphyritic quartz syenite

The fourth volcanic unit K1g

Early Cretaceous volcanic rocks

Yandang Town

Dalongqiu

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The first volcanic unit

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Porphyritic rhyolite

Lava dome

Fault

Quaternary

Inferred caldera rim

Sample location

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Welded crystal vitric tuff (Ky4) 130°

4

U

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U U U U U U U

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U U U U U

Baigangjian 102 ±2–98 ±1 Ma

U U

U U U U

U U U U

U U

m

99 ±2 –98 ±2 Ma

Fangdong

Ky

Shanglingyan

3

103±2 Ma

Ky 2 102 ±2

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Ky

Autobrecciated rhyolite

m

Rhyolitic lapilli tuff (Ky )

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Rhyolite (Ky )

Rhyolitic vitric tuff

Rhyolite U U UU

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Rhyolitic crystal-lapilli tuff Rhyolitic lapilli tuff

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–99 ±2 Ma m m

3

m m

0

U U UU

Rhyolitic crystal-vitric tuff Porphyritic quartz syenite

Fig. 2. (a) Geological sketch map of the Yandangshan caldera. (b) Geological profile along Shanglingyan–Baigangjian, showing emplacement ages of the Yandangshan volcanic–plutonic complex. (c) Field photograph illustrating the vertical sequences of the Yandangshan volcanic rocks.

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a

b

c

d

e

f

g

h

Fig. 3. Field photographs of the Yandangshan volcanic–plutonic complex. (a) Rhyolitic welded crystal-lapilli tuff (the first volcanic unit) with flattened fiamme. (b) Rhyolite from the second volcanic unit with flow structure. (c) Spherulite-rich rhyolite from the second volcanic unit. (d) Rhyolite from the second volcanic unit with lithophysae-rich domain. (e) Rhyolitic lapilli tuff and the rhyolite layer of the third volcanic unit. (f) Rhyolitic welded crystal-vitric tuff of the fourth volcanic unit with well-developed columnar jointing. (g) Mafic enclave-bearing rhyolitic welded crystal-vitric tuff of the fourth volcanic unit. (h) Mafic microgranular enclave and the host porphyritic quartz syenite.

Table 1 Representative electron microprobe analyses of minerals (wt.%). Unit

The first unit

The second unit

The third unit

The fourth unit

Lithology

Rhyolitic welded crystal-lapilli tuff

Rhyolite

Rhyolitic lapilli tuff

Rhyolitic welded crystal-vitric tuff

Mineral

Cpx

Bt

Pl

Afs

Afs

Afs

Bt

Or

Afs

Bt

Cpx

Amp

Pl

Afs

Cpx

Afs

Afs

Pl

Pl

Amp

Cpx

Bt

Pl

Afs

SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2 O Total Si Al Fe3+ Ti Fe2+ Mn Mg Ba Ca Na K Cations Ab An Or

52.24 0.24 0.79 8.64 1.14 14.89 21.54 0.43 − 99.95 1.94 0.04 0.10 0.01 0.17 0.04 0.83 0.00 0.86 0.03 0.00 4.00

38.37 5.71 13.04 12.33 0.40 15.67 0.06 0.75 8.65 95.01 2.88 1.15 0.00 0.32 0.77 0.03 1.75 0.00 0.01 0.11 0.83 7.84

58.88 − 25.44 0.34 0.01 0.01 7.42 6.58 0.63 99.34 2.65 1.35 0.00 0.00 0.01 0.00 0.00 0.00 0.36 0.57 0.04 4.98 59.3 37.0 3.7

65.61 0.02 17.83 0.03 − − − 0.27 16.00 99.78 3.03 0.97 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.94 4.97 2.5 0.0 97.5

67.19 − 16.54 0.08 0.02 0.00 0.02 0.19 15.19 99.29 3.10 0.90 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.89 4.91 1.9 0.1 98.0

65.91 0.02 21.76 0.73 0.08 0.07 0.22 8.65 2.40 99.87 2.91 1.13 0.00 0.00 0.03 0.00 0.01 0.00 0.01 0.74 0.14 4.96 83.6 1.1 15.3

35.96 0.03 20.44 9.99 2.50 17.03 0.13 0.01 2.90 89.02 2.59 1.73 0.00 0.00 0.60 0.15 1.83 0.00 0.01 0.00 0.27 7.18

65.22 0.01 17.70 0.03 − − 0.02 0.28 16.49 99.84 3.02 0.97 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.98 4.99 2.5 0.1 97.4

67.58 − 18.75 0.13 − 0.12 0.29 7.52 4.61 99.22 3.01 0.99 0.00 0.00 0.01 0.00 0.01 0.00 0.01 0.65 0.26 4.94 70.2 1.5 28.3

35.97 6.64 14.08 16.01 0.74 13.90 − 0.65 8.24 96.23 2.69 1.24 0.00 0.37 1.00 0.05 1.55 0.00 0.00 0.09 0.79 7.78

52.51 0.28 0.91 8.56 1.36 14.30 21.37 0.61 − 99.94 1.95 0.04 0.08 0.01 0.19 0.04 0.79 0.00 0.85 0.04 0.00 4.00

47.69 1.08 5.10 12.48 1.52 15.60 10.97 2.24 0.76 97.46 7.00 0.88 0.43 0.12 1.11 0.19 3.41 0.00 1.72 0.64 0.14 15.63

57.29 − 26.02 0.39 0.02 0.00 9.49 5.70 0.41 99.33 2.59 1.39 0.00 0.00 0.02 0.00 0.00 0.00 0.46 0.50 0.02 4.98 50.8 46.7 2.4

66.73 0.04 17.72 0.29 − 0.01 0.17 3.39 11.42 99.81 3.04 0.95 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.30 0.66 4.97 30.8 0.8 68.4

52.71 0.27 1.28 9.19 1.52 13.50 20.64 0.74 0.02 99.88 1.97 0.06 0.05 0.01 0.24 0.05 0.75 0.00 0.83 0.05 0.00 4.00

65.11 0.02 18.39 − 0.02 − − 0.11 16.30 99.98 3.01 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.96 4.98 1.0 0.0 99.0

68.83 0.01 19.53 0.02 0.03 − 0.61 10.88 0.04 99.96 3.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.92 0.00 4.96 96.8 2.9 0.2

54.04 0.05 28.96 0.23 0.03 − 11.03 4.87 0.31 99.56 2.45 1.55 0.00 0.00 0.01 0.00 0.00 0.00 0.54 0.43 0.02 4.99 43.6 54.6 1.8

60.75 0.02 24.28 0.25 0.01 0.01 5.78 7.47 0.95 99.57 2.72 1.28 0.00 0.00 0.01 0.00 0.00 0.00 0.28 0.65 0.05 4.99 66.2 28.3 5.5

41.81 5.00 11.56 11.61 0.18 13.27 11.30 2.53 0.93 98.19 6.17 1.83 0.12 0.56 1.32 0.02 2.92 0.11 0.72 0.61 0.18 14.55

50.29 1.18 4.30 7.75 0.18 14.47 20.76 0.36 0.00 99.49 1.87 0.19 0.03 0.03 0.22 0.01 0.80 0.00 0.83 0.03 0.00 3.99

37.12 6.48 14.18 12.64 0.18 16.34 0.01 0.69 8.10 95.81 2.73 1.23 0.00 0.36 0.78 0.01 1.79 0.00 0.00 0.10 0.76 7.76

55.34 0.07 28.03 0.50 − 0.02 10.03 5.14 0.33 99.46 2.51 1.49 0.00 0.00 0.02 0.00 0.00 0.00 0.49 0.45 0.02 4.98 47.2 50.8 2.0

66.05 0.04 18.15 0.12 0.05 − 0.08 1.87 13.53 99.89 3.02 0.98 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.17 0.79 4.97 17.3 0.4 82.3

Porphyritic quartz syenite

Mafic microgranular enclave

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a

b

c

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respectively. The geochemical and petrological similarities suggest that the individual bodies may be connected at depth as a subvolcanic pluton. Mafic microgranular enclaves are randomly distributed in the porphyritic quartz syenite. They have 5 to 15 cm in diameter and show subspherical to irregular shapes. Commonly, their grain size is finer than that of the host rocks. The mafic microgranular enclaves show sharp or gradational contact with the host rocks and phenocrysts transfers between the mafic microgranular enclave and host porphyritic quartz syenite could be observed (Fig. 3h). A total of 36 samples representing the entire spectrum of the Yandangshan volcanic–plutonic complex were collected for geochemical and age analyses. The locations for the studied samples are shown in Fig. 2a and the GPS positions of samples are given in Supplementary Table 1. A Google Earth file with sample numbers and locations is also available in the Supplementary data (KMZ file). 3. Analytical methods 3.1. Mineral compositions Mineral chemical compositions were analyzed using a JEOL JXA 8100 microprobe at the Institute of Geology, Chinese Academy of Geological Sciences (CAGS). Operating conditions were a 15 kV accelerating voltage and a 20 nA beam current. A 5 μm defocused beam was used throughout to avoid Na migration during the analysis of feldspar. The representative microprobe analytical results are listed in Table 1. 3.2. SHRIMP and LA-ICP-MS zircon U–Pb dating Cathodoluminescence (CL) images of the analyzed zircon grains were obtained using an FEI NOVA NanoSEM 450 scanning electron microscope equipped with a Gatan Mono CL4 cathodoluminescence system at the Institute of Geology, CAGS. Zircons from four samples (Z359-1, Z338-1, Z340-1 and Z340-2) were dated using the SHRIMP II ion probe at the Beijing SHRIMP Center (National Science and Techonology Infrastructure), Institute of Geology, CAGS. Detailed analytical procedures and conditions were described by Williams (1998). The intensity of the primary O2 − ion beam was 4.0–5.0 nA, the spot size was 23 μm, and each analytical site was rastered for 2–3.5 min prior to analysis to remove surface common Pb. Five scans through the mass stations were made for each age determination of zircon. The reference material used for calibration of instrumental mass fractionation (IMF) was TEMORA-2 zircon (416.8 Ma; Black et al., 2004). The TEMORA-2 standard was analyzed after every 3 sample analyses. Common lead corrections were applied using the measured 204Pb abundances. Data processing was carried out using the SQUID and ISOPLOT (ver. 3.70) software (Ludwig, 2001). Zircon U–Pb isotope and trace elements were analyzed simultaneously for the other ten samples, using an Agilent 7500a ICP-MS equipped with a Coherent GeoLas Pro 193-nm laser ablation system in the State Key Laboratory of Mineral Deposits Research, Nanjing University (NJU). Analyses were carried out with a beam diameter of 32 μm, 5 Hz repetition rate, and energy of 10–20 J/cm2. Data acquisition for each analysis took 100 s (40 s on background, 60 s on signal). Detailed analytical procedures are described by He et al. (2010). Zircon standard GJ-1 was used as external standard to calibrate isotope fractionation. NIST 610 glass was analyzed in order to correct the time-dependent drift of sensitivity and mass discrimination for the trace element analysis. Samples are analyzed in “runs” of ca. 18 analyses, which include 10–12 unknowns, bracketed by two analyses of the GJ-1 and NIST 610

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standards. The “unknowns” include 2 analyses of well-characterized zircon, Mud Tank and KL2-G which were analyzed frequently as an independent control on reproducibility and instrument stability. The raw ICP-MS data were processed using GLITTER, which calculates the relevant isotopic ratios, ages and errors, and trace element concentrations (Van Achterbergh et al., 2001). Common Pb was corrected according to the method proposed by Andersen (2002). The corrected age calculations and plotting of concordia diagrams were made using ISOPLOT (ver. 3.70) software (Ludwig, 2001). Data-point error ellipses shown in the concordia diagrams are 68.3% conf.

3.3. Zircon Hf isotopic compositions Zircon Hf isotope analyses were carried out in situ using a Coherent GeoLas Pro 193-nm laser ablation system with a Thermo Scientific Neptune Plus MC–ICP-MS at State Key Laboratory for Mineral Deposits Research, NJU. Analyses were carried out with a beam diameter of 44 μm, 8 Hz repetition rate, and energy of 15 J/cm2. The detailed procedure and interference correction method of 176Yb on 176Hf are similar to those described by Wu et al. (2006). In order to evaluate the reliability of the analytical data, standard zircon 91500 and Mud Tank were analyzed during the course of this study and yielded a mean 176Hf/177Hf ratio of 0.282331 ± 17 (2σ, n = 21) and 0.282514 ± 12 (2σ, n = 22), respectively. The measured 176Lu/177Hf ratios and the 176Lu decay constant of 1.867 × 10−11 yr−1 (Söderlund et al., 2004) were used to calculate initial 176Hf/177Hf ratios. The chondritic values of 176Lu/177Hf = 0.0336 and 176 Hf/177Hf = 0.282785 reported by Bouvier et al. (2008) were used for the calculation of the εHf values. The depleted mantle Hf model ages (TDM) were calculated using the measured 176Lu/177Hf ratios based on the assumption that the depleted mantle reservoir has a linear isotopic growth from 176Hf/177Hf = 0.279718 at 4.55 Ga to 0.283250 at present, with 176Lu/177Hf = 0.0384 (Griffin et al., 2000). Two-stage model ages (TDM2) were also calculated for each zircon, using 176Lu/177Hf value of 0.019 for a mafic to intermediate crust (Hawkesworth et al., 2010).

3.4. Zircon O isotopes Zircon oxygen isotope ratios were analyzed on the SHRIMP-IIe/MC at the Beijing SHRIMP Center (National Science and Techonology Infrastructure), Institute of Geology, CAGS. The intensity of the Cs+ primary ion beam was ~ 3 nA, producing secondary 16O− count rates over 109 cps. The spot diameter for all analyses was ~ 23 μm. The instrument and the analytical procedure have been described by Ickert et al. (2008). The measured oxygen isotopic data were corrected for instrumental mass fractionation (IMF) using the TEMORA-2 zircon standard (δ18OVSMOW = 8.2‰; Black et al., 2004). Zircon 91,500 was also measured as an unknown sample, yielded a mean δ18O value of 10.19 ± 0.51‰ (2σ, n = 23), which is consistent with the reported value of 9.9‰ (Wiedenbeck et al., 2004). The standard deviations of TEMORA2 zircon for the two analytical sessions during the course of this study are 0.62 (2σ, n = 26) (mount G5359 with samples Z338-1, Z340-1 and Z340-2) and 0.47 (2σ, n = 24) (mount G5360 with sample Z3591). As pointed by Ickert et al. (2008), the internal errors for individual spot analyses significantly underestimate the true analytical uncertainty. We therefore adopt an external error which is the within-spot uncertainty of a single spot and the spot-to-spot uncertainty of TEMORA-2 for the analytical session added in quadrature (Ickert et al., 2008).

Fig. 4. Photomicrographs of the Yandangshan volcanic–plutonic complex. (a, b) Rhyolitic welded crystal-lapilli tuff of the first volcanic unit, showing the crystal fragments, fiamme lapilli and large glomerocrysts. (c) Rhyolite from the second volcanic unit with perlitic matrix. (d) Rhyolitic lapilli tuff of the third volcanic unit. (e, f) Rhyolitic welded crystal-vitric tuff of the fourth volcanic unit, showing the crystal fragments and the sintered juvenile shards. (g) Porphyritic quartz syenite. (h) Mafic microgranular enclave of the porphyritic quartz syenite. Mineral abbreviation: Afs, alkali feldspar; Amp, amphibole; Bt, biotite; Cpx, clinopyroxene; Mag, magnetite; Or, orthoclase; Pl, plagioclase; Qtz, quartz.

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3.5. Whole-rock major element, trace element and Sr–Nd isotopes

a

Whole-rock major element analysis was performed using a Rigaku3080 X-ray fluorescence spectrometer (XRF) at the National Research Center for Geoanalysis, CAGS. The analytical precision was generally better than 2% for all elements. Trace element abundances were measured using an Agilent 7500a ICP-MS in the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, which gives a precision better than 10% for most of the elements analyzed. The Sr and Nd isotopic compositions were measured using a Finnigan MAT262 thermal ionization mass spectrometer (TIMS) at the Institute of Geology and Geophysics, Chinese Academy of Sciences following the procedure of Zhang et al. (2002). Procedural blanks were less than 100 pg for Rb and Sr, and 50 pg for Sm and Nd. Sr and Nd isotopic ratios were corrected for mass fractionation by normalizing to 86 Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219, respectively. The measured 87Sr/86Sr ratio and 143Nd/144Nd ratio of the BCR-2 standard were 0.704997 ± 10 (2σ) and 0.512630 ± 7 (2σ), respectively. 4. Petrography and mineralogy 4.1. Rhyolitic crystal-lapilli tuff of the first volcanic unit The rock is gray or grayish purple, lithic-poor (generally b2 vol.%), and crystal-rich (~ 30–40 vol.%). The crystals range in size from b1 mm to 3 mm, containing quartz, alkali feldspar, plagioclase, augite, biotite and minor Fe–Ti oxides (Fig. 4a). Feldspar glomerocrysts are common, with partially melted grain boundaries (Fig. 4b). The fiamme lapilli (~10 vol.%) range from 2 cm to 30 cm in length, and are flattened and stretched along the flow direction, defining a clear eutaxitic texture (Fig. 3a). Phenocrysts in the fiamme are small (b2 mm) and euhedral to subhedral with low contents (b10 vol.%), comprising feldspar, biotite, quartz and Fe–Ti oxides. Vitric fine ash matrix is weakly devitrified, locally replaced by microcrystalline quartzofeldspathic textures. Plagioclase crystals are normally zoned, with An content decreasing from 40.8% to 19.1% outwards (Fig. 5a). Locally, they are altered into fine-grained aggregates of Na-rich plagioclase (An2.9), sericite, calcite and epidote-group minerals. Alkali feldspar consists of pure K-feldspar (average 96.8% Or) or pure albite (average 93.4% Ab). Pyroxene is classified as augite with a composition of Wo43–44En41–42Fs15–16 (Fig. 5b). Biotite has high TiO2 contents (5.43–5.55 wt.%) and is Mg-rich with XFe values of 0.30–0.31 [XFe = Fe2+/(Fe2+ + Mg)].

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4.2. Rhyolite of the second volcanic unit Rhyolite of this unit is grayish purple, and shows porphyritic, massive, perlitic or flow-banded structure (Fig. 3b). It consists of phenocrysts of alkali feldspar, plagioclase, quartz, biotite and minor titanite and Fe–Ti oxides set in a vitric, perlitic, spherulitic or microcrystalline matrix (Fig. 4c). Alkali feldspar phenocrysts commonly occur as euhedral crystals up to 5 mm in length and range in composition from pure K-feldspar (average 98% Or) to pure albite (average 98.9% Ab) with low An content (b4.5) (Fig. 5a; Table 1).

Fig. 5. Mineral classification of (a) feldspar; (b) clinopyroxene (after Morimoto et al., 1988); (c) amphibole (after Leake et al., 1997).

orthoclase (Or94.8–97.9) to albite (Ab97.7–98.1) (Fig. 5a). Biotite has low TiO2 content with XFe value of 0.25 (Table 1).

4.3. Rhyolitic lapilli tuff of the third volcanic unit

4.4. Rhyolitic crystal-vitric tuff of the fourth volcanic unit

The rock is light gray-grayish purple, and is non-welded to weaklywelded with a weakly eutaxitic texture. The main constituents include crystal fragments (~ 30 vol.%), slightly deformed pumice lapilli (~5 vol.%), glass shards (~10 vol.%) and minor lithic lapilli (~ 2 vol.%), set in a variably devitrified fine ash matrix (~50 vol.%). Glass shards typically show crescentic and biconcave shapes (Fig. 4d). The crystals are composed of alkali feldspar, plagioclase and biotite with accessory titanite and Fe–Ti oxides. Alkali feldspar ranges in composition from

The rock is gray, intensely welded throughout the flattened fiamme and sintered glass shards. The crystal fragments (~ 30 vol.%) range in size from 0.5 mm to 2.5 cm, consisting of alkali feldspar, plagioclase, clinopyroxene, amphibole and biotite with accessory titanite and Fe– Ti oxides. Glomerocrysts of feldspar, biotite and Fe–Ti oxides are also present, showing partially melted grain boundaries. Fiamme (~10 vol.%) range from five to ten centimeters in length. Glass shards, fiamme and vitriclastic matrix are partially devitrified and recrystallized

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to microcrystalline quartz and feldspar (Fig. 4e and f), showing moderate to well-preserved fluidal textures. Plagioclase crystals are normally zoned, with compositions from An46.7 in the core to An24.9 in the rim. Some are locally altered into fine sodic plagioclase (An1.6–5.7). Alkali feldspar has varying Or contents (Or52.3–98.4) (Fig. 5a). Amphibole is edenite with Mg/(Mg + Fe2+) ratios of 0.74–0.76 (Fig. 5c). The compositions of amphibole were adopted for thermobarometric calculations using the formulations for amphibolebearing calc-alkaline magmas (Ridolfi et al., 2010). The calculation yielded crystallization P–T conditions of approximately 859 °C and 65 MPa. Pyroxene can be classified as augite, with a composition of Wo42–44En40–42Fs14–17 (Fig. 5b). Biotite has TiO2 contents of 5.64 wt.% to 9.12 wt.% and XFe values of 0.34 to 0.39 (Table 1).

4.5. Porphyritic quartz syenite and mafic microgranular enclave Porphyritic quartz syenites from different plutons are petrographically similar. They are gray-red with a porphyritic texture. The phenocrysts (~40–50 vol.%), ranging in size from 1 to 5 mm, are dominated by alkali feldspar (~ 40–50 vol.%), plagioclase (~ 10%), clinopyroxene (~ 5%), (Figs. 3h and 4g). Alkali feldspar occurs as orthoclase (Or96.4–98.3) mantled by albite, or albite (Ab97.4–98.4) mantled by orthoclase. Plagioclase has an anorthite content of 13.5–57.8 (Fig. 5a) and is commonly mantled by orthoclase (Or42.6–97.4), showing an anti-rapakivi texture. Pyroxene can be classified as augite, with a composition of Wo40–45En37–43Fs14–18 (Fig. 5b). The matrix consists of alkali feldspar (~ 85%), quartz (~ 7%), clinopyroxene (~3%), with minor biotite, magnetite, titanite and allanite.

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Fig. 6. CL images of zircon grains. (a, b) The first volcanic unit. (c–e) The second volcanic unit, (f) The third volcanic unit, (g, h) The fourth volcanic unit, (i–k) Porphyritic quartz syenite. (l–n) Mafic microgranular enclave. Scale bars are 100 μm. White open circles indicate the spots of LA-ICP-MS U–Pb dating, white open ellipses indicate the spots of SHRIMP U–Pb dating, white dashed circles indicate the spots of Hf isotope analyses, and yellow dashed ellipses indicate the spots of O isotope.

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Table 2 Representative chemical compositions of the studied samples. Unit

The first unit

Sample

Z336-1

PQS

MME

Z356-2

The second unit Z426-1

Z438-1

The third unit Z357-1

Z425-2

The fourth unit Z350-1

Z354-1

Z347-2

Z347-1

Major elements (in wt.%) 71.57 SiO2 TiO2 0.41 Al2O3 14.77 T FeO 1.98 MnO 0.04 MgO 0.20 CaO 0.24 Na2O 5.02 4.74 K2O P2O5 0.07 LOI 0.96 Total 100.00

69.59 0.43 14.85 2.15 0.08 0.43 1.23 4.12 5.52 0.07 1.28 99.75

76.27 0.19 12.51 1.57 0.07 0.09 0.19 3.26 5.72 0.01 0.37 100.25

73.59 0.31 13.45 2.04 0.12 0.29 1.12 2.66 5.60 0.04 1.32 100.54

70.69 0.40 14.38 2.00 0.07 0.33 1.16 4.82 4.58 0.06 1.45 99.94

70.3 0.38 14.91 1.68 0.06 0.27 0.82 5.07 5.15 0.05 0.78 99.47

71.08 0.36 14.60 1.90 0.07 0.42 0.81 4.13 5.84 0.06 0.66 99.93

74.74 0.24 13.35 1.45 0.05 0.21 0.46 3.84 5.60 0.03 0.59 100.56

65.59 0.57 16.21 2.72 0.10 0.68 1.73 4.91 5.26 0.12 1.43 99.32

55.10 1.11 18.14 5.85 0.19 2.65 5.69 4.10 3.35 0.36 2.60 99.14

Trace elements (in ppm) V 9.26 Cr 0.24 Ni 0.17 Ga 17.5 Rb 123 Sr 140 Y 25.2 Nb 16.1 Ta 0.95 Ba 1552 Zr 356 Hf 8.40 Pb 16.8 Th 14.1 U 2.61 La 27.8 Ce 84.7 Pr 6.83 Nd 25.6 Sm 4.96 Eu 0.97 Gd 4.14 Tb 0.67 Dy 4.16 Ho 0.86 Er 2.52 Tm 0.41 Yb 2.74 Lu 0.41 Eu/Eu* 0.64

17.6 0.45 0.27 17.3 158 244 28.1 15.9 0.95 1865 305 7.63 29.8 15.0 2.46 55.7 109 11.6 42.5 7.33 1.63 5.69 0.81 4.79 0.92 2.80 0.42 2.63 0.42 0.75

3.41 16.3 4.19 14 217 49.4 22 16.9 1.18 247 168 5.75 50.7 16.2 3.44 24 65.6 4.49 15.4 3.08 0.4 2.95 0.54 3.29 0.76 2.52 0.38 2.69 0.41 0.40

13.0 8.96 4.56 18.3 207 97.8 24.1 15.8 1.22 1302 306 7.97 18.4 12.5 2.85 44.2 76.4 8.98 33.6 6.67 1.02 5.17 0.81 4.12 0.87 2.57 0.39 2.60 0.43 0.51

21.1 0.43 0.31 17.3 129 138 27.9 16.4 0.95 1687 336 8.25 32.0 15.2 2.26 55.4 108 11.8 42.5 7.32 1.61 5.75 0.84 4.95 0.93 2.77 0.45 2.75 0.42 0.73

8.69 0.65 0.75 17.1 141 138 26.8 17.2 0.97 2104 381 9.10 27.7 15.8 3.81 58.8 113 13.0 44.6 7.58 1.53 5.48 0.83 4.70 0.91 2.75 0.43 2.76 0.46 0.69

12.0 0.34 0.21 17.1 153 147 31.4 16.9 1.01 1602 350 8.48 31.2 15.8 2.70 68.0 131 14.3 51.9 8.88 1.75 6.65 1.00 5.60 1.03 3.13 0.50 2.96 0.48 0.67

6.45 0.28 0.100 17.1 191 60.9 33.0 19.4 1.19 506 232 6.83 24.7 18.1 2.55 50.6 101 11.0 40.0 7.25 1.00 5.78 0.92 5.39 1.07 3.23 0.52 3.17 0.49 0.46

24.4 0.93 0.66 18.7 103 324 26.3 13.3 0.70 2809 500 10.8 25.5 11.9 1.61 94.3 173 18.6 67.5 10.5 2.77 7.08 0.91 5.08 0.96 2.66 0.39 2.61 0.42 0.93

110 39.8 22.7 22.1 72.6 643 25.0 10.1 0.52 2527 390 7.91 23.8 6.50 1.68 47.7 90.2 10.4 41.7 7.60 2.73 5.84 0.84 4.80 0.87 2.31 0.35 2.00 0.32 1.21

Note: LOI: loss on ignition. Eu/Eu* = 2 × EuN/(SmN + GdN). Abbreviations: PQS—Porphyritic quartz syenite; MME—Mafic microgranular enclave.

Alkali feldspar in the matrix is either orthoclase (Or97.3–97.6) or albite (Ab91.9–99.2). Mafic microgranular enclaves in the porphyritic quartz syenites often show a quench texture. They are deep gray and medium-fine grained, and they have dioritic composition (Fig. 3h). The phenocrysts are mainly composed of plagioclase, which is commonly zoned and rimmed by orthoclase, with composition varying from An69.7 to An28.8. The matrix contains alkali feldspar, plagioclase (An10.5–45) rimmed by orthoclase, clinopyroxene, amphibole, biotite and quartz, with minor acicular apatite (Fig. 4h). Amphiboles generally have high TiO2 contents (2.83 wt.% to 5.00 wt.%) and belong to the calcic group with CaB N 1.5. Amphiboles can be further classified as pargasite and kaersutite (Mg/ (Fe2+ + Mg) = 0.68–0.76; Si = 6.06–6.19 apfu) (Fig. 5c; Leake et al., 1997). The compositions of amphibole were adopted for the thermobarometric calculation using the formulations for amphibolebearing calc-alkaline magmas (Ridolfi et al., 2010). The results yielded crystallization P–T conditions of ca. 984 °C and 316 MPa, corresponding to a depth of ~10 km. Pyroxene is classified as augite and diopside, with

a composition of Wo42-46En39-44Fs12–17 (Fig. 5b). Biotite is Mg-rich with XFe values of 0.29 to 0.34; it has high TiO2 content of 5.01 wt.% to 6.48 wt.%. 5. Analytical results 5.1. Zircon U–Pb dating Fourteen samples of the Yandangshan volcanic–plutonic complex were subject to zircon U–Pb dating using SHRIMP and LA-ICP-MS techniques. CL images of zircon grains are shown in Fig. 6. The zircon dating results are given in Supplementary Tables 2 and 3. The REE compositions of zircon grains (if analyzed) are given in Supplementary Table 4. Zircon crystals from all rock types (volcanic rocks, porphyritic quartz syenites and mafic microgranular enclaves) are colorless, short prismatic, and euhedral. They range from 80 to 120 μm in length, and show absence of inherited cores. In CL images, clear oscillatory growth zoning suggests a magmatic origin (Fig. 6). However, some grains from the

Fig. 7. Zircon U–Pb concordia diagrams and weighted mean 206Pb/238U ages for the Yandangshan volcanic–plutonic complex. (a, b) The first volcanic unit, marked by I. (c–e) The second volcanic unit, marked by II. (f) The third volcanic unit, marked by III. (g, h) The fourth volcanic unit, marked by IV. (i–k) Porphyritic quartz syenite, marked by S. (l–n) Mafic microgranular enclave, marked by M. Zircon U–Pb dating by SHRIMP is typically marked by stars.

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porphyritic quartz syenites and mafic microgranular enclaves have CLbright unzoned or weakly zoned rims or patches, which may be related to multistage crystallization (e.g., Medlin et al., 2015; Miller et al., 2007; Wang et al., 2013). The analyzed zircon grains have variable Th (16–1870 ppm) and U contents (10–540 ppm) but all show typical magmatic Th/U ratios (0.65–3.58). The zircon REE patterns show characteristic HREE enrichment and Eu depletion, which are indicative of a magmatic origin. Two samples (Z359-1 and Z336-1) were selected from the first volcanic unit. Thirteen U–Pb spots were analyzed on 13 zircon grains for sample Z359-1. Except two highly discordant spots (5.1 and 9.1), eleven spot analyses yielded a weighted mean 206Pb/238U age of 99 ± 3 Ma (MSWD = 8.10; Fig. 7a). Meanwhile, sixteen analyses were undertaken on 16 zircon grains from sample Z336-1. The result yielded a weighted mean 206Pb/238U age of 104 ± 2 Ma (MSWD = 0.12; Fig. 7b). The above two age values are interpreted as the crystallization ages of the first volcanic unit. Three samples (Z426-1, Z438-1 and Z342-1) from the second volcanic unit were analyzed. Nineteen spots on 19 zircon grains from sample Z426-1 yielded a weighted mean 206Pb/238U age of 102 ± 2 Ma (MSWD = 0.14; Fig. 7c). Nineteen spot analyses on 19 zircon grains from sample Z438-1 yielded a weighted mean 206Pb/238U age of 100 ± 3 Ma (MSWD = 0.18; Fig. 7d). Eighteen spots on 18 zircon grains from sample Z342-1 plot on or near the concordia, and yielded a weighted mean 206Pb/238U age of 99 ± 2 Ma (MSWD = 1.19; Fig. 7e). Sample Z357-1 was selected from the third volcanic unit. Twenty spot analyses on 20 zircon grains plot on or near the concordia, and yielded a weighted 206Pb/238U age of 103 ± 2 Ma (MSWD = 0.61; Fig. 7f).

Two samples (Z338-1 and Z349-1) were selected from the fourth volcanic unit. Thirteen U–Pb analyses were conducted on 13 zircon grains from sample Z338-1. All the analyses are concordant or nearly concordant yielding a weighted mean 206Pb/238U age of 98 ± 2 Ma (MSWD = 0.57; Fig. 7g). Eighteen analyses on 18 zircon grains were obtained for sample Z349-1, yielding a weighted mean 206Pb/238U age of 99 ± 2 Ma (MSWD = 0.35; Fig. 7h). Three samples (Z340-1, Z344-1 and Z348-1) of porphyritic quartz syenites were selected for U–Pb dating. Fifteen spots were analyzed on 13 zircon grains for sample Z340-1, yielding a weighted 206Pb/238U age of 102 ± 2 Ma (MSWD = 0.76; Fig. 7i). For sample Z344-1, seventeen U–Pb spot analyses on 17 zircon grains yielded a weighted mean 206 Pb/238U age of 99 ± 1 Ma (MSWD = 1.20; Fig. 7j). Thirteen analyses on 13 zircon grains were obtained for sample Z348-1, yielding a weighted mean 206Pb/238U age of 99 ± 1 Ma (MSWD = 1.06; Fig. 7k). All the above age values are thought to be the crystallization age of the porphyritic quartz syenite. Three samples (Z340-2, Z347-1 and Z348-2) of mafic microgranular enclaves from the porphyritic quartz syenite were dated. Sixteen spots were analyzed on 16 zircon grains for sample Z340-2, yielding a weighted mean 206Pb/238U age of 98 ± 1 Ma (MSWD = 0.40; Fig. 7l). Nineteen spot analyses on 19 zircon grains were conducted for sample Z347-1, yielding a weighted mean 206Pb/238U age of 98 ± 1 Ma (MSWD = 2.40; Fig. 7m). Sixteen analyses on 16 zircon grains from sample Z348-2 yielded a weighted mean 206Pb/238U age of 98 ± 1 Ma (MSWD = 1.90; Fig. 7n). In summary, the crystallization ages of the volcanic rocks and subvolcanic intrusions from the Yandangshan caldera are considered “identical” within analytical uncertainties. The apparent large time span (104–98 Ma) shown by the results of LA-ICP-MS dating can be

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Fig. 8. Geochemical classification for the Yandangshan volcanic–plutonic complex. (a) TAS classification diagram of volcanic rocks (after Le Maitre et al., 2002). (b) TAS classification diagram of plutonic rocks (after Middlemost, 1994). (c) Plot of Al2O3/(Na2O + K2O) versus Al2O3/(CaO + Na2O + K2O) (all in molar proportion) (Maniar and Piccoli, 1989). (d) (Na2O + K2O − CaO) versus SiO2 diagram (after Frost et al., 2001).

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rationalized when the accuracy of the LA-ICP-MS zircon dating technique is further considered (Horstwood et al., 2009; Li et al., 2015). Therefore, the large volume of silicic magma in the Yandangshan caldera was produced in a short period (a few Ma) and a genetic link between the different volcanic units and subvolcanic intrusions could be established. 5.2. Major and trace element characteristics A complete set of whole-rock chemical data for the samples from the Yandangshan volcanic–plutonic complex is given in Supplementary Table 1. Table 2 shows an abbreviated version of the data set. From the first to the fourth volcanic unit, SiO2 contents roughly show an increasing trend. The rocks are highly silicic, with SiO2 contents of 70–72 wt.% for the first unit, 73–76 wt.% for the second unit, 70–71 wt.% for the third unit, and 71–75 wt.% for the fourth unit. All the volcanic rock samples have high total alkali (Na2O + K2O) contents (8.2–10.0 wt.%) and plot in the “rhyolite” field on the TAS diagram (Fig. 8a). In addition, they show metaluminous to slightly peraluminous compositions with A/CNK ratios [molar Al2O3/(CaO + Na2O + K2O)] = 0.96–1.15 (Fig. 8c). In comparison with the volcanic rocks, porphyritic quartz syenites have lower SiO2 (65–66 wt.%), thus showing a compositional gap (from about 66 to 70 wt.% SiO2) between the porphyritic quartz syenites and volcanic rocks. The porphyritic quartz syenite also shows high total alkali contents (10.1–10.7 wt.%), and plot in the alkaline field in the TAS diagram (Fig. 8b). They are metaluminous with A/CNK ratios of 0.93–0.99 (Fig. 8c). The mafic microgranular enclave samples show lower SiO2 (55.1–58.2 wt.%) and total alkali (7.5–9.1 wt.%); they are metaluminous with A/CNK ratios of 0.82–0.96. Furthermore, the volcanic rocks and the mafic microgranular enclaves followed the boundary

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between the alkalic and alkali-calcic fields, while all the porphyritic quartz syenites are within the alkalic field (Fig. 8d). In the chemical variation diagrams of major oxides vs. silica, a linear correlation may be discerned between the porphyritic quartz syenites and volcanic rocks (Fig. 9). Moreover, compared with the first unit, the other three volcanic units have lower Fe2O3, MgO, CaO and P2O5, suggesting that the magmas of the three units have experienced higher degrees of fractional crystallization with respect to the first unit (Fig. 9). All volcanic samples show similar chondrite-normalized REE patterns with LREE enrichment (Fig. 10a) and distinct Eu anomalies (Eu/Eu* = 0.32–0.81). Some rocks show tetrad REE patterns with the TE1,3 value ranging from 1.01 to 1.29 (Supplementary Table 1), which are usually observed in highly differentiated acid magmas (e.g., Jahn et al., 2001, 2004). Moreover, some volcanic rocks from the second and fourth volcanic units show relatively high K/Ba ratios (N 100) and low Zr/Hf ratios (b 35), which is also similar to highly evolved granites with REE tetrad effect (e.g., Jahn et al., 2001). In contrast, the porphyritic quartz syenites have more enrichment of LREE and higher total REE (327–421 ppm) with negligible Eu anomalies (Eu/Eu* = 0.90–0.99) (Fig. 10b). In the spidergrams (Fig. 10c and d), the volcanic rocks are generally characterized by positive Rb anomalies and depletions of Ba, Sr, P and Ti, except that the first unit shows negligible Ba depletions and relatively weak Sr, P and Ti depletions. The porphyritic quartz syenites show complementary patterns with negative Rb anomalies and positive Ba anomalies, and their Sr, P and Ti depletions are distinctly weak. 5.3. Zircon Hf isotopic compositions The analytical results of Lu–Hf isotopic compositions are given in Supplementary Table 5, and illustrated in Figs. 11 and 12.

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Fig. 9. Selected major element oxides versus SiO2 plots for the Yandangshan volcanic–plutonic complex.

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Fig. 10. Chondrite-normalized REE patterns (a and b) and primitive mantle-normalized multiple trace element diagrams (c and d) of the Yandangshan volcanic–plutonic complex. The chondrite values are from Taylor and McLennan (1985). The primitive mantle values are from McDonough and Sun (1995).

Two samples (Z336-1 and Z359-1) were analyzed for the first volcanic unit. Fifteen Hf isotopic spot analyses of sample Z336-1 gave εHf(t) values of −7.9 to −4.0 and TDM2 model ages of 1.95 to 1.65 Ga. Sample Z359-1 shows similar Hf isotopic compositions with εHf(t) values of −9.1 to −3.9, and TDM2 model ages of 2.03 to 1.64 Ga. Three samples (Z426-1, Z438-1 and Z342-1) were analyzed for the second volcanic unit. These samples show similar Hf isotopic compositions, but with a larger range. Twenty-one Hf isotopic analyses for sample Z426-1 show εHf(t) values of − 8.6 to − 3.6 and TDM2 = 2.00 to 1.62 Ga. Twenty spot analyses were obtained for sample Z438-1, yielding εHf(t) values of − 9.0 to − 5.6, and TDM2 model ages of 2.03 to 1.77 Ga. Fifteen spot analyses for sample Z342-1 gave εHf(t) values of −7.3 to −3.2 and TDM2 of 1.89 to 1.59 Ga. Sample Z357-1 was selected for the third volcanic unit. Nineteen zircon grains were analyzed, yielding εHf(t) values of −6.8 to −0.6, and TDM2 model ages of 1.86 to 1.39 Ga. Two samples (Z338-1, Z349-1) were selected for the fourth volcanic unit. Fifteen Hf isotopic spot analyses on 15 zircon grains from sample Z338-1 yielded εHf(t) values of −8.4 to −5.0 and TDM2 model ages of 1.98 to 1.72 Ga. Sample Z349-1 shows similar Hf isotopic compositions with εHf(t) values of − 8.5 to − 4.8 and TDM2 model ages of 1.99 to 1.71 Ga. Three samples (Z340-1, Z344-1 and Z348-1) from porphyritic quartz syenites were analyzed. All these samples show a wide range of Hf isotopic compositions. Sixteen spot analyses for sample Z340-1 yielded εHf(t) values of −8.2 to −2.5, and TDM2 model ages of 1.97 to 1.53 Ga. Fifteen spot analyses for sample Z344-1 showed εHf(t) values of − 8.9 to −4.6, and TDM2 model ages of 2.01 to 1.69 Ga. Fifteen spot analyses for sample Z348-1 gave εHf(t) values of − 10.0 to − 6.9, and TDM2 model ages of 2.10 to 1.87 Ga.

Three samples (Z340-2, Z347-1 and Z348-2) were analyzed for the mafic microgranular enclaves of the porphyritic quartz syenites. All the samples show a wide range of Hf isotopic compositions. Twenty Hf isotopic spot analyses for sample Z340-2 gave εHf(t) values of −9.5 to −4.3 and TDM2 model ages of 2.06 to 1.67 Ga. Twelve spot analyses for sample Z347-1 yielded the largest variation of εHf(t) values of −9.4 to 1.5, and TDM2 model ages of 2.06 to 1.23 Ga. Fifteen spot analyses for sample Z348-2 gave εHf(t) values of − 9.0 to − 4.3 and TDM2 model ages of 2.03 to 1.67 Ga. 5.4. Zircon oxygen isotopes Zircon oxygen isotopic composition is particularly useful for determining the origin of magmatic rocks. It could also be used to track the isotopic evolution of a magmatic system through inter- or intra-grain variation due to the long residence time of zircon in magma chambers (Hawkesworth and Kemp, 2006; Kemp et al., 2007; Peck et al., 2003; Wang et al., 2013). In this study, zircon O isotope compositions were determined for four samples (Fig. 13 and Table 3) including two volcanic rocks (Z359-1, Z338-1), one porphyritic quartz syenite (Z340-1) and one mafic microgranular enclaves sample (Z340-2). Fifteen analyses on 15 zircon grains from sample Z359-1 yielded a narrow range of δ18O from 4.88 to 6.43‰, with a mean value of 5.49 ± 0.78‰ (2σ). Fifteen analyses on 15 zircon grains of sample Z338-1 gave δ18O of 4.31‰ to 6.14‰, with a mean value of 5.00 ± 1.07‰ (2σ). Seventeen analyses on 14 zircon crystals of sample Z340-1 yielded δ18O values from 4.51 to 6.17‰, with an average of 5.06 ± 0.79‰ (2σ). Among the 17 analyses, 8 spots were done on oscillatory zoned domains, and 9 analyses were on the CL-bright unzoned domains

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c

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(Table 3). Both domains yielded similar δ18O values, suggesting that the oscillatory zoned and CL-bright unzoned domains formed by two-stage crystallization of a single magma (e.g., Wang et al., 2013). Seventeen analyses on 13 zircon grains from sample Z340-2 were carried out. Seven spots on the oscillatory zoned domains yielded δ18O from 3.67 to 5.86‰, while ten spots on the CL-bright unzoned domains gave δ18O from 4.44 to 6.51‰ (Table 3). Consequently, the two domains may also be interpreted as two-stage crystallization of a single magma (e.g., Wang et al., 2013). However, they gave a considerable variation in δ18O from 3.67 to 6.51‰, with a mean value of 5.14 ± 1.34‰ (2σ). 5.5. Sr and Nd isotopic compositions

d

e

f

g

Whole-rock Sr and Nd isotopic compositions of the Yandangshan volcanic–plutonic complex are presented in Supplementary Table 6. The volcanic rocks, subvolcanic intrusions of porphyritic quartz syenites and mafic microgranular enclaves show comparable Sr and Nd isotopic compositions (Fig. 14). The volcanic rocks have a narrow range of εNd(t) values (−7.8 to −7.0), TDMC of 1.53 to 1.47 Ga and initial 87Sr/86Sr ratios (0.7084–0.7090). Initial 87Sr/86Sr ratios are 0.7086–0.7089 for the porphyritic quartz syenites and 0.7082–0.7088 for the mafic microgranular enclaves. εNd(t) values of the porphyritic quartz syenites range from −7.6 to − 6.5 and that of mafic microgranular enclaves from −7.3 to −6.6. The porphyritic quartz syenites and mafic microgranular enclaves show TDMC ages of 1.52 to 1.43 Ga and 1.49 to 1.44 Ga, respectively. Overall, the Sr–Nd isotopic compositions of the Yandangshan volcanic–plutonic complex are comparable with that of the Cretaceous basalts and rhyolites in SE China (Fig. 14). 6. Discussion

h

i

j

k

l

m

n

6.1. Magma sources of the Yandangshan volcanic–plutonic complex and the nature of the eastern Cathaysia crust The result of zircon geochronology for the Yandangshan volcanic– plutonic complex indicates that all rock types have indistinguishable ages (104–98 Ma), hence suggesting that they were derived from the same magmatic cycle. Furthermore, the volcanic rocks and porphyritic quartz syenites have very similar Sr–Nd–Hf isotopic compositions (Figs. 11–14). Therefore, the various rock-types of the Yandangshan volcanic–plutonic complex could have been derived from a common magma source. Note that some mafic microgranular enclaves occurred in the fourth volcanic unit and the porphyritic quartz syenites (Fig. 3g and h). Mafic microgranular enclaves are common in intermediate and felsic igneous rock suites, which generally display different but correlated major and trace element compositions with their host rocks. Both the mafic microgranular enclaves and the host igneous rocks are considered to be produced by the mixing of two components in different proportions (Barbarin and Didier, 1992; Browne et al., 2006; Cantagrel et al., 1984; Humphreys et al., 2006; Perugini and Poli, 2012; Vernon, 1984). In this study, the mafic microgranular enclaves and their host porphyritic quartz syenites have similar Sr–Nd isotopic compositions (Fig. 14). However, the zircon εHf(t) values of the mafic microgranular enclaves show a large variation (− 9.4 to 1.5), and especially one zircon grain gives a positive εHf(t) value (1.5) and a distinctly younger Hf model age (~1.23 Ga) (Figs. 11 and 12). This may suggest that magma mixing and mantle-derived magma have probably played an important role in the generation of the Yandangshan volcanic–plutonic complex. Magma mixing might be responsible for the large variation in the zircon εHf(t) values (3.1–6.2 εHf unit) and zircon Hf model ages (2.10–1.23 Ga) Fig. 11. Histograms of zircon εHf(t) values. (a, b) The first volcanic unit, marked by I. (c-e) The second volcanic unit, marked by II. (f) The third volcanic unit, marked by III. (g, h) The fourth unit, marked by IV. (i–k) Porphyritic quartz syenite, marked by S. (l–n) Mafic microgranular enclave, marked by M.

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a

b

Fig. 12. (a) Diagram of zircon εHf(t) versus U–Pb ages for the Yandangshan volcanic–plutonic complex. (b) Histogram of zircon Hf model ages.

observed in many Yandangshan rocks. In addition to magma mixing, the large range in εHf(t) values might have resulted from crustal contamination during the magmatic differentiation (Jahn et al., 2014, 2015). On the other hand, the rather homogeneous Sr–Nd isotope compositions (Fig. 14) and narrow range of Nd model ages (1.53–1.43 Ga) may represent the end product of magma mixing and crustal contamination (e.g., Griffin et al., 2002; Hawkesworth and Kemp, 2006; Shaw and Flood, 2009). Such a magma mixing scenario may be supported by the occurrence of anti-rapakivi texture within the porphyritic quartz syenites (Fig. 4g; Hibbard, 1981; Yan et al., 2015). The Yandangshan volcanic–plutonic complex shows primitive zircon oxygen isotopic compositions, with δ18O values dominantly in the range of 4.5‰ to 6.0‰ (Fig. 15), which are close to the value of zircon in equilibrium with mantle-derived melts (5.3 ± 0.6‰; 2σ; Valley, 2003; Valley et al., 2005). It is widely accepted that the continental crust is an important contributor to the voluminous silicic magmas (e.g., Huppert and Sparks, 1988; Lundstrom and Glazner, 2016; Scaillet et al., 2016). Therefore, the mantle-like zircon δ18O values coupled with the Paleo- to Mesoproterozoic Hf model ages (2.10–1.23 Ga; with a peak at ca. 1.85–1.80 Ga; Fig. 12) may suggest that the magma of the Yandangshan volcanic–plutonic complex has been generated by partial melting of an ancient mafic lower crust. A few exceptional zircon grains with elevated δ18O values (maximum = 6.5‰) might have been produced by a limited supracrustal contamination (Valley, 2003; Valley et al., 2005). It is commonly accepted that the Hf model ages of zircon grains that retain mantle-like δ18O values are the best estimate of the time of crust generation (Hawkesworth and

Kemp, 2006; Kemp et al., 2007). In this context, the zircon Hf model ages with elevated δ18O values (N 6.0‰) from a few zircon grains could have little significance. Furthermore, as we argue above, magma mixing and mantle-derived magma probably have been involved in the petrogenesis of the Yandangshan volcanic–plutonic complex. Because the input of mantle-derived magma would lead to the decrease of the model ages of the samples, the actual age of ancient crustal source of the Yandangshan volcanic–plutonic complex would be somewhat older than the youngest Hf model ages (~1.23 Ga). The available data showed that the oldest Precambrian rocks in the eastern Cathaysia block are Paleoproterozoic granitic gneisses and minor metabasic rocks (amphibolites). They were formed in the period 1890–1815 Ma, and are exposed in the Wuyishan area (Chen and Jahn, 1998; Li et al., 2000; Xia et al., 2012; Xiang et al., 2008; Yu et al., 2012). The granitic rocks generally show negative εHf(t) or εNd(t) values and Archean Hf and Nd model ages (4.0–2.5 Ga, with a peak at ca. 2.8 Ga), suggesting that they were mainly originated by reworking of older (Archean) crust material (Xia et al., 2012; Yu et al., 2012). However, the presence of basic rocks (amphibolites), especially its high positive εNd(t) values, indicates Paleoproterozoic mantle-derived magmatism and possible crustal growth (Li et al., 2000; Xiang et al., 2008). The Paleoproterozoic (~1.85 Ga) juvenile crust addition was also indicated by the detrital zircon from the Paleoproterozoic supracrustal rocks in the block (Yu et al., 2012). Chen and Jahn (1998) have suggested that the Paleoproterozoic crust was an important source for the majority of felsic igneous rocks in Cathaysia, which is endorsed by the magma source of the Yandangshan volcanic–plutonic complex. Therefore, the

Fig. 13. Plot of zircon oxygen isotope ratios for the Yandangshan volcanic–plutonic complex. Error bars are at 2σ. The shaded field represents δ18O of zircon in equilibrium with the mantlederived melts (5.3 ± 0.6‰; 2σ), while values above 6.5‰ indicate recycling of supracrustal material (Valley, 2003; Valley et al., 2005).

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Table 3 Oxygen isotope ratio of zircon. Sample-analysis

δ18O (‰)

2σa (‰)

Z359-1-1.1 Z359-1-2.1 Z359-1-3.1 Z359-1-4.1 Z359-1-5.1 Z359-1-6.1 Z359-1-7.1 Z359-1-8.1 Z359-1-9.1 Z359-1-10.1 Z359-1-11.1 Z359-1-12.1 Z359-1-13.1 Z359-1-14.1 Z359-1-15.1 Mean (n = 15)

4.88 5.07 6.43 5.44 5.65 5.72 5.30 5.37 5.43 5.01 5.67 6.04 5.45 5.47 5.43 5.49

0.52 0.51 0.50 0.53 0.53 0.50 0.50 0.51 0.56 0.53 0.65 0.51 0.55 0.61 0.50 0.78 (2σ)

Z340-1-1.1 Z340-1-2.1 Z340-1-3.1 Z340-1-4.1 Z340-1-4.2 Z340-1-5.1 Z340-1-6.1 Z340-1-7.1 Z340-1-8.1 Z340-1-8.2 Z340-1-9.1 Z340-1-10.1 Z340-1-10.2 Z340-1-11.1 Z340-1-12.1 Z340-1-13.1 Z340-1-14.1 Mean (n = 17)

5.05 4.89 4.90 5.50 4.51 5.53 4.76 5.14 4.77 5.08 5.28 4.84 4.79 4.79 4.83 5.15 6.17 5.06

0.68 0.65 0.63 0.64 0.66 0.66 0.63 0.66 0.63 0.64 0.68 0.69 0.64 0.70 0.70 0.66 0.65 0.79 (2σ)

Zircon domains

UZ OZ OZ OZ OZ UZ UZ UZ OZ UZ OZ OZ UZ UZ OZ UZ UZ

Sample-analysis

δ18O (‰)

2σa (‰)

Z338-1-1.1 Z338-1-2.1 Z338-1-3.1 Z338-1-4.1 Z338-1-5.1 Z338-1-6.1 Z338-1-7.1 Z338-1-8.1 Z338-1-8.2 Z338-1-9.1 Z338-1-11.1 Z338-1-12.1 Z338-1-13.1 Z338-1-14.1 Z338-1-15.1 Mean (n = 15)

4.53 6.14 4.73 5.46 4.65 4.47 4.31 4.95 4.88 5.13 4.54 6.01 5.02 5.10 5.15 5.00

0.65 0.65 0.63 0.68 0.64 0.67 0.70 0.66 0.66 0.63 0.64 0.83 0.65 0.66 0.80 1.07 (2σ)

Z340-2-1.1 Z340-2-2.1 Z340-2-3.1 Z340-2-3.2 Z340-2-4.1 Z340-2-5.1 Z340-2-5.2 Z340-2-6.1 Z340-2-8.2 Z340-2-9.1 Z340-2-9.2 Z340-2-10.1 Z340-2-11.1 Z340-2-11.2 Z340-2-12.3 Z340-2-13.1 Z340-2-13.2 Mean (n = 17)

5.58 5.45 5.13 3.67 5.03 4.53 5.68 5.50 4.92 5.86 5.33 4.93 4.44 5.16 6.51 4.20 5.43 5.14

0.63 0.67 0.66 0.64 0.66 0.66 0.64 0.64 0.63 0.67 0.64 0.64 0.63 0.64 0.64 0.67 0.65 1.34 (2σ)

Zircon domains

UZ UZ UZ OZ UZ OZ UZ OZ OZ OZ UZ UZ UZ OZ UZ OZ UZ

Note: δ18O (‰) = ((18O/16OSample)/(18O/16OVSMOW) − 1) × 1000. The mean δ18O value and standard deviation (2σ) of each sample are listed in bold. Abbreviations: UZ−CL—bright unzoned; OZ—oscillatory zoned. a Quadratic addition of the within-spot uncertainty and the spot-to-spot uncertainty of TEMORA-2 zircon standard for the analytical session.

Paleoproterozoic Hf model ages (with a peak at ca. 1.85–1.80 Ga; Fig. 12) and mantle-like δ18O values of the Yandangshan volcanic– plutonic complex further substantiate that the Paleoproterozoic crustal accretion did occur in the eastern Cathaysia block. 6.2. Fractional crystallization of the volcanic magma As shown in Harker diagrams (Fig. 9), samples from the Yandangshan volcanic rocks show an increasing trend of SiO2 contents from the first volcanic unit to the fourth volcanic unit and SiO2

Fig. 14. εNd(t) versus (87Sr/86Sr)i diagram for the Yandangshan volcanic–plutonic complex, also shown the Cretaceous basalts and rhyolites from SE China (Chen and Zhou, 1999; Shen et al., 1999; Xu and Xie, 2005; Yang et al., 1999).

correlates well with selective major element oxides. A good linear correlation between trace elements was also displayed among these volcanic rocks (Fig. 15). All samples show negative Eu, Sr, P and Ti anomalies in their normalized trace element patterns (Fig. 10), and the second and fourth volcanic units further have marked positive Rb anomalies and negative Ba anomalies, indicating the removal of alkali feldspar is more important than plagioclase during magma differentiation (e.g., Klimm et al., 2008; Medlin et al., 2015). Compared with the other three volcanic units, the first volcanic unit samples are characterized by highest Sr, Ba and Zr contents and Eu/Eu* values and lowest Rb/ Ba and Rb/Sr ratios (Figs. 10 and 15), suggesting that the Yandangshan volcanic rocks are likely the result of crystal fractionation from a parental magma close to that of the least-evolved sample of the first volcanic unit. A Rayleigh fractional crystallization modeling (Rollinson, 1993) was undertaken on the Yandangshan volcanic rocks in terms of the variations of Rb, Sr, Ba and Eu/Eu* (Fig. 15), which are useful trace elements to describe fractionation of alkali feldspar and plagioclase (Halliday et al., 1991; Hanson, 1978; Icenhower and London, 1996). The equation for Rayleigh fractionation is CL/C0 = F(D−1); where CL is the concentration of an element in a liquid after fractional crystallization, C0 is the concentration of the same element in the liquid before any fractionation has occurred, F is the fraction of original liquid remaining and D is the bulk partition coefficient (D = ΣXiDi with Xi the modal fraction of a given mineral phase and Di the bulk partition coefficient for element i) (Rollinson, 1993). The modeling results further test the above hypotheses that the Yandangshan volcanic rocks could be linked by fractional crystallization of K-feldspar, plagioclase, clinopyroxene, quartz, biotite and magnetite (at proportions of 55:15:10:10:5:5) when we used the lowest SiO2 sample from the first volcanic unit as the parental magma (Fig. 15).

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a

b

c

d

Fig. 15. Results of Rayleigh fractional crystallization modeling (Rollinson, 1993) on the Yandangshan volcanic rock samples in terms of the variations of (a) Rb versus Sr, (b) Ba versus Sr, (c) Rb/Ba versus Rb/Sr, and (d) Eu/Eu* versus Sr. Note that the porphyritic quartz syenites plot in the opposite direction of fractional crystallization vector roughly fitting the accumulation of K-feldspar, plagioclase and clinopyroxene. The lowest SiO2 sample (Z356–2; 69.59 wt.%) from the first volcanic unit was chosen as the parental magma composition for fractionation modeling (green-filled triangle). Fractionation of Kfs-Plag-Cpx-Qtz-Bt-Mgt (55:15:10:10:5:5) well links the studied volcanic rocks. The crosses on the fractionation vectors with numbers indicate progressive percent fractional crystallization. Partition coefficient values are from www.earthref.org/GERM and given in Supplementary Table 7.

It should be noted that although the Yandangshan volcanic rocks show a good correlation from the first volcanic unit to the fourth volcanic unit, the third volcanic unit is less evolved than either the older second unit or the younger fourth unit with relatively high Fe, Mg, Ca, Sr, P and Ba, low Rb and Eu/Eu* (Figs. 9, 10 and 15). This may indicate a magma recharge event occurred before the eruption of the third volcanic unit. The injection of primitive magma caused the magma reservoir to be chemically less evolved. Recharge of the magma chamber by the arrival of a new magma batch is almost ubiquitous at an active volcano, which may be a trigger for eruptions (Humphreys et al., 2006; Tepley et al., 2000), and the effects also include MgO and SiO2 fluctuations in lavas (Ustunisik and Kilinc, 2011), as well as compositional and isotopic zonation in phenocrysts of volcanic rocks (Davidson and Tepley, 1997; Ginibre and Davidson, 2014; Tepley et al., 2000). A possible magma recharge event is also consistent with the occurrence of a deeper magma chamber beneath the shallow chamber that feeds the eruptions (see below). 6.3. Crystal accumulation and petrogenesis of the porphyritic quartz syenites Compared with the volcanic rocks, the subvolcanic porphyritic quartz syenites have distinctly lower SiO2 contents (65–66 wt.%) and higher TiO2, Al2O3, MgO, P2O5, FeO and CaO contents. A prominent silicic gap (from about 66 to 70 wt.% SiO2) exists between the porphyritic quartz syenites and volcanic rocks (Fig. 9). Furthermore, the porphyritic quartz syenites exhibit a linear correlation with the volcanic rocks in the major elements variation diagrams (Fig. 9). They typically show no or little Eu anomalies and higher REE (∑ REE = 327–421 ppm) (Fig. 10b), and more pronounced LREE enrichment ([La/Yb]N ratios =20–26 for quartz syenites and =7–20 for volcanic rocks) (Fig. 10b).

In contrast with the volcanic rocks, the porphyritic quartz syenites are characterized by negative Rb anomalies, positive Ba and thus lower Rb/Ba and Rb/Sr ratios. Similarly, their Zr and Hf enrichments are heavier and Sr, P and Ti depletions are weaker (Figs. 10d and 15). The above features suggest that the porphyritic quartz syenites might have formed by crystal accumulation in magma chamber. Their negative Rb anomalies, positive Ba anomalies and high total alkaline contents are probably resulted from accumulation of K-feldspar, the high P2O5 and LREE contents may be due to accumulation of apatite and allanite, and the positive Zr and Hf anomalies may be the role of accumulation of zircon (Deering and Bachmann, 2010; Klimm et al., 2008; Linnen and Keppler, 2002; Thomas et al., 2002; Wolff et al., 2015). Therefore, the porphyritic quartz syenites could be the materials left behind by extraction of rhyolite melts which formed the Yandangshan volcanic rocks (e.g., Bachmann and Bergantz, 2004; Deering et al., 2011). Further evidence includes the similar compositions of the phenocrysts of alkali feldspar, plagioclase and clinopyroxene in the volcanic rocks and porphyritic quartz syenites (Fig. 5). This hypothesis may be supported by a trace element modeling that the porphyritic quartz syenites plot in the opposite direction of fractional crystallization vectors calculated from accumulation of K-feldspar, plagioclase and clinopyroxene (Fig. 15). 6.4. Implications for the petrogenetic model of volcanic–plutonic complex in SE China As discussed above, the apparent fractional crystallization trend and almost identical isotopic compositions of the coexisting volcanic rocks and subvolcanic intrusions of the Yandangshan caldera indicate that they were comagmatic (Figs. 9 and 11–14). Their complementary geochemical relationships (Fig. 10) further suggest that they were

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produced by extraction of melts and crystal accumulation from the same magma. This is well in agreement with the recent model proposed for generation of rhyolitic eruptions that rhyolites were extracted from crystal mushes via gravitational collapse of the crystal mushes, rather than being stored in magma chambers prior to eruption (Bachmann and Bergantz, 2004; Bachmann et al., 2007; Eichelberger et al., 2006). Moreover, some zircon grains from the volcanic rocks, porphyritic quartz syenites and mafic microgranular enclaves have CL-bright unzoned or weakly zoned rims or patches (Fig. 6). This may be indicative of a prolonged and multi-stage zircon growth and suggests that a deep magma reservoir is linked with a shallow magma chamber and periodically feed the eruptions (e.g., Medlin et al., 2015; Miller et al., 2007; Wang et al., 2013). The cores of these zircon grains, which might have crystallized from the deep magma chamber, were partially to completely resorbed during rim formation within the shallow magma chamber. Annen et al. (2006) suggested a model for the generation of intermediate and silicic igneous rocks in a subduction-related tectonic setting, in which sills of mantle-derived basaltic magma injected into the lower crust, generating a deep crustal hot zone and promoting partial melting of the pre-existing crustal rocks. For the Yandangshan volcanic–plutonic complex, the widespread and contemporaneous calc-alkaline basalts in the coastal SE China (Chen et al., 2008b; He and Xu, 2012; Xu and Xie, 2005) may support the involvement of mantle-derived magma. The crustal-derived melts ascended from the hot zone to form a deep acid magma reservoir in the mid- to upper crust, feeding and recharging a shallow upper-crustal magma chamber, which is necessary for the generation of high-silica rhyolitic rocks (e.g., Gualda and Ghiorso, 2013) and is consistent with the crystallization depth of ~ 2 km for the volcanic unit estimated by the

305

thermobarometric calculations. Some crystals such as the above mentioned zircon cores also formed and migrated together to the shallow upper-crustal magma chamber. Continued fractional crystallization and crystal accumulation in the caldera magma chamber formed the crystal mushes and the evolved silicic melts (Bachmann and Bergantz, 2004; Bachmann et al., 2007; Eichelberger et al., 2006). Gravitational collapse of the crystal mushes expel silicic melt accumulating at the top of the magma chamber (Bachmann and Bergantz, 2004; Deering and Bachmann, 2010), and then the extracted silicic melts are erupted in stages forming as the Yandangshan volcanic rocks, whereas the non-erupted portion and the residual crystal mushes (dominated by alkali feldspar) “freezed” as the subvolcanic porphyritic quartz syenites. A petrogenetic model for the Yandangshan volcanic–plutonic complex is shown in Fig. 16. The model is similar to that presented by Medlin et al. (2015) for the intra-caldera Kathleen ignimbrite and Rowland Suite intrusions (West Musgrave Province, Australia). Medlin et al. (2015) used geochemical modeling to suggest that the crystal-rich, porphyritic rhyolite intrusions of the Rowland Suite represent a primitive cumulate end-member of the magmatic system, whereas the Kathleen ignimbrite eruption sequence represents the evolved and highly fractionated end-member of the system. In addition to the Yandangshan volcanic–plutonic complex, other rhyolite calderas in SE China are also accompanied by coexisting shallow plutons. He and Xu (2012) studied some shallow plutons (being subvolcanic intrusions of calderas) from a larger areas in SE China, and found that shallow plutons are generally characterized by high REE concentrations, little negative Eu anomalies, negative Rb and positive Ba, K, Zr and Hf anomalies (see Fig. 7 in He and Xu, 2012). These features are very similar to the Yandangshan porphyritic quartz syenites. Therefore,

Fig. 16. Schematic model illustrating the magma origin of the Yandangshan volcanic–plutonic complex (modified after Annen et al., 2006; Bachmann and Bergantz, 2004; Cole et al., 2014; Medlin et al., 2015). Lower-crust derived melt induced by underplating or intraplating of mantle-derived basaltic magma ascended to form a deep silicic magma reservoir in the mid- to upper crust, which feeds and recharges the shallow upper-crustal magma chamber. Continuing fractional crystallization and crystal accumulation in the shallow magma chamber formed the crystal mushes and the evolved silicic melts. Most the extracted silicic melts were erupted in stages forming as the Yandangshan volcanic rocks, whereas the non-erupted portion and the residual crystal mushes (dominated by alkali feldspar) freezed as the subvolcanic porphyritic quartz syenites. At the same time, the mafic magma which stored and partially crystallized and fractionated in a deep mafic chamber injected into the shallow silicic chamber, inducing a lesser degree of magma mixing and the formation of the mafic microgranular enclaves (MMEs).

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the magma evolution model of the Yandangshan calderas presented above is probably applicable for the widespread Cretaceous volcanic– plutonic complexes in SE China. However, deep-seated plutons in SE China are entirely independent because they are tectonically unrelated to the coexisting volcanic rocks. They were exposed by tectonic uplift, and have different emplacement ages with the associated volcanic rocks (see Zhou et al., 2006). 7. Conclusions 1) Zircon U–Pb dating revealed that the crystallization ages of the volcanic rocks and subvolcanic intrusions in the Yandangshan caldera are practically identical within analytical errors (104–98 Ma). 2) The similar zircon Hf–O and whole-rock Sr–Nd isotopic compositions of the Yandangshan volcanic and intrusive rocks suggest that the rocks are derived from a common magma pool, which was generated by partial melting of an ancient mafic lower crust. The mantle-like δ18O values further suggest that a major crustal growth probably took place during the Paleoproterozoic (~1.85 Ga) in the eastern Cathaysia block of SE China. 3) On the basis of the geochemical and isotopic data, we suggest that the magmas of the Yandangshan volcanic rocks were extracted from a shallow crystal-rich magma chamber, while the nonerupted portion and the residual crystal mushes in the chamber solidified as the subvolcanic intrusions. This documents a genetic connection between shallow plutons and volcanic rocks. This model may be applicable for the Cretaceous volcanic–plutonic complexes in SE China. Acknowledgments We thank Prof. Nelson Eby, Dr. Rongfeng Ge and one anonymous reviewer for their constructive comments on the manuscript. We are also thankful to Prof. Guangfu Xing for his valuable discussion and to Lei Liu and Qin-Fei Lu for the assistance with field studies. This work was supported by the National Natural Science Foundation of China (41102028), the Research Grant from Institute of Geology, CAGS (J1311) and the scholarships from the China Scholarship Council (to L.L. Yan and Z.Y. He). Bor-ming Jahn acknowledges the support of the MOST (Taiwan) through research projects of MOST 104-2923-M-002005, MOST 105-2116-M-002-007 and MOST 105-2923-M-002-002. Appendix A. Supplementary data Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.lithos.2016.10.029. These data also include the Google map of the most important areas described in this article. References Andersen, T., 2002. Correction of common Pb in U–Pb analyses that do not report 204Pb. Chemical Geology 192, 59–79. Annen, C., 2009. From plutons to magma chambers: thermal constraints on the accumulation of eruptible silicic magma in the upper crust. Earth and Planetary Science Letters 284, 409–416. Annen, C., Blundy, J.D., Sparks, R.S.J., 2006. The genesis of intermediate and silicic magmas in deep crustal hot zones. Journal of Petrology 47, 505–539. Bachmann, O., Bergantz, G.W., 2004. On the origin of crystal-poor rhyolites: extracted from batholithic crystal mushes. Journal of Petrology 45, 1565–1582. Bachmann, O., Miller, C., de Silva, S., 2007. The volcanic–plutonic connection as a stage for understanding crustal magmatism. Journal of Volcanology and Geothermal Research 167, 1–23. Barbarin, B., Didier, J., 1992. Genesis and evolution of mafic microgranular enclaves through various types of interaction between coexisting felsic and mafic magmas. Transactions of the Royal Society of Edinburgh: Earth Sciences 83, 145–153. Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N., Valley, J.W., Mundil, R., Campbell, I.H., Korsch, R.J., Williams, I.S., Foudoulis, C., 2004. Improved 206Pb/238U microprobe geochronology by the monitoring of a trace-element-related matrix effect;

SHRIMP, ID-TIMS, ELA-ICP-MS and oxygen isotope documentation for a series of zircon standards. Chemical Geology 205, 115–140. Bouvier, A., Vervoort, J.D., Patchett, P.J., 2008. The Lu–Hf and Sm–Nd isotopic composition of CHUR: constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth and Planetary Science Letters 273, 48–57. Breitkreuz, C., 2013. Spherulites and lithophysae—200 years of investigation on hightemperature crystallization domains in silica-rich volcanic rocks. Bulletin of Volcanology 75, 705. Browne, B.L., Eichelberger, J.C., Patino, L.C., Vogel, T.A., Dehn, J., Uto, K., Hoshizumi, H., 2006. Generation of porphyritic and equigranular mafic enclaves during magma recharge events at Unzen Volcano, Japan. Journal of Petrology 47, 301–328. Cantagrel, J.M., Didier, J., Gourgaud, A., 1984. Magma mixing: origin of intermediate rocks and “enclaves” from volcanism to plutonism. Physics of the Earth and Planetary Interiors 35, 63–76. Chen, J.F., Jahn, B.M., 1998. Crustal evolution of southeastern China: Nd and Sr isotopic evidence. Tectonophysics 284, 101–133. Chen, R., Zhou, J.C., 1999. Information of crust–mantle interaction implied in early Cretaceous composite lavas and dikes from eastern Zhejiang. Geology Review 45, 784–795 (in Chinese with English abstract). Chen, C.H., Lee, C.Y., Shinjo, R., 2008b. Was there Jurassic paleo-Pacific subduction in South China?: constraints from 40Ar/39Ar dating, elemental and Sr–Nd–Pb isotopic geochemistry of the Mesozoic basalts. Lithos 106, 83–92. Chen, C.H., Lee, C.Y., Lu, H.Y., Hsieh, P.S., 2008a. Generation of Late Cretaceous silicic rocks in SE China: age, major element and numerical simulation constraints. Journal of Asian Earth Sciences 31, 479–498. Cole, J.W., Deering, C.D., Burt, R.M., Sewell, S., Shane, P.A.R., Matthews, N.E., 2014. Okataina Volcanic Centre, Taupo Volcanic Zone, New Zealand: a review of volcanism and synchronous pluton development in an active, dominantly silicic caldera system. Earth-Science Reviews 128, 1–17. Davidson, J.P., Tepley, F.J., 1997. Recharge in volcanic systems: evidence from isotope profiles of phenocrysts. Science 275, 826–829. de Silva, S.L., Gosnold, W.D., 2007. Episodic construction of batholiths: insights from the spatiotemporal development of an ignimbrite flare-up. Journal of Volcanology and Geothermal Research 167, 320–335. Deering, C.D., Bachmann, O., 2010. Trace element indicators of crystal accumulation in silicic igneous rocks. Earth and Planetary Science Letters 297, 324–331. Deering, C.D., Bachmann, O., Vogel, T.A., 2011. The Ammonia Tanks Tuff: erupting a meltrich rhyolite cap and its remobilized crystal cumulate. Earth and Planetary Science Letters 310, 518–525. Eichelberger, J.C., Izbekov, P.E., Browne, B.L., 2006. Bulk chemical trends at arc volcanoes are not liquid lines of descent. Lithos 87, 135–154. Feng, C.G., Yu, Y.W., Dong, Y.H., 1997. Petrogenetic sources and tectonic characteristics of Yandangshan caldera, Zhejiang Province. Geology of Zhejiang 13, 18–25 (in Chinese with English abstract). Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J., Frost, C.D., 2001. A geochemical classification for granitic rocks. Journal of Petrology 42, 2033–2048. Ginibre, C., Davidson, J.P., 2014. Sr isotope zoning in plagioclase from Parinacota Volcano (Northern Chile): quantifying magma mixing and crustal contamination. Journal of Petrology 55, 1203–1238. Glazner, A.F., Bartley, J.M., Coleman, D.S., Gray, W., Taylor, R.Z., 2004. Are plutons assembled over millions of years by amalgamation from small magma chambers? GSA Today 14, 4–12. Glazner, A.F., Coleman, D.S., Mills, R.D., 2015. The Volcanic–Plutonic Connection. Springer, Berlin Heidelberg, pp. 1–22. Griffin, W.L., Pearson, N.J., Belousova, E., Jackson, S.E., Van Achterbergh, E., O'Reilly, S.Y., Shee, S.R., 2000. The Hf isotope composition of cratonic mantle: LAM-MC-ICPMS analysis of zircon megacrysts in kimberlites. Geochimica et Cosmochimica Acta 64, 133–147. Griffin, W.L., Wang, X., Jackson, S.E., Pearson, N.J., O'Reilly, S.Y., Xu, X., Zhou, X., 2002. Zircon chemistry and magma mixing, SE China: in situ analysis of Hf isotopes, Tonglu and Pingtan igneous complexes. Lithos 61, 237–269. Gualda, G.A., Ghiorso, M.S., 2013. Low-pressure origin of high-silica rhyolites and granites. Journal of Geology 121, 537–545. Halliday, A.N., Davidson, J.P., Hildreth, W., Holden, P., 1991. Modelling the petrogenesis of high Rb/Sr silicic magmas. Chemical Geology 92, 107–114. Hanson, G.N., 1978. The application of trace elements to the petrogenesis of igneous rocks of granitic composition. Earth and Planetary Science Letters 38, 26–43. Hawkesworth, C.J., Kemp, A.I.S., 2006. Using hafnium and oxygen isotopes in zircons to unravel the record of crustal evolution. Chemical Geology 226, 144–162. Hawkesworth, C.J., Dhuime, B., Pietranik, A.B., Cawood, P.A., Kemp, A.I.S., Storey, C.D., 2010. The generation and evolution of the continental crust. Journal of the Geological Society, London 167, 229–248. He, Z.Y., Xu, X.S., 2012. Petrogenesis of the Late Yanshanian mantle-derived intrusions in southeastern China: response to the geodynamics of paleo-Pacific plate subduction. Chemical Geology 328, 208–221. He, Z.Y., Xu, X.S., Yu, Y., Zou, H.B., 2009. Origin of the Late Cretaceous syenite from Yandangshan, SE China, constrained by zircon U–Pb and Hf isotopes and geochemical data. International Geology Review 51, 556–582. He, Z.Y., Xu, X.S., Zou, H.B., Wang, X.D., Yu, Y., 2010. Geochronology, petrogenesis and metallogeny of Piaotang granites in the tungsten deposit region of South China. Geochemical Journal 44, 299–313. Hibbard, M.J., 1981. The magma mixing origin of mantled feldspars. Contributions to Mineralogy and Petrology 76, 158–170. Horstwood, M.S., Kosler, J., Jackson, S.E., Pearson, N.J., Sylvester, P.J., 2009. Investigating age resolution in laser ablation geochronology. Eos, Transactions American Geophysical Union 90. http://dx.doi.org/10.1029/2009EO060004.

L.-L. Yan et al. / Lithos 266–267 (2016) 287–308 Humphreys, M.C., Blundy, J.D., Sparks, R.S.J., 2006. Magma evolution and open-system processes at Shiveluch Volcano: insights from phenocryst zoning. Journal of Petrology 47, 2303–2334. Huppert, H.E., Sparks, R.S.J., 1988. The generation of granitic magmas by intrusion of basalt into continental crust. Journal of Petrology 29, 599–624. Icenhower, J., London, D., 1996. Experimental partitioning of Rb, Cs, Sr, and Ba between alkali feldspar and peraluminous melt. American Mineralogist 81, 719–734. Ickert, R.B., Hiess, J., Williams, I.S., Holden, P., Ireland, T.R., Lanc, P., Schram, N., Foster, J.J., Clement, S.W., 2008. Determining high precision, in situ, oxygen isotope ratios with a SHRIMP II: analyses of MPI-DING silicate-glass reference materials and zircon from contrasting granites. Chemical Geology 257, 114–128. Jahn, B.M., 1974. Mesozoic thermal events in southeast China. Nature 248, 480–483. Jahn, B.M., Capdevila, R., Liu, D., Vernon, A., Badarch, G., 2004. Sources of Phanerozoic granitoids in the transect Bayanhongor–Ulaan Baatar, Mongolia: geochemical and Nd isotopic evidence, and implications for Phanerozoic crustal growth. Journal of Asian Earth Sciences 23, 629–653. Jahn, B.M., Usuki, M., Usuki, T., Chung, S.L., 2014. Generation of Cenozoic granitoids in Hokkaido (Japan): constraints from zircon geochronology, Sr–Nd–Hf isotopic and geochemical analyses, and implications for crustal growth. American Journal of Science 314, 704–750. Jahn, B.M., Valui, G., Kruk, N., Gonevchuk, V., Usuki, M., Wu, J.T.J., 2015. Emplacement ages, geochemical and Sr–Nd–Hf isotopic characterization of Mesozoic to Early Cenozoic granitoids of the Sikhote-Alin Orogenic Belt, Russian Far East: crustal growth and regional tectonic evolution. Journal of Asian Earth Sciences 111, 872–918. Jahn, B.M., Wu, F., Capdevila, R., Martineau, F., Zhao, Z., Wang, Y., 2001. Highly evolved juvenile granites with tetrad REE patterns: the Woduhe and Baerzhe granites from the Great Xing'an Mountains in NE China. Lithos 59, 171–198. Kemp, A.I.S., Hawkesworth, C.J., Foster, G.L., Paterson, B.A., Woodhead, J.D., Hergt, J.M., Gray, C.M., Whitehouse, M.J., 2007. Magmatic and crustal differentiation history of granitic rocks from Hf–O isotopes in zircon. Science 315, 980–983. Kemp, A.I.S., Hawkesworth, C.J., Paterson, B.A., Foster, G.L., Kinny, P.D., Whitehouse, M.J., Maas, R., EIMF, 2008. Exploring the plutonic–volcanic link: a zircon U–Pb, Lu–Hf and O isotope study of paired volcanic and granitic units from southeastern Australia. Transactions of the Royal Society of Edinburgh: Earth Sciences 97, 337–355. Klimm, K., Holtz, F., King, P.L., 2008. Fractionation vs. magma mixing in the Wangrah Suite A-type granites, Lachlan Fold Belt, Australia: experimental constraints. Lithos 102, 415–434. Lapierre, H., Jahn, B.M., Charvet, J., Yu, Y.W., 1997. Mesozoic felsic arc magmatism and continental olivine tholeiites in Zhejiang province and their relationship with the tectonic activity in southeastern China. Tectonophysics 274, 321–338. Le Maitre, R.W., Streckeisen, A., Zanettin, B., Le Bas, M.J., Bonin, B., Bateman, P., Bellieni, G., Dudek, A., Efremova, S., Keller, J., Lameyre, J., Sabine, P.A., Schmid, R., Sorensen, H., Woolley, A.R., 2002. Igneous Rocks; a Classification and Glossary of Terms; Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Cambridge University Press. Leake, B.E., Woolley, A.R., Arps, C.E.S., Birch, W.D., Gilbert, M.C., Grice, J.D., Hawthorne, C., Kato, A., Kisch, H.J., Krivovichev, V.G., Linthout, K., Laird, J., Mandarino, J.A., Maresch, W.V., Nickel, E.H., Rock, N.M.S., Schumacher, J.C., Smith, D.C., Stephenson, N.C.N., Ungaretti, L., Whittaker, E.J.W., Youzhi, G., 1997. Nomenclature of amphiboles: report of the Subcommittee on Amphiboles of the International Mineralogical Association, Commission on New Minerals and Mineral names. American Mineralogist 82, 1019–1037. Li, X., Liu, X., Liu, Y., Su, L., Sun, W., Huang, H., Yi, K., 2015. Accuracy of LA-ICPMS zircon U–Pb age determination: an inter-laboratory comparison. Science China Earth Sciences 58, 1722–1730. Li, X.H., Sun, M., Wei, G.J., Liu, Y., Lee, C.Y., Malpas, J., 2000. Geochemical and Sm–Nd isotopic study of amphibolites in the Cathaysia Block, southeastern China: evidence for an extremely depleted mantle in the Paleoproterozoic. Precambrian Research 102, 251–262. Linnen, R.L., Keppler, H., 2002. Melt composition control of Zr/Hf fractionation in magmatic processes. Geochimica et Cosmochimica Acta 66, 3293–3301. Lipman, P.W., 1984. The roots of ash-flow calderas in western North America: windows into the tops of granitic batholiths. Journal of Geophysical Research 89, 8801–8841. Lipman, P.W., 2007. Incremental assembly and prolonged consolidation of Cordilleran magma chambers: evidence from the Southern Rocky Mountain volcanic field. Geosphere 3, 42–70. Liu, L., Xu, X.S., Zou, H.B., 2012. Episodic eruptions of the Late Mesozoic volcanic sequences in southeastern Zhejiang, SE China: petrogenesis and implications for the geodynamics of paleo-Pacific subduction. Lithos 154, 166–180. Ludwig, K.R., 2001. User's Manual for Isoplot/Ex (Rev.2.49): A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center, Special Publication 1a 55. Lundstrom, C.C., Glazner, A.F., 2016. Silicic magmatism and the volcanic–plutonic connection. Elements 12, 91–96. Maniar, P.D., Piccoli, P.M., 1989. Tectonic discrimination of granitoids. Geological Society of America Bulletin 101, 635–643. McDonough, W.F., Sun, S.S., 1995. The composition of the Earth. Chemical Geology 120, 223–253. Medlin, C., Jowitt, S., Cas, R., Smithies, R., Kirkland, C., Maas, R., Raveggi, M., Howard, H., Wingate, M., 2015. Petrogenesis of the A-type, Mesoproterozoic intra-caldera rheomorphic Kathleen ignimbrite and comagmatic Rowland suite intrusions, West Musgrave Province, Central Australia: products of extreme fractional crystallization in a failed rift setting. Journal of Petrology 56, 493–525. Middlemost, E.A.K., 1994. Naming materials in the magma/igneous rock system. EarthScience Reviews 37, 215–224. Miller, J.S., Matzel, J.E., Miller, C.F., Burgess, S.D., Miller, R.B., 2007. Zircon growth and recycling during the assembly of large, composite arc plutons. Journal of Volcanology and Geothermal Research 167, 282–299.

307

Morimoto, N., Fabries, J., Ferguson, A.K., Ginzburg, I.V., Ross, M., Seifert, F.A., Zussman, J., Aoki, K., Gottardi, G., 1988. Nomenclature of pyroxenes. American Mineralogist 73, 1123–1133. Müller, A., Breiter, K., Seltmann, R., Pécskay, Z., 2005. Quartz and feldspar zoning in the eastern Erzgebirge volcano–plutonic complex (Germany, Czech Republic): evidence of multiple magma mixing. Lithos 80, 201–227. Peck, W.H., Valley, J.W., Graham, C.M., 2003. Slow diffusion rates of O isotopes in igneous zircons from metamorphic rocks. American Mineralogist 88, 1003–1014. Perugini, D., Poli, G., 2012. The mixing of magmas in plutonic and volcanic environments: analogies and differences. Lithos 153, 261–277. Reubi, O., Blundy, J., 2009. A dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc andesites. Nature 461, 1269–1273. Ridolfi, F., Renzulli, A., Puerini, M., 2010. Stability and chemical equilibrium of amphibole in calc-alkaline magmas: an overview, new thermobarometric formulations and application to subduction-related volcanoes. Contributions to Mineralogy and Petrology 160, 45–66. Rollinson, H.R., 1993. Using Geochemical Data: Evaluation, Presentation, Interpretation. Longman. Scaillet, B., Holtz, F., Pichavant, M., 2016. Experimental constraints on the formation of silicic magmas. Elements 12, 109–114. Shaw, S.E., Flood, R.H., 2009. Zircon Hf isotopic evidence for mixing of crustal and silicic mantle-derived magmas in a zoned granite pluton, eastern Australia. Journal of Petrology 50, 147–168. Shen, W.Z., Ling, H.F., Wang, D.Z., Xu, B.T., Yu, Y.W., 1999. Study on Nd–Sr isotopes of Mesozoic igneous rocks in Zhejiang, China. Scientia Geologica Sinica 34, 223–232 (in Chinese with English abstract). Smith, R.L., Bailey, R.A., 1966. The Bandelier Tuff: a study of ash-flow eruption cycles from zoned magma chambers. Bulletin of Volcanology 29, 83–103. Söderlund, U., Patchett, P.J., Vervoort, J.D., Isachsen, C.E., 2004. The 176Lu decay constant determined by Lu–Hf and U–Pb isotope systematics of Precambrian mafic intrusions. Earth and Planetary Science Letters 219, 311–324. Tappa, M.J., Coleman, D.S., Mills, R.D., Samperton, K.M., 2011. The plutonic record of a silicic ignimbrite from the Latir volcanic field, New Mexico. Geochemistry, Geophysics, Geosystems 12, 10. Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: its Composition and Evolution. Blackwell. Tepley, F.J., Davidson, J.P., Tilling, R.I., Arth, J.G., 2000. Magma mixing, recharge and eruption histories recorded in plagioclase phenocrysts from El Chichon Volcano, Mexico. Journal of Petrology 41, 1397–1411. Thomas, J., Bodnar, R., Shimizu, N., Sinha, A., 2002. Determination of zircon/melt trace element partition coefficients from SIMS analysis of melt inclusions in zircon. Geochimica et Cosmochimica Acta 66, 2887–2901. Ustiyev, Y.K., 1965. Problems of volcanism and plutonism. Volcano–plutonic formations. International Geology Review 7, 1994–2016. Ustunisik, G., Kilinc, A., 2011. The role of fractional crystallization, magma recharge, and magma mixing in the differentiation of the Small Hasandag volcano, Central Anatolia, Turkey. Lithos 125, 984–993. Valley, J.W., 2003. Oxygen isotopes in zircon. Reviews in Mineralogy and Geochemistry 53, 343–380. Valley, J.W., Lackey, J.S., Cavosie, A.J., Clechenko, C.C., Spicuzza, M.J., Basei, M.A.S., Bindeman, I.N., Ferreira, V.P., Sial, A.N., King, E.M., Peck, W.H., Sinha, A.K., Wei, C.S., 2005. 4.4 billion years of crustal maturation: oxygen isotopes in magmatic zircon. Contributions to Mineralogy and Petrology 150, 561–580. Van Achterbergh, E., Ryan, C.G., Jackson, S.E., Griffin, W.L., 2001. Data Reduction Software for LA-ICP-MS. Laser-ablation-ICPMS in the earth sciences—principles and applications. Miner Assoc Can (short course series) 29 pp. 239–243. Vernon, R.H., 1984. Microgranitoid enclaves in granites—globules of hybrid magma quenched in a plutonic environment. Nature 309, 438–439. Wang, D.Z., Zhou, J.C., Qiu, J.S., Fan, H.H., 2000. Characteristics and petrogenesis of Late Mesozoic granitic volcanic–intrusive complexes in Southeastern China. Geological Journal of China Universities 6, 487–498 (in Chinese with English abstract). Wang, X.L., Zhou, J.C., Wan, Y.S., Kitajima, K., Wang, D., Bonamici, C., Qiu, J.S., Sun, T., 2013. Magmatic evolution and crustal recycling for Neoproterozoic strongly peraluminous granitoids from southern China: Hf and O isotopes in zircon. Earth and Planetary Science Letters 366, 71–82. Wiedenbeck, M., Hanchar, J.M., Peck, W.H., Sylvester, P., Valley, J., Whitehouse, M., Kronz, A., Morishita, Y., Nasdala, L., Fiebig, J., Franchi, I., Girard, J.P., Greenwood, R.C., Hinton, R., Kita, N., Mason, P.R.D., Norman, M., Ogasawara, M., Piccoli, R., Rhede, D., Satoh, H., Schulz-Dobrick, B., Skar, O., Spicuzza, M.J., Terada, K., Tindle, A., Togashi, S., Vennemann, T., Xie, Q., Zheng, Y.F., 2004. Further characterisation of the 91500 zircon crystal. Geostandards and Geoanalytical Research 28, 9–39. Williams, I.S., 1998. U–Th–Pb geochronology by ion microprobe. In: McKibben, M.A., Shanks, W.C., Ridley, W.I. (Eds.), Application of Microanalytical Techniques to Understanding Mineralizing Processes. Review in Economic Geology vol. 7, pp. 1–35. Wolff, J.A., Ellis, B.S., Ramos, F.C., Starkel, W.A., Boroughs, S., Olin, P.H., Bachmann, O., 2015. Remelting of cumulates as a process for producing chemical zoning in silicic tuffs: a comparison of cool, wet and hot, dry rhyolitic magma systems. Lithos 236, 275–286. Wu, F.Y., Yang, Y.H., Xie, L.W., Yang, J.H., Xu, P., 2006. Hf isotopic compositions of the standard zircons and baddeleyites used in U–Pb geochronology. Chemical Geology 234, 105–126. Wyborn, D., Chappell, B.W., 1986. The petrogenetic significance of chemically related plutonic and volcanic rock units. Geological Magazine 123, 619–628. Xia, Y., Xu, X.S., Zhu, K.Y., 2012. Paleoproterozoic S- and A-type granites in southwestern Zhejiang: magmatism, metamorphism and implications for the crustal evolution of the Cathaysia basement. Precambrian Research 216–219, 177–207.

308

L.-L. Yan et al. / Lithos 266–267 (2016) 287–308

Xiang, H., Zhang, L., Zhou, H., Zhong, Z., Zeng, W., Liu, R., Jin, S., 2008. U–Pb zircon geochronology and Hf isotope study of metamorphosed basic-ultrabasic rocks from metamorphic basement in southwestern Zhejiang: the response of the Cathaysia Block to Indosinian orogenic event. Science in China Series D: Earth Sciences 51, 788–800. Xing, G.F., Lu, Q.D., Chen, R., Zhang, Z.Y., Nie, T.C., Li, L.M., Huan, G.J., Lin, M., 2008. Study on the ending time of Late Mesozoic tectonic regime transition in South China: comparing to the Yanshan area in North China. Acta Geologica Sinica 82, 451–463 (in Chinese with English abstract). Xu, X.S., Xie, X., 2005. Late Mesozoic–Cenozoic basaltic rocks and crust–mantle interaction, SE China. Geological Journal of China Universities 11, 318–334 (in Chinese with English abstract). Xu, X.S., O'Reilly, S.Y., Griffin, W.L., Wang, X.L., Pearson, N.J., He, Z.Y., 2007. The Crust of Cathaysia: age, assembly and reworking of two terranes. Precambrian Research 158, 51–78. Yan, L.L., He, Z.Y., Liu, L., Zhao, Z.D., 2015. Magma mixing in the Yandangshan volcanic– intrusive complex, Zhejiang Province: evidence from feldspar zoning of the mafic microgranular enclave. Geological Bulletin of China 34, 466–473 (in Chinese with English abstract). Yang, Z.L., Shen, W.Z., Tao, K.Y., Shen, J.L., 1999. Sr, Nd and Pb isotopic characteristics of early Cretaceous basaltic rocks from the coast of Zhejiang and Fujian: evidences for ancient enriched mantle souce. Scientia Geologica Sinica 34, 59–68 (in Chinese with English abstract).

Yu, J.H., O'Reilly, S.Y., Griffin, W.L., Zhou, M.F., Wang, L.J., 2012. U–Pb geochronology and Hf–Nd isotopic geochemistry of the Badu Complex, Southeastern China: implications for the Precambrian crustal evolution and paleogeography of the Cathaysia Block. Precambrian Research 222–223, 424–449. Yu, M.G., Xing, G.F., Shen, J.L., Chen, R., Zhou, Y.Z., Wei, H.M., Tao, K.Y., 2008. Volcanism of the Yandang mountain world geopark. Acta Petrologica et Mineralogical 2, 101–112 (in Chinese with English abstract). Zhang, H.F., Sun, M., Zhou, X.H., 2002. Mesozoic lithosphere destruction beneath the North China Craton: evidence from major-, trace-element and Sr–Nd–Pb isotope studies of Fangcheng basalts. Contributions to Mineralogy and Petrology 144, 241–253. Zhao, G., 2015. Jiangnan Orogen in South China: developing from divergent double subduction. Gondwana Research 27, 1173–1180. Zhou, X.M., Sun, T., Shen, W.Z., Shu, L.S., Niu, Y.L., 2006. Petrogenesis of Mesozoic granitoids and volcanic rocks in South China: a response to tectonic evolution. Episodes 29, 26–33. Zimmerer, M.J., McIntosh, W.C., 2012. The geochronology of volcanic and plutonic rocks at the Questa caldera: constraints on the origin of caldera-related silicic magmas. Geological Society of America Bulletin 124, 1394–1408.