ISSN 0869-5911, Petrology, 2017, Vol. 25, No. 6, pp. 535–565. © Pleiades Publishing, Ltd., 2017. Original Russian Text © A.V. Kargin, Yu.Yu. Golubeva, E.I. Demonterova, E.V. Koval’chuk, 2017, published in Petrologiya, 2017, Vol. 25, No. 6, pp. 547–580.
Petrographic-Geochemical Types of Triassic Alkaline Ultramafic Rocks in the Northern Anabar Province, Yakutia, Russia1 A. V. Kargina, *, Yu. Yu. Golubevab, **, E. I. Demonterovac, ***, and E. V. Koval’chuka aInstitute
of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), Russian Academy of Sciences, Moscow, 119017 Russia b Central Institute of Geological Exploration for Base and Precious Metals (TsNIGRI), Moscow, 113545 Russia cInstitute of the Earth’s Crust, Siberian Branch, Russian Academy of Sciences, Irkutsk, 664033 Russia *e-mail:
[email protected] **e-mail:
[email protected] ***e-mail:
[email protected] Received March 10, 2016; in final form, January 11, 2017
Abstract—A classification suggested for alkaline ultramafic rocks of the Ary-Mastakh and Staraya Rechka fields, Northern Anabar Shield, is based on the modal mineralogical composition of the rocks and the chemical compositions of their rock-forming and accessory minerals. Within the framework of this classification, the rocks are indentified as orangeite and alkaline ultramafic lamprophyres: aillikite and damtjernite. To estimate how much contamination with the host rocks has modified their composition when the diatremes were formed, the pyroclastic rocks were studied that abound in xenogenic material (which is rich in SiO2, Al2O3, K2O, Rb, Pb, and occasionally also Ba) at relatively low (La/Yb)PM, (La/Sm)PM, and not as much also (Sm/Zr)PM and (La/Nb)PM ratios. The isotopic composition of the rocks suggests that the very first melt portions were of asthenospheric nature. The distribution of trace elements and REE indicates that one of the leading factors that controlled the diversity of the mineralogical composition of the rocks and the broad variations in their isotopic–geochemical and geochemical characteristics was asthenosphere–lithosphere interaction when the melts of the alkaline ultramafic rocks were derived. The melting processes involved metasomatic vein-hosted assemblages of carbonate and potassic hydrous composition (of the MARID type). The alkaline ultramafic rocks whose geochemistry reflects the contributions of enriched vein assemblages to the lithospheric source material, occur in the northern Anabar Shield closer to the boundary between the Khapchan and Daldyn terranes. The evolution of the aillikite melts during their ascent through the lithospheric mantle could give rise to damtjernite generation and was associated with the separation of a C–H–O fluid phase. Our data allowed us to distinguish the evolutionary episodes of the magma-generating zone during the origin of the Triassic alkaline ultramafic rocks in the northern Anabar Shield. DOI: 10.1134/S0869591117060030
INTRODUCTION The geological evolution of the Siberian craton (SC) is known to have involved a number of Phanerozoic episodes of deep alkaline ultramafic diamondiferous magmatism: in the Late Silurian–Early Devonian, Devonian–Early Carboniferous, Middle/Late Triassic, Middle/Late Jurassic, at the boundary between the Early and Late Cretaceous, and in the Paleogene (see reviews in Zaitsev and Smelov, 2010; Sun et al., 2014). Multistage magmatism within a single field/area/province is also typical of several other large cratons worldwide (see a review in Tappe et al., 2014). The Lena–Anabar subprovince in the northern SC hosts two areas of Mesozoic kimberlite and related 1 Supplementary
materials are available for this article at 10.1134/S0869591117060030 and are accessible for authorized users.
magmatism: the Anabar province in the north and the Alakit-Olenek one in the northwest (Fig. 1). Because of the low economic potential of these provinces, the petrography and geochemistry of their magmatism are still known inadequately poorly (Chernysheva and Kostrovitsky, 1998; Bogatikov et al., 2004; Kostrovitsky et al., 2007; Babushkina et al., 2012), in contrast to Devonian kimberlites in central SC, which were studied much more thoroughly because of their economic diamond reserves (see, for example, Agashev et al., 2000; Bogatikov et al., 2004; Kononova et al., 2005; Kostrovitsky et al., 2007; Kargin et al., 2011). Alkaline ultramafic rocks in the northern Anabar Shield comprise not only kimberlites but also other related alkaline ultramafic rocks, whose composition and contents of silicate (olivine, phlogopite, monticellite, clinopyroxene, nepheline, etc.) and carbonate phases significantly vary. These rocks are classified into kimberlite, carbonatite, alnoite, (Kornilova et al.,
535
536
KARGIN et al.
96° E
120°
108°
Laptev Sea
n ldy
Da
Khapchan terrane
132°
AR + PR
Birekte terrane
r
Orto-Yarga field
Ana ba
Lena
Ko tu i
64°
Aldan e Lenae– t rran
11 14 21 23 10 13 20 17 19 15 8 12 9 22 18 7 Muna PR1 16 6 Olenek AR 5 4 3 Tunguska 2 ilyui terrane
PR2
Delta 236 ±13 Gamma
V
Age of kimberlites and alkaline ultramafic rocks: 1 2
Tungus terrane
AR + PR
1
0
a amk
uon
at K Gre
Ulybka Viktoriya
200 km
Little Kuonamka
e
Kheta
Anabar
an terr
72° N
Predmaiskaya Maiskaya, 224 ± 9 Pyroclastic aillikite Coherent aillikite Orangeite PR3 Damtjernite Found occurrences of alkaline ultramafic rocks
Staraya Rechka field
Nebaibyt, 226 ± 6 Mukunskaya
Cholbon AR + PR
Kharakhtakh
Gr ea t
Ku o
na
mk a
Ary-Mastakh field
Vechernyaa
Arktika, 213 ± 13 10 km Orion
Fig. 1. Schematic map showing the distribution of alkaline ultramafic rocks in the northern Anabar province and their estimated age according to (Zaitsev and Smelov, 2010). The inset is a location map of the study area in the Yakutian diamondiferous province (Khar’kiv et al., 1998; Zaitsev and Smelov, 2010; Kostrovitsky et al., 2016): (1, 2) fields of kimberlites and related alkaline ultramafic rocks of mid-Paleozoic (open circles) and Mesozoic (solid circles) age. Fields: (1) Malo-Botuobino, (2) Nakyn, (3) Alakit-Markha, (4) Daldyn, (5) Upper Muna, (6) Chomurdakh, (7) West Ukukit, (8) East Ukukit, (9) Oroneg-Yuryakh, (10) Merchimden, (11) Kuoisk, (12) Molodin, (13) Toluop, (14) Khorbusuon, (15) Luchakan, (16) Kuranakh, (17) Dyuken, (18) Biriginda, (19) Ary-Mastakh, (20) Staraya Rechka, (21) Orto-Yarga, (22) Kuruisk; (23) carbonatites of the Tomtor Massif. PETROLOGY
Vol. 25
No. 6
2017
PETROGRAPHIC-GEOCHEMICAL TYPES OF TRIASSIC ALKALINE ULTRAMAFIC ROCKS
1983; Bogatikov et al., 2004; Kononova et al., 2005; Kostrovitsky et al., 2007, 2016; Sun et al., 2014; Ashchepkov et al., 2015), alkaline picrite, and olivine melilitite of the kimberlite and carbonatite associations (Koval’skii et al., 1969; Kornilova et al., 1983; Chernysheva and Kostrovitsky, 1998; Babushkina et al., 2012); and kimpicrite and alpicrite (Lapin, 2001). The petrographic systematics and geochemical types of the rocks are still unclear, and this makes it difficult to compare these rocks with other alkaline ultramafic rocks found elsewhere. The rocks were previously studied fairly cursorily and were often classified based solely on single arbitrarily chosen feature, such as their petrography, geochemistry, etc. Studies of kimberlites and related magmatism in large provinces/areas shows that their detailed classification should be underlain by comprehensive petrographicgeochemical data, with information on the chemical composition of their rock-forming minerals (phlogopite, spinel, and olivine) playing a determining role (see, for example, Mitchell, 1995; Tappe et al., 2005, 2006). The diversity of the terminology and classification schemes of alkaline ultramafic rocks (Wooley et al., 1996; Mitchell, 1995; Le Maitre et al., 2002; Tappe et al., 2005) allowed us to design a classification of alkaline ultramafic rocks in SC and revise their nomenclature with reference to the Anabar area. Kimberlite and related rocks within a single field, or a number of closely spaced pipes, sometimes significantly differ in concentrations of primary carbonate minerals, as do, for example, Devonian “magnesian” and “carbonate” kimberlites in the Daldyn– Alakit area in the central SC (Ilupin et al., 1990; Kargin et al., 2011), Devonian sills in the Mela River area in the Arkhangelsk diamondiferous province (Pervov et al., 2005), Mesoproterozoic orangeites in the Kostomuksha–Lentiira area (Kargin et al., 2014) in the East European craton. A number of models was suggested to explain the origin of the silicate and carbonate varieties based on the concept of the heterogeneous distribution of metasomatic vein-hosted mineral assemblages of carbonate and/or potassic hydrous composition in the lithospheric mantle (Foley, 1992; Grégoire et al., 2002; Mitchell, 1995; and others) and the model of the compositional evolution of primary kimberlite magmas from carbonate- to silicate-rich ones due to interaction with lithospheric mantle material (see, for example, Kamenetsky and Yaxley, 2015; Giuliani et al., 2016). It is important to study alkaline ultramafic rocks in the northern fields of SC in view of the probable diamondiferous potential of these rocks (see, for example, Grakhanov et al., 2010; Grakhanov and Smelov, 2011; Smelov et al., 2011). The prime objective of our work was to classify the Triassic alkaline ultramafic rocks in the northern Anabar province based on their petrography and geochemistry (including adaptation of preexisting classiPETROLOGY
Vol. 25
No. 6
2017
537
fications of alkaline ultramafic rocks to these ones), to document in detail their petrography with regard for recommendations for petrographic descriptions of kimberlites and related rocks (Scott Smith et al., 2013), to identify factors that controlled the petrochemical and geochemical characteristics of these rocks, and to estimate the composition and heterogeneity of their mantle source and its relations with the structure of the regional lithospheric mantle. GEOLOGY AND MATERIALS The Siberian craton was produced by the collision and accretion of microcontinents of various age, which were terranes whose basements consolidated at 3.6–3.1, 2.8–2.5, 2.4–2.2, and 2.1–1.7 Ga (Rosen et al., 2003; Smelov and Timofeev, 2007; Zaitsev and Smelov, 2010; Kostrovitsky et al., 2016). The major tectonic basement structures are (Zaitsev and Smelov, 2010) granite–greenstone and tonalite–trondhjemite–granodiorite terranes of the West Yakutian (West Aldan, Tunguska, Sharyzhalgay, and likely the Magan terranes) and East Yakutian protocratons (Birekte, Tyryn, and Batomga terranes), whose consolidation ages are older than 2.6–2.5 and 2.4–2.1 Ga, respectively; and the terranes of the Daldyn–Aldan (Central Aldan, Tungus, and Daldyn) and Khapchan–Uchur (Khapchan and Uchur) granulite belts in between (Fig. 1). Most kimberlites with economic diamond mineralization are hosted in terranes with Archean–Proterozoic crust (Zaitsev and Smelov, 2010), as is typical of other kimberlite provinces, for example, the Arkhangelsk diamondiferous province in the northeastern East European craton (Samsonov et al., 2012). The Anabar province is restricted to the Khapchan terrane (Smelov and Timofeev, 2007) in the eastern flank of the Anabar anteclise. The terrane is bounded by the Billyakh and Olenek zones of tectonic mélange in the west and east, respectively, which are characterized by strike slip–reverse faulting kinematics and are traced northward and southward beneath the sedimentary cover based on geophysical data. The terrane is made up mostly of marbles, calciphyres, calc-silicate rocks, and garnet paragneisses (with carbonate rocks accounting for up to 40% of all rocks by volume), with subordinate enderbites and crystalline schists (Rosen et al., 2003; Zaitsev and Smelov, 2010). The Khapchan terrane was produced in three episodes (Kostrovitsky et al., 2016): in the Paleoproterozoic, Neoarchean, and Paleoarchean. The regional lithospheric mantle was recycled during tectono-thermal events at 2.5–2.8 and 1.8–2.1 Ga. The Anabar province comprises seven fields (Fig. 1): Luchakan, Kuranakh, Birigda, Dyuken, AryMastakh, Staraya Rechka, and Orty-Yarga. They define a continuous north-trending zone 300 km long and no more than 30 km wide (Khar’kiv et al., 1998;
538
KARGIN et al.
Rosen et al., 2003; Zaitsev and Smelov, 2010). We have studied 16 rock samples from 13 pipes in the AryMastakh and Staraya Rechka fields (Table 1, Fig. 1) dated at the Triassic. The Ary-Mastakh field in the western portion of the Khapchan terrane comprises more than 40 diatremes and alkaline ultramafic dikes (Fig. 1). Most of the pipes are equant in map view and are 35 × 35 to 420 × 120 m in horizontal section. The host rocks are Proterozoic and Lower Cambrian sedimentary and crystalline rocks of the Anabar Massif. The Staraya Rechka field is the northern continuation of the Ary-Mastakh field. Its pipes are ellipsoidal in map view and range from 25 × 130 to 300 × 15 m in horizontal section. Most of the bodies are hosted in Proterozoic rocks, and only a few occur in Lower Cambrian ones. The distribution of the pipes was controlled first of all by basement faults of northwestern and northeastern trend. Detailed isotopic geochronologic data on wholerock samples of the alkaline ultramafic rocks and their phlogopite (Zaitsev and Smelov, 2010) point to five pulses of alkaline ultramafic magmatism in the field: mid-Paleoproterozoic, Triassic, Jurassic, Late Cretaceous, and Paleogene. The Staraya Rechka field hosts rocks produced during the Triassic and Jurassic episodes. Most alkaline ultramafic rocks of the fields were formed during the Late Triassic (235–205 Ma) and Jurassic (171–149 Ma) episodes (Zaitsev and Smelov, 2010; Sun et al., 2014). METHODS Before their crushing and powdering, the rock samples were disintegrated to fragments a few millimeters across and slightly more to get rid of xenogenic material and nodules of deep rocks by hand-picking under a binocular magnifier. Pyroclastic varieties were studied in magmaclasts enriched in melts. According to provisional petrographic data, these were least contaminated with xenogenic material (10 wt %. The limits of detection of elements were 0.1–0.3 wt %. Rock samples were analyzed for major elements by XRF on a PW-2400 (Philips Analytical B.V.) spectrometer at the Laboratory for Analysis of Mineral Material at the Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), Russian Academy of Sciences, in Moscow. Preparatorily to analysis for major elements, the samples (0.3 g) were fused with Li tetraborate (3 g) in an induction furnace. The analyses were accurate to 1‒5% at concentrations >0.5 wt % and up to 12% at concentrations
