A REVIEW OF E ARLY P ERMIAN (300–270 M A ) MAGMATISM IN E ASTERN K AZAKHSTAN AND IMPLICATIONS FOR PLATE TECTONICS AND PLUME INTERPLAY

: The history of the Central Asian Orogenic Belt (CAOB) was marked by several major events of magmatism which produced large volumes of volcanic and intrusive (mafic‐ultramafic and granitic) rocks within a relatively short time span (30–40 Ma) over a vast area. The magmatic activity postdated the orogenic stages of accretionary‐ collisional belts in Central Asia and likely resulted from the impact of mantle plumes that formed Large Igneous Pro‐ vinces (LIPs). The formation of the Tarim–South Mongolia LIP at 300–270 Ma is the best known among the major Permian events of basaltic and granitic magmatism. Early Permian igneous rocks (volcanic, subvolcanic and intrusive suites that vary from ultramafic to felsic compositions) of the same age range (300 to 270 Ma) have been recently found also in Eastern Kazakhstan, within the late Paleozoic Altai collisional system. The compositions and ages of the rocks suggest that the Eastern Kazakhstan magmatism was the northward expansion of the Tarim LIP. The spread of the Tarim LIP was apparently facilitated by lithospheric extension after the Siberia‐Kazakhstan collision. The exten‐ sion led to rheological weakening of the lithosphere whereby deep mantle melts could penetrate to shallower depths. The early Permian history of Eastern Kazakhstan was controlled by the interplay of plate tectonic and plume proces‐ ses: plate‐tectonic accretion and collision formed the structural framework, and the Tarim mantle plume was a heat source maintaining voluminous magma generation.


INTRODUCTION
The Central Asian Orogenic Belt (CAOB) is the largest accretionary structure in the Earth's history, also known as Altaids [Şengör et al., 1993], formed by closure of the Paleoasian Ocean.The Altaid tectonic collage includes numerous terranes of different origin amalgamated by multiple accretionary and collisional events in tectonic settings changing from compression to extension and shear [Şengör et al., 1993;Dobretsov, 2003;Windley et al., 2007;Levashova et al., 2009;Xiao et al., 2010;Xiao, Santosh, 2014].Its history included several major events of magmatism which produced significant volumes of volcanic and intrusive (maficultramafic and granitic) rocks in a relatively short time span (30-40 Ma) over a large area.The magmatic activity postdated the orogenic stages in the evolution of accretionary-collision systems.From the viewpoints of plate tectonics, the post-orogenic magmatism is caused by post-orogenic lithospheric extension as a result of its delamination [Xiao et al., 2008;Xiao, Santosh, 2014;Konopelko et al., 2018] or results from active transtensional strike-slip tectonics accompanied by upwelling of the asthenosphere [Seltmann et al., 2011;Wang et al., 2014] or breaking of subducted oceanic plate (slab break-off) [Konopelko et al., 2017].The alternative viewpoint for large-scale magmatism in accretionarycollision systems is the impact of mantle plumes.The plume activity leading to the formation of Large Igneous Provinces (LIPs) [Ernst et al., 2005;Bryan, Ernst, 2008;Ernst, 2014] can account for a number of Paleozoic magmatic events in CAOB: (1) early Paleozoic, with a late Cambrian -early Ordovician LIP in the Altai, Sayan and Western Mongolia regions [Izokh et al., 2010;Dobretsov, 2011;Vladimirov et al., 2013]; (2) middle Paleozoic, with a Devonian LIP in the Minusa basin and the Vilyui rift in East Siberia [Vorontsov et al., 2013;Kiselev et al., 2014]; and (3) late Paleozoic, with Permian LIPs in Central Asia.Large-scale mafic and granitoid magmatism in Permian time produced the Tarim-South Mongolia LIP at 300-270 Ma [Zhang et al., 2010;Wei et al., 2014;Xu et al., 2014;Yu et al., 2017]; the Barguzin LIP at 330-280 Ma [Kuzmin, Yarmolyuk, 2014;Yarmolyuk et al., 2014]; and the Khangai LIP at 270-245 Ma [Yarmolyuk et al., 2014] (Fig. 1).
The Tarim -South Mongolia Province is the largest area of diverse late Paleozoic magmatism in Central Asia, with voluminous continental flood basalts and other volcanic rocks found within the Tarim continental block [Yu et al., 2011;Li et al., 2014Li et al., , 2017]].As confirmed by recent studies, the Tarim LIP spreads over the regions of South Mongolia [Kozlovsky et al., 2015], Chinese Altai [Zhang et al., 2014], North-Western Xinjiang [Pirajno et al., 2011;Gao et al., 2014], and Tien Shan [Seltmann et al., 2011], as well as into Eastern Kazakhstan.

SYSTEM
Eastern Kazakhstan is part of the Altai collisional system in the western Central Asian Orogenic Belt.The system formed in late Paleozoic as a result of an oblique collision of Siberia with the Kazakhstan composite terrane [Vladimirov et al., 2003[Vladimirov et al., , 2008;;Xiao et al., 2010].In Devonian through early Carboniferous time, the paleocontinents of Siberia and Kazakhstan were separated by the Ob'-Zaisan oceanic basin (a fragment of the western Paleoasian Ocean) with subduction involving continental blocks (Rudny-Altai and Zharma-Saur terranes) on its margins.Remnant oceanic crust and subduction-related sedimentary and volcanic rocks can be found as numerous fault blocks within the Central part of Altai collisional system [Safonova et al., 2012[Safonova et al., , 2018]].Collisional crust thickening and orogeny show up in the presence of late Carboniferous continental molasse with basal conglomerates in several intermontane basins (Fig. 2).The post-orogenic (latest Carboniferous -earliest Permian) tectonic activity occurred mainly as strike-slip motions [Buslov, 2011].
The igneous rocks of Eastern Kazakhstan, including various ultramafic to felsic volcanic, subvolcanic and intrusive suites, were studied in detail in the 1970s [Shcherba et al., 1976[Shcherba et al., , 1998;;Ermolov et al., 1977Ermolov et al., , 1983;;Lopatnikov et al., 1982].Variations in their forms and compositions allow suggesting their origin at different evolution stages, from the early Carboniferous to the Triassic.The studies of magmatism in Eastern Kazakhstan remained suspended in the 1990s -2000s, until we resumed the work in 2005 at a more advanced level.Since then, a wealth of data has been obtained on the compositions and ages of igneous rocks in the region, which bracket the magmatic activity between 300 and 270 Ma, or within the early Permian (Fig. 2).The results from some units have been reported in recent publications [Khromykh et al., 2011[Khromykh et al., , 2013[Khromykh et al., , 2014[Khromykh et al., , 2016[Khromykh et al., , 2017a[Khromykh et al., , 2017b[Khromykh et al., , 2018]].In this paper, we present a brief overview of the obtained data with implications for post-collisional processes in the region.

VOLCANIC BASINS AND STRUCTURES (297-290 MA)
There are several volcanic basins filled with subalkaline basalts, basaltic andesites and andesites in the central part of the studied region (Fig. 2) and some basins filled with dacites and rhyolites in the southeastern areas.Some basins contain also small subvolcanic bodies of andesite and dacite porphyries.
Trachydacites from the Daubai and Tyureshoke basins have LA-ICP-MS U-Pb zircon ages of 297±1 Ma and 290±4 Ma, respectively (Fig 3, e-f).Felsic volcanics in some basins coexist with subvolcanic garnet dacites and clinopyroxene andesites derived from magmas that were generated in the lower crust at ~10 kbar and 1000 to 1200 °C by partial melting of the crustal substrate under the effect of hot mantle melts [Khromykh et al., 2011].
The Preobrazhenka mafic and granitic rocks have independent composition trends in binary diagrams   [Khromykh et al., 2017a[Khromykh et al., , 2018]].Blue circles mark mingling relations between granosyenite (phase 3) and monzodiorite (phase 4).(b-d) -photographs illustrating relationships between igneous rocks: monzodiorite (dark gray) and porphyritic granosyenite (light gray) nodules in granite of phase 3 (b); contact of monzodiorite and porphyritic granosyenite in an outcrop photo (c) and in the photo of a sample (d); U-Pb ages of Qtz monzonite of phase 1 (e) and granite of phase 3 (f).
(Fig. 7) and show distinct dissimilarity in the contents of Al 2 O 3 , MgO, CaO and Rb, Ba, Zr, La, and Eu.Mafic subalkaline rocks have high alkali contents, with K 2 O up to 2 wt.% in gabbro and 2.5 wt.% in diorite, LREE higher than HREE, and relatively high Ba, K, Ti, Zr, and Sr. Granitic rocks are likewise rather rich in alkalis (3 to 6 wt.% K 2 O); the contents of Al 2 O 3 , FeO, TiO 2 , MgO, CaO, Ba, Sr, and Eu decrease progressively from monzonite to granite and leucogranite.
The detailed petrological studies of the Preobrazhenka rocks showed that mafic lithologies were derived from trachybasaltic magma by fractionation and contamination with crustal anatectic melts, while the granitic lithologies result from melting of the lower or middle crust under a thermal impact of hot mafic magma.The origin of the intrusion was explained [Khromykh et al., 2018] in the context of interaction between mafic magma and granitic anatectic melts at different depths.This interaction led to reciprocal contamination of the mafic and felsic magmas and formation of Qtz-bearing monzogabbro and Qtz monzonite at the lower-crust level, but mingling structures formed at the middle-crust level where chemical mixing was minor; in the upper crust, mafic magmas did not interact with granitic material and formed a few dikes only.Рис. 7. Состав базитовых (долериты и габбро), кислых (Кв монцониты, граносиениты и граниты) и гибридных (монцодиориты) пород из Преображенского массива.

LARGE GRANITOID BATHOLITHS (295-275 MA)
Remelting of the clastic metasedimentary and metamorphic rocks led to the formation of two large granitoid batholiths in Eastern Kazakhstan: Zharma in the west, and Kalba-Narym in the east (see Fig. 2).The Kalba-Narym batholith extends from NW to SE within the Kalba-Narym turbidite terrane.According to a classical interpretation [Lopatnikov et al., 1982;Shcherba et al., 1998], it would be of collisional origin and would form during an orogenic stage, while the respective plutonic event would last 50-60 myr from the C 3 -P 1 boundary to the P 2 -T 1 boundary.However, new petrological and geochronological data [Kotler et al., 2015;Khromykh et al., 2016] show (Fig. 8) a shorter duration (20-25 myr, i.e. from 300-295 to 280-275 Ma, P 1 ) and post-orogenic origin of the plutonism.The Kalba-Narym batholith consists of (1) an S-type granodiorite-granite suite making up most of the batholith volume, which emplaced in two phases at 296-288 Ma and 286-285 Ma, and (2) an A-type leucogranite-granite suite occurring as several large independent intrusions (283-276 Ma).
Suite 1 granodiorites and granites vary in SiO 2 from 64 to 75 wt.%, and all elements except K 2 O decrease with increasing silica contents (Fig. 9), which is common to S-type granites.The leucogranite-granite suite (2) shows a narrower SiO 2 range of 73-76 wt.% and enrichment in Fe, REE, and HFSE (Ta, Nb, Zr, Hf) with silica increase (Fig. 9), as well as elevated contents of F and Li, which is closer to A-type granite compositions.Fig. 8. Simplified geology of the Kalba-Narym batholith, and the results of U-Pb (black squares) and Ar-Ar (white squares) isotopic dating [Kotler et al., 2015;Khromykh et al., 2016].Inset shows the U-Pb ages of granitic samples of suites 1 and 2.
Suite 2 granites and leucogranites form large independent intrusions, and there is a small gap between suite 1 and suite 2. We suggest the origin of Suite 2 in a separate melting pulse.The sources and conditions of granitic magma generation for the two suites were inferred from their mineralogy and chemistry, with reference to the compositions of the sedimentary and metamorphic rocks in the region, as well as to the experimental data on melting of crust protoliths.The rocks of suite 1 (similar to S-type granites) formed by partial melting of mixed metapelitic and metabasaltic substrates.The leucogranites and granites of suite 2 (similar to A-type granites) originated by melting of metapelitic crust, with participation of juvenile fluids enriched in HSFE and REE which interacted with the metamorphic material during melting.

RARE-METAL GRANITE DIKES AND PEGMATITES (290-285 MA)
Granitic pegmatites in the Kalba-Narym zone bear extensive rare-metal mineralization (Ta, Nb, Li, Be, Sn, W etc.).They occur as veins in granitic rocks of phase 1 of the granodiorite-granite suite.Their relative chronology is confirmed by 40 Ar/ 39 Ar isotopic dating: the ages obtained for 12 mica samples from pegmatites range from 292 to 285 Ma [Kotler et al., 2014].Raremetal pegmatites are similar to ongonite and raremetal granite-porphyry that form two dike swarms near Ust-Kamenogorsk city (Fig. 10).The larger Chechek dike swarm comprises about 15 dikes, 2 to 5 m thick and hundreds of meters long [Sokolova et al., 2016].The age of the dikes was determined as Fig. 9. Composition of granodiorite-granite (red circles, grey arrows) and granite-leucogranite (green squares, white arrows) suites from the Kalba-Narym batholith in the binary diagrams.
The mineralogy and chemistry of the dike rocks [Sokolova et al., 2016] suggests their origin from granitic melts that were enriched in rare metals.This makes them closer to rare-metal granite pegmatites of the Kalba-Narym batholith.We assume that magmas rich in rare metals formed in the granite chambers of the Kalba-Narym batholith.However, their local occurrence indicates that their generation involved inputs of F, P 2 O 5 , rare metals, as well as other specific components with juvenile fluids, besides intra-chamber differentiation.This formation mechanism of the rare metal magmas is similar to that for suite 2 granites and leucogranites in the Kalba-Narym batholith.

CORRELATION OF MAGMATIC EVENTS AND MECHANISMS OF PLUME-LITHOSPHERE INTERACTION
Thus, voluminous mantle and crustal magmatism affected the whole Eastern Kazakhstan in the interval of 300-270 Ma (Fig. 13, a).The rocks of mantle origin are enriched in alkalis, phosphorus, titanium and incompatible elements notably different from the older accretionary mafic-ultramafic complexes with subduction signatures [Safonova et al., 2012[Safonova et al., , 2018]].The appearance of enriched mantle magmas at the post-orogenic stage usually indicates their deeper sources.There are also assumptions that the appearance of enriched mantle magmas may be caused by remelting of metasomatised mantle wedges [Konopelko et al., 2017].Anyway, melting of the mantle indicates an increasing thermal gradient.The high thermal gradients most likely resulted from the activity of the Tarim mantle plume which produced the early Permian Tarim LIP [Ernst, 2014;Gao et al., 2014;Wei et al., 2014;Xu et al., 2014;Yarmolyuk et al., 2014;Yu et al., 2017].Based on the reported data, we infer that the Tarim LIP extends to the north, into the region of Eastern Kazakhstan (Fig. 13, b).The far-reaching influence of the Tarim LIP may have been facilitated by post-orogenic lithospheric extension [Buslov, 2011] after the Siberia-Kazakhstan collision.The extension led to rheological weakening of the lithosphere, whereby deep mantle melts could intrude into the sublithospheric mantle.The style of the mantle-crust interaction varied over the region depending on the permeability of the lithospheric blocks [Khromykh et al., 2017b].In the central part of the region (see Fig. 2), where the fragments of accretionary and paleooceanic complexes still exist, mafic magmas could easily penetrate into the lower crust through the quite thin lithosphere.This may lead to intensive interactions of the mafic magmas with the crustal substrates and anatectic melts, forming the gabbro-monzonitegranite intrusions with a wide spectrum of rocks and mingling and mixing processes, and the appearance of syn-plutonic Mafic Microgranular Enclaves (MME) and combined mafic-felsic dikes [Wiebe, 1973;Furman, Spera, 1985;Litvinovsky et al., 1995;Barbarin, 2005;Renna et al., 2006;Burmakina, Tsygankov, 2013;Burmakina et al., 2018] In the northeastern part of the territory, clastic sediments (sandstones and siltstones) deposited in the Devonian-Early Carboniferous within the Kalba-Narym terrane were deformed and metamorphosed in the course of collisional processes, and then were molten anatectically at high temperature gradients across the mantle chambers.Mafic Fig. 11.Composition features of ongonites from Chechek and Akhmirovka dike belts [Sokolova et al., 2016].
Рис. 11.Особенности состава онгонитов из Чечекского и Ахмировского дайковых поясов [Sokolova et al., 2016].magmas could not penetrate through thick viscous migmatite-granite lenses ('density filter') [Huppert, Sparks, 1988].This mechanism includes interaction of the juvenile mantle fluids with the crust or with granitic magma in the chambers, as well as the inputs of some elements responsible for rare-metal mineralization in granites [Abramov, 2004;Annikova et al., 2006;Zagorsky et al., 2014;Sokolova et al., 2016].Thus, we revealed two main types of mantle-crust interaction: (1) direct interaction of mantle magmas with crustal material and ana- tectic melts that produced large gabbro-granite intrusions, volcanic structures, and numerous small gabbropicrite intrusions in central part of studied region; and (2) the effects of mantle heat and fluids on the crust.The intrusion of the mafic magmas into the middle and upper crust became possible only after large-scale granitoid magmatism had completed and the lithosphere had cooled down and deformed.This led to the formation of the Mirolyubovka dike swarms.
Thus, the early Permian history of Eastern Kazakhstan was controlled by the interplay of the plate tectonic and plume processes: plate-tectonic accretion and collision formed the structural framework, and the Tarim mantle plume provided a heat source to maintain voluminous magmatism.