Tarim Plate Research Articles

Quaternary structural partitioning within the rigid Tarim plate inferred from magnetostratigraphy and sedimentation rate in the eastern Tarim Basin in China

It has been proposed that within the Tarim Basin tectonic activity has been limited since Triassic time. However, on the basis of magnetostratigraphy from the eastern Tarim Basin, which defines the chronology of sedimentation and structural evolution of the basin, we show that the basin interior has been uplifted and partitioned during Quaternary. The magnetostratigraphy was constructed from 2228 samples that yielded acceptable inclination values. Characteristic remnant magnetization (ChRM) with both normal (N1–N11) and reversed (R1–R11) polarity was isolated by thermal demagnetization. The data correlate best with polarity chrons C3r to C1n, which range from 5.39Ma to recent on the geological time scale 2004 (GTS2004). An abrupt decrease in the sedimentation rate is observed at 1.77Ma in the Ls1 core. This change does not overlap with known Pleistocene climate-change events. We attribute this sedimentation rate decrease to a structurally controlled local decrease in accommodation space where basin basement uplifts occur. This period of sedimentary environmental change reveals that structural partitioning in the basement of the Tarim Basin occurred since ~1.77Ma, and we speculate that tilting of the Southeast Uplift (a sub-basin unit) within the Tarim Basin began in early Pleistocene time.

Geochemical and isotopic constraints on the genesis of the Jueluotage native copper mineralized basalt, Eastern Tianshan, Northwest China

The Jueluotage native copper mineralized basalt is located in the Jueluotage Volcanic-sedimentary Belt, Eastern Tianshan, Xinjiang Uygur Autonomous region. The basalt, amygdaloidal basalt and tuff, which host native copper mineralization, were erupted in the lower strata of the Late Carboniferous Matoutan Formation. Whole-rock geochemistry shows that the basaltic occurrences at Shilipo, Heilongfeng, Changchengshan and Dongjianfeng have fractionated chondrite-normalized REE distributions and distinctly negative primitive mantle-normalized Nb, Ta and Ti anomalies. The whole-rock strontium, neodymium and lead isotopic data indicate low εSr(t) (−7.9 to +23.6), high εNd(t) (+2.5 to +7.1), with restricted 206Pb/204Pb (18.152–18.491), 207Pb/204Pb (15.521–15.562) and 208Pb/204Pb (37.978–38.251) ranges. On the basis of these data, we report that the Cu-bearing basalt is associated with high-iron tholeiitic basalts that were sourced from depleted continental lithosphere mantle garnet-bearing peridotite. The primary magma of the Cu-bearing basalt was: (1) relatively low in silica and magnesium; and (2) underwent only slight olivine and clinopyroxene crystal fractionation during the magmatic evolution process. In the Jueluotage belt, the Shilipo basalt lavas display significant geochemical similarities to numerous mafic intrusions that are present throughout the Jueluotage belt. Those mafic lavas and intrusions probably represent successive pulses of mafic magmatism, which lasted between ca. 310 and 270Ma.A crucial empirical observation is that the Jueluotage volcanic-sedimentary belt is a well-known metallogenic province that contains a wide range of copper, nickel, gold, and iron mineral deposits. These mineral systems were formed at different times and are associated with radically different ore-forming processes. However, they are all within the Jueluotage belt, which is interpreted to be a suture zone between the Junggar and Tarim plates, northwestern China. We propose that the Jueluotage volcanic-sedimentary belt reflects the occurrence of a major lithospheric discontinuity that favored the emplacement of different magma types and the circulation of hydrothermal fluids over a long span of time, thus controlling the spatial clustering of a range of mineral systems.

SHRIMP zircon age of the high aeromagnetic anomaly zone in central Tarim Basin and its geological implications

In order to get the correct isotopic age, SHRIMP U-Pb zircon date of Precambrian hornblende granite in Well TD2, located in the central aeromagnetic belt in the eastern of the Tarim basin, was carried out. The result showed a dependable age of 1908.2 ± 8.6 Ma, which demonstrated that the granite pluton is the result of the magmatic activity in early Palaeoproterozoic. It is indicated that the central aeromagnetic belt across Tarim basin, divided it into north and south block, is formed before Neoproterozoic by a large scale tectonothermal events based on the seismic and drilling date. The Tarim continent may have different age and type basements formed the united crystalline basement in Precambrian. This result has yielded new intraplate evidence to constrain the relation between the Tarim plate and the Colombia supercontinent.

THE APPLICATION OF REMOTE SENSING DATA TO REGIONAL STRATIGRAPHIC CORRELATION IN KARAKORUM AREA

The Triassic metamorphic rocks south of Kangxiwa fault in Karakorum Mountain area are composed of two sorts of rocks with different remote sensing characteristics. Field work shows that one sort is hypometamorphic rock whose lithologic features, deformation and metamorphic facies are similar to those of Proterozoic Group in Tarim plate, and the other belongs really to Triassic. There exists an unknown deep fault between the two sorts of rocks, which has a distinct linear feature in the remote sensing image. Based on geological analysis, it is considered that this fault is an important geological boundary.

Did the growth of Tibetan topography control the locus and evolution of Tien Shan mountain building?

The Tien Shan in Central Asia are the pre-eminent example of intraplate mountain building, and are typically considered an indirect result of the India-Eurasia collision, via the northward indentation of the relatively strong Precambrian lithosphere of the Tarim plate into the relatively weak Paleozoic lithosphere of the Tien Shan region. This hypothesis fails to fully explain the concentration of Tien Shan mountain building along a Tibet-parallel axis, located 500–700 km from Tibet, and also fails to explain the close synchronization of Tien Shan mountain-building events with mountain building in Tibet. I suggest that bending stresses from lithospheric flexure in Central Asia exerted a critical influence on the locus and evolution of the Tien Shan. Models of Paleogene to Middle Miocene flexure indicate that the growth of northeast Tibet may have superimposed a strong bending stress field on the regional stress field. The resultant stress field is characterized by strong topography-normal tensile stress in the Tarim Basin, and an ∼15% increase in compressive stress in the vicinity of the Tien Shan. This stress field severely reduces the likelihood of mountain building south of the Tien Shan, and increases the likelihood of mountain building within the Tien Shan. This result suggests that the generation of bending stresses from lithospheric flexure is a viable and important mechanism for the propagation of stress, and hence deformation, into continental interiors.

Paleozoic structural deformation of Bachu uplift, Tarim basin of Northwest China: Implications for plate drifting

Based on high-resolution 2D seismic profiles, the Paleozoic structural deformation characteristics of Bachu (巴楚) uplift of northwestern Tarim basin, NW China, are exhibited in this article. The deformation happened during three main geological periods: the end of Middle-Late Ordovician (O2–3), the end of Early-Middle Devonian (D1–2), and the end of Late Permian (P2). In the Bachu uplift, there developed a series of NW-trending thrust faults and imbricate structures due to the effect of the NW-SE compression stress towards the end of Middle-Late Ordovician (O2–3) (middle Caledonian movement), and there developed some NNE-trending thrust faults and fault blocks under the control of the NEE-SWW compression stress at the end of Early-Middle Devonian (D1–2) (early Hercynian movement). However, at the end of Late Permian (P2) (late Hercynian movement), some NE-trending thrust faults and associated folds developed as a result of the NE-SW compression stress. The first-stage (O2–3) deformation is obviously more violent than those of the latter two stages (D1–2 and P2), which implies that the Tarim plate drifted quickly to the north at around the same time basin.

Tectonic evolution of the South Tianshan orogen and adjacent regions, NW China: geochemical and age constraints of granitoid rocks

Geochemical and geochronological evidence was obtained from granitoids of the South Tianshan orogen and adjacent regions, which consist of three individual tectonic domains, the Kazakhstan–Yili plate, the Central Tianshan Terrane and the Tarim plate from north to south. The Central Tianshan Terrane is structurally bounded by the Early Paleozoic ‘Nikolaev Line–North Nalati Fault’ and Late Paleozoic ‘Atbashy–Inyl’chek–South Nalati–Qawabulak Fault’ zones against the Kazakhstan–Yili and Tarim plates, respectively. The meta-aluminous to weakly peraluminous granitic rocks, which are exposed along the Kekesu River and the Bikai River across the Central Tianshan Terrane, have a tholeiitic, calc-alkaline or high-potassium calc-alkaline composition (I-type). Geochemical trace element characteristics and the Y versus Rb–Nb or Y versus Nb discrimination diagrams favor a continental arc setting for these granitoid rocks. SHRIMP U–Pb and LA-ICP-MS U–Pb zircon age data indicate that the magmatism started at about 480 Ma, continued from 460 to 330 Ma and ended at about 275 Ma. The earlier magmatism (>470 Ma) is considered to be the result of a simultaneous southward and northward subduction of the Terskey Ocean beneath the northern margin of the Tarim plate and the Kazakhstan–Yili plate, respectively. The later magmatism (460–330 Ma) is related to the northward subduction of the South Tianshan Ocean beneath the southern margin of the Kazakhstan–Yili–Central Tianshan plate. The dataset presented here in conjunction with previously published data support a Late Paleozoic tectonic evolution of the South Tianshan orogen, not a Triassic one, as recently suggested by SHRIMP U–Pb zircon dating for eclogites.

A review of the geological characteristics and geodynamic mechanisms of Late Paleozoic epithermal gold deposits in North Xinjiang, China

In this review, we describe the geological characteristics of Late Paleozoic epithermal gold deposits in North Xinjiang, and place these into their metallogenic–tectonic context. These gold deposits can be divided into high-sulfidation and low-sulfidation types, with the latter being predominant. The spatial distribution of epithermal gold deposits in North Xinjiang is controlled by calderas, craters, diatremes and related faults. The volcanic and sub-volcanic host lithologies of the gold deposits are mainly of calc-alkaline affinity and dominated by basalt–andesite–dacite–rhyolite suites, and associated pyroclastic rocks. Alteration assemblages are dominated by adularia–chalcedony–sericite for low-sulfidation gold deposits, and alunite–kaolinite–quartz (chalcedony) for high-sulfidation gold deposits. Homogenization temperatures of fluid inclusions in the high-sulfidation type epithermal deposits range from 200 to 300 °C, and ore-forming fluids were mainly of magmatic-hydrothermal origin (e.g. Jingxi–Yelmand), with some contributions from meteoric water. Homogenization temperatures of fluid inclusions in the low-sulfidation type epithermal deposits range mainly from 120 to 210 °C, and ore-forming fluids were largely derived from meteoric water. The high-sulfidation type and low-sulfidation type epithermal deposits have similar salinities, ranging from 0.2 to 19.2 wt.% NaCl equiv. with a cluster between 0.3 and 13 wt.% NaCl equiv. Based on isotopic age data, the epithermal gold deposits essentially appear to have formed during three broad intervals: 346–300 Ma (with a peak at ~ 340–330 Ma), 290–270 Ma, and 240–226 Ma. Each of these episodes corresponds to a period of syncollision, postcollision and intraplate tectonics during Late Paleozoic, accretionary and collisional evolution of the Siberian, Junggar–Kazakhstan and Tarim plates.

Deep dynamical processes in the central-southern Qinghai-Tibet Plateau—Receiver functions and travel-time residuals analysis of north Hi-Climb

Teleseismic receiver functions and travel-time residuals along the north Hi-Climb broadband seismic array in the central-southern Qinghai-Tibet Plateau show that the lithosphere structures in the central and western Qinghai-Tibet Plateau are different. In the central Qinghai-Tibet Plateau, the Indian Plate is northward subducted beneath the Qiangtang block and arrives at the greatest depth beneath the central-southern Qiangtang block. The delaminated Indian lithospheric slab remains beneath the central Lhasa block to a depth possibly greater than that of the upper interface of the mantle transform zone. In the western Qinghai-Tibet Plateau, the Indian lithospheric plate is gently northward subducted and may have arrived to the south of Tarim plate. Due to the resistance from the gently northward subduction of the Indian mantle lithosphere in the western Qinghai-Tibet Plateau, the upwelling mantle material beneath the Qiangtang block moves mostly toward the east to bring about the lateral eastward flow of the deep mantle hot material in the central Qinghai-Tibet Plateau.

EVEREST: ARCHETYPAL ENVIRONMENTAL MODEL FOR ETIOLOGY OF BRAIN PRIMEVAL DISORDERS

Bouguer gravity anomalies in the region of the Western Himalayas, Karakoram and Tien Shan show large negative values, but classical isostatic models are insufficient to account for the detailed pattern of the observed anomalies. In the past years gravimetric surveys in the Karakoram (Marussi, Caputo and others in 1954) have been extended and densified. The full body of available gravimetric data, including the pendulum observations by De Filippi in 1913–14 and Hedin in 1929–33 have been re-analyzed. Terrain corrections have been computed systematically for all available data using an algorithm and Digital Terrain Model. The isostatic anomalies along a profile from the Indo-Gangetic foredeep, across the Karakoram Range and terminating in the Tarim Basin show the oscillating values already noticed by Marussi. This oscillatory pattern can be explained by a model in which the convergent boundaries of the Indian and Tarim plates deform by elastic flexure, besides isostasy. The gravity data are used to constrain the numerical values of the model parameters, particularly the flexural rigidity of the plates. For the Indian Plate it is found that the best fitting value of the flexural rigidity is D=5×1024 N m, a value very similar to those reported in the Central Himalayas. The flexural rigidity of the Tarim Plate turns out to be considerably larger, D=7×1025 N m, which makes the Tarim more rigid than the neighboring Central Tibet. Both plates are loaded by an estimated shear force of 7 1012 N m−1 located in a region corresponding to the Nanga Parbat Haramosh syntaxis. It is concluded that the Indo–Asian continental collision in Western Himalaya and Karakoram results in the development of flexural basins on both sides, unlike in Central Himalaya where the collision produces a flexural basin, the Ganga Basin, to the South and, to the North, the indentation of an isostatically supported Tibetan Block with possible rheological layering and eastward lateral extrusion.

Controls of tectonics on both sedimentary sequences and petroleum systems in Tarim Basin, northwest China

Various orders of sequences were recognized in the Tarim Basin from unconformities. Three mega-sequence groups, six mega-sequences, sixteen super-sequences and forty-two sequences were determined from the Sinian to the Quanternary. The mega-sequences and super-sequences were in accordance with the locally tectonic events occurring in both the north and the south margins of the Tarim plate. The global sea level changes only worked to control formations in the tectonically stable periods or in the low order sequences. The sequences had close relationship to the source rocks, reservoirs and cap rocks, and the tectonic events determined the migration, accumulation, and preservation of the hydrocarbon. The three mega-sequence group cycles, including the early cycle-the Sinian-middle Devonian, the middle cycle the upper Devonian-Triassic, and the late cycle-the Jurassic Quaternary, corresponded to three reservoir formation cycles. So, it can be concluded that the local tectonic events controlled both the sequences and the distribution of oil and gas in the Tarim Basin.

A tomographic image of Indian lithosphere break-off beneath the Pamir-Hindukush region

SUMMARY The P and S seismic anomalies in the upper mantle beneath the Pamir‐Hindukush collision zone and surrounding areas are investigated using more than 4 × 10 5 traveltimes from 5775 events located in the study region, recorded by the stations of the worldwide seismic network and reported in the ISC catalogue. All available epicentral distance ranges of seismic rays are considered. All sources are relocated using an algorithm, which includes the double-difference method. In addition, source parameters are corrected in the main inversion step, simultaneously with the velocity models. The high reliability of the resulting P-velocity images is confirmed by various tests. The S model provides much smoother patterns, which are, however, generally consistent with P anomalies. Our model shows a complex image of lithospheric plate under the study region. Under SW Hindukush, the northwards subducting Indian plate is imaged throughout the upper mantle and transition zone. Further to the NE, within a 300-km-wide zone the upper part of the plate overturns and then the slab breaks off after it narrows at ∼250 km depth. The tomographic model also provides evidence for the southward subduction of the lithosphere beneath the southern Tien Shan down to at least 250 km depth. To the north of Tarim, we observe a northward-dipping of the Tarim plate down to ∼500 km depth. At the crustal depth our model shows alternating belts of high and low velocities parallel to the main thrusting faults, which indicate complex crustal structure in this region.

Geological characteristics and genesis of the Tuwu porphyry copper deposit, Hami, Xinjiang, Central Asia

The Tuwu copper deposit, located in the Dananhu–Tousuquan island arc between the Kazakhstan–Junggar and Tarim plates, is one of the largest porphyry copper deposits in western China. Ore-hosting rocks consist of Early Carboniferous (333 ± 2 Ma) granodiorite- and plagiogranite-porphyries. Both the porphyries are elongate. The orebodies, consisting of veinlet-disseminated mineralization within the porphyries, grade range from 0.30% to 1.50% Cu. Mineralization can be assigned to six stages. Wall-rock alteration associated with the mineralization include silicification, chloritization, epidotization, sericitization and carbonatization. Three alteration zones have been recognized: phyllic zone, chlorite–biotite zone and propylitic zone. Re–Os dating indicates a 322.7 ± 3 Ma age for the deposit. δ 34S values of the ore sulfides range from − 0.9‰ to + 1.3‰, with a mean of 0.11‰, reflecting a deep sulfur source. δ 18O values of quartz in the ores range from 7.70‰ to 9.70‰, and the δ 18O value of chlorite in the ores is 6.62‰. Calculated δ 18O water values of quartz and chlorite range from − 5.37‰ to + 6.62‰ and the δD values range from − 48‰ to − 63‰, suggesting that the ore fluids were mainly magma-derived in the early stage of mineralization. However, values for the late mineralization stage decrease, suggesting the addition of meteoric waters during the mineralization. Fluid inclusions within quartz grains are generally 3 to 30 μm in size, with gas proportions ranging from 5% to 60%, mostly from 10% to 15%. Homogenization temperatures of fluid inclusions are relatively low, bracketed between 101 and 409 °C, mostly between 100 and 200 °C. Salinities exhibit a wide range from 0.35 to 14.61 wt.% NaCl equiv., with a mean of 7.72 wt.% NaCl equiv., suggesting that ore fluids have low to moderate salinity. The ore-bearing plagiogranite porphyries show a strong depletion in heavy rare-earth elements, with average values of Yb and Y of 0.65 and 5.90 ppm, respectively, this being a characteristic geochemical signature for adakite. The geochemical signature of the adakites within the granitoid rocks represents a characteristic guide for further exploration for copper porphyry-type ore deposit in Eastern Tianshan.

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.

Teleseismic imaging of subducting lithosphere and Moho offsets beneath western Tibet

Teleseismic images suggest that the Tarim plate plunges ∼45°S, down to ∼300 km depth, beneath NW Tibet. The 410 km discontinuity shallows by ∼10 km under the plateau, implying ∼100°C cooler upper mantle. The deepest Moho on record (∼90 km) lies under W Qiangtang. It rises abruptly by ∼20 and ∼10 km beneath the Altyn Tagh Fault and Bangong Suture, respectively. V p/ V s ratios are normal, except in the Yecheng flexural basin and deep under the south Karakax volcanics (∼1.92). W Kunlun’s Neogene tectonics are simply accounted for by oblique subduction of lithospheric mantle beneath an upward-extruding thrust wedge of the Tarim crust.

Recent developments in study of the typical superimposed basins and petroleum accumulation in China: Exemplified by the Tarim Basin

Most of petroliferous sedimentary basins in China have experienced multiple phases of tectonic evolution and deposition, and are characterized by tectonic and depositional superimposition. The term “superimposed basin” is suggested to describe those basins which consist of two or more simple prototype basins superimposing vertically and/or coalescing laterally. The characteristics of petroliferous superimposed basins are “multiple stages of basin forming and reworking, multiple layers of source rocks, multiple periods of hydrocarbon generation and expulsion, multiple periods of petroleum migration-accumulation-escape”. Therefore, applying the wave process analysis method to studying the process of basin formation, hydrocarbon generation, and reservoir formation, and then establishing theory of “petroleum accumulation system” is helpful to enhancing petroleum exploration efficiency in superimposed basins. This paper will, based on case study in the Tarim basin, report the major developments in studying basin formation, hydrocarbon generation and petroleum accumulation. In study of basin formation, (1) geophysical comprehensive profiles reveal that the Tarim plate has been subducted beneath the Tianshan orogenic belt with an interfinger structure and that the deep structure in the eastern section of the Tianshan orogenic belt is different from that in the western section. (2) The vertical variation in debris and geochemical composition reveals the nature and Mesozoic-Cenozoic evolution history of the Kuqa Depression. (3) Field investigation and paleostress reconstruction show that the Kuqa Depression has undergone gravity-driven extension in sedimentary cover when the Tianshan uplifted vertically. In hydrocarbon generation study, new developments include (1) setting environmental index to judge high grade source rocks in marine carbonates, and (2) establishing the lower limit of the organic carbon content for effective carbonate source rocks. In petroleum accumulation study, (1) methods of determining paleopressure and paleotemperature of forming fluid inclusions have been established. (2) The petroleum source analysis has indicated that the crude oil in the Lunnan and Tahe oilfields are derived from the source rocks of the Middle and Upper Ordovician. (3) Three generations of oil inclusions from the Lunnan oilfield have been recognized and dated.

Characteristics and dynamic origin of the large-scale Jiaoluotage ductile compressional zone in the eastern Tianshan Mountains, China

The Jiaoluotage ductile compressional zone (JDCZ) in the eastern Tianshan Mountains, China, developed in volcanic and sedimentary rocks that were deposited in a Carboniferous back-arc basin situated between the Jungar plate and middle Tianshan terrane. The ductile compressional zone, ∼500 km long and 20–50 km wide, consists of a number of east-trending vertical foliation zones that display an augen geometry in plan view and a fan-like geometry in transverse profiles. Ductile compressional deformation has produced pervasive foliation, radial stretching lineations, contemporaneous folds, and various macroscopic to microscopic symmetric structures within the JDCZ. Rotations of most clasts and porphyroclasts are bidirectional. The preferred orientation patterns of the optical axes of calcite and quartz display axial or orthorhombic symmetry. Three kinds of strain patterns have been determined in the JDCZ: apparent flattening, plane strain and apparent constriction. The overall strain character of the JDCZ is ‘cream-cake’ style. The volcanic and sedimentary rocks within the JDCZ were metamorphosed into greenschist facies with temperature of 400–600 °C and pressure of 300–400 MPa. Development of the JDCZ is interpreted as due to N–S coaxial compression caused by the collision between the Tarim plate and the middle Tianshan arc–Jiaoluotage basin–Jungar plate system during the Permian between 270 and 290 Ma.

C-isotope composition and significance of the Sinian on the Tarim plate

102 samples of limestones, mudrocks shales and tillites from the Sinian in Kuluketage have been analyzed. Four formations in the Sinian belong to glacial deposits in which the differences in δ13C are distinct (−14.7−+4.2‰). Distinctly negative δ13C excursions for three times support the view of three glacial deposits in this area suggested by previous authors, except for the durations of them. δ13C values are generally positive in the Beiyixi Formation of lower part of the Lower Sinian, representing probably the rock records of a continental rift related to break-up of the Rodinian supercontinent. There are three times of distinct excursions of δ13C curve in all strata. The first one is from positive values at the bottom to about −5‰ at the top of the Beiyixi Formation. The second one, from 0‰–3‰ in the Arletonggou Formation of upper part of the Lower Sinian to −3.4‰–−14.4‰ in the Teruiaiken Formation. The third one, from positive values in the Zhamoketi Formation of lower part of the Upper Sinian to negative values in glacial varves at the top of the Hankeerqiaoke Formation.

C-isotope composition and significance of the Sinian on the Tarim plate

C-isotope composition and significance of the Sinian on the Tarim plate

Silurian to Devonian foreland basin in the south edge of Tarim Basin

Based on the theory of plate tectonics, combining with the isotopic dating of ophiolite, igneous and volcanics, geochemical test, rare earth element analyze and seismic interpretation, this paper studies the pre-Carboniferous tectonics and sedimentary formation of the south edge of the Tarim Basin and proves that there exists the Kunlun Ocean under tensional tectonics during the Sinian and Cambrian in the south edge of the Tarim Plate. After that, due to the collision orogenesis, there formed the peripheral foreland basin in the south edge of Tarim. The Upper Silurian and Devonian molasses sedimentary system superposed on the Sinian and Middle Silurian passive margin flysch sedimentary system and formed the bivariate structure of the foreland basin. And at the same time, based on the field geology and seismic interpretation, we have identified that the formation of the Silurian and Devonian have the character of half deposit which shows thick in the south area and thin in the north, and the pre-Carboniferous thrust compression tectonics remained in the foreland thrust belt, which further demonstrates that there existed the Silurian and Devonian peripheral foreland basin on the south edge of the Tarim Basin.