ISSN 00168521, Geotectonics, 2015, Vol. 49, No. 3, pp. 219–241. © Pleiades Publishing, Inc., 2015. Original Russian Text © S.G. Samygin, T.N. Kheraskova, A.M. Kurchavov, 2015, published in Geotektonika, 2015, No. 3, pp. 66–92.
Tectonic Evolution of Kazakhstan and Tien Shan in Neoproterozoic and Early–Middle Paleozoic S. G. Samygina, T. N. Kheraskovaa, and A. M. Kurchavovb a
b
Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017 Russia Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017 Russia email:
[email protected] Received January 23, 2014
Abstract—Geological information on Kazakhstan and the Tien Shan obtained up to the present time has been considered and integrated in order to demonstrate the main features of continental massifs, basins with oceanic crust, island arcs, marginal volcanic–plutonic belts, and transform fault zones differing in type and age. We ascertained the character and probable causes of their evolution and transformations resulting in the origination and development of mosaic structural assembly at margin of the Paleoasian ocean that existed from Neoproterozoic. The main stages of the geodynamic history of Paleozoides in Kazakhstan and Tien Shan are characterized, and a model of the probable course of regional tectonic events has been proposed. This model is illustrated by published paleomagnetic data and a series of paleotectonic reconstructions for time intervals 950–900, 850–800, 750–700, 650–630, 570–550, 530–515, 500–470, 460–440, and 390– 380 Ma. Keywords: Rodinia, Paleoasian Ocean, microcontinent, island arc, transform fault zone DOI: 10.1134/S0016852114060065
INTRODUCTION The vast territory of Kazakhstan and the Tien Shan occupies the central part of the Ural–Mongolian Fold Belt—one of the most extended and complex terres trial structural assemblies, which evolved over several hundred million years. The onset of these tectonic processes was related to the breakdown of the epi Grenville Rodinia supercontinent and the opening of the Paleoasian ocean. This evolution was completed by the closure of the basins inherited from this ocean at the end of Middle Paleozoic [1, 37, 56]. The lithotectonic complexes formed in various geo dynamic settings at the place of continental massifs, oceanic basins, island arcs, interarc and marginal seas, volcanic–plutonic belts, and transform fault zones participate in the geological structure of Kazakhsatn and Tien Shan, making up accretionary and collisional structural units [20]. The accretionary units are typical of Central Kazakhstan and the North Tien Shan (Fig. 1). They are characterized by variable strikes of tectonic zones with junctions along large faults; zones of stacking, variously oriented strikeslip faults, and sigmoids are widespread. Taken together, they create a complex mosaic pattern. The collisional tectonic units are characteristic of the South Tien Shan and Eastern Kazakhstan. They are distinguished by tense fold– nappe structure and persistent strike of relatively nar row linear zones, including ophiolite sutures, which
alternate with less deformed blocks; longitudinal and oblique strikeslip faults dominate among the late dis turbances. The accretionary tectonic units progres sively built up continental massifs at the boundaries with oceanic basins. The collisional processes resulted in squeezing of the paleooceanic basins between sialic masses and their amalgamations [37]. New data on the age of the stratigraphic subdivi sions, intrusive complexes, and rocks of ophiolitic associations obtained in recent years for Kazakhstan and Tien Shan made it possible to specify and in some cases to revise the previously existing tectonic con cepts. Taking new evidence into account, we strive to show the main stages of the tectonic evolution of Kazakhstan and Tien Shan using all available geologi cal information in combination with paleomagnetic characteristics of certain complexes. As a result, a series of paleotectonic maps with elements of paleo geography has been created for a series of time intervals: 950–900, 850–800, 750–700, 650–630, 570–550, 530–515, 500–470, 460–440, and 390–380 Ma. The reconstructions of Neoproterozoic intervals repeat in many respects the earlier interpretation [56]. In the Paleozoic reconstructions, published here for the first time, attention is focused on the main regional paleo structures. Adjacent regions are depicted in different styles. In the Altai–Sayan region and Mongolia, typo morphic structural elements related to evolution of the
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Fig. 1. Tectonic scheme of the central and eastern parts of the Ural–Mongolian Foldbelt and adjacent territories, modified after [37]. (1) Siberian Platform and continental blocks of Siberian origin; (2) other platforms, microcontinents, and blocks; (3–5) accrecio nary fold zones: (3) Late Riphean, (4) Salairian, (5) Caledonioan; (6, 7) residual troughs: (6) Caledonian, (7) Variscan; (8–11) col lisional fold zones and sutures: (8) Caledonian, (9) Variscan, (10) Indosinian and Late Variscan, (11) Kimmerian; (12) Kunlun Fore deep; (13) large fault. Abbreviations in boxes. Platforms, microcontinents, blocks: Ks, Kokshetau; She, Shet; Io, Ishkeolmes; U, Ulytau; AM, Aqtau– Mointy; Zh, Zhongar; SQ, Shu–Qendyktas; TQ, Talas–Qaratau; Yk, YsykKöl; CT, Central Tien Shan; Hs, Hanshan; SG, South Gobi; CM, Central Mongolian; Z, Zabhan; TM, Tuva–Mongolia; accretionary fold zones: ES, Eastern Sayan; KA, Kuznetsk Ala tau; BR, Batenev Ridge; WS, Western Sayan; O, Ozerny; Dd, Dzhida; Zk, Zharkainagach; Bn, Bayqonyr; GQ, Greater Qaratau; CN, Chatkal–Naryn; ZN, Zhalair–Nayman; (I), Ili; As, Atasu; St, Stepnyak; Se, Selety; E, Erementau; Tt, Teqturmas; BA, Bay daulet–Aqbastau; B, Bozshakol; Sh, Shyngyz; Sa, Salair; GA, Gorny Altay; MA, Mongolian Altay; Bh, Bayanhongor; Shm, Shar Muren; residual troughs: Ag, Aghadir; AC, Anui–Chuya; NB, North Balqash; H, Hangay; fold zones and sutures: T, Terskey; Ga, Gobi Altay; Tu, Turkestan; OZ, Ob–Zaysan; SM, South Mongolian; S, Solonker; WK, West Kunlun; NP, North Pamir.
Paleoasian ocean are shown, whereas oceanic basins of China unrelated to the Paleoasian ocean are only outlined without designation of continental blocks and various arcs. The tectonic evolution of the Chi nese domains was briefly considered in [7]. Paleodynamic reconstructions start from the final stage of the Rodinia supercontinent evolution, which arose, as is generally recognized, in the Grenville epoch 1100–950 Ma ago. The map of Rodinia [74], with some modifications, was taken as the basis. In the subsequent reconstructions that reflect the breakdown of Rodinia in Neoproterozoic, the paleostructures of Kazakhstan and Tien Shan have been inscribed into a general pattern characterizing the evolution of the Paleoasian ocean and the sialic masses in its frame work. The Early–Middle Paleozoic geodynamic evo lution of the region under consideration began ~550 Ma ago after the appearance of a new Paleogondwana supercontinent. The chosen time intervals correspond to the main global structural rear rangements and important tectonic events, including destruction of continental massifs, formation of oce anic crust, manifestations of islandarc and marginal continental magmatism, accretion, and collision. Tables with paleomagnetic pole coordinates for each continent involved in our reconstruction were pub lished in [20, 56]. Alternative paleoreconstructions were critically analyzed earlier [1]. The age estimates of rocks indicated in the paper correspond to the last version of the Geological Time Scale [78].
nic rocks with UPb age of protolith at 1156 ± 4 and 1136 ± 4 Ma, respectively [49, 52] occur in the Kok shetau (Kokchetav)1 massif of Kazakhstan, and granitoids dated at 1131 ± 4 Ma crop out in the Maqbal (Makbal) Block of the Tien Shan [16]. Small granodiorite bodies that cut through gneisses and crystalline schists of the Kokshetau massif have a similar age of 1128 ± 12 Ma [34].
NEOPROTEROZOIC
Thus, Rodinia, which arose at the Mesoprotero zoic–Neoproterozoic boundary, did not become epi Grenville Pangea. Paleosiberia surrounded by basins with oceanic crust dated at ~1 Ga [39, 56] was left beyond its boundary (Fig. 2). These basins became embryos of the Paleoasian ocean. The North China and a number of other sialic blocks, which are now localized in Central Asia and Kazakhstan, occurred closer to Rodinia and made up an independent paleo continent after breakdown of Rodinia.
950–900 Ma. The Rodinia supercontinent arose as a result of collision of ancient sialic massifs during the Grenville Orogeny 1100–950 ma ago, however, collision and orogeny combined not all Grenville cratons [56]. The Siberian and North China paleo continents did not entered into Rodinia (Fig. 2). In addition, an extended orogen primarily consisting of fragments of the continental crust with preGrenville age of consolidation was situated separately at the northeastern periphery of Rodinia and included ter ritories of Tarim, Qaidam, smaller massifs and blocks in the North Tien Shan and western Central Kazakh stan. For example, gneissose granite and metavolca GEOTECTONICS
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We assume that the Tarim–Tien Shan–Kazakhstan orogen could have been formed during the origination of Rodinia or immediately after this event due to local collision or accretion above a probable subduction zone. The Grenville Orogeny was completed here by emplacement of granites and granitization dated at 1050–945 Ma [56], and this resulted in the formation of a paleocontinent significant in size. Subduction of the oceanic crust beneath this paleocontinent started almost synchronously with its formation. This is indi cated by suprasubduction felsic volcanism and associ ated granites dated at 925–917 Ma in the Aqtau (Aktau)–Mointy and Ulytau (Ulutau) blocks [1, 19]. At the presentday southern margin of Tarim, facing north at that time, basic and intermediate volcanic rocks with UPb age of 963–945 Ma are known [53]. The epiGrenville continental cover accumulated in back zone of this volcanic–plutonic belt. The Koksh etau Group and its analogs, composed of terrigenous, often quartzitic and fissile quartzitic sequences with carbonate lenses and felsic tuff interlayers, are an example. The Kokshetau quartzites contain detrital zircons, the age of which is 2850–1020 Ma [24, 30].
1 The spelling of proper geographic names adopted in independent
republics of Central Asia differs in many cases from that tradition ally used in the literature published in Russian. The latter is shown in parentheses at the first mention. Translator’s comment.
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850–800 Ma. Rodinia began to break down at this time. Various parts of the supercontinent had broken up with pulling apart and separation of fragments. Narrow oceanic basins—the Protopacific and oth
ers—appeared between them, being opened in differ ent directions. The Paleoasian ocean was at that time a relatively large, expanding basin with extended sub duction zones (Fig.3). It was situated between North GEOTECTONICS
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Fig. 2. Supercontinent Rodinia and adjacent paleostructures: geodynamic reconstruction for time interval 950–900 Ma. (1–6) Pale otectonic and paleogeographic elements: (1) collisional and accretionary zones, (2) Andeantype continental margins, (3) passive continental margins and shelves, (4) intracontinental basins, (5) continental domains free of sediments, (6) continental rifts*; (7) inferred contour of Rodinia; (8–12) boundaries of lithospheric plates and fault zones: (8, 9) subduction zones*: (8) ensialic island arcs and Andeantype margins, (9) ensimatic island arcs; (10) spreading zone; (11) transform fault; (12) front of collision and nappe formation; (13–18) indicators of geodynamic regimes*: (13) ophiolites, (14) continental basalts, alkaline volcanic rocks, (15) bimodal volcanism, (16) granitic rocks, hightemperature metamorphism, (17) island arc volcanism, (18) tillites and tilloids. * age, Ma. Numeral in boxes: 1, Zabhan massif; 2–4, volcanic arcs: 2, Dunjugur; 3, Baikal–Muya; 4, Taimyr.
The Tarim–Tien Shan–Kazakhstan paleocontinent was pulled apart eastward along strikeslip faults. The Andeantype suprasubduction felsic volcanic rocks were formed along the southern margin of this paleo continent. According to [29], the age of tuffs in the Lesser Qaratau (Karatau) in Kazakhstan (Qorghan
China, the Tarim–Tien Shan–Kazakhstan paleocon tinent, and Siberia to the east of the originating Proto pacific, probably connecting with the latter along a transform fault zone [56]. The expansion of the Paleoasian ocean brought about the northward displacement of North China.
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Fig. 3. Geodynamic reconstruction for time interval 850–800 Ma. Numeral in boxes: 1, Zabhan massif; 2, Baikal–Muya. See Fig. 2 for legend. GEOTECTONICS
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Fig. 4. Geodynamic reconstruction for time interval 750–700 Ma. Numerals in boxes are microcontinents: 1, Zabhan; 2, Bar guzin. See Fig. 2 for legend.
(Kurgan) Formation) is 831–766 Ma, and the area occupied by these rocks was located at 34.2° ± 5.3° N. Rhyolites dated at 830 ± 20 Ma are also known in the North Tien Shan. The coeval granitoid magmatism is known in the North Tien Shan (837 Ma), the Talas Range in Kazakhstan (825 Ma), and the Shu (Chu) Block (840 Ma) [4]. The granitoids locally acquired gneissic appearance. In the AkTüz (Aktyuz) block of the North Tien Shan, the time of their emplacement and crystallization is estimated at 844 ± 9–778 ± 6 Ma (UPb zircon age) [71]. In the southern Ulytau (Kaza khstan), the age of granite gneiss protolith is 841 ± 11 Ma [22]; the granites pertaining to other complexes are dated at 803 ± 27 and 791 ± 7 Ma [51]. Later on, the Tarim–Tien Shan–Kazakhstan pale ocontinent was destroyed behind the volcanic–plu tonic belt, which spread from west to east. Riftrelated igneous rocks (primally mafic and less frequent ultra mafic dikes) occurred along the Tien Shan margin of Tarim. They are dated at 821 to 807 Ma, becoming
younger in the eastern direction. The swarm of dolerite dikes dated at 807 Ma was located at an latitude 43° ± 6° N [65]. It is evident that a chain of mafic igneous rocks marks a back zone of rifting. Subduction beneath the Tarim–Tien Shan–Kazakhstan paleocontinent was apparently conjugated with subduction beneath Mongolian margin of North China [56]. The function ing of these zones partly compensated for the spreading in the Paleoasian ocean. 750–700 Ma. The breakdown of Rodinia mark edly increased due to appearance of new oceanic basins. The Paleoasian ocean continued to widen along with Protopacific, and its northern continental margins lost their active character as compared with the preceding stage (Fig. 4). Subduction beneath the Tarim–Tien Shan–Kazakhstan paleocontinent and North China ceased, giving way to magmatic pro cesses related to the subsequent fragmentation and sep aration of microcontinental blocks. The bimodal rift related volcanism of elevated alkalinity (755–690 Ma) GEOTECTONICS
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