Geochemical similarity of Cambrian alkaline and subalkaline magmatism (Kuznetsk Alatau Orogen, Siberia): a new data synt.pdf Introduction Multiple events of alkaline and subalkaline intraplate magmatism in the geological history of the Central Asian Orogenic Belt (CAOB) have been attributed to the action of mantle plumes [Ernst, 2014; Yarmolyuk, Kuzmin, Ernst, 2014]. Most of Paleozoic intrusions are located in the western flank of the orogenic belt, in the regions of Kuznetsk Alatau, Minusa, Altai-Sayan, Lake Baikal, southeastern Tuva, western Transbaikalia, and northern Mongolia [Yashina, 1982; Nikiforov, Yarmol-yuk, 2007; Sklyarov et al., 2009; Yarmolyuk, 2010; Doroshkevich et al., 2012, 2018; Vrublevskii et al., 2012, 2014, 2016а, 2016b, 2018а, 2019, 2020 а, 2020b; Vrublevskii, 2015; Izbrodin et al., 2017; Vrublevskii, Kruk, 2018; Salnikova et al., 2018; Vorontsov et al., 2021; Vrublevskii, Gertner, 2021]. The Early Paleozoic (Caledonian) Kuznetsk Alatau orogen is an island arc terrane within CAOB that formed along the Paleo-Asian active margin. The collisional and accretionary processes were associated with closure of the Paleo-Asian Ocean which, together with the Protopacific ocean, opened as a result of the plume-induced break-up of the Neoproterozoic Rodinia supercontinent about 900-800 Ma ago |Sengor, Natal'in, Burtman, 1993; Khain, 2003; Dobretsov, Buslov, Vernikovsky, 2003; Windley et al., 2007; Li et al., 2008; Kheraskova et al., 2010; Wilhelm, Windley, 2015; Wan et al., 2018]. The regional-scale event of late- and post-orogenic magmatism, which spanned an interval from ~510 to 490 Ma, produced granitic, gabbro-monzonitic, and mafic alkaline rocks with the respective U-Pb, Sm-Nd, and Rb-Sr ages. It is important to identify the mantle sources of parent melts that produced the diverse subal-kaline and alkaline plutonic rocks of the Kuznetsk Alatau terrane |Vrublevskii et al., 2014, 2015, 2016a, 2016b, 2018a]. The aim of this paper is to bring together previously published |Vrublevskii et al., 2016a, 2018a; Vrublevskii, Gertner, 2021] but dispersed geochemical results for specific intrusions within the Kuznetsk Alatau terrane, which are nearly coeval but compositionally different. The synthesized trace-element and isotopic data from the Cambrian igneous rocks of the area reveal several components in parent magmas that represent an active margin setting and an effect of a mantle plume. The geochemical and geochronological proximity of different igneous lithologies suggests similarity of their magma sources and almost synchronous emplacement in the conditions of a possible plume impact on the lithospheric complexes of a former island arc. The model of regional-scale Cambrian magmatism is new for the Kuznetsk Alatau area. The chronology and evolution trends of the Cambrian magmatism have implications for exchange and/or recycling of material at convergent plate boundaries. Geological background The Kuznetsk Alatau accretionary-collisional terrane borders the Minusa and Kuznetsk rift basins in the west and east, respectively (Fig. 1), and has a complex tectonic framework. It comprises abundant Early Paleozoic oceanic and island arc complexes with fragments of the Precambrian basement and small superimposed Devonian graben-like basins |Kungurtsev et al., 2001], as well as deformed Neoproterozoic-Cambrian volcanics and clastic-carbonate sediments, Middle Paleozoic subcontinental volcano-sedimentary deposits, Late Precambrian ophiolites, and Cambrian plutons. Less abundant Devonian and Permian intrusions appear most often as small mafic alkaline stocks and dikes |Vrublevskii, Gertner, 2021]. The general tectonic style of the Kuznetsk Alatau terrane, like the whole Central Asian Orogenic Belt, records the history of its collisions with other terranes during the Paleo-Asian Ocean closure |Dobretsov, Buslov, Vernikovsky, 2003; Yarmolyuk et al., 2003]. The Cambrian plutons of different compositions discussed in this paper are located in the northern (Mariinsk segment) and eastern (Batenev segment) slopes of the Kuznetsk Alatau Range, where they intrude metamorphosed volcanic and carbonate sediments (Fig. 1 b, 2). Mafic alkaline magmatism occurs as the Upper Petropavlovka and University small (~0.8-3 km2) gabbro-foidolite intrusions cut by foyaite and few calcite carbonatite dikes and veins in the Mariinsk segment. Legend for panel b: О Cenozoic sediments I I Late Paleozoic-Mesozoic basins Cambrian granitoids Cambrian gabbro-monzonite ☆ Cambrian gabbro-foidolite Fig. 1. (a) Location map of the Kuznetsk Alatau area in the Central Asian Orogenic Belt, simplified after [§engor, Natal'in, Burtman et al., 1993; Jahn, Wu, Chen, 2000]; (b) tectonic framework of the Kuznetsk Alatau terrane and clusters of Cambrian magmatism, after [Vrublevskii et al., 2016a; Vrublevskii et al., 2018a; Vrublevskii, Gertner, 2021] Paleozoic and older structures Рис. 1. (a) Схема размещения Кузнецкого Алатау в Центрально-Азиатском орогеническом поясе, по [§engor, Natal'in, Burtman et al., 1993; Jahn, Wu, Chen, 2000]; (b) тектоническая схема террейна Кузнецкого Алатау и проявлений кембрийского магматизма, по [Vrublevskii et al., 2016a; Vrublevskii et al., 2018a; Vrublevskii, Gertner, 2021] The foidolite and carbonatite rocks have Sm-Nd isochron ages of ~510-500 Ma [Vrublevskii, 2015; Mustafaev et al., 2020]. Gabbro-monzonite plutons of similar ages (~490-505 Ma, U-Pb) cluster among Early Paleozoic granitoids of the Batenev segment. The structural and compositional frameworks of large (~40 to 200 km2) plutons correspond to a two-phase history [Dovgal', Shirokikh, 1980; Vrublevskii et al., 2018a]. The Cambrian (~490-510 Ma, U-Pb) plutons reaching sizes of 60-70 to 500 km2 consist mainly of granodiorite-tonalite and later granites [Vrublevskii et al., 2016a]. Coeval granitoids in the Mariinsk segment form up to 300-500 km2 batholiths composed of diorite-tonalite, plagiogranite, and granite, as well as quartz syenite and granosyenite [Rudnev, 2013]. Compositions of main igneous lithologies Various aspects of chemistry and isotope systematics of the Kuznetsk Alatau igneous rocks were detailed in numerous earlier publications [Rudnev, 2013; Vrublevskii, 2015; Vrublevskii et al., 2016a, 2018a; Mustafaev et al., 2020; Vrublevskii, Gertner, 2021]. Main features of different rock types are summarized as selected analyses in Tables 1 and 2 and illustrated by trace-element and Nd and Sr isotope patterns in Figures 3 and 4. Major- and trace-element chemistry. The Kuznetsk Alatau gabbro-foidolite intrusions typically have low silica (~44-53 wt. % SiO2), high calcium (to ~10-15 wt. % CaO), and elevated aluminum (to 18-22 wt. % Al2O3) and alkali (to 9-12 wt. % (Na2O + K2O), Na2O/K2O » 2-7) contents. Compared to gabbro, the later foyaite and foidolite have lower MgO# (0.5-0.1) and compatible elements (529-4 ppm Cr, 1123 ppm Ni, 200-8 ppm V, 48-2 ppm Co), but higher LILE and HFSE reaching ~10 to 90 ppm Rb, ~2000 ppm Ba, 540 to 1180 ppm Sr, 0.4 to 7 ppm Th, 0.3 to 5.4 ppm U, 46 to 240 ppm REE, ~100 to 280 ppm Zr, and ~10 to 50 ppm Nb). The patterns of REE (La/YbN » 6-11; Eu/Eu* » 1) and other trace elements in these intrusions look like those of average ocean island basalts (OIB) but bear additional island-arc basalt (IAB) signatures. The IAB contribution appears in multi-element spectra with distinct Nb-Ta and Zr-Hf depletion. The gabbro-monzonitic intrusions of the area contain moderate amounts of alkalis (~3-10 wt. % Na2O + K2O) and show large ranges of silica (~43 to 65 wt. % SiO2) and alumina (~15-20 wt. % Al2O3), while Fe# is about 0.5. Some of the rocks have relatively high K2O contents of ~5-6 wt. % (K2O/Na2O from 0.2-0.7 to 0.5-1.5), along with quite low TiO2 (~2.2 to 0.5 wt. %). The concentrations of compatible elements decrease markedly in the series from gabbro to monzodiorite and monzonite: 436 to 12 ppm Cr, 182 to 9 ppm Ni, 574 to 32 ppm V, and 56 to 5 ppm Co, whereas LILE and HFSE become times higher: ~3 to 134 ppm Rb, ~100 to 2900 ppm Ba, ~0.2 to 31 ppm Th, ~0.4 to 37 ppm Nb, and ~60 to 336 ppm REE (Eu/Eu* » 0.7-1.3); Sr reaches ~1400 to 2500 ppm. The REE (La/YbN » 7-30) and other trace-element patterns in gabbro are similar to the average IAB composition, with typical minimums in Nb-Ta and Zr-Hf. The LILE and HFSE concentrations in more strongly fractionated (La/YbN » 14-34) monzonites approach or even exceed the OIB average but the general shapes of the spectra remain as in IAB. ZU Middle Devonian-Early Carboniferous carbonate and clastic sediments I Volcanic rocks and clastics of Early Devonian grabens I ] Ordovician-Early Devonian volcanosedimentary deposits I I Early and Middle Cambrian volcanic rocks and carbonate deposits I I Neoproterozoic and Cambrian schists, volcanic and carbonate deposits | Neoproterozoic ophiolites | Early Devonian granites | Early Paleozoic gabbro-syenite intrusions [_. Cambrian-Ordovician granitoids Ц Cambrian gabbro-monzonite X Faults Ф Cambrian gabbro-foidolite О Devonian gabbro-foidolite Fig. 2. (a) Location map of gabbro-foidolite plutons (not to scale) and (b) granitoids in the Mariinsk segment, after [Rudnev, 2013; Vrublevskii et al., 2014; Vrublevskii, Gertner, 2021] Gabbro-foidolite intrusions: UP = Upper Petropavlovka, Un = University; (b) Geological framework of gabbro-monzonitic and granitic intrusions in the Batenev segment, after [Dovgal', Shirokikh, 1980; Vrublevskii et al., 2016a, 2018a]. Gabbro-monzonite intrusions: Kg = Kogtakh, Bl = Balakhcha, Ksh = Kashpar, Ks = Kiskach, Cht = Chas-Taiga, Pt = Pistag, Kt = Karatag Рис. 2. (a) Локализация габбро-фойдолитовых плутонов (вне масштаба) и (b) гранитоидов в Мариинском сегменте, по [Vrublevskii et al., 2014; Vrublevskii, Gertner, 2021; Rudnev, 2013] Габбро-фойдолитовые интрузивы: UP = Верхнепетропавловский, Un = Университетский; (b) Геологическая карта габбро-монцонитовых и гранитных интрузивов в Батеневском сегменте, по [Dovgal', Shirokikh, 1980; Vrublevskii et al., 2016a, 2018a]. Габбро-монцонитовые интрузивы: Kg = Когтахский, Bl = Балахчинский, Ksh = Кашпарский, Ks = Кискачинский, Cht = Частай-гинский, Pt = Пистагский, Kt = Каратагский Table 1 Selected analyses of the Kuznetsk Alatau Cambrian granitic, gabbro-monzonitic, and gabbro-foidolitic rocks Таблица 1 Выборка анализов кембрийских гранитоидов, габбро-монцонитов и габбро-фойдолитов Кузнецкого Алатау Intrusion Gabbro-foidolite Gabbro-monzonite Granitoids Rock type SG AG I SG MD M Tn Tn GD S GS Gr SiO2, wt, % 44,98 46,46 44,38 44,77 53,47 58,90 64,04 65,72 67,85 63,14 68,60 70,76 TiO2 0,95 1,27 0,91 1,57 0,89 1,01 0,43 0,41 0,32 0,60 0,32 0,17 Al2O3 15,11 14,71 18,57 14,31 18,89 17,59 16,28 15,09 15,26 17,26 16,65 15,54 Fe2O3 11,20 11,34 10,68 14,83 7,83 6,51 5,00 5,82 3,84 3,69 2,88 2,03 MnO - - 0,22 0,14 0,12 0,10 0,12 0,10 0,11 0,08 0,06 0,08 MgO 8,93 6,92 2,34 8,12 4,42 3,41 4,12 2,33 1,33 0,51 0,81 0,76 CaO 14,63 10,53 11,42 12,52 7,44 4,67 3,01 4,24 2,46 3,15 2,55 1,35 Na2O 2,96 4,23 7,22 2,25 4,55 4,06 4,53 1,65 5,07 7,42 4,19 5,55 K2O 0,95 2,43 2,44 0,96 1,96 2,58 1,94 1,64 2,25 3,38 3,20 3,35 P2O5 0,09 0,50 0,69 0,21 0,53 0,33 0,07 0,09 0,05 0,22 0,05 0,06 LOI 1,13 1,26 1,18 0,41 0,13 0,30 0,43 1,82 0,71 0,24 0,12 0,17 Total 100,93 99,65 100,05 100,09 100,23 99,46 99,98 98,91 99,25 99,70 99,43 99,82 Cr, ppm 224 56 28 57 49 35 96 - 51 38 - 40 Ni 56 7 22 86 16 15 32 - 16 7 - 8 V 155 12 81 274 159 125 - - - - - - Co 49 12 21 56 26 17 15 - 10 4 - 5 Sc 24 0,9 5,8 53 19 12 11 - 6 1,6 - 2,4 Pb - - 5,4 - 13 11 7 - 9 11 - 14 Cs 0,8 1 0,5 0,6 0,7 1,6 0,9 - 0,4 0,2 - 0,8 Rb 24 42 34 13 69 83 51 44 62 94 64 85 Ba 303 726 1802 231 1105 1076 658 531 1024 1110 1030 785 Sr 538 893 869 720 1407 1336 648 401 809 979 442 745 Nb 9 42 12 4,6 19 21 11 2,4 19 16 14 22 Ta 0,6 2,5 0,7 0,24 1,1 1,5 0,8 0,4 1,4 1 1,3 1,7 Zr 124 279 144 71 157 368 23 23 47 76 209 42 Hf 2,7 4 2,6 1,9 2,6 4,7 0,8 1,2 1,6 2,2 6,5 1,4 Y 22 45 27 15 31 18 10 19 15 11 10 11 Th 2,7 7 3 1,7 6,7 8,9 2,7 2,2 7,5 4,2 4,9 5 U 1,9 5,5 2 0,53 1,5 1,8 1,2 0,8 1,3 0,8 2,6 1,8 La 21 49 32 13 52 49 22 11 47 31 31 35 Ce 45 101 63 29 115 125 43 23 84 60 52 63 Pr 5,2 9,1 7,3 4,4 13 14 5 2,2 8,3 6 6,2 6,4 Nd 21 44 28 20 45 55 19 10 30 20 20 24 Sm 4,6 8,5 5,3 3,9 7,4 9,8 3,3 2,2 4,7 3,1 2,9 3,7 Eu 1,3 2,6 1,8 1,2 2,4 2,3 1 0,72 1,2 0,75 1 0,87 Gd 4,4 8,1 4,8 3,6 6,6 9,1 3,2 2,3 4,5 2,4 2,2 3,4 Tb 0,7 1,3 0,7 0,51 0,8 1,2 0,45 0,4 0,63 0,37 0,36 0,5 Dy 4,3 8,2 4,2 2,9 3,8 6,4 2,1 2,6 3 1,7 2 2,3 Ho 0,9 1,8 0,9 0,57 0,77 1,3 0,4 0,6 0,57 0,35 0,4 0,43 Er 2,4 5,1 2,5 1,5 2,1 3,4 1,1 1,9 1,6 0,98 1,1 1,2 Tm 0,4 0,8 0,4 0,2 0,3 0,53 0,15 0,35 0,22 0,15 0,21 0,17 Yb 2,2 4,8 2,6 1,3 1,8 2,3 1 2,1 1,6 1 1,4 1,1 Lu 0,3 0,7 0,4 0,18 0,27 0,35 0,15 0,29 0,24 0,16 0,18 0,17 SREE 114 245 155 82 251 280 102 59 188 128 121 142 LREE/HREE 6,3 7 8,3 6,8 14,5 10,2 10,7 5 13,7 16,1 14,3 14,7 Note. SG = subalkaline gabbro, AG = alkaline gabbro, I = feldspar ijolite, MD = monzodiorite, M = monzonite, Tn = tonalite, GD = granodiorite, S = quartz syenite, GS = granosyenite, Gr = subalkaline granite. (-) is not detected. Major and trace elements and REE in rocks were analyzed by XRF and ICP-MS, respectively, under standard operating conditions. Data after [Rudnev, 2013; Vrublevskii, 2015; Vrublevskii et al., 2016a, 2018a; Mustafaev et al., 2020]. Примечания. SG = субщелочное габбро, AG = щелочное габбро, I = полевошпатовый ийолит, MD = монцодиорит, M = монцонит, Tn = тоналит, GD = гранодиорит, S = кварцевый сиенит, GS = граносиенит, Gr = субщелочной гранит. (-) не обнаружено. Петрогенные, редкие и редкоземельные элементы в породах анализировались методами XRF и ICP-MS соответственно, в стандартных условиях . Данные по [Rudnev, 2013; Vrublevskii, 2015; Vrublevskii et al., 2016a, 2018a; Mustafaev et al., 2020]. Fig. 3. Chemical classification and compositions of the Kuznetsk Alatau Cambrian igneous rocks a - R1-R2 diagram [De la Roche et al., 1980]; b-d - Primitive mantle-normalized [Sun, McDonough, 1989] multi-element spectra. All diagrams include selected analyses (Table 1) and published data from [Rudnev, 2013; Vrublevskii, 2015; Vrublevskii et al., 2016a, 2018a; Mustafaev et al., 2020; Vrublevskii, Gertner, 2021]. Average ocean island basalt (OIB) and island-arc basalt (IAB) compositions are after [Sun, McDonough, 1989; Kelemen, Hangh0j, Greene, 2003], respectively Рис. 3. Химическая классификация и состав кембрийских изверженных пород Кузнецкого Алатау a - диаграмма R1-R2 [De la Roche et al., 1980]; b-d - мультиэлементные спектры (нормализация по составу примитивной мантии [Sun, McDonough, 1989]). На диаграммах нанесены табличные (табл. 1) и литературные данные по [Rudnev, 2013; Vrublevskii, 2015; Vrublevskii et al., 2016a, 2018a; Mustafaev et al., 2020; Vrublevskii, Gertner, 2021]. Средние составы базальтов океанских островов (ocean island basalt = OIB) и островных дуг (island-arc basalt = IAB) по [Sun, McDonough, 1989; Kelemen, Hangh0j, Greene, 2003] соответственно Most of the Kuznetsk Alatau granitoids are subalka-line, alkaline or less often peralkaline varieties (~58-76 wt. % SiO2; ~3-13 wt. % (Na2O + K2O); K2O/Na2O ~0.2-1.7) with a relatively low Al saturation index (ASI s Ет о И# / “e-morb ° Marnnsk granitoids, Fig. 5. Trace-element contents and their ratios in the Kuznetsk Alatau Cambrian igneous rocks a - Th/Yb-Ta/Yb diagram [Gorton, Schandl, 2000]: OIA = oceanic island arc, ACM = active continental margin, WPVZ = within-plate volcanic zone, E-MORB = enriched mid-ocean ridge basalt; WPB = within-plate basalt; b - ThN-NbN diagram [Saccani, 2015]: АВ = alkaline basalt, BABB = back-arc basin basalt; N-MORB-normalized [Sun, McDonough, 1989] Th and Nb; c - Ba/Nb-La/Nb diagram [Bi et al., 2015]; d - Rb-(Y + Nb) diagram [Pearce, Harris, Tindle, 1984]: syn-COLG = syncollisional granite, VAG = volcanic arc granite; WPG = within plate granite; e - (Nb/Zr)N-Zr diagram [Thieblemont, 1999]: BSE-normalized [Hofmann, 1988] Nb/Zr; f -Yb/Ta-Y/Nb diagram [Eby, 1990]. Diagrams in panels d and e include only granitic and monzonitic compositions Рис. 5. Соотношения микроэлементов в кембрийских изверженных породах Кузнецкого Алатау a - диаграмма Th/Yb-Ta/Yb [Gorton, Schandl, 2000]: OIA = океанская островная дуга (oceanic island arc), ACM = активная континентальная окраина (active continental margin), WPVZ = внутриплитная вулканическая зона (within-plate volcanic zone), E-MORB = обогащенный базальт срединно-океанического хребта (enriched mid-ocean ridge basalt); WPB = внутриплитный базальт (within-plate basalt); b - диаграмма ThN-NbN [Saccani, 2015]: АВ = щелочной базальт (alkaline basalt), BABB = базальт задугового бассейна (back-arc basin basalt); содержание Th и Nb нормализовано по N-MORB [Sun, McDonough, 1989]; c -диаграмма Ba/Nb-La/Nb [Bi et al., 2015]; d - диаграмма Rb-(Y + Nb) [Pearce, Harris, Tindle, 1984]: syn-COLG = синколлизион-ный гранит (syncollisional granite), VAG = островодужный гранит (volcanic arc granite); WPG = внутриплитный гранит (within plate granite); e - диаграмма (Nb/Zr)N-Zr [Thieblemont, 1999]: Значения Nb/Zr нормализованы по BSE (Bulk Silicate Earth) [Hofmann, 1988]; f - диаграмма Yb/Ta-Y/Nb [Eby, 1990]. На панелях «d» и «e» нанесены составы только гранитов и монцонитов Fig. 6. Ce/Nb-Th/Nb (a) and £Nd(t)-Ce/Pb (b) diagrams for the Kuznetsk Alatau Cambrian igneous rocks Compositions of primitive (PM) and depleted (DMM) mantle, E-MORB, OIB, PREMA, BSE (bulk silicate Earth), and UC (upper crust) are after [Zindler, Hart, 1986; Sun, McDonough, 1989; Rudnick, Gao, 2003; Salters, Stracke, 2004] Рис. 6. Диаграммы Ce/Nb-Th/Nb (a) и cNd(t)-Ce/Pb (b) для кембрийских изверженных пород Кузнецкого Алатау Составы примитивной (PM) и деплетированной (DMM) мантии, E-MORB, OIB, PREMA, BSE и UC (upper crust = верхняя кора), по [Zindler, Hart, 1986; Sun, McDonough, 1989; Rudnick, Gao, 2003; Salters, Stracke, 2004] Meanwhile, some trace-element and isotopic dissimilarity of the rocks may result from their emplacement among compositionally and structurally heterogeneous accretion-ary-collisional complexes. Signatures of such plumelithosphere interaction were reported from different areas of the Paleo-Asian active margins [Dobretsov, 2011; Vrublevskii et al., 2012, 2016a, 2018a; Gordienko, Metel-kin, 2016; Gordienko, 2019; Vrublevskii, Gertner, 2021]. The subcontinental lithospheric mantle (SCLM) apparently played a subordinate role in the process, as a mantle wedge effect. Any significant involvement of SCLM components was hardly possible, given the island arc origin of the Kuznetsk Alatau terrane and the Nd isotope composition of the analyzed rocks corresponding to moderately depleted mantle. Conclusion Cambrian magmatism in the Kuznetsk Alatau orogen produced granitic, gabbro-monzonitic, and gabbrofoidolitic intrusions within the ~510 to 490 Ma time span and terminated the collisional processes along the Early Paleozoic Paleo-Asian active margin. The observed Sm-Nd isotopic patterns in main igneous lithologies indicate parentage of the magma sources and involvement of PREMA-type and EM-type mantle components in the magma generation. The existence of the prevalent mantle (PREMA) reservoir was possibly maintained by the activity of the North Asian superplume, which induced the Early Paleozoic magmatism of the Western CAOB. The trace-element compositions of igneous rocks record possible mixing of IAB- and OIB-like components in the source magma, whereas relatively high Sr, Pb and O isotope ratios record crustal contamination of the melts. The revealed geochemical similarity of the Kuznetsk Alatau Cambrian igneous complexes is not fortuitous but may be due to their emplacement in the former active margin exposed to the impact of a mantle plume.

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