571
ARTICLE Petrogenesis and tectonic implications of Late Jurassic – Early Cretaceous granitic magmatism in the Xing’an Block, Northeast China: geochronological, geochemical, and Hf isotopic evidence Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Jilin University on 05/30/18 For personal use only.
Yue He, Zhong-Hua He, Wen-Chun Ge, Hao Yang, Zhi-Hui Wang, Yu Dong, Jun-Hui Bi, and Di Zhao
Abstract: This study presents new geochronological, whole-rock geochemical, and zircon Hf isotopic evidence for the age, petrogenesis, and source of Mesozoic granitic rocks of the Xing’an Block, Northeast China. This evidence reveals the Late Mesozoic tectonic evolution of the eastern section of the Central Asian Orogenic Belt. Laser-ablation inductively coupled plasma – mass spectrometryzircon U–Pb age data indicate that the syenogranite, monzogranite, and alkali feldspar granite units, as well as their associated diorite microgranular enclaves, were emplaced between 150–142 Ma, providing evidence of Late Jurassic to Early Cretaceous magmatic events within the Xing’an Block. The granites contain high concentrations of SiO2 (65.24%–75.73 wt.%) and K2O (3.94%–5.30 wt.%), low concentrations of MgO (0.10%–1.30 wt.%), and A/CNK values of 0.92–1.06. In addition, Hf isotopic analysis of zircons from the 150–142 Ma granites yields Hf(t) values of +4.54 to +12.16 and two-stage Hf model aged from 906 to 423 Ma, indicating that they formed from magmas generated by partial melting of a juvenile Neoproterozoic–Phanerozoic accreted crustal source. The basic magma source for the diorite microgranular enclaves most likely formed from partial melting of a depleted mantle that had been metasomatized by subduction-related fluids. Combining these new geochemical data with the geology of this region, Late Jurassic to Early Cretaceous magmatism in the Xing’an Block most likely occurred in an extensional environment associated with closure of the Mongol–Okhotsk Ocean. Résumé : L’article présente de nouvelles données géochronologiques, géochimiques sur roche totale et d’isotopes de Hf dans des zircons sur l’âge, la pétrogenèse et la source de roches magmatiques mésozoïques du bloc de Xing’an (nord-est de la Chine). Ces données révèlent l’évolution tectonique au Mésozoïque tardif de la section est de la ceinture orogénique d’Asie centrale. Des données de datation U–Pb sur zircon par LA-ICP-MS indiquent que les unités de syénogranite, de monzogranite et de granite à feldspath alcalin, ainsi que les enclaves microgranulaires de diorite qui leur sont associées, ont été mises en place entre 150 Ma et 142 Ma, ce qui fournit des preuves d’épisodes magmatiques d’âge jurassique tardif à crétacé précoce dans le bloc de Xing’an. Les granites présentent de fortes concentrations de SiO2 (65,24 %–75,73 % en poids) et en K2O (3,94 %–5,30 % en poids), de faibles concentrations de MgO (0,10 %– 1,30 % en poids), et des rapports A/CNK de 0,92–1,06. L’analyse des isotopes de Hf dans les zircons des granites de 150–142 Ma donne en outre des valeurs de Hf(t) de +4,54 à +12,16 et des âges de Hf pour un modèle à deux étapes de 906 Ma à 423 Ma, ce qui indique que les granites se sont formés à partir de magmas produits par la fusion partielle d’une source crustale accrétée d’âge néoprotérozoïquephanérozoïque. La source de magma basique pour les enclaves de diorite microgranulaire s’est vraisemblablement formée par la fusion partielle d’un manteau appauvri métasomatisé par des fluides associés à la subduction. En combinant ces nouvelles données géochimiques à la géologie de la région, il ressort que le magmatisme d’âge jurassique tardif à crétacé précoce dans le bloc de Xing’an est probablement survenu dans un milieu d’extension associé à la fermeture de l’océan Mongol-Okhotsk. [Traduit par la Rédaction]
1. Introduction The Central Asian Orogenic Belt, located between the Siberia and North China cratons and extending from the Ural Mountains in the west to the Pacific coast in the east (Sengör et al. 1993; Jahn et al. 2000; Fig. 1a), is one of the largest accretionary orogens on Earth (Sengör et al. 1993; Windley et al. 2007). Its formation is associated with multiple episodes of subduction and long continuous periods of accretion (Kröner et al. 2007, 2014; Windley et al. 2007; Safonova et al. 2011). Owing to the unique nature and structural complexity of the Central Asian Orogenic Belt, this area has long been considered an ideal natural laboratory for studying the processes involved in accretionary orogenesis and continental growth (Xiao and Santosh 2014). The Great Xing’an Range (GXR), Northeast China, is located in the eastern segment of the Central Asian Orogenic Belt, and consists of several microcontinental blocks, including, from west to
east, the Erguna, Xing’an, Songliao, and Jiamusi-Khanka Blocks, in addition to the Nadanhada Terrane (IMBGMR 1991; HBGMR 1993; Wang and Guo 2012; Fig. 1b). The GXR contains voluminous volcanic rocks as well as associated granitoids (Wu et al. 2002, 2011; Zhang 2009), the majority of which were originally believed to have been emplaced during the Paleozoic (JBGMR 1988; IMBGMR 1991; HBGMR 1993). However, geochronological data from the GXR indicate that the majority of these intrusions are actually Mesozoic I-type granites (Wu et al. 2002; Tian et al. 2015; Ji et al. 2016). Wu et al. (2011) used zircon U–Pb dating to identify four stages of magmatism in the central GXR, the first two of which occurred at 466–446 (granite and quartz diorite intrusions) and 359–249 Ma (granodiorite and monzogranite intrusions). Granitoids in the southern part of the range yielded zircon U–Pb ages of 179–157 Ma. In addition, final stage of magmatism within both the Xing’an and Songliao terranes occurred during the Early Cretaceous
Received 6 November 2017. Accepted 11 March 2018. Paper handled by Associate Editor Li Qiuli. Y. He, Z.-H. He, W.-C. Ge, H. Yang, Z.-H. Wang, Y. Dong, J.-H. Bi, and D. Zhao. College of Earth Sciences, Jilin University, Changchun 130061, China. Corresponding author: Zhong-Hua He (email:
[email protected]). Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from RightsLink. Can. J. Earth Sci. 55: 571–588 (2018) dx.doi.org/10.1139/cjes-2017-0226
Published at www.nrcresearchpress.com/cjes on 13 March 2018.
572
Can. J. Earth Sci. Vol. 55, 2018
Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Jilin University on 05/30/18 For personal use only.
Fig. 1. (a) Map of Northeast China (after Safonova and Santosh, 2014). (b) Tectonic sketch map of Northeast China. (F1 = Xiguitu–Tayuan Fault, F2 = Hegenshan–Heihe Fault, F3 = Solonker–Xar Moron–Changchun zone, F4 = Chifeng–Bayan Fault, F5 = Dunhua–Mishan Fault, F6 = Yitong– Yilan Fault, F7 = Jiayin–Mudanjiang Fault). (c) Map showing the spatial and temporal distribution of Mesozoic volcanic rocks in Northeast China (after Xu et al. 2013b). (d) Map showing the distribution of Mesozoic granitoids in Northeast China (after Wu et al. 2011). [Colour online.]
Published by NRC Research Press
Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Jilin University on 05/30/18 For personal use only.
He et al.
(145–120 Ma), contemporaneous with the formation of voluminous Mesozoic volcanic rocks that outcrop in this area (Wu et al. 2011; Wang et al. 2006; Xu et al. 2008, 2013c; Zhang et al. 2010; Fig. 1c). This indicates that Mesozoic igneous rocks formed as a result of multi-stage magmatism. The temporal and spatial distribution of these Mesozoic igneous rocks in the GXR, as well as the nature of the tectonic system that generated this magmatism (i.e., Paleo–Pacific or Mongol– Okhotsk tectonic events or some combination of the two) remains controversial. Therefore, to constrain the age, source, and petrogenesis of the magmas that formed these intrusions, this study uses new zircon U–Pb and Hf isotopic and whole-rock geochemical data of the Banlashan granitoids of the central GXR. These new data allow us to better establish the temporal and spatial distribution of Mesozoic igneous rocks throughout the GXR, and gain insights into the tectonic evolution of Northeast China.
2. Geological background The Great Xing’an Range is located within the western part of the Xing’an–Mongolian Orogenic Belt and corresponds to a sharp gravity anomaly, an east–west topographic boundary, and a boundary associated with lithosphere-penetrating deep-seated faults (Xu et al. 2013a). The Tayuan–Xiguitu and Hegenshan–Heihe faults divide the range into the northwestern Erguna, the central Xing’an, and the southeastern Songliao blocks (Wu et al. 2005, 2007a, 2011; Yang et al. 2014, 2015a, 2015b, 2016). The Erguna Block was originally believed to contain Proterozoic to Paleozoic granitoids and sedimentary units (HBGMR 1993). However, recent research has determined that this block records multiple magmatic events, indicating that the majority of the igneous rocks were emplaced during the early Paleozoic and early Mesozoic, with minor magmatism during the late Paleozoic and Precambrian (Ge et al. 2015; Wu et al. 2011). In addition, the metavolcanics within the Xinghuadukou Complex yield Neoproterozoic magmatic ages of ⬃850 Ma (Ge et al. 2015), which indicate the timing of supracrustal protolith formation that defined the original Xinghuadukou Group. The Xing’an Block contains voluminous Mesozoic volcanic and granitic rocks (IMBGMR 1991; Ge et al. 2007a, 2007b; Wilde 2015; Figs. 1c and 1d). It was originally thought to contain Precambrian basement material, as suggested by the presence of “Precambrian” amphibolite to greenschist facies metamorphic units, as well as undeformed Cambrian limestones (IMBGMR 1991; HBGMR 1993). However, recent research has revealed that this so-called “Precambrian” basement material is actually a series of metamorphic complexes that formed during late Paleozoic to early Mesozoic orogenic processes (Miao et al. 2004, 2007). In addition, this block contains significant amounts of Paleozoic sedimentary units dominated by early Paleozoic limestone and late Paleozoic clastic sedimentary units (Wu et al. 2011). The area also contains several island arcs, including the 490 Ma Duobaoshan Arc (Ge et al. 2007a), 450 Ma Dongwuqi Arc (Shi et al. 2003), 298–276 Ma Dashizhai Arc (Yu et al. 2017), and 322–300 Ma Baoligaomiao– Delewula Arc (Fu et al. 2016); thus, the Xing’an Block most likely represents an accretionary terrane related to the closure of the Paleo–Asian Ocean. The Songliao Block is largely covered by the Mesozoic Songliao Basin, which formed in an intra-continental or active continental margin setting during the late Mesozoic (Gao et al. 2007; Wu et al. 2002). Traditionally, the Songliao Block was considered to consist of a Proterozoic metamorphic basement and stable cover sequences (Wu et al. 2000, 2002; Gao et al. 2007). However, the widespread existence of Precambrian materials on this block could not be verified with new geochronological data. In detail, the Lesser Xing’an and Zhangguangcai Ranges are characterized by voluminous Phanerozoic granitoids along with rare Paleozoic strata that occur as remnants in a “sea” of granitoids (Wu et al.
573
2000, 2002). A large proportion of the basin is underlain by Late Jurassic to Early Cretaceous volcanic rocks (Gao et al, 2007) with thicknesses of 1300 and 2800 m, which make up the bulk of the lower basin fill. Initial late Mesozoic rifting in this area generated several rifted basins (Ouyang et al. 2013). In addition, data from several hundred drillholes in this region indicate that the majority of the basin basement consists of Paleozoic–Mesozoic granitoids and Paleozoic units (Gao et al. 2007; Pei et al. 2007; Wu et al. 2011), with minor amounts of Proterozoic granitoids (Pei et al. 2007) that may represent a tectonic slice of the North China Craton (Wu et al. 2011). The granitic rocks of the Banlashan pluton analyzed in this study were sampled in the Wuerqihan area of northern Inner Mongolia, within the central Xing’an Block. This region contains voluminous granitoids and volcano-sedimentary sequences (Zhang 2009; Cui et al. 2013), most of which formed during the Mesozoic and some during the Paleozoic (Wu et al. 2011). The Wuerqihan area and adjacent regions are dominated by (i) early Paleozoic marine facies strata (e.g., the Duobaoshan Formation [O1–2d]), which is characterized by turbidites; (ii) Devonian marine facies endogenetic sedimentary, terrigenous clastic, and pyroclastic rocks (i.e., the Daminshan Formation [D2–3d]); (iii) Jurassic terrigenous facies volcanic and pyroclastic rocks (i.e., the Tamulangou Formation [J2–3tm]); (iv) Cretaceous terrigenous facies volcanic, pyroclastic, and terrigenous clastic rocks (i.e., the Manketouebo [K1mk], Manitu [K1mn], Baiyingaolao [K1b], Meiletu [K1m], and Damoguaihe [K1d] formations); and (v) Quaternary sediments (i.e., the Mianduhe [Q pm] and Hongqigou [Q phq] formations).
3. Sample descriptions The Banlashan pluton crops out in an area near the Banlashan Forest Farm, ⬃20 km southeast of Wuerqihan. It intruded into Jurassic volcano-sedimentary units and was in turn overlain by Cenozoic sediments (Fig. 2; HBGMR 1993). The pluton contains monzogranite, alkali feldspar granite, and syenogranite phases as well as dioritic microgranular enclaves (MEs). These MEs are also abundant within the monzogranite phase of the pluton (Figs. 3a and 3c); they are mesocratic to melanocratic, have noncumulate igneous textures, and range in diameter from 10 to 20 cm (typically
