Tarim Block Research Articles

Petrogenesis of early Paleozoic syn-collisional granitoids and enclaves in Western Kunlun, Northwest China: Implications for the growth of continental crust

The Western Kunlun Orogenic Belt (WKOB), along the northwestern margin of the Qinghai–Xizang Plateau, was formed by the collision of Gondwana-derived terranes to the south and the Tarim Block to the north and was closely associated with closure of the Proto-Tethys Ocean during the late Neoproterozoic to early Paleozoic. We present a combined zircon UPb geochronology, whole-rock composition, and Sr–Nd–Hf isotopic study of syn-collisional granitoid plutons and mafic microgranular enclaves (MMEs) in the region. Zircon UPb dating yields ages of 443.8 ± 4.4, 451.9 ± 4.2, 462.9 ± 3.5, and 456 ± 4.2 Ma for the Tongayoupuagezi, Shanjie, and Pishigai plutons and MMEs from the Pishigai pluton, respectively. The granitoids are metaluminous to weakly peraluminous (A/CNK = 1.00–1.17) and belong to the high-K calc-alkaline series. They have (87Sr/86Sr)i ratios of 0.7058–0.7154, εNd(t) values of −8.78 to −0.93, and εHf(t) values of −19.72 to +6.87. The MMEs have variable SiO2 contents (45.7–60.2 wt%) and are more mafic than the host granitoids, but have similar Sr–Nd–Hf isotopic compositions to the host granitoids [(87Sr/86Sr)i = 0.7102–0.7110; εNd(t) = −6.57 to −3.56; εHf(t) = −7.17 to −1.81]. The MMEs are fragments of cumulates formed during the early stages of magma evolution. The granitoids were produced by the partial melting of a mélange source. The new data support the view that the Middle–Late Ordovician syn-collisional granitoids with MMEs distributed along the WKOB represent a magmatic response to terrane collision. This suggests that juvenile crustal growth in older orogenic systems, which occurs by arc addition, also involves some vertical addition during the final stage of orogenic collision. Our study suggests that mélange diaper melting is a key mechanism of crustal growth during the syn-collision stage in continental collision zones, associated with slab breakoff.

Receiver function image of the mantle transition zone beneath western China: Fragmented subduction and counterflow upwelling

A uniform image of the mantle transition zone (MTZ) beneath western China and neighboring regions is produced through Variable Bin Radius Stacking of receiver functions. We utilized a large data set of 218,050 receiver functions from 1,991 broadband seismic stations. Our results, after 3-D velocity corrections, show significant lateral variations in topography of the 410- and 660-km discontinuity and thickness of the MTZ. The observed lateral variations of the MTZ correlate with seismic-velocity anomalies identified in independent tomographic studies, which are interpreted as cold and hot thermal anomalies from lithospheric downwellings and mantle upwellings, respectively. In the southern Tibetan Plateau, the MTZ topography reveals four segmented zones of up to ∼20 km thicker-than-average MTZ from west to east interfingered with regions of thin-to-normal MTZ. These segmented MTZ thickenings likely originate from a series of cold lithospheric fingers associated with the fragmented subduction of the Indian lithosphere, while the thin-to-normal MTZ may result from an absence of the subducting Indian slab. These observations provide novel evidence for the proposed fragmentation of the Indian subduction. Moreover, we observe regions of thickened MTZ under the Tien Shan orogen and the Qaidam block, which likely result from the foundering of cold delaminated/broken-off lithospheric blocks triggered by the underthrusting of the Junggar and Tarim blocks. Regions of thinned MTZ beneath the Tien Shan region are additionally observed, which could be attributed to counterflow upwellings.

Synchrotron-based P K-edge XANES spectroscopy reveals the transition of phosphorus cycling in the early Cambrian ocean

Phosphorus, as a long-term limiting nutrient, is essential for the rapid animal diversification in the early Cambrian ocean. However, the widespread occurrence of phosphorites during this period indicates anomalous phosphorus cycling mechanisms that remain inadequately explored. To investigate the interplay between marine redox conditions and phosphorus cycling, we used geochemical proxies and synchrotron-based P K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy to analyze the Cambrian Terreneuvian Yurtus Formation (Fortunian to Stage 2) from the Tarim Block. Redox-sensitive elements, iron speciation and nitrogen isotopes reveal an expansion of the surface oxygenated waters, despite persistent ferruginous bottom waters. Moreover, a shift of phosphorus speciation was observed in bedded cherts via P K-edge XANES, suggesting a transition of phosphorus cycling. Specifically, the samples exhibit low total phosphorus contents with a high rate of carbonate-fluorapatite authigenesis in the lower Yurtus Formation. This is followed by an increase in the proportion of terrestrial-derived fluorapatite and iron-bound phosphorus, corresponding to the expansion of surface oxygenated waters. Our findings reveal a significant shift in dominant phosphorus speciation in the early Cambrian marine sediments, which is intricately linked to the coupled phosphorus‑iron‑carbon‑oxygen cycles in the Cambrian ocean.

Diverse magmatism along the northern margin of Tarim during the Ediacaran: Transition from Rodinian dispersing to Gondwana assemblage

The Ediacaran igneous rocks and sedimentary sequences play a key role for our understanding the transition from dispersing of the Rodinian continents to the assemblage of the Gondwana. On the other hand, some continental massifs at the marginal area of the Rodinia and Gondwana could preserve solid evidences for deciphering the geodynamic background from the break-up of Rodinia to the assemblage of Gondwana. In this contribution, we report field observations, petrography, ages and systematic geochemistry of the diverse Ediacaran igneous activities in the northern margin of the Tarim Block, which was favored as a marginal continental massif in the Rodinia configuration by most geologists. The Ediacaran igneous rocks along the northern margin of Tarim include the Baicheng and Yangxia granites, Tiemenguan syenite, Kurle mafic dykes and the basalt layers in the Zamoketi Formation (northeastern Tarim) and the Sugetbrak Formation (northwestern Tarim). Precise zircon UPb dating revealed that these distinct rocks were broadly coeval with crystallization/eruption ages of 630–600 Ma. Bulk-rock elemental and SrNd isotope compositions as well as zircon LuHf isotope compositions demonstrate that the Baicheng and Yangxia granites were derived from Neoarchean mafic lower crust and underwent intensive fractionation before their emplacements. The Tiemenguan syenites have potassic andesitic compositions, in combination with their pronounced enriched NdHf isotopes and extremely high Zr saturation temperatures (∼900 °C), we argue that their possible shoshonitic primary magmas were derived from previously metasomatized subcontinental lithospheric mantle source (amphibole-bearing) and then, coupling with assimilation and fractional crystallization (AFC) effects in magma chamber and/or en route to the emplacement space. This can account for their intriguing geochemical features. The ca. 615 Ma Zamoketi and Sugetbrak basalts and the slightly younger porphyrite dykes (ca. 580 Ma) cutting the Zamoketi basalt layer, show typical OIB-like geochemical signatures, they were most likely derived from a depleted asthenospheric mantle source with variable fractionation of olivine and pyroxene and negligible crustal contamination before eruption. On the whole, the geochemistry of the diverse Ediacaran igneous rocks unambiguously demonstrates that they were genetically related to an extensional environment. In combination with the significant passive continental features of the Ediacaran-Cambrian sedimentary sequences, we consider that these Ediacaran igneous rocks were the latest phase of igneous activity related to the dispersing of the Tarim at the margin of the Rodinia supercontinent.The dispersing of the Rodinian supra-continent was diachronic with the assemblage of the Gondwana. Late Tonian to Ediacaran dispersing of the Tarim from northern margin of Australia induced the opening of the Proto-Tethys Ocean. Then the initiation of the southward subduction of the Proto-Tethys Ocean at ca. 530 Ma (Fortunian) led to the Tarim assemblage to Gondwana at ca. 440 Ma.

Neoproterozoic transition from subduction to breakup along the margin of the Rodinia supercontinent: Sedimentary evidence from the northwestern Tarim Block, Northwest China

The Tarim Block, northwest China, was positioned on the periphery of Rodinia during the Neoproterozoic Era, and preserves a geological archive chronicling the assembly and breakup of the supercontinent. Due to its antiquity and limited exposure, sedimentary records along the margin of the Rodinia supercontinent remain sparsely documented. This study focuses on the Xifangshan and Dongqiaoenbrak formations, the oldest sedimentary units in the northwestern Tarim Block, which comprise a Neoproterozoic sedimentary record at the supercontinent margin during the transition from subduction to breakup. A comprehensive analysis employing sedimentology, petrology, elemental geochemistry, and UPb detrital zircon chronology was undertaken, to elucidate paleoenvironment, parent rocks, and tectonic-sedimentary evolution. Findings show that the Neoproterozoic witnessed the subduction of an oceanic plate beneath the Tarim Block, resulting in the formation of a continental margin magmatic arc. The Xifangshan Formation, deposited during the late phase of this arc (with the earliest sedimentary age recorded at 770 Ma), represents a submarine fan dominated by turbidity currents. Around 760 Ma, rapid crustal uplift occurred, and the tectonic setting gradually shifted from subduction to rift, giving rise to the coastal alluvial fan sedimentary system observed in the Dongqiaoenbrak Formation. Both the Xifangshan and Dongqiaoenbrak Formations record deposition in an oxic to suboxic marine environment with moderate salinity, influenced by a semiarid to semihumid palaeoclimate. The continental margin arc served as the primary source for sedimentation in both formations, and a few magmatic products linked to extension (syenite, monzonite) were also cannibalized into the sedimentary system of Dongqiaoenbrak Formation. This transition from a turbidite system to a coastal alluvial fan represents a sedimentary response to the subduction-to-breakup dynamics along the margin of the Rodinia supercontinent.

Precambrian geological history of the Tarim Craton (NW China) involving the assembly and fragmentation of the Columbia and Rodinia supercontinents: review and synthesis

The Tarim Craton (NW China) is a significant archive of the tectonic events that occurred during the assembly and break-up of the Precambrian supercontinents Columbia and Rodinia. It provides a comprehensive record of crustal development during the Proterozoic. We review and synthesize the magmatic, metamorphic and stratigraphic records of the Precambrian Tarim Craton and delineate the geochronology of significant geological events that led to the formation of this major cratonic block. The extant geophysical and geological data show that the Tarim Craton consists mainly of the South and North Tarim blocks. The record of late Paleoproterozoic tectonothermal events is displayed well in and across the craton, involving the amalgamation of these two blocks to form its unified crystalline basement during the build-up of Columbia. However, the record of mid-Neoproterozoic events during the assembly of Rodinia is only exposed around its periphery. The Proterozoic record of the craton includes Mesoproterozoic–early Neoproterozoic low-grade metamorphic rock units and a late Neoproterozoic sedimentary cover. The early Mesoproterozoic stratigraphy in the SW, NE and SE of the Tarim Basin suggests a period of tectonic stability following the amalgamation of the North and South Tarim blocks in the late Paleoproterozoic, indicating the completion of its cratonic build-up.

Discovery of Late Carboniferous high-grade carbonate-hosted manganese mineralization in the Maerkansu area of the Western Kunlun Orogen, Northwest China

The Aoertuokanashi deposit located in the Western Kunlun Orogen is the first known Late Carboniferous large high-grade carbonate-hosted Mn deposit in the world and it has been mined since 2018. The deposit is considered to have formed in a back-arc basin developed during the northward subduction of the Paleo-Tethys Ocean beneath the Tarim Block. The Re-Os isotope isochron age of Mn ore at the Aoertuokanashi deposit is 302 ± 9 Ma. The minimum initial 187Os/188Os values obtained from the deposit is 0.28, which indicates the presence of a mantle source for the mineralization. The Aoertuokanashi deposit is similar in age to the 301 ± 5 Ma Wajilitag kimberlite in the Tarim Block, which is considered to be the initial magmatic pulse triggered by the Tarim mantle plume. The Late Carboniferous Aoertuokanashi Mn deposit was likely promoted by igneous activity from the Tarim mantle plume.The Aoertuokanashi deposit shows geochemical characteristics of hot water activity in a back-arc basin. The Mn mineralization is hosted in the restricted platform facies. Framboidal pyrite, typical biomat, and authigenic quartz are observed in the Mn deposit, indicating the influence of microbial processes. The sedimentary facies show a starving basin feature that can enhance microbial mediation. The δ13CV-PDB values of mineralized rocks (from −19.5 to −8.2 ‰) are more negative than those of wall rocks (from −5.3 to + 4.2 ‰), whereas the δ13CV-PDB values (around −29 ‰) of kerogen for the Mn ore are significantly lower than those of the whole rock. These compositions indicate that the reducing function of organic matter played an important role in Mn mineralization. In the inferred extensional tectonic environment, under the influence of a mantle plume, the stratum with strong hot water activities and a large amount of organic matter becomes the focal point for the formation of carbonate type manganese ore deposit.

New findings of Changxingaspis (Xiushuiaspidae, Galeaspida) from the Silurian of Tarim Basin and Zhejiang Province, China

AbstractNew discovery of the early Silurian fossil fish Changxingaspis (Xiushuiaspidae, Galeaspida), Changxingaspis nianzhongi sp. nov. and C. gui, are described from the Tataertag Formation in Tarim Basin and the Kangshan Formation in Zhejiang Province, respectively. C. nianzhongi mainly differs from C. gui in the shape of the median dorsal opening that is transverse elliptic with a width/length ratio of about 3.0, the long lateral transverse canals extending to the lateral margin of the headshield, and the second lateral transverse canal with dichotomous branchings. Discovery of C. nianzhongi from the Tataertag Formation and C. gui from the Kangshan Formation provide direct evidence on the specific level for the correlation between these two formations, which further supports the Silurian fish‐bearing red beds in northwest Zhejiang belonging to the Silurian Lower Red Beds (LRBs) rather than the Upper Red Beds (URBs). Additionally, as the first record of the Changxingaspis in Tarim Basin, it extends the paleogeographical distribution of this genus from the South China Block to the Tarim Block, providing new evidence to support faunal exchanges between these two blocks and the hypothesis of a united Tarim–South China Block during the early Silurian.

Multi-stages of Paleozoic deformation of the fault system in the Tazhong Uplift, Tarim Basin, NW China: Implications for hydrocarbon accumulation

The Tazhong Uplift is an important petroliferous secondary structure unit in the Tarim Basin and has undergone multiple structural deformation. In the current study, we use 3D and 2D seismic data to investigate the nature of the fault system in the Tazhong Uplift. The deformation of the Cambrian sedimentary rocks in the Tazhong Uplift is generally neglected but noted in this study. We found that the Lower–Middle Cambrian rocks are involved in thrust faults. NE-trending weak zones acted as accommodation faults formed at the connective positions and bends of the deep thrust faults. The Middle Cambrian compressional stress stemmed from the northeastern margin of the Tarim Block, pointed SW, and caused the uprising of the Tabei Uplift. The second deformation occurred in the Late Ordovician. In this instance, the compressional stress stemmed from the SW direction of the Tazhong Uplift, which originated from the amalgamation of the Western Kunlun Terrane and Tarim Block. The main strike–slip fault surfaces and subordinate faults developed along the weak zones generated in the Middle Cambrian. The collision that occurred in the southeast part of the Tarim Block in the Middle Silurian to Middle Devonian resulted in the third deformation. The representative structures that occurred during this compressive deformation were the intensive NEE-trending thrust faults in the southeast of the Tazhong Uplift. The three stages of deformation played different and important roles in hydrocarbon accumulation. These strike–slip faults holding the high-productivity hydrocarbon wells generally experienced early-stage Cambrian deformation, had wide fracture damage zones in the Ordovician carbonate rock strata, and had weak en echelon faults in the Silurian to Middle Devonian clastic rocks.

Late Neoproterozoic tectonic evolution of the northern Tarim block: New insights from integrated detrital zircon and rutile geochronology and trace element geochemistry

In the Neoproterozoic era, the breakup of the Rodinia supercontinent had a profound impact on different aspects of Earth; yet, the precise driving mechanism behind this event has been a source of ongoing controversy. The Tarim block, as a crucial component, presents an opportunity to gain valuable insights into the breakup process through its tectonic-sedimentary evolution history and dynamic background. However, the comprehension of basin evolution is limited due to the presence of an ambiguous prototype basin during the late Neoproterozoic and its intricate interconnections with surrounding blocks. In this contribution, we integrate detailed field observations, U-Pb dating of detrital zircon and rutile, and trace element analysis of detrital rutile to elucidate the source-to-sink relationships and the tectonic setting of Ediacaran sedimentary strata in the Aksu area (northern Tarim block, China). Detrital zircon age spectra exhibit consistent distributions with ages between ∼850 and ∼600 Ma and between ∼2100 and ∼1800 Ma. Rutile age groups however exhibit an abrupt transition between the lower member of the Sugatbrak Formation and the succeeding upper member to the Qigebrak Formation in the basin, with ages between ∼1800 and ∼900 Ma and nearly identical to those between ∼2100 and ∼1800 Ma. Calculated Zr-in-rutile temperatures and Cr-Nb compositions imply that the majority of the detrital rutiles were sourced from amphibolite facies metapelites, with an abrupt transition from amphibolitic schist to amphibolite-granulite facies for the ∼1800 Ma group grains. Provenance tracing shows that the detrital sediments of the lower Sugatbrak Formation are sourced from both the Central Tianshan and the Tarim blocks, and that the overlying strata have a single source in the Tarim block. A corresponding change from syn-rift detrital facies to a shallow-marine environment in on a passive continental margin is suggested in terms of depositional setting. In light of prior published evidence from petrology, geochronology and paleomagnetism, we propose that the Neoproterozoic northern Tarim margin was affected by a protracted subduction zone retreat. Associated back-arc spreading eventually was responsible for the opening of the southern Tianshan Ocean and rifting of the Central Tianshan block from the Tarim block in the late Ediacaran. This development ultimately prevented detrital material from the Central Tianshan block from reaching the northern Tarim depocenters as the latter evolved into a passive continental margin.

Palaeomagnetic results from Early Mesozoic strata in the Qaidam Basin and their implications for the formation of the Northern China Domain

SUMMARY The Northern China Domain is located between the Central Asian Orogenic Belts to the north and the Kunlun–Qinling belt to the south, and it comprises the North China, Alxa and Tarim blocks. The relationships among the Northern China domain and the southern tectonic elements such as the Qaidam Basin/Terrane are debated because of the major modification by crustal deformation in the late Mesozoic–Cenozoic. To address this issue, we conducted a palaeomagnetic and high-precision radiometric dating study of Triassic volcanic rocks and Middle Jurassic strata in the Qaidam Terrane. Our objective was to determine the relationship between the Qaidam Terrane with the Tarim Block and the North China Block (NCB) during the late Palaeozoic and early Mesozoic. Four volcanic samples yielded zircon U-Pb ages of 236–243 Ma. The characteristic remanent magnetizations (Middle Triassic: D = 40.2°, I = 54.6°, α95 = 3.4°; Middle Jurassic: D = 27.4°, I = 48.0°, α95 = 7.9°) passed the fold and reversal tests, and yielded Middle Triassic and Middle Jurassic palaeopole positions at 57.6° N, 178.2° E, A95 = 4.0° and 65.8° N, 197.6° E, A95 = 7.8°, respectively. Based on these new poles, combined with other reliable data, we compared the apparent polar wander path (APWP) of the Qaidam Terrane with those of the NCB and Tarim Block. The results show that, from the Carboniferous through Early Cretaceous, the APWP of the Qaidam Terrane resembles that of the Tarim Block, but it is quite different from that of the NCB. Combined with other reported evidence, we conclude that the Qaidam Terrane was an independent dynamic unit during the late Palaeozoic until its connection with the Tarim Block, which was followed by continuous eastward motion. During this process, the connection between the Qaidam Terrane and the NCB–Alxa blocks occurred in the Middle Triassic, and subsequently the Qaidam Terrane underwent multiple tectonic responses to collisions with the Qiangtang Terrane, Lhasa Terrane and the India Plate, before the formation of its modern tectonic configuration.

Emplacement and ore potential of the Permian Pobei mafic–ultramafic complex, NE Tarim, NW China

A number of mafic–ultramafic intrusions with variable degrees of Ni-Cu sulfide mineralization occur in the northeastern Tarim Block and East Tianshan Orogenic Belt (NW China). Among them, the Pobei complex is composed of a gabbro body intruded by several ultramafic bodies including Poyi and Poshi. These bodies have similar mineralogy and chemical compositions and were derived from a common magma. Olivine crystals from the Poyi and Poshi bodies generally have high Fo contents with the highest Fo value of 89.5 and Ni up to 3300 ppm Ni, indicative of crystallizing from Ni-undepleted, high-Mg basaltic magmas. Sr-Nd-Pb isotopic compositions show that more mafic rocks show relatively low degrees of crustal contamination, whereas more evolved rocks experienced higher degrees of contamination, especially in the upper part of the complex. Olivine crystals from both the Poyi and Poshi bodies show sharp decrease of Ni with decreasing Fo values, indicating sulfide segregation in these two bodies. Gabbros may have potential of reef-type chromite mineralization at the deep level, and V-bearing magnetite mineralization at higher stratigraphic level corresponding to the current surface level, but the potential of PGE mineralization is low. We propose that the ultramafic bodies of the Pobei complex may have been formed from the injection of olivine- and sulfide-laden crystal slurry from the bottom of a large magma chamber. The Ni-Cu mineralization was triggered by the crustal contamination. The Pobei complex was formed by the multiple intrusions of magmas to form the current complex.

Tarim rotation mechanism and the differential deformation responses along the Tian Shan

SUMMARY Rotation of rigid blocks within continental interiors far from the plate convergence boundary is an unusual process, the dynamics of which is not clear. The Tarim block, as a rigid Precambrian block in central Asia, is surrounded by the Tibetan–Pamir plateau to the south and Tian Shan mountains to the north. Numerous geophysical data suggested that the Tarim block experienced significant clockwise rotation in the Cenozoic. Meanwhile, contrasting deformation patterns and associated topographic responses were observed between the western–central and eastern Tian Shan. The relationship among the India–Asia collision, Tarim rotation, and Tian Shan responses are poorly constrained. Here, a series of large-scale, high-resolution 3-D numerical models were constructed. The model results reveal that the collision of the indenting Indian lithosphere with the southwestern rim of the Tarim block triggers clockwise rotation of the Tarim block. Further on, the Tarim rotation produces differential deformation responses along the strike of Tian Shan, that is convergence-induced higher compression and strong uplifting in central Tian Shan but divergence-induced less compression and moderate uplifting in eastern Tian Shan. Thus, the Tarim rotation serves as an indispensable linkage between the Tibetan plateau evolution and the far-field Tian Shan activation.

Paleo-marine redox environment fluctuation during the early Cambrian: Insight from iron isotope in the Tarim Basin, China

The Ediacaran to Cambrian period is generally considered to be the vital transition in the history of marine redox environment and life evolution on earth. The ocean oxygenation levels during this transition period are still debated. Since iron is widely involved in biogeochemical cycles and undergoes redox cycling both in the seawater and sediments, it has become a significant proxy to reconstruct paleo-marine environment. In order to constrain the paleo-marine redox state in the early Cambrian, the iron isotope composition of bulk rock (δ56FeT) is interpreted combining with iron-speciation, redox sensitive elements and pyrite sulfur isotope (δ34Spy) of Yuertusi Formation in Tarim Block. The δ56FeT values varies from −0.39 ‰ to 0.48 ‰, with an average of 0.07 ‰, mainly controlled by pyrite mineral facies in this study. Based on the mechanism of pyrite generation in different redox condition, it is proposed that the marine environment of the lower Cambrian in the Tarim basin is dominated by anoxic with intermittent euxinic state. The dynamic evolution of redox environment can be divided into three intervals. The gradual decrease of δ56Fe in Interval I indicates the paleo-marine environment changed from anoxic ferruginous to euxinic, and the paleo-marine sulfate reservoir decreased to a limited level, which might be attributed to abundant burial of organic matter and pyrite. For Interval II, δ56Fe values first increase to evident positive because of partial oxidization then decreased to that of seawater (about 0 ‰) due to complete oxidization. In Interval III, the continuous decrease of δ56Fe values infers a sustaining oxidization. In summary, the paleo-marine environment of the lower Cambrian Yuertusi Formation evolved from anoxic ferruginous to euxinic and then oxidized continuous. Iron isotope statistics from geological historical periods indicate that seawater was relatively oxidized after the NOE event but did not reach the oxidation levels of present-day seawater.

New paleomagnetic and geochronologic results from late Paleozoic rocks in the Turfan-Hami block (NW China) and implications for the geodynamic evolution of the western Altaids

How and when the ocean-continent transition started in the western Altaids remain controversial. The paleomagnetic signals recorded by late Paleozoic rocks in the Turpan-Hami block can provide critical constraints on this issue. We conducted a new combined paleomagnetic and geochronologic study on the late Paleozoic rocks from the Turpan-Hami block. Laser ablation−inductively coupled plasma−mass spectrometry zircon U-Pb dating of volcanic beds from the Upper Carboniferous Qijiaojing and Julideneng Formations yielded ages of 313.1 ± 4.3 Ma and 309.6 ± 1.9 Ma to 308.1 ± 3.6 Ma, respectively. Meanwhile, the U-Pb age of the granite intruding the Julideneng Formation is 300.3 ± 2.4 Ma. Passing a series of fold tests, the characteristic remanent magnetization (ChRM) directions of the Qijiaojing Formation are likely primary and consistent with the Kiaman reversed superchron (ca. 319−267 Ma). However, the ChRM values of the Dananhu (Middle Devonian) and Julideneng Formations all represent reverse polarity with negative fold tests, which indicate remagnetizations related to the magmatic thermal events during the late Carboniferous. Thus, two high-quality paleomagnetic poles were obtained for the periods ca. 313−308 Ma at 44.4°N, 177.3°E (K = 22.1, A95 = 8.0°) and ca. 300 Ma at 47.8°N, 173.9°E (K = 116.0, A95 = 4.8°), respectively. Comparison with published coeval paleomagnetic poles of the blocks on both sides of the Tianshan sutures suggests that the central oceanic basin of the western Paleo-Asian Ocean (between the Siberian and Tarim blocks) had been closed since the late Carboniferous (ca. 310 Ma), apart from remnant seas. In addition, a sizeable clockwise rotation (∼58°) of the Turpan-Hami block had taken place during the early Permian, with a scissor-style shrinking of the remnant Bogda marine basin in the meantime. This study provides a new perspective for understanding the tectonic evolution of the western Altaids.

Zircon U–Pb geochronology, Hf–O isotopes and whole-rock geochemistry of A-type granitoids in Halajun, South Tienshan, NW China: Implications for subdivision, petrogenesis and tectonic settings

Abundant A-type granitic intrusions are located within the South Tienshan Orogenic Belt (STOB) and the adjacent area to the Tarim Block. Most of these intrusions share the analogical epoch of the Tarim Large Igneous Province (TLIP), however display diverse alkalinity and geochemical signature. There is controversy in deciphering the subdivision, petrogenesis and geodynamic setting of these intrusions based on their varied geochemical compositions. In this contribution, we conduct integrated research of whole-rock major and trace element compositions, zircon U–Pb geochronology, and in-situ zircon Hf–O isotopic characteristics of several Halajun intrusions in the STOB, to unravel their subdivision, petrogenesis and geodynamics. The Halajun IV quartz-syenite, Kaladuowei quartz-monzonite and tourmaline-rich granite show Permian crystallization ages of 283.4 ± 1.1 Ma, 280.2 ± 1.3 Ma and 270.7 ± 1.5 Ma, respectively. These intrusions exhibit high Zr + Nb + Ce + Y concentrations (449–1592 ppm), 10,000 × Ga/Al values (3.31–4.47), Na2O + K2O (6.9–10.9 wt%), (K2O + Na2O)/CaO (3.5–19.2) and FeOT/(FeOT + MgO) (0.67–0.95), which are similar to those of typical A-type granitoids. These samples show various degrees of enriched Rb, Th, U, Zr, Hf and Pb, and depleted Ba, Sr and Eu. Decoupling of Nb and Ta in late granitic phases infers that the Nb–Ta differentiation occurred during the magmatic evolution. The in-situ zircon Hf and O isotopes of these intrusions show wide ranges of εHf(t) (−1.2 to +4.7) and δ18O (+6.2‰ to +8.2‰), indicating that crust- and mantle-derived materials were both involved in the quartz-syenite, quartz-monzonite and tourmaline-rich granite. End-member mixing model shows that the mantle contribution is ∼80% for quartz-syenite and ∼60–65% for quartz-monzonite and tourmaline-rich granite, respectively. With the increasing crustal materials of the parental magma and the subsequent fractionation of ilmenite and biotite, they exhibit a gradual tendency from A1-type to A2-type granitoids. This suggests that A-subtypes may evolve during the magmatic process. Considering the same tectonic setting and a common parental source, the quartz-syenite, quartz-monzonite and tourmaline-rich granite should be A1-type. The Halajun plutons were emplaced between the STOB and Tarim Block, and their generation might be related to the contemporaneous Permian Tarim mantle plume. The primitive magmas, derived from mantle plume, was mixed with the ancient Proterozoic crust and formed the Halajun A1-type granitoids.These alkaline intrusions share two tectonic regimes, i.e., the southern margin of the Tienshan Orogenic Belt and the northern margin of TLIP. The regional tectonic setting was in the transitional period from a compressive regime to an extensional or post-collisional one in the Late Paleozoic. The rising plume generated the ultramafic pipes, and provided dynamic energy to the extensional motion. The collapse of the Tienshan Orogenic Belt and the contemporary heavy eruption of TLIP not only afforded channels for the upwelling mantle magma, but also cycled the lithosphere or crustal materials into the mantle, which might have been involved in the formation of the A2-type granitoids in the STOB. The A1-type granitoids were mainly derived from the mantle source along the terminal suture.

The first Eugaleaspiforme fish from the Silurian of the Tarim Basin reveals a close relationship between the Tarim and South China blocks at 438 mya

The first Eugaleaspiforme fish, Jiangxialepis rongi sp. nov., from the lower Telychian (Llandovery, Silurian) Tataertag Formation in the Tarim Basin is described and its palaeogeographic significance is evaluated. The new species can be assigned to the family Shuyuidae and distinguished from J. retrospina and J. jiujiangensis by its comparatively broader headshield, ornamentation, and serrated margin of the headshield and median dorsal opening. The discovery of J. rongi provides direct fossil evidence for the correlation of lower Telychian marine red beds between the Tarim Basin and South China and expands our knowledge of the distribution of Eugaleaspiforme fish into the Tarim Basin. An analysis of galeaspid paleogeographic distribution within a phylogenetic framework reveals at least five galeaspid dispersal events between the blocks of South China and the Tarim Basin during the early Telychian age. This indicates that the South China and Tarim blocks were close enough to share the same shallow marine environment, and perhaps comprise a united Tarim-South China Block during the early Silurian.

Reconstruction of the proto-type basin and tectono-paleogeography of Tarim Block in the Mesozoic

The reconstruction of the proto-type basin and tectono-paleogeography of the Tarim Basin during the Mesozoic is crucial for hydrocarbon exploration, particularly for identifying hydrocarbon source rocks. This study reconstructs the position, thickness, and distribution of the original stratigraphy, the shortening amount by structural deformation, and the distribution of sedimentary facies in each Mesozoic period using paleomagnetic data, residual stratigraphy data, seismic profiles, and lithofacies distribution. During the Triassic period, a syn-collision thrust fault structure formed in the southern Tarim Block due to the successive collision of the Tianshuihai-Bayankara terrane, North Qiangtang terrane, and South Qiangtang terrane with the Tarim Block. The sedimentary strata mainly distributed in the Northern Depression and Kuqa Depression, and their sedimentary centers continuously moved northward. In the Early-Middle Jurassic, faulted basins representing post-collision extensional structures developed on the margins of the Tarim Block. In the Late Jurassic, the Tarim Block was compressed, and the faulted basin transformed into a depressional downwarped basin with red coarse clastic sediments due to the collision of the Amdo-Dongkacuo microcontinent with the Tarim Block. In the late Early Cretaceous, the collision between the Lhasa Block and the Tarim Block caused the entire uplift of the Tarim Block, which stopped accepting deposition except for the deposition of marine facies in the southwestern Tarim Basin influenced by a large-scale transgression event. The complex evolution of the Paleo-Tethys and Neo-Tethys Oceans during the Mesozoic significantly influenced the sediment distribution and structural features of the Tarim Basin.

The origin of cap carbonate after the Ediacaran glaciations

Cap carbonate is the most unique component of a Snowball Earth glaciation, i.e., two Cryogenian global glaciations. In the canonical model, cap carbonate precipitation requires a deglacial extremely high atmospheric pCO2 level, which is unique for a Snowball Earth glaciation but did not occur in other non-Snowball Earth glaciations. However, some Ediacaran glacial successions also have a carbonate unit directly overlying the glacial deposits, although the Ediacaran glaciation is widely accepted to be a non-Snowball Earth ice age. Therefore, occurrence of Ediacaran glacial cap carbonate is counterintuitive, challenging the traditional model of cap carbonate precipitation. Here, we investigate two Ediacaran glacial cap carbonates, i.e. the Zhoujieshan cap carbonate above the Hongtiegou glacial deposits in the Chaidam Block, and the Hankalchough cap carbonate overlying the Hankalchough glacial deposits in the Tarim Block. The Zhoujieshan cap carbonate shows a transitional contact with the underlying glacial deposits, and has a nearly invariant carbonate carbon isotope value (δ13Ccarb) of ∼ + 1‰. The Hankalchough cap carbonate from the Luobupo section has a persistent δ13Ccarb value of ∼ − 5‰, but display a ∼ 15‰ spatial isotopic gradient in the Quruqtagh area. Combining with other occurrences, the Ediacaran glacial cap carbonate differs from the Snowball Earth cap carbonate in paleogeographic distributions, sedimentary structures, and mineralogical and geochemical compositions. We noticed that the Ediacaran glacial cap carbonates were restricted at ∼30–50° N/S, which may reflect a rapid transition from glaciation to carbonate deposition in subtropics. Thus, we speculate that the Ediacaran glaciation might have extended to latitude low enough, while the subsequent deglaciation and global warming may associate with an expansion of carbonate precipitation toward higher latitudes. Thus, the Ediacaran glacial cap carbonate precipitation occurred when carbonate precipitation and glaciation spatially overlapped in subtropics. Alternatively, considering paleomagnetic evidence for a ∼ 90° reorientation of all continents due to the Ediacaran true polar wander (TPW) event, some Ediacaran glacial cap carbonates could also be driven by glaciated continents moving into lower latitudes, where glacier melt and carbonate precipitated. Either way, a typical Snowball Earth glaciation may lead to global cap carbonate depositions, while most of Phanerozoic glaciations are characterized by glacial deposits in mid- to high-latitude and carbonate precipitation in tropics, i.e., showing no spatial overlapping of glaciation and carbonate precipitation. Thus, the enigmatic cap carbonate precipitation after the Ediacaran glaciations imply a unique climatic condition that differs from either a Snowball Earth glaciation or a Phanerozoic ice age.

Neoproterozoic reorganization of the Circum- Mozambique orogens and growth of megacontinent Gondwana

The serpentine orogenic belts that formed during the Neoproterozoic assembly of Gondwana resulted in geodynamic changes on the planet in advance of the Cambrian radiation. The details of Gondwana assembly associated with the closure of the Mozambique Ocean are enigmatic. We compile published geological and paleomagnetic data to argue that the Tarim block was associated with the Azania and Afif–Abas–Lhasa terranes and they were the locus of long-lived Andean-type subduction during the ~900–650 Ma interval. Our model suggests a subduction system reorganization between 750-720 Ma, which resulted in two distinct phases of Mozambique ocean evolution. Between 870-750 Ma, a N-S oriented subduction system marks the locus of ocean crust consumption driven by the extension of the Mozambique Ocean. Beginning ~720 Ma, a newly developed ~E-W oriented subduction system began to consume the Mozambique Ocean and led to the assembly of eastern Gondwana. Our new reconstruction uses true polar wander to constrain the relative paleolongitude of Tarim, South China and West Africa. In this scenario, the closure of the Mozambique Ocean and formation of Gondwana was orthogonal to the preceding supercontinent Rodinia.