Tarim Terrane Research Articles

South Tarim tied to north India on the periphery of Rodinia and Gondwana and implications for the evolution of two supercontinents

Abstract Constraining the positions of, and interrelationships between, Earth's major continental blocks has played a major role in validating the concept of the supercontinent cycle. Minor continental fragments can provide additional key constraints on modes of supercontinent assembly and dispersal. The Tarim craton has been placed both at the core of Rodinia or on its periphery, and differentiating between the two scenarios has widespread implications for the breakup of Rodinia and subsequent assembly of Gondwana. In the South Tarim terrane, detrital zircon grains from Neoproterozoic–Silurian strata display two dominant populations at 950–750 and 550–450 Ma. Similarly, two main peaks at 1000–800 and 600–490 Ma characterize Neoproterozoic–Ordovician strata in northern India. Moreover, the two dominant peaks of South Tarim and north India lag two global peaks at 1200–1000 and 650–500 Ma, which reflect Rodinia and Gondwana assembly, arguing against a position within the heart of the two supercontinents. Ages and Hf isotopes of Tarim's detrital zircons argue for a position on the margin of both supercontinents adjacent to north India with periodic dispersal through opening and closing of small ocean basins (e.g., the Proto-Tethys). Alternating tectonic transitions between advancing and retreating subduction in North Tarim coincide with periodic drift of South Tarim from north India in Rodinia and Gondwana, emphasizing the importance of retreating subduction in supercontinent dispersal. Moreover, the Rodinia-related orogenic belts spatially overlap the Gondwana-related orogenic belts in the two blocks, indicating no significant relative rotation of India and Tarim during the evolution from Rodinia to Gondwana.

Revisiting to the Neoproterozoic tectonic evolution of the Tarim Block, NW China

The Tarim Block comprises two terranes, namely, the Northern Tarim terrane (NTT) and the Southern Tarim terrane (STT). The distinct geological features of the Pre- Cryogenian basement and igneous activity between these two terranes that share common Cryogenian cover sequences strongly suggest that they underwent independent pre-Cryogenian evolutions. However, owing to the likely position of the Tarim Block on the margin of Rodinia, the Neoproterozoic igneous rocks and sedimentary sequences of this block should provide important insights into the geodynamics of the evolution of this supercontinent. In this contribution, our new geochronological data show that the earliest glacial deposit in the Tarim Block, namely, the Beiyixi tillite, was deposited a little later than 720 Ma, which is consistent with the timing of the global Sturtian glaciation. The other two glacial deposits, namely, the Altungol–Tereenken and Hankachocugh tillites, were deposited at 685–635 Ma and later than 591 Ma, consistent with the global Marinoan and Gaskiers glaciations, respectively.Combining our field observations and new geochronological data with a comprehensive synthesis of the Precambrian basement rock units, metamorphic events, and igneous activities in both the NTT and STT, we construct a detailed late Mesoproterozoic to Cryogenian evolution for the Tarim Block, and discuss its relationship to Precambrian supercontinent evolution. We suggest that the STT might be a continental fragment that separated and drifted from the Congo Craton during the initial breakup of Rodinia and subsequently docked along the northern fringe of Australia a little later than ca. 800 Ma. In contrast, the NTT might be a continental fragment that detached and drifted from North China–India during the breakup of the Columbia supercontinent. During the process of breakup of Columbia and the assembly of Rodinia, the NTT amalgamated with the STT a little earlier than 800 Ma, owing to circum-Rodinia subduction between 1000 and 760 Ma. However, upwelling of the Rodinia plume could have affected subduction along the northern margin of the Tarim Block, as demonstrated by a voluminous ca. 770 Ma mafic dyke swarm. The Rodinia plume terminated the subduction along the northern margin of the Tarim Block at ca. 740 Ma, suggesting that the plume could have played a key role in the breakup of Rodinia. This conclusion is supported by Cryogenian–Cambrian sedimentary sequences with passive-continental-margin affinity in the Tarim Block, indicating the detachment and movement of this block from Rodinia. Both the characteristics of Cryogenian–Cambrian basins and coeval igneous activity argue strongly against long-term subduction along the northern margin of the Tarim Block.

A fragment of the ca. 890 Ma large igneous province (LIP) in southern Tarim, NW China: A missing link between São Francisco, Congo and North China cratons

We identify an early Neoproterozoic Large Igneous Province (LIP) fragment in the South Tarim Terrane (STT) of the NW China (herein term as the Sailajiazitage LIP fragment). The thickness of the volcanic sequence, mainly composed of basalts (ca. 4600 m) and minor rhyolites (ca. 800 m), is up to ca.5300 m. Four zircon samples from the three units of rhyolite at the top, middle and lower parts of the lava sequence yield consistent and concordant SHRIMP/LA-ICPMS U-Pb ages of 895.8 ± 3.7 /892.0 ± 4.1 Ma, 891.8 ± 3.5/894.5 ± 5.8 Ma, 899.0 ± 4.6/893.0 ± 5.9 Ma and 884.5 ± 4.9/894.2 ± 4.8 Ma, respectively, indicating the short duration of the thick volcanic sequence. Systematic geochemical data revealed that the basalts were derived from partial melting of a depleted asthenenospheric mantle source coupled with variable degrees of AFC effect. The rhyolites show typical A-type (or A1-type) granite geochemical features as demonstrated by their high HFSE contents (e.g., Zr = 400–900 ppm, Nb = 70–140 ppm). Both elemental and Nd-Hf-O isotope compositions argue that the silicic magma was the daughter product of the intensive fractionation of the coeval basalts and their zirconium saturation temperature was up to 900 °C, significantly higher than those of A-type granites emplaced in a post-orogenic setting but consistent with those A-type granites genetically related to a mantle plume. Its huge thickness (>5300 m), short duration at ca. 890 Ma and typical continental flood basalt (CFB) geochemical features argue for this being a fragment of an early Neoproterozoic LIP and likely proximal to its plume centre.The c. 890 Ma age suggests a link with the previously proposed reconstruction of North China, São Francisco and Congo cratons, based on their shared 920–890 Ma LIP fragments. This study supplies further evidence for a ca. 920–890 Ma plume or superplume inducing the initial breakup of the supercontinent Rodinia.

Revisiting the Precambrian evolution of the Southwestern Tarim terrane: Implications for its role in Precambrian supercontinents

The Tarim block in NW China consists of a Precambrian basement and late Neoproterozoic to Paleozoic cover sequences. In order to better understand its roles in Precambrian supercontinent evolution, we used SHRIMP and LA-ICPMS U-Pb methods to date late Paleoproterozoic rifting-related mafic dykes and Mesoproterozoic igneous activity in the Precambrian of the southwestern Tarim terrane (STT): 1) WNW trending mafic dyke swarm emplaced at ca. 1785 Ma; 2) Mesoproterozoic bimodal volcanic sequence (the lower member) and marble- clastic-quartzite sequences (the upper member) deposited at ca. 1525 Ma and 1500–1400 Ma, respectively; 3) late Mesoproterozoic granodiorite-augen granite-leucogranite complex emplaced at ca. 1117 Ma. Geochemistry revealed that the 1784 ± 12 Ma mafic dykes were derived from an E-MORB – like mantle source suggesting an extensional setting, and likely linked with coeval major large igneous provinces (LIPs) on several crustal blocks which collectively suggest a pulse of rifting associated with assembly of the Columbia supercontinent. The obtained U-Pb age of 1525 ± 4 Ma from a meta-rhyolite in the bimodal sequence matches a recently discovered 1525–1529 Ma Large Igneous Province from the southern West African craton (Essakane-Sambarabougou swarm) and formerly adjacent Amazonian craton (Kayser event). Geochemistry of the ca. 1117 Ma granitic intrusions defines their A-type signature. These may be linked to coeval intraplate mafic magmatism of a reconstructed 1110 Ma LIP involving Kalahari, Congo, India (Bundelkhand block), Amazonia cratons. In line with these three newly recognized pulses of Precambrian igneous activities in STT and the significant diachroneity of the Precambrian tectono-magnetic events between the STT and the Northern Tarim terrane (NTT), we argue that the Precambrian basement of the Tarim were most likely composed of two distinct terranes (i.e., the STT and the NTT). These originated from different Precambrian nuclei and they did not amalgamate as the Tarim block until to the early middle Neoproterozoic.

Tectonic evolution of the West Kunlun Orogenic Belt along the northern margin of the Tibetan Plateau: Implications for the assembly of the Tarim terrane to Gondwana

The West Kunlun orogenic belt (WKOB) along the northern margin of the Tibetan Plateau is important for understanding the evolution of the Proto- and Paleo-Tethys oceans. Previous investigations have focused on the igneous rocks and ophiolites distributed mostly along the Xinjiang-Tibet road and the China-Pakistan road, and have constructed a preliminary tectonic model for this orogenic belt. However, few studies have focused on the so-called Precambrian basement in this area. As a result, the tectonic affinity of the individual terranes of the WKOB and their detailed evolution process are uncertain. Here we report new field observations, zircon and monazite U-Pb ages of the “Precambrian basement” of the South Kunlun terrane (SKT) and the Tianshuihai terrane (TSHT), two major terranes in the WKOB. Based on new zircon U-Pb age data, the amphibolite-facies metamorphosed volcano-sedimentary sequence within SKT was deposited during the late Neoproterozoic to Cambrian (600–500 Ma), and the flysch-affinity Tianshuihai Group, as the basement of the TSHT, was deposited during the late Neoproterozoic rather than Mesoproterozoic. The rock association of the volcano-sedimentary sequence within SKT suggests a large early Paleozoic accretionary wedge formed by the long-term low-angle southward subduction of the Proto-Tethys Ocean between Tarim and TSHT. The amphibolite-facies metamorphism in SKT occurred at ca. 440 Ma. This ca. 440 Ma metamorphism is genetically related to the closure of the Proto-Tethys Ocean between Tarim and the Tianshuihai terrane, which led to the assembly of Tarim to Eastern Gondwana and the final formation of the Gondwana. Since the late Paleozoic to early Mesozoic, the northward subduction of the Paleo-Tethys Ocean along the Hongshihu-Qiaoertianshan belt produced the voluminous early Mesozoic arc-signature granites along the southern part of NKT-TSHT. The Paleo-Tethys ocean between TSHT and Karakorum closed at ca. 200 Ma, as demonstrated by the monazite age of the paragneiss in the Kangxiwa Group. Our study does not favor the existence of a Precambrian basement in SKT.

Role of mantle dynamics in rebuilding the Tianshan Orogenic Belt in NW China: A seismic tomographic investigation

The Tianshan orogenic belt, Junggar terrane and Altai terrane are located at the southwestern part of the Central Asian Orogenic Belt (CAOB). Here, we investigate the velocity structure beneath the Xinjiang region in NW China, which includes the Tarim terrane, Tianshan orogenic belt, Junggar terrane and Altai terrane with a view to evaluate the mantle dynamics based on teleseismic data recorded by 103 seismic stations. Our tomographic results show both high and low velocity perturbations beneath the Tianshan orogenic belt. We suggest that the high velocity perturbations beneath this orogenic belt might represent the northward subducted lithosphere of the Tarim Basin and the southward subducted lithosphere of the Junggar Basin. The low velocity structure beneath the Tianshan orogenic belt might represent asthenosphere upwelling that triggered the extensive magmatism which contributed to rebuilding of the Tianshan orogenic belt.

Paleoproterozoic assembly of the North and South Tarim terranes: New insights from deep seismic profiles and Precambrian granite cores

The basement of the Tarim Craton in NW China is divided into northern and southern terranes by the central 1500 km long Central Tarim Terrain (CTT) demarcated by a high aeromagnetic anomaly. However, the nature of the CTT remains enigmatic because of sparse data from basement below the deep basin. In this contribution we report new U-Pb ages from Precambrian granites from boreholes in the CTT to constrain the timing of the assembly of the northern and southern Tarim terranes. Zircon U-Pb ages from four samples of metagranite yielded four U-Pb ages of 1927.3 ± 7.5 Ma and 1920.4 ± 9.8 Ma, 1915.3 ± 5.4 Ma and 1968 ± 8.4 Ma along the CTT. Geochemically, the granitoids display high K2O and high K2O/Na2O ratios, showing their high-potassium calc-alkaline nature. They are rich in Ba, Sr, LREE and LILE, and depleted in Nb, Ta, Ti and Nd, Zr, Y, with variable negative Eu anomaly. The zircons have a large range of εHf(t) values (−14.6–16.1). Geochemical and isotopic characteristics suggest that the granites were derived from partial melting of crust and partial of the depleted mantle, and are geodynamically related to subduction in an arc setting. Collectively, our study argues that the assembly of the northern and southern Tarim terranes took place in the late Paleoproterozoic rather than the Neoproterozoic. We suggest that the amalgamation between the southern and northern terranes was completed by ∼1.91 Ga, which led to extensive contemporaneous magmatism rather than the assembly with the Columbia supercontinent.

An early Emsian (Zlichovian) ammonoid assemblage from Sangibaland Mountain (Shakhimardan River Basin) (South Tien Shan, Kyrgyzstan)

Early Emsian (Zlichovian) ammonoids are recorded from a section of neritic deposits on the western and northwestern slopes of Sangibaland Mountain (right bank of the Shakhimardan River, near the village of Jiydelik, South Fergana, South Tien Shan, Kyrgyzstan) including other faunas such as conodonts, dacryoconarids, brachiopods, trilobites, and corals. The ammonoid fauna includes Erbenoceras cf. solitarium (Barrande, 1865), E. kimi Bogoslovsky, 1980 and new species of teicherticeratids. This combination of taxa allows the host beds to be correlated with the Zlichovian LDIII Zone. Ammonoids come from the Katran Formation, from beds previously recognised as the Sandal Formation, which is well–known for its neritic assemblages, interpreted as inhabitants of shallow shelf zones in the northern regions of the Paleozoic Alai–Tarim Terrane. Near the end of the Zlichovian, when the Dalejan transgression spread to the Sangibaland Region, ammonoids colonised the neritic basin near a carbonate platform, already inhabited by abundant benthic fauna. The co-occurrence of neritic and pelagic organisms is a useful feature providing a basis for the correlation between the pelagic and neritic successions of the lower Emsian (Zlichovian).

Upper Ordovician conodont biostratigraphy and biofacies from the Sigang section, Neixiang, Henan, central China

The 186-m-thick Shiyanhe Formation exposed at the Sigang section, Neixiang area, Henan Province, central China has been investigated for conodonts. The collected 33 samples yielded 8858 conodont specimens. The conodonts are referred to 15 genera and 34 species, but four species cannot be positively identified and one taxon is kept in open nomenclature. The Oulodus ulrichi, the Oulodus robustus, the Aphelognathus grandis and the Aphelognathus divergens conodont biozones are introduced and the conodont fauna and biozones of the Shiyanhe Formation are referred to the Katian Stage (Stage slices Ka2–Ka4) of the Upper Ordovician. The presence of biostratigraphically important species of the genera Aphelognathus, Oulodus and Yaoxianognathus allows for the recognition of the previously defined local conodont biozones that were established from the studied section. Regionally, the Shiyanhe Formation fauna is relatively similar to the contemporaneous faunas from the Tarim terrane in western China and from the southwestern margin of the North China Platform. However, the faunal composition also shows a close affinity to the North American Midcontinent Province and correlation to North America is clear. The conodont fauna is dominated by the species of Aphelognathus, Belodina, Drepanoistodus, Oulodus, Panderodus, Phragmodus, “Plectodina” and Yaoxianognathus. The Aphelognathus–Oulodus biofacies, the “Plectodina” biofacies, the Panderodus biofacies, the Drepanoistodus biofacies and the Phragmodus biofacies have been established using multivariate statistical techniques on the conodont assemblage. As their turnovers were related to sea-level changes, the conodont biofacies are used to demonstrate the transgressive-regressive pattern in the studied section.

Conodonts and tabulate corals from the Upper Ordovician Angullong Formation of central New South Wales, Australia

Zhen, Y.Y., Wang, G.X. & Percival, I.G., August 2016. Conodonts and tabulate corals from the Upper Ordovician Angullong Formation of central New South Wales, Australia. Alcheringa 41, xxx–xxx. ISSN 0311-5518.The Angullong Formation is the youngest Ordovician unit exposed in the Cliefden Caves area of central New South Wales. Its maximum age is constrained by a Styracograptus uncinatus graptolite Biozone fauna at the very top of the underlying Malongulli Formation, but the few fossils previously reported from higher in the Angullong Formation are either long-ranging or poorly known. From allochthonous limestone clasts in the middle part of the formation, we document a conodont fauna comprising Aphelognathus grandis, A. solidum, Aphelognathus sp., Aphelognathus? sp., Belodina confluens, Drepanoistodus suberectus, Panderodus gracilis, Panderodus sp., Phragmodus undatus, Pseudobelodina inclinata and Pseudobelodina? sp. aff. P. obtusa, which supports correlation with the Aphelognathus grandis Biozone (late Katian) of the North American Midcontinent succession. The species concepts of Aphelognathus and Pseudobelodina are reviewed in detail. Associated corals are exclusively tabulates, dominated by agetolitids, including Agetolites angullongensis sp. nov., Heliolites orientalis, Hemiagetolites breviseptatus, Hemiagetolites sp. cf. H. spinimarginatus, Navoites sp. cf. N. circumflexa, Plasmoporella bacilliforma, P. marginata, Quepora sp. cf. Q. calamus and Sarcinula sp. Affinities of the coral fauna from the Angullong Formation are closer to faunas from northern NSW and northern Queensland than to the locally recognized Fauna III of late Eastonian age in central NSW. We propose a subdivision of Fauna III to account for this difference, with the late Katian Fauna IIIB characterized by the incoming of agetolitid corals. The currently known distribution of representatives of this group with adequate age constraints suggests that agetolitids possibly originated in North China, subsequently migrating to Tarim, South China and adjacent peri-Gondwanan terranes while also spreading eastward to northern Gondwana, where they progressively moved through eastern Australia to reach the central NSW region by the early Bolindian.Yong Yi Zhen* (yong-yi.zhen@industry.nsw.gov.au) and Ian G. Percival (ian.percival@industry.nsw.gov.au), Geological Survey of New South Wales, W.B. Clarke Geoscience Centre, 947–953 Londonderry Road, Londonderry, NSW 2753, Australia; Guangxu Wang (gxwang@nigpas.ac.cn), State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road Nanjing 210008 PR China.

Paleomagnetic data bearing on the Mesozoic deformation of the Qiangtang Block: Implications for the evolution of the Paleo- and Meso-Tethys

Paleomagnetism has played an important role in quantifying the Mesozoic evolution of “Proto-Tibet”. In this paper, we present new paleomagnetic data from five Middle-Upper Jurassic sedimentary sequences (Quemo Co, Buqu, Xiali, Suowa and Xueshan Fms.) of the eastern North Qiangtang Terrane (QT) at Yanshiping (33.6°N, 92.1°E). The new paleomagnetic results form a large dataset (99 sites, 1702 samples) and reveal a paleopole at 79.1°N/306.9°E (dp=3.9°, dm=6.3°) for the Quemo Co Fm., at 68.9°N/313.8°E (dp=2.1°, dm=3.7°) for the Buqu Fm., at 66.1°N/332.1°E (dp=2.7°, dm=4.6°) for the Xiali Fm., at 72.4°N/318.6°E (dp=3.9°, dm=6.7°) for the Suowa Fm., and at 76.9°N/301.1°E (dp=7.9°, dm=13.2°) for the Xueshan Fm. These results indicate clockwise (CW) rotations of ~19.8±9.4° between ~171.2 and 161.7Ma and counterclockwise (CCW) rotations of ~15.4±13.4° between ~161.7 and <157.2Ma for Yanshiping. We attribute the change in rotation sense at approximately ~161.7Ma to the initial collision of the Lhasa and Qiangtang terranes. Using this and other paleomagnetic data from the Lhasa, Qiangtang and Tarim terranes, as well as other geological evidence (e.g., tectonism-related sedimentary sequences, volcanism, and HP metamorphism), we propose a new conceptual evolution model for the Mesozoic QT and Tethyan Oceans. The Longmo Co-Shuanghu oceanic slab was subducted before 248Ma, followed by continental collision of the North-South Qiangtang subterranes between ~245 and 237Ma. The Qiangtang Terrane experienced post-collisional exhumation between ~237 and 230Ma during subduction of the Jinsha oceanic slab. The collision of the Qiangtang and Songpan-Ganzi terranes occurred between ~230 and 225Ma. The QT experienced post-collisional relaxation from ~225 to ~200Ma, followed by subsidence and extension-related exhumation between ~200 and 162Ma in association with subduction of the Bangong-Nujiang oceanic slab. Finally, these events were followed by the scissor-like diachronous collisions of the Lhasa and Qiangtang terranes between ~162Ma and the mid-Cretaceous.

Growth and evolution of Precambrian continental crust in the southwestern Tarim terrane: New evidence from the ca. 1.4 Ga A-type granites and Paleoproterozoic intrusive complex

The Precambrian tectonic evolution and growth of continental crust in the southwestern Tarim Craton in NW China remain enigmatic. In this contribution, we report petrography, zircon U–Pb ages, geochemistry and Nd–Hf–O isotope data on the ca. 1.4Ga granitic pluton in southwestern Tarim Terrane. We also present zircon U–Pb ages and Hf isotope data on the Paleoproterozoic intrusive complex from this area, and use the combined data to evaluate Precambrian tectonic evolution of the region in relation to the Columbia supercontinent. The ca. 1.4Ga Azibailedi pluton is mainly composed of biotite monzogranite with contents SiO2 (72.8–75.1wt.%). The major element chemistry of the pluton reveals alkali-calcic and ferroan affinities and metaluminous to peraluminous feature with A/CNK ranging from 0.86 to 1.15. The granite shows high total REE contents with variable enrichment in LREE ((La/Yb)N=8.5–12.2). Both REE and other incompatible elements features define A-type affinities. The initial epsilon Nd values vary from −3.5 to −2.2 and zircon ɛHf(t) and δ18O values range from −4.1 to +6.1 and 7.1‰ to 8.6‰. Integrating geological, geochemical and Nd–Hf–O isotope data, we suggest that the Azibailedi A-type granites were derived from pre-existing early Paleoproterozoic mafic lower crust with involvement of variable amount of Paleoproterozoic juvenile crust, possibly trigged by basaltic magma upwelling, during the breakup of the Columbia supercontinent.U–Pb geochronology and Hf isotopic analyses of zircons from the Paleoproterozoic Heluositan intrusive complex show crustal growth episodes during 2.2–4.2Ga with peaks at 2.3–2.5Ga, 3.3Ga and 3.6–3.8Ga, distinct from the other Precambrian terranes of the Tarim Craton. A comprehensive synthesis of the records of assembly and breakup of Columbia supercontinent from different Precambrian terranes in the Tarim Craton show significant differences. The temporal distinction in tectonothermal events and the marked difference in the continental crust growth processes suggest that the early Precambrian basement of the Tarim Craton was possibly composed of discrete terranes which were fragmented from different ancient cratonic nuclei.

Tectonic framework and crustal evolution of the Precambrian basement of the Tarim Block in NW China: New geochronological evidence from deep drilling samples

Based on new petrographic observations and zircon U–Pb geochronological data of the Precambrian basement from deep drilling cores in the Tarim basin and comparison with the Precambrian basements surrounding orogenic belts of the Tarim basin, we reconstruct a possible unified Tarim block. Data presented in this contribution lead to a three-fold subdivision of the pre-900Ma basement of the Tarim block into the North Tarim terrane, the South Tarim terrane and the Central Tarim terrane. The North Tarim terrane containing Precambrian basements of the northern part of the Tarim basin, the Korla-Kuluketage and the Dunhuang area possesses a ca. 2.7–2.5Ga or an even older continental nucleus and underwent multiple phases of magmatic and metamorphic events at ca. 2.0–1.8Ga, 1.0–0.8Ga and 760–687Ma. The South Tarim terrane including Precambrian basements of the southern part of the Tarim basin, eastern Kunlun and western Kunlun orogenic belts, possesses a 2.4–2.3Ga continental nucleus and underwent 2.0–1.75Ga and 1.0–0.8Ga metamorphic and magmatic events. The Central Tarim terrane encompassing Precambrian basement of the central part of the Tarim basin and the Altun orogenic belt, is characterized by magmatic arc system during 940–890Ma. The unified Tarim Block was assembled as part of Rodinia supercontinent after series of geological processes, e.g. (1) breakup between the North and South Tarim terranes, (2) formation of the Central Tarim ocean, (3) subduction-related magmatic arc accretion, and (4) finally amalgamation of the North and South Tarim terranes during 1.0–0.8Ga. There are two phases of the middle Neoproterozoic magmatic activities at 820–760Ma and 760–687Ma, respectively. They were most possibly related to the two phases of the Rodinia plume activities. The late Mesoproterozoic to Sinian assembly and breakup of the Rodinia led to the typical double-layered structure of the Tarim Block, i.e. the Pre-Nanhuaian basement and the Nanhuaian to Sinian cover sequence. Based on this study, we suggest that the unified Tarim Block, composed of Precambrian basement of Tarim basin and its surrounding orogenic belts, should be more large than the present Tarim basin.

Siberia, the wandering northern terrane, and its changing geography through the Palaeozoic

Siberia, the wandering northern terrane, and its changing geography through the Palaeozoic

Palaeozoic and Mesozoic tectonic evolution and palaeogeography of East Asian crustal fragments: The Korean Peninsula in context

East and Southeast Asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments (terranes) together with volcanic arcs, and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the Eurasian, Indo-Australian and Pacific Plates. The former wide separation of Asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation, different palaeoclimates, and biogeographic isolation. The boundaries between Asian terranes are marked by major geological discontinuities (suture zones) that represent former ocean basins that once separated them. In some cases, the ocean basins have been completely destroyed, and terrane boundaries are marked by major fault zones. In other cases, remnants of the ocean basins and of subduction/accretion complexes remain and provide valuable information on the tectonic history of the terranes, the oceans that once separated them, and timings of amalgamation and accretion. The various allochthonous crustal fragments of East Asia have been brought into close juxtaposition by geological convergent plate tectonic processes. The Gondwana-derived East Asia crustal fragments successively rifted and separated from the margin of eastern Gondwana as three elongate continental slivers in the Devonian, Early Permian and Late Triassic–Late Jurassic. As these three continental slivers separated from Gondwana, three successive ocean basins, the Palaeo-Tethys,. Meso-Tethys and Ceno-Tethys, opened between these and Gondwana. Asian terranes progressively sutured to one another during the Palaeozoic to Cenozoic. South China and Indochina probably amalgamated in the Early Carboniferous but alternative scenarios with collision in the Permo–Triassic have been suggested. The Tarim terrane accreted to Eurasia in the Early Permian. The Sibumasu and Qiangtang terranes collided and sutured with Simao/Indochina/East Malaya in the Early–Middle Triassic and the West Sumatra terrane was transported westwards to a position outboard of Sibumasu during this collisional process. The Permo–Triassic also saw the progressive collision between South and North China (with possible extension of this collision being recognised in the Korean Peninsula) culminating in the Late Triassic. North China did not finally weld to Asia until the Late Jurassic. The Lhasa and West Burma terranes accreted to Eurasia in the Late Jurassic–Early Cretaceous and proto East and Southeast Asia had formed. Palaeogeographic reconstructions illustrating the evolution and assembly of Asian crustal fragments during the Phanerozoic are presented.

40Ar/39 Ar Age and Geological Significance of Lamprophyres in Pishan on the SW Margin of the Tarim Terrane, NW China

Abstract The dike swarm of lamprophyres at Pishan on the SW margin of the Tarim terrane is composed of ultra‐potassic lamprophyres that have intruded into the Proterozoic hornblende schists. 40Ar/39 Ar dating data suggest that the isochron ages for phlogopite and whole rock separates of the lamprophyres are 231.7±0.3 Ma and 228.5±0.3 Ma, respectively. Geochemical data indicate that the dikes were derived from a subduction‐related or metasomatized mantle. During the Middle‐Late Triassic the western Kunlun area entered the post‐orogeny period, and thus the occurrence of the dike swarm in the study area may have been controlled by underplating.

Crustal evolution and Phanerozoic crustal growth in northern Xinjiang: Nd isotopic evidence. Part I. Isotopic characterization of basement rocks

The Central Asian Orogenic Belt (CAOB) is known as the most important site of juvenile crustal growth during the Phanerozoic. In order to examine the processes of such crustal generation and the role of Precambrian crust in the magma genesis, we conducted geochemical and Nd isotopic studies on both the basement rocks and Phanerozoic granites from the major tectonic terranes in northern Xinjiang: Altai, Junggar, Tianshan and North Tarim. In this paper only the results on the basement rocks are reported. The North Tarim Terrane is composed of Archean bimodal suite (TTG gneisses and amphibolites) and Proterozoic granitic gneisses. This terrane is a fragment of ancient continental crust and is tectonically dissociated from the CAOB. The other terranes in northern Xinjiang (Altai, Junggar, and Tianshan) belong to the CAOB. The Altai and Tianshan are composite terranes probably formed by accretion of Phanerozoic subduction complexes with entrained Proterozoic basement rocks as microcontinental blocks. Geochemical characteristics of amphibolites from Altai and Tianshan suggest their formation in island arc settings. Sm–Nd model ages of the Tianshan basement rocks vary from 1.2 to 2.2 Ga, but mainly concentrated in 1.7–2.1 Ga. Similarly, amphibolites and gneisses of the Altai terrane have T DM in two apparently discrete groups at 0.9–1.5 Ga and 2.4–2.6 Ga. The initial Nd isotope ratios or ε Nd( T) values indicate that a large proportion of basement gneisses from Tianshan were derived from remelting of Paleo- to Mesoproterozoic protoliths (1.7–2.1 Ga). However, this is not the case for the Altai basement gneisses. Granitic gneisses and metasedimentary rocks (schists and phyllites) from the East and West Junggar terranes have much younger T DM ages of 0.7–1.4 Ga. Presence of a minor Precambrian crustal component is possible as inferred from the model ages, but no data have shown Precambrian ages for the Junggar basement rocks. The model age and ϵ Nd( T) data support the idea that the Junggar terrane is composed of young island arc assemblages, and the Junggar Basin itself could be a trapped Paleozoic oceanic crust. Together with some reliable radiometric ages for basement rocks, the present isotopic data and T DM ages indicate that ancient microcontinental blocks constitute a significant proportion of the continental crust in northern Xinjiang, and probably also in the entire CAOB.

Pre-Cretaceous evolution of SE Asian terranes

Abstract During the last decade, a wide range of geological and geophysical data has led to the recognition of various continental terranes in SE Asia which, on tectonostratigraphic, palaeobiogeographic and palaeomagnetic grounds are ‘suspect’ or allochthonous in nature. Some of the recognized terranes may be composite and there is some disagreement with regard to the number of terranes and their boundaries. The continental terranes are bounded by sutures (representing former oceans), by narrow mobile belts or major fault zones. Comparative studies of the stratigraphy, palaeontology, and palaeomagnetism of the various pre-Cretaceous continental terranes of East and SE Asia suggest that they were all derived directly or indirectly from Gondwanaland. Asian continental terranes that are placed on the India-Australian margin of Gondwanaland in the Early Palaeozoic include Tarim (here regarded to include the Kunlun and Ala Shan terranes), Qaidam, Indochina/East Malaya (which includes the Qamdo-Simao block of western China), North &amp; South China, Sibumasu, Qiangtang, Lhasa, Kurosegawa, NW and SE Hainan, West Burma and the Woyla terranes. The evolution of Gondwanaland and Tethys during the Palaeozoic and Mesozoic involved the rifting of continental slivers/fragments from northern Gondwanaland, and the northwards drift and amalgamation/accretion of these to form proto-East and SE Asia. Three continental slivers were rifted from the northern margin of Gondwanaland in the Early to Late Devonian (North China, South China, Indochina/East Malaya/Qamdo-Simao, Qaidam and Tarim terranes); Early-Middle Permian (the Cimmerian continent including the Sibumasu and Qiangtang terranes and possibly NW and SE Hainan); and Late Triassic to Late Jurassic (Lhasa, West Burma and Woyla terranes). The northwards drift of these terranes was accompanied by the opening and closing of three successive oceans, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. Assembly of Gondwanaland-derived Asian terranes began with the amalgamation of South China and Indochina/East Malaya along the Song Ma/Song Da zone during the Late Devonian/Early Carboniferous to form ‘Cathaysialand’. Palaeomagnetic, climatic and biogeographic data indicate that Cathaysialand and North China were located within the Palaeo-Tethys at low northern/equatorial latitudes during the Late Carboniferous and Permian. Palaeomagnetically determined palaeolatitudes are consistent with the development of tropical Cathaysian floras on these terranes. The Tarim, Kunlun, Qaidam and Ala Shan terranes accreted to Kazakstan/Siberia in the Permian. A major episode of rifting occurred on the northern margin of Gondwanaland in the Late Carboniferous-Early Permian and the Cimmerian continent separated in the late Early Permian resulting in the opening of the Meso-Tethys. Suturing of Sibumasu and Qiangtang to Cathaysialand occurred in the Late Permian-Triassic, closing a major branch of the Palaeo-Tethys. South and North China amalgamated and then accreted to Laurasia by Late Triassic-Early Jurassic times. The highly disrupted Kurosegawa terrane of Japan, possibly derived from Australian Gondwanaland, accreted to Japanese Eurasia, also in the Late Jurassic. The Lhasa, West Burma and Woyla terranes rifted from NW Australian Gondwanaland in the Late Triassic to Late Jurassic and drifted northwards during the Jurassic and Early Cretaceous as the Ceno-Tethys opened and the Meso-Tethys was destroyed by subduction beneath Eurasia. Accretion of these terranes to proto-SE Asia occurred in the Cretaceous. The SW Borneo and Semitau terranes were derived from the South China/Indochina margin by the opening of a marginal basin in the Cretaceous which was subsequently destroyed by southwards subduction during the rifting of the Reed Bank-Dangerous Grounds terrane from South China when the South China Sea opened. The NW and SE Hainan terranes, which formed part of Early Palaeozoic and possibly Late Palaeozoic Gondwanaland, reached their current positions, relative to South China, sometime in the Jurassic-Cretaceous.

Gondwanaland origin, dispersion, and accretion of East and Southeast Asian continental terranes

East and Southeast Asia is a complex assembly of allochthonous continental terranes, island arcs, accretionary complexes and small ocean basins. The boundaries between continental terranes are marked by major fault zones or by sutures recognized by the presence of ophiolites, mélanges and accretionary complexes. Stratigraphical, sedimentological, paleobiogeographical and paleomagnetic data suggest that all of the East and Southeast Asian continental terranes were derived directly or indirectly from the Iran-Himalaya-Australia margin of Gondwanaland. The evolution of the terranes is one of rifting from Gondwanaland, northwards drift and amalgamation/accretion to form present day East Asia. Three continental silvers were rifted from the northeast margin of Gondwanaland in the Silurian-Early Devonian (North China, South China, Indochina/East Malaya, Qamdo-Simao and Tarim terranes), Early-Middle Permian (Sibumasu, Lhasa and Qiangtang terranes) and Late Jurassic (West Burma terrane, Woyla terranes). The northwards drift of these terranes was effected by the opening and closing of three successive Tethys oceans, the Paleo-Tethys, Meso-Tethys and Ceno-Tethys. Terrane assembly took place between the Late Paleozoic and Cenozoic, but the precise timings of amalgamation and accretion are still contentious. Amalgamation of South China and Indochina/East Malaya occurred during the Early Carboniferous along the Song Ma Suture to form “Cathaysialand”. Cathaysialand, together with North China, formed a large continental region within the Paleotethys during the Late Carboniferous and Permian. Paleomagnetic data indicate that this continental region was in equatorial to low northern paleolatitudes which is consistent with the tropical Cathaysian flora developed on these terranes. The Tarim terrane (together with the Kunlun, Qaidam and Ala Shan terranes) accreted to Kazakhstan/Siberia in the Permian. This was followed by the suturing of Sibumasu and Qiangtang to Cathaysialand in the Late Permian-Early Triassic, largely closing the Paleo-Tethys. North and South China were amalgamated in the Late Triassic-Early Jurassic and finally welded to Laurasia around the same time. The Lhasa terrane accreted to the Sibumasu-Qiangtang terrane in the Late Jurassic and the Kurosegawa terrane of Japan, interpreted to be derived from Australian Gondwanaland, accreted to Japanese Eurasia, also in the Late Jurassic. The West Burma and Woyla terranes drifted northwards during the Late Jurassic and Early Cretaceous as the Ceno-Tethys opened and the Meso-Tethys was destroyed by subduction beneath Eurasia and were accreted to proto-Southeast Asia in the Early to Late Cretaceous. The Southwest Borneo and Semitau terranes amalgamated to each other and accreted to Indochina/East Malaya in the Late Cretaceous and the Hainanese terranes probably accreted to South China sometime in the Cretaceous.

Hercynian Orogenic Fold Belts and the Terrane Tectonics in Northern Xinjiang, China

There are eight Hercynian orogenic fold belts in northern Xinjiang. The traditional viewpoint is that the orogeny was related to collision between the Siberian plate, Kazakhstan-Junggar and Tarim-Sinokorean plates. The recent investigation indicates that in northern Xinjiang, geological entity of continental plate did not exist during the Hercynian cycle. It is suggested that the orogenic processes in this area are the results of displacement and accretion between the Tarim terrane, Junggar terrane, central Tianshan (Ili-Isaik Lake)