Kazakhstan Plate Research Articles

Geophysical Implications for Prospective Prediction of Copper Polymetallic Ore Bodies: Northern Margin of Alxa Block, China

The Alxa Block is located in the middle part of the Central Asian orogenic belt, which is the coupling belt of the North China, Tarim, and Kazakhstan Plates. The east–west-trending deep faults control stratigraphic distribution and magmatic activity in the region. To detect the EW-trending ore-controlling deep structures, a 440 km NS section of magnetotelluric sounding was conducted from Minle to Ejinaqi. The phase tensor and electrical principal axis were analyzed based on the measured data to build the exploration model. The electrical structure model along the section was obtained using nonlinear conjugate gradient (NLCG) 2D inversion. Combined with the geological, geophysical, and deposit distribution characteristics in the area, the comprehensive study of magnetotelluric sounding profile shows that the resistivity presents as zoned along the profile. The Engelwusu ophiolite mélange belt is stacked in clumps with high and low resistivity, indicating that the northern margin of the Engelwusu Belt subducts below the high-resistivity zone, representing the passive continental margin. The southern end of the Engelwusu ophiolite belt is primarily the prospecting potential area for copper–gold deposits, whereas the northern end of the Engelwusu ophiolite belt corresponds to copper polymetallic deposits.

First record of the latest Devonian ostracods from Xainza region, Tibet, China: implications on palaeoenvironment and palaeobiogeography

Ostracods of the Devonian–Carboniferous transitional interval in the Lhasa Block are described for the first time at the stratotype section of the Chaguoluoma Formation, Xainza, Tibet. Fifty-three ostracod species of 19 genera are identified and figured including a new species Bairdiacypris xainzaensis n. sp. The ostracod fauna in the Chaguoluoma section may represent an age close to the Devonian–Carboniferous boundary. The benthic ostracods from the Chaguoluoma section belong to the Podocopid association (i.e., Eifelian Mega-Assemblage), which implies an offshore environment. Additionally, ostracods from the Chaguoluoma Formation show a high similarity to the Devonian taxa from South China, suggesting a close biogeographic affinity between the Lhasa Block and South China Plate. They are also compared to the ostracod faunas from Laurentia–Baltica, Gondwana, and Kazakhstan plates, which implies that ostracods could probably benefit from oceanic circulations and sea-level changes to experience faunal exchanges between peri-Gondwana and Laurentia–Baltica during the latest Devonian.

Evolution of the genus Cribroconcha (Ostracoda, Crustacea) in relationship to palaeoecological changes during the late Palaeozoic

To date, 37 species and 2 subspecies (36 species plus 1 species that with 2 subspecies) of the ostracode genus CribroconchaCooper, 1941 have been reported worldwide, ranging in age from the Middle Devonian to the Early Permian with an acme during the Carboniferous. Based on the geographical distribution and morphological characteristics of Cribroconcha, two evolutionary lineages (i.e., Lineage 1 and Lineage 2) are identified, which originated in the European and the Kazakhstan plates, respectively. Lineage 1 can be subdivided into three types: 1-A (stable type), 1-B (reshaped type) and 1-C (spiny type). Lineage 2 has a simpler pattern of evolution compared to Lineage 1. Although there were certain accompanying changes in the morphology of carapaces, the general pattern and most successful evolutionary novelty of Cribroconcha appears to be the appearance of spiny forms in the Early Carboniferous, which continued to be preserved until the Early Permian. The habitats of Cribroconcha may have changed from shallow, warm waters to deep, calm and colder waters in the basinal environments. Four Cribroconcha biozones, extending from the Givetian Stage to Serpukhovian Stage are established in the Euramerica plate, namely C. beckmanni Zone, C. triquetra triquetra Zone, C. cooperi Zone and C. caneyensis Zone.

Keraphyton gen. nov., a new Late Devonian fern-like plant from Australia.

The first plants related to the ferns are represented by several extinct groups that emerged during the Devonian. Among them, the iridopterids are closely allied to the sphenopsids, a group represented today by the genus Equisetum. They have been documented in Middle to early Late Devonian deposits of Laurussia and the Kazakhstan plate. Their Gondwanan record is poor, with occurrences limited to Venezuela and Morocco. Here we describe a new genus from a late Late Devonian locality of New South Wales. It is represented by a single anatomically preserved large stem characterized by a star-shaped vascular system with protoxylem strands located at rib tips, and by a lack of secondary tissues. Within the first fern-like plants, this stem shares the largest number of characters with iridopterid axes but differs by the pattern of its vascular system. Keraphyton mawsoniae gen. et sp. nov. adds a new record of early fern-like plants in eastern Gondwana. It provides new insights into the anatomical diversity within this key group of plants and supports the distinctiveness of the Australian flora in the latest Devonian.

Mo deposits in Northwest China: Geology, geochemistry, geochronology and tectonic setting

Northwest China, covering northern Xinjiang, northern Gansu and westernmost Inner Mongolia, mainly includes Junggar Basin and its surrounding mountains such as Chinese Altay, Junggar, Chinese Tianshan and Beishan. It lies at the junction of Siberia, Tarim and Kazakhstan plates, and is a key sector of the Central Asian Orogenic Belt (CAOB), characterized by multistage Phanerozoic continental growth. Herein at least nine Mo-only or Mo-dominated, fourteen Cu-Mo, two W-Mo and one Be-Mo deposits have been discovered. These 27 deposits occur in Altay, West Jungar, West Tianshan, East Tianshan and Beishan areas, and have been formed during accretionary or collisional orogenies. The majority of the deposits are porphyry type, followed by the skarn and quartz vein types. The orebodies occur mainly as veins, lens, pods in the positions from inner intrusions through contact zones to the hostrocks distal to causative intrusions. The host-rocks are variable in lithologies, including granites, porphyries, volcanic breccias and tuffs, and sedimentary rocks. Outward from orebodies to hostrocks, the wallrock alteration is zoning from potassic (K-feldspar-quartz-mica), through phyllic (quartz-sericite-chlorite-epidote), to propylitic or argillic alterations, with skarn specifically occurring in skarn-type systems. Hydrothermal mineralization generally includes four stages, from early to late, represented by (1) potassic feldspar-quartz veins or veinlets, (2) quartz-molybdenite stockworks, (3) quartz-polymetallic sulfide stockworks, and (4) quartz±carbonate±fluorite veins or veinlets. The ore-forming fluids were initially magmatic in origin and shew high-temperature and high-salinity, containing daughter mineral- and/or CO2-bearing fluid inclusions; and eventually evolved to low-temperature, low-pressure, low-salinity and CO2-poor meteoric water. The porphyry Mo deposits can be further subdivided into two subtypes, i.e., Dabie- and Endako-types. The Endako-type Mo deposits, e.g., Suyunhe and Hongyuan, together with all the Cu-Mo systems, were formed in the Palaeozoic subduction-related magmatic arcs. The Dabie-type porphyry Mo deposits, represented by giant Donggebi and Baishan, together with the Mo-only, Mo-dominated and W-Mo or Be-Mo deposits were formed in syn- to post-collisional tectonic setting, with isotope ages ranging 260–213.2Ma, with the Kumutage skarn-type Mo system being an exception aged 319Ma. The Dabie-type porphyry Mo deposits are characterized by the CO2-bearing fluid inclusions that cannot be observed in the Endako-type porphyry Mo systems. The Re contents in molybdenites from porphyry and porphyry-skarn Cu-Mo systems are mainly >100ppm, suggesting a source significantly contributed by the mantle; whereas the Re contents in molybdenites from the Mo-only or W-Mo deposits are mainly <100ppm, indicating a genetic relation to the crust-sourced granitic magmatism. Therefore, the types of porphyry Mo deposits and their contrasting geological and geochemical characteristics are a powerful indicator of the tectonic settings; and the available data from the Mo deposits in NW China indicate a Late Carboniferous-Permian transformation from subduction-related accretionary orogeny to continental collision orogeny.

Late Devonian global ostracod palaeobiogeography

A global Late Devonian ostracod database is constructed, incorporating new materials from South China and Northwest China. Four palaeobiogeographical units (Cathaysia, North America, Europe and peri-Gondwana) are recognized during the Frasnian and five palaeobiogeographical units (Cathaysia, North America, Europe, Siberia and Australia) in the Famennian. Three controlling factors (climatic zonation, geographical isolation and global sea-level changes) are identified to have played roles in shaping the palaeogeographical regionalization of ostracod faunas in the Late Devonian. The ostracod palaeobiogeography in the Frasnian was mainly influenced by climatic zonation, while rapid changes in tectonic configuration in the Famennian drastically altered the global palaeobiogeography of ostracods. The palaeobiogeographical regionalization of ostracod faunas suggests that Laurussia and Gondwana continued to draw near during the Late Devonian, with the first collision occurring in Southern Central Europe in the Famennian. The South China plate drifted northward to the Kazakhstan plate away from the Australian plate, which gradually became isolated during the Famennian Stage.

Coevolution of brachiopod Boreal Realm and Pangea

The Boreal Realm originated in the early Carboniferous; the realm became more firmly established during the late Carboniferous and early Permian, and peaked in the middle Permian before decaying in the late Permian. In the early Carboniferous, the geographic distribution of the Boreal Realm was latitudinally narrow, and many brachiopod genera of the realm were also common in the Tethys Realm. The Boreal Realm faunas were, however, also characterized by many geographically and temporally restricted genera. The Boreal Realm was well developed in the late Carboniferous, as represented by the continued expansion of the geographical ranges and numbers of occurrences of many Permian characteristic Boreal Realm genera. In the early Permian, the geographic distribution of the Boreal Realm expanded further, as did the distribution of characteristic Boreal Realm genera. In the middle Permian, the geographic distributions of the Boreal Realm had expanded to their greatest extent, and the characteristic Boreal Realm genera were most abundant and diverse. In the late Permian, the cool-water characteristic genera, which flourished during the Carboniferous to middle Permian, disappeared in these areas, and resulted in the decay of Boreal Realm.The development of the Boreal Realm was closely related to events leading to the formation of Pangea, in which a variety of plates (Laurussian, Siberian, etc.) were continuously drifting northwards; some plates/blocks entered middle- and high-latitudinal regions and were located in cool climatic environments. During the evolution of Pangea, the Siberian, Kazakhstan, and Eastern European plates were continuously located in the center of the Boreal Realm; the Barents Ocean developed to the west and the Paleo-Asian Ocean developed to the east of these plates. This configuration of oceans and continents differentiated the eastern Central Asia Region and the western Barents Region. In the Paleo-Asian Ocean tectonic domain, the northern branch of the Paleo-Asian Ocean was surrounded by the Siberian plate, the Kazakhstan plate, and the Jiamusi–Mongolia Block, and named the Mongolia–Okhotsk Ocean. The Mongolia–Okhotsk brachiopod fauna developed on the southern margin of the Mongolia–Okhotsk Ocean (i.e., the northeastern margins of the Siberian and Kazakhstan plates, and the northern margin of the Jiamusi–Mongolia Block), thus forming the Mongolia–Okhotsk Province. During the middle Permian, the Xar Moron Ocean was enclosed by the Jiamusi–Mongolia Block and the Kazakhstan, Tarim, and South China plates. On the southern margin of the Xar Moron Ocean (i.e., the southern margin of the Jiamusi–Mongolia Block), the Zhesi brachiopod fauna developed, and the Inner Mongolia Province was formed. During the Carboniferous–Permian, the Kolyma-Chukchi block, Siberian plate, and North American plate comprised the Barents Ocean tectonic domain. The Verkhoyansk brachiopod fauna developed on the northern margin of the Barents Ocean (i.e., on Verkhoyansk and the southwestern margin of the Siberian plate), thus forming the Verkhoyansk–Taymyr Province. Starting in the late Carboniferous, a cool-water brachiopod fauna developed on the southern margin of the Barents Ocean (i.e., the northern margin of the North American plate and the northern margin of the Eastern European plate), thus forming the Yukon–Pechora Province, the geographical range of which extended continuously with time.

Zircon U-Pb age, geochemistry and geological implications of granitoids in Tuerkubantao, Xinjiang

Three types of granitoids were recognized in Tuerkubantao(土尔库班套) district, located on the northwestern margin of the Junggar Block. The zircon U-Pb age of the three types of granitoids suggests that they formed in different orogenic stage in response to the convergence and collision between Siberian and Kazakhstan plates. Biotite granite is similar to the volcanic arc granites in composition, with zircon U-Pb age of 382.8±2.5 and 355.6±2.4 Ma. The former is crystallizing age of the volcanic arc granite, while the later record the time of hydrothermal alteration induced by a later magmatism. The granite is severe altered and its zircon grain get a lower intercept age of 324.4±7.3 Ma, which is possibly coursed by magmatism in syn-collision. The rhyolite with composition similar to A-type granites in adjacent area, crystallized at 295.9±1.4 Ma, is possibly the extrusive phase of A-type granite formed in the post-orogenic tectonic setting. The granitoids in Tuerkubantao area record the evolution of the northwestern Junggar orogen. The area has been in convergence setting from Middle to Late Devonian, and stepped into syn-collisional tectonic setting in Early Carboniferous, finally evolved into the post-orogenic tectonic stage since Early Permian.

Epithermal deposits in North Xinjiang, NW China

The North Xinjiang region (NW China) is an important part of the Central Asia Orogenic Belt, situated at the junction of Siberia, Tarim and Kazakhstan plates. It is an area characterized by multiple stages of Phanerozoic continental growth, during which several porphyry and epithermal systems were formed. The relationship of these mineral systems to the geodynamic evolution of the region has not yet been well understood. In this paper, we list the main geological characteristics of 21 significant epithermal precious and base metal deposits in North Xinjiang, and classify them into high-sulfidation and low-sulfidation styles, with the latter being predominant. We have selected seven epithermal deposits representing different styles formed under different tectonic regimes and discuss their geology and geochemistry in some detail. The deposit-scale geology and geochemistry of epithermal systems in North Xinjiang are essentially similar to those in other parts of the world. All epithermal deposits in North Xinjiang are hosted in volcanic rocks with ages ranging from Devonian to Triassic, with the Early Carboniferous volcanic sequences being the most important, followed by the Permian and Triassic. The Devonian–Early Carboniferous host rocks belong to the calc-alkaline series that developed in pre-collisional arc-back-arc basin systems; whereas the Permian–Triassic host volcanic rocks of shoshonite series formed in post-subduction regimes. Available isotopic ages of these epithermal systems cluster in two periods: Early Carboniferous (>320 Ma) and Late Carboniferous–Triassic (320–220 Ma), reflecting two metallogenic episodes that occurred during subduction-related accretion and post-subduction collision regimes, respectively. Accordingly, three groups of epithermal deposits in North Xinjiang can be recognized as (1) pre-collisional deposits without or with negligible collisional-related modification, (2) deposits formed in collision regime and (3) ore systems strongly overprinted by fluid flow in post-subduction collision regime.

Distribution of Tuvaella brachiopod fauna and its tectonic significance

Tuvaella brachiopod fauna are distributed in an arc in three areas, including the Zeya-Hailar (海拉尔)-Shinejinst area, the Najramdal Uul-Kyzyl area, and the Barkol-Fuyun (富蕴) area. The Tuvaella fauna in the Zeya-Hailar-Shinejinst area are distributed in the northern margin of Jiamusi (佳木斯)-Mongolia block along the Mongolia-Okhotsk suture between the Siberia plate and the Jiamusi-Mongolia block but not appear in the corresponding Siberia plate. The Tuvaella fauna in the Najramdal Uul-Kyzyl area are distributed in the southwestern part of the Siberia plate as the accelerated fold belts during the Salairian-Caledonian periods, and those in the Barkol-Fuyun area are distributed in the northeastern margin of Kazakhstan plate. They are distributed along the Irtysh suture between the Siberia plate and the Kazakhstan plate. The Tuvaella fauna became domestic fauna during the Wenlock and Pridoli (Middle-Late Silurian) and form a unique biogeographic province, i.e., the Mongolia-Okhotsk Province. This biogeographic province is sustained to the Mississippian (Carboniferous), perhaps due to the semiclosed state of the Mongolia-Okhotsk Ocean. The northeastern margin (right now the southwestern margin) of Siberia plate, the northern margin of Jiamusi-Mongolia block, and the northeastern margin of Kazakhstan plate might be conjuncted in an arc region from Wenlock to Mississippian, along the southern margin of the Irtysh-Mid Mongolia-Okhotsk Ocean. This is coincident with the fact that the Siberia plate rotated 180° clockwise since the Mesozoic and located in the middle-high latitude during Devonian, and the coral reef limestone is widely developed in the Jiamusi-Mongolia block during the Early and Middle Devonian, which suggests that the block was positioning in middle-lower latitude at that time and that the Kazakhstan plate was also located in low latitude then.

Multi-method chronometric constraints on the evolution of the Northern Kyrgyz Tien Shan granitoids (Central Asian Orogenic Belt): From emplacement to exhumation

Multichronological data reveal the thermotectonic history of the northern Kyrgyz Tien Shan granitoids (Kyrgyzstan) from emplacement to exhumation. Zircon SHRIMP and LA-ICP-MS U/Pb concordia ages suggest a Middle to Late Ordovician crystallization age (440–470 Ma) for the most voluminous; Caledonian intrusion phase, which is associated with the evolution and closure of the Early Palaeozoic Terskey Ocean. The presence of some additional Early Ordovician – Cambrian U/Pb ages point towards a prolonged production of granitoids during the entire Early Palaeozoic. A sampled younger granitoid (292 ± 5 Ma) was formed during the final closure of the Turkestan Ocean when Tarim eventually collided with the Kazakhstan plate during Hercynian orogeny. 40Ar/ 39Ar step-wise heating plateau-ages (biotite Ar/Ar: 400–440 Ma; K-feldspar Ar/Ar: 235–375 Ma) bear witness to rapid Silurian – Early Devonian post-magmatic cooling of the Caledonian intrusives, followed by a more modest rate of cooling during the Late Devonian until the Late Triassic. Low-temperature techniques such as apatite fission track (AFT) and Apatite (U–Th–Sm)/He (AHe) thermochronology, give Late Jurassic – Cretaceous ages (90–160 Ma) with some Cenozoic outliers. Thermal history modelling allows us to distinguish two marked cooling phases: (1) Mesozoic cooling occurred as the result of denudation and exhumation of the Tien Shan basement during a pulse of tectonic reactivation, associated with the Cimmerian orogeny. (2) Late Cenozoic cooling (∼10–3 Ma) reflects a far-field effect of the India–Eurasia collision. Some samples also experienced a Late Oligocene – Miocene reheating event, which could be the result of burial due to sediment load stripped from the adjacent, eroding mountain ranges.

Tectonic processes in the Southern and Middle Urals: an overview

Abstract The tectonic evolution of the Uralide orogen began during the Late Palaeozoic as the continental margin of Baltica entered an east-dipping (today's coordinates) subduction zone beneath the Magnitogorsk and Tagil island arcs. The subsequent arc-continent collision resulted in the development and emplacement of an accretionary complex over the continental margin, the development and deformation of a foreland basin, and the extrusion of high-pressure rocks along the arc-continent suture. There is mounting evidence that, at about the same time as arc-continent collision was occurring along this margin of Baltica, eastward-directed subcontinental subduction of the Uralian oceanic crust was also taking place beneath the Kazakhstan plate. This subcontinental subduction is thought to have resulted in the formation of a continental volcanic arc. The final closure of the Uralian ocean basin and the start of collision between the Baltica and Kazakhstan plates occurred during the Late Carboniferous. This continent-continent collision resulted in development of the Late Carboniferous to Early Triassic western foreland fold and thrust belt and foreland basin of the Uralides. The foreland fold and thrust belt displays a large amount of basement involvement, extensive reactivation of pre-existing faults, and a small amount of shortening. At the same time, widespread strike-slip faulting accompanied by melt generation and granitoid emplacement took place in the interior part of the Uralides, leading to the transfer of material laterally along the strike of the orogen. The final crustal structure of the Uralides that resulted from the combination of all of these tectonic events is bivergent, with a crustal root reaching c. 53 km depth.

Gold Deposits in Beishan Mountain, Northwestern China

Abstract. The Beishan Mountain spans three provinces ‐ Gansu, Xinjiang and Inner Mongolia, having an area of 120,000 km2 Tectonically, it transverses three different tectonic units, i.e. Siberia, Kazakhstan and Tarim plates, and is composed of nine ter‐rains with widely exposed Precambrian and Paleozoic strata, complex structures, intensive magmatic activities and widespread ore deposits. It is not only a main part of Tianshan‐Yinshan‐Great Hinggan metallogenic belt in China, but also a key to under‐stand the evolution of central‐Asian orogenic system.At present, more than 100 gold deposits and prospects have been discovered, explored and mined, among which Nanjinshan, Mazhuangshan, Liushashan, Jinwozi, Zhaobishan and Xiaoxigong are the most important ones. Based on the host rocks and the geological features, all these gold occurrences can be subdivided into three groups (or types): (1) hosted by Carboniferous or Permian volcanic or subvolcanic rocks; (2) hosted by or related to plutonic intrusions; and (3) hosted by Precambrian metamorphic rocks. The first group includes the Mazhuangshan gold deposit, which occurs in Hercynian quartz por‐phyry and rhyolite porphyry as gold‐bearing quartz veins. The second group is composed of the Liushashan, Nanjinshan Zhaobishan and Jinwozi gold deposits. Gold mineralization at these four deposits occurs within Hercynian granitoids intrusion: or late Paleozoic sedimentary rocks as quartz veins, veinlets and altered rocks. The Xiaoxigong gold deposit belongs to the third group, and is hosted by Precambrian schist, amphibolite and migmatite as quartz veins and altered rocks.Isotopic age dating data, geological and geochemical evidence suggest that most of the groups 1 and 2 gold deposits were generated during the emplacement of the Hercynian or partly Indosinian intrusions. These intrusions may provide both heat and metals for groups 1 and 2 deposits. In contrast, although the formation is closely related to the Hercynian magma‐tism, the ore‐forming materials of the group 3 deposits may not only come from the intrusions, but also from the Precambrian metamorphic rocks.

Late Paleozoic depositional history of the Tarim basin, northwest China: An integration of biostratigraphic and lithostratigraphic constraints

This study provides the first detailed lithostratigraphic and biostratigraphic constraints for improving stratigraphic resolution for hydrocarbon prospecting and exploration in the Tarim basin. A total of 49 stratigraphic units (38 formations and 11 members), ranging in age from the latest Devonian to Permian, are reviewed or redefined in terms of nomenclatures, lithology, age constraints, and lateral distributions based on the detailed field works or newly published data. Of these, the Piqiang Formation (new formation) is proposed to include the reefal carbonates of Asselian–Sakmarian age from the northern Tarim. The subsurface upper Paleozoic stratigraphic framework of the desert areas of the basin is also established for the first time. The high-resolution, basinwide stratigraphic correlations reveal that the sedimentation of the basin in the late Paleozoic was extremely uneven. Of these, the Famennian to Changhsingian successions are completely recorded in the southwestern margin areas of the basin. Here, five eustatic sedimentary cycles are well recognizable, suggesting the sedimentation was more eustatically controlled and little affected by local tectonism. The late Paleozoic successions of both Kalpin and Taklimakan regions are commonly interrupted by major hiatuses at various horizons, suggesting that the sedimentation was apparently modified by local tectonism. Of these, the northward movement of the Tarim block and its subsequent collision with the Yili microcontinent (part of the Kazakhstan plate) may be principally accountable for the discrepancy in the sedimentation of the various regions in the basin in the late Paleozoic.

Cenozoic paleomagnetic results and phanerozoic apparent polar wandering path of Tarim Block*

New paleornagnetic data from Cenozoic rocks in Tarim enable people to revise the Phanerozoic apparent polar wandering path (APWP) of this block. This modified Tarim APWA is supported by data from other Chinese blocks. On the basis of the APWA, it is concluded that Tarim rode on a plate subducting under the Kazakhstan plate between Carboniferous and Permian time. By the Late Permian, subduction had finished. The APWP also revealed that tectonic evolution of the Tarim was characterized by northern latitudinal displacement during the Paleozoic time, while Tarim remained at relative low latitude (about 20°) until1 Cretaceous.

An apparent polar wander path from the Tarim Block, China

The apparent polar wander (APW) path from the Tarim Block consists of Devonian ( λ = 16° N, φ = 165° E, A 95= 4°), Late Carboniferous ( λ = 41° N, φ = 160° E, A 95 = 4°), Permian ( λ = 61° N, φ = 177° E, A 95= 9°), Early Triassic ( λ = 69° N, φ = 183° E, A 95 = 11°) and Jurassic/Cretaceous ( λ = 65° N, φ = 214° E, A 95 = 6°) poles. On the basis of this APW path, we conclude that Tarim rode on a plate subducting under the Kazakhstan plate between Devonian and Permian times. By the end of the Permian, subduction had almost finished. Early Triassic poles from Tarim, Siberia, North China and South China are discordant, indicating post-Early Triassic relative motions among them. Cretaceous paleomagnetic poles from Tarim, North China and South China, however, are consistent, suggesting that China has been a coherent tectonic unit since Cretaceous time. The shape of the APW path from Tarim is similar to that of Siberia, except that Tarim's APW path is systematically displaced to the east. A 26° clockwise rotation of Tarim's APW path about the Euler pole λ = 60°N and φ =14°E reconciles these two APW paths. Tarim has moved northeastward some 2000 km relative to a fixed Siberia since the Cretaceous. This northeastward motion of Tarim with respect to Siberia agrees well with the overall Cenozoic tectonic style of Asia. Most of southern China has been pushed eastward to give way to the penetrating Indian continent. East-west- and northeast-trending left-lateral strike-slip faults north of the Tarim Block have been documented; however, the exact amounts of displacement along these faults are not well known. Using paleomagnetic data from Tarim, we will also discuss the tectonic evolution of terranes in central Asia and the amount of continental shortening in the Tibetan plateau.

Tectonic evolution of the West Junggar Region, Xinjiang, China

The West Junggar region of northwestern China consists of a Hercynian‐age fold belt occupying a late Paleozoic zone of convergence between three major Eurasian plates: Siberian, Tarim, and Kazakhstan. The northern part of the West Junggar area includes part of the Irtysh‐Zaysan fold belt that extends to the northwest into the USSR, where it marks a broad boundary between the Siberian and Kazakhstan plates. The central part of the West Junggar area includes the southeastern extension of the Chingiz‐Tarbgatay early Paleozoic island arc sequence. The southern part of the West Junggar area is truncated by the deep fundamental Junggar‐Alakol fault that has brought the Yili microplate into juxtaposiition with the West Junggar region in the vicinity of Ebin Nur Lake. To the east the Junggar area is covered by sediments of the Junggar Basin. Paleogeographic reconstructions and geologic evidence indicates that these plates began converging in the Middle Carboniferous, and by Late Carboniferous alkali granites began invading the imbricated leading edges of the coalescing plates. Paleomagnetic data reveals that the plates continued to move along strike‐slip faults, bringing the Tarim plate and Yili microplate into their present positions sometime in the early Mesozoic. Six separate ophiolite occurrences in the West Junggar region are strongly tectonized and dismembered. The Tangbale ophiolite is considered to be Late Cambrian (508 ± 20 Ma.) and represents the earliest known oceanic crust in Western China. Petrologic and chemical data indicate that the Tangbale ophiolite represents a possible back arc or forearc tectonic setting situated close to a developing island arc. The Darbut ophiolite has been tectonized to a melange and is overlain by Late Devonian flysch. Ages of the radiolaria in the cherts associated with the pillow lavas indicate that it formed in the Middle Devonian. Other occurrences of ophiolite melange in the northern part of the West Junggar region may be as young as Late Devonian. These ophiolites record ocean crust formation in the Early to Middle Paleozoic within the Junggarian ocean, and their present tectonic setting indicates continental accretion and imbrication shortly after their formation. Associated blueschist blocks in the ophiolite melange further supports the concept of imbrication brought about by B‐type subduction and associated obduction. Postcollisional alkali granites intrude the oceanic sequences of the West Junggar Region and are considered to represent melted lower crustal material. Lead isotopic systematics on feldspars from six separate granite plutons indicate ratios that could only be considered oceanic as far as the magmas are concerned. The implications of this finding is that the Junggar Basin basement rocks in the north and west are probably oceanic. Evidence presented in this study shows a complex history for the development of the West Junggar region. Major movements of consolidating plates in the Late Paleozoic followed by rejuvenation of these same zones of closure during the Himalayan tectonic event of the Late Tertiary demonstrates that convergence zones and fold belts may respond to vertical and horizontal stress even after many million years of inactivity.

Continental growth of northwest China

The northwest corner of China is the most interior part of Central Asia and includes parts of the Siberian, Tarim, and Kazakhstan plates where the Junggar and Tarim basins are separated by the east‐west trending Tianshan Range. A preliminary terrane map divides the area into thirteen separate areas which are classified into four types: (l) continental, (2) oceanic crust, (3) island arc, (4) composite. The boundaries for these terranes are faults that have been previously defined either by geologic mapping or Holocene activity. Passive consolidation of the southern margin of Paleo‐Asia is marked by accretion and subduction of the Paleo‐Tethys oceanic basins and by development of volcanic arcs. Paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the Permian or later. The stratigraphic record reveals development of intracontinental basins in the late Carboniferous followed by the Pan‐Asian thermal event that gave rise to widespread intrusion of A‐type granites of late Paleozoic age. The frontal collision of India along the southern border of Asia in the Paleocene reactivated nearly all of the older major strike‐slip and thrust faults formed during the late Paleozoic consolidation of Paleo‐Asia. The complex nature of the continental growth of Central Asia has produced and destroyed many varieties of sutures, and reconstruction of the original plate and terrane configurations therefore is enigmatic.