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Permian magmatism occurred widely in the Tarim basin and adjacent areas of NW China, resulting in the emplacement of numerous carbonatite plutons and alkaline rock intrusions, which are likely to have been derived from mantle sources. In addition, at least one large igneous province (LIP) can be recognized in NW China; namely, the ca. 270–290 Ma Tarim LIP, and it can be inferred that the peak age of magma activity is ~ 280 Ma. Therefore, the mantle plume is limited spatially within southern Tianshan and the Tarim Basin and temporally in the Early Permian. Age and field evidence suggest a spatial and temporal relationship between the carbonatites and alkaline rocks within the Tarim LIP, and their genesis is related to the Tarim mantle plume. In this paper, we direct our attention to the mineral assemblages that are related to carbonatites and alkaline rocks which host REE deposits (Wajilitag, Boziguoer) in the northern Tarim Craton. Alkaline rocks typically are related to rifts and/or extensional tectonics, and we suggest that these magmatic and metallogenic events occurred during an extensional regime, possibly related to the Tarim mantle plume event that affected much of South Tianshan during the Permian. [ABSTRACT FROM AUTHOR]

The southern Altaids is of critical significance for a better understanding of the orogenic architecture and continental growth in Central Asia. The tectonic setting of the South Tianshan, a typical Paleozoic accretionary orogen within the southern Altaids, is controversial. This study reports new structural relations, geochemistry, and geochronology of previously assigned Late Silurian–Early Devonian strata in the Karaghol area of the South Tianshan. The constituent rocks are pillow basalts, ribbon cherts, limestones, siliceous mudstones, and turbiditic sandstones. Field relations show that these rocks are characterized by fault-bound tectonic slices and mélanges with typical block-in-matrix structures. The pillow basalts show N-MORB, E-MORB, and OIB geochemical fingerprints, and our new LA-ICP-MS zircon U–Pb dates indicate that the maximum eruption age of the OIB-type basalts was ca. 386 Ma, whereas the Maximum Depositional Ages (MDAs) of the turbiditic sandstones were ca. 369 Ma and 355 Ma. The age spectra of the detrital zircons, which define prominent peaks at ca. 370 Ma, ca. 420 Ma, ca. 770 Ma, ca. 960 Ma with subordinate Proterozoic ages, are a good match with the igneous ages of intermediate to felsic magmatism in the Yili–Central Tianshan arc. We conclude that the previously assigned Late Silurian–Early Devonian strata in the Karaghol area are mostly dismembered structural components and mélanges that belonged to an accretionary complex of Late Devonian to Early Carboniferous age, into which fragments of a Late Devonian seamount along with South Tianshan oceanic crustal rocks were likely emplaced during north-dipping subduction in the Early Carboniferous. This well-documented accretionary orogen in the Chinese South Tianshan is a key constraint on the accretionary orogenesis of the southern Altaids. [ABSTRACT FROM AUTHOR]

• Rb-Sr dating indicated strata-bound mineralization at 791 Ma and vein-type mineralization at 380 Ma. • RF classification confirmed strata-bound mineralization as sedimentary and vein-type mineralization as magmatic-hydrothermal. • A two-episode mineralization model was proposed at the Haerdaban deposit. The Haerdaban Pb–Zn deposit, located in the eastern West Tianshan Orogen, hosts stratiform and vein-type mineralization within Precambrian carbonate rocks. However, there has been limited research on the distinctions and relationships between these two mineralization styles. In this study, we compared trace element distributions, fluid conditions, material sources, and mineralization ages between stratiform and vein-type mineralization and reconstructed a detailed genetic model. Two episodes and four stages of mineralization were identified, including five generations of pyrite and two generations of sphalerite. The sedimentary exhalative episode represents stratiform mineralization including Stage I pyrite–pyrrhotite layers (Py-1, Py-2a, Py-2b, and Py-3) and Stage II sphalerite–galena layers (Sph-1). The magmatic–hydrothermal episode represents vein-type mineralization including Stage III pyrite–quartz–calcite veins (Py-4) and Stage IV sphalerite–galena–quartz–calcite veins (Sph-2). LA–ICP–MS analysis of Se–Co–Ni–As–Ag–Sb–Bi contents in pyrite suggests that Py-1 to Py-3 formed under relatively low temperatures (280 ± 8 °C) and high ƒO 2 sedimentary conditions. Py-4 formed under relatively high temperatures (339 ± 18 °C) and low ƒO 2 hydrothermal conditions. Variations in Fe–Mn–In–Ga–Ge–Cd–Cu contents in sphalerite indicate that Sph-1 formed under relatively low temperature (211 ± 7 °C), intermediate ƒS 2 (logƒS 2 = −11.1 ± 0.5), and moderate pH sedimentary exhalative conditions. Sph-2 formed under relatively high temperature (292 ± 5 °C), high ƒS 2 (logƒS 2 = −7.4 ± 0.2), and low pH hydrothermal conditions. In situ analysis of sulfide S–Pb suggests that ore-forming materials for stratiform mineralization were primarily derived from marine sediments, while those for vein-type mineralization primarily originated from magmatic sources. Sph-1 from stratiform mineralization yielded an Rb–Sr isochron age of 719 ± 16 Ma, while Sph-2 from vein-type mineralization exhibited an Rb–Sr isochron age of 380.3 ± 7.7 Ma. Random Forest classification of trace elements in pyrite and sphalerite predicted that stratiform mineralization is of sedimentary genesis, whereas vein-type mineralization is of magmatic–hydrothermal genesis. Based on our results, we identified a two-episode mineralization history for the Haerdaban Pb–Zn deposit: Neoproterozoic syngenetic sedimentary exhalative mineralization overprinted by Devonian epigenetic magmatic–hydrothermal mineralization. The results of this study highlight the importance of considering multiple geological events in ore-forming processes and will facilitate the exploration of similar deposits in the West Tianshan Orogen. [ABSTRACT FROM AUTHOR]

The Pamir orogen originated through the amalgamation of various arc terranes. Despite undergoing numerous studies, the subduction polarity and time regarding the accretion processes remain inadequately constrained. To address these issues, we carried out a detailed study of zircon and apatite U-Pb ages, zircon Hf isotopes, and whole-rock geochemistry for the Permian to Cretaceous gabbro, volcanic rocks and granitoids from the Southern Pamir and the Rushan-Pshart suture. Three stages of magmatism are identified, including 279–266 Ma gabbro and andesite to dacite, 209–208 Ma granitoids, and 108–103 Ma gabbro and granitoids, respectively. The Permian gabbro and basaltic andesite to dacite in Pshart Range are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), but are depleted in Ta, Nb, and Ti, suggesting formation from an enriched mantle source in a subduction zone. The Late Triassic I-type granitoids are typical arc calc-alkaline magmatic rocks with ε Hf (t) values varying from −8.7 to −3.5, which mainly sourced from the partial melting of mixed crustal sources predominately consisting mafic rocks with minor metasedimentary rocks. The Early Cretaceous Pshart granites are I-type granites with relatively low ε Hf (t) values ranging from −14.6 to −2.9, suggesting that they were crust-derived rocks. The Early Cretaceous Bazardara granites are identified as A 2 -type granites with the ε Hf (t) values ranging from −18.3 to +5.3, and were derived from mixing of mantle-derived and crust-derived magmas, or interaction between mantle melts and old crustal rocks. The early Cretaceous gabbro exhibits -MORB-like geochemical characteristics with flat REE pattern (La/Yb N = 4.96), moderate enrichment of LILEs and weak depletion of Nb, Ta and Ti (Nb/La PM = 0.94). Thus, the early Cretaceous A 2 -type granite, E-MORB-like gabbro and volcanic rocks were formed in an extensional setting. Our new data indicate that the southward subduction of the Rushan-Pshart oceanic slab started in the Early Permian and continued to the Late Triassic. Moreover, combining the previous data, we conclude that the Early Cretaceous granites and gabbro in the Southern Pamir formed in an extensional environment due to the southward rollback after northward near-flat subduction of the Neo-Tethyan oceanic lithosphere. [Display omitted] • Permian, Triassic, and Cretaceous arc rocks are identified in the South Pamir. • Southward subduction of the Rushan-Pshart Ocean began before the Permian. • The southward subduction formed the late Triassic I-type granites. • Slab roll-back of the Shyok Ocean caused within-plate magmatism in the South Pamir. [ABSTRACT FROM AUTHOR]

The widespread Late Paleozoic-Early Mesozoic magmatism in the Eastern Tianshan provides critical insights into geodynamic evolution of the southern Altaids. In this study, we conduct an integrated study of field geology, petrology, U-Pb zircon geochronology and major-trace elemental and Sr–Nd–Hf isotopic geochemistry on the Late Carboniferous monzogranite and diorite dyke and the Late Triassic gabbroic diorite dyke in the central part of the Eastern Tianshan. Geochronological data indicate that the monzogranite, diorite dyke and gabbroic diorite dyke formed at ∼318 Ma, ∼317 Ma and ∼235 Ma, respectively. The Late Carboniferous monzogranite shows transitional characteristics between highly fractionated and A-type granites, with relatively high zircon saturation temperatures (800–836 °C). It was derived by partial melting of juvenile infracrustal rocks, followed by plagioclase-dominated fractional crystallization. The Late Carboniferous diorite dyke has high Al 2 O 3 contents (mostly >17 wt%) and Ba/La ratios, indicating an origin from a hydrous lithospheric mantle source that had been metasomatized by slab-derived fluids. The Late Triassic gabbroic diorite dyke, with relatively high Mg# values (57–58) and Th contents (3.28–3.46 ppm), originated from a less hydrous lithospheric mantle source containing significant sediment-derived components. Our new results, combined with previous studies, reveal an end-Early Carboniferous to middle Late Carboniferous magmatic flare-up in the Dananhu arc. The magmatic flare-up occurred in a long E -W trending banded zone parallel to the strike of the arc and was accompanied by significant normal arc magmatism, which widely migrated to the south of the Dananhu arc in comparison to prior magmatism. These together with coeval extension-related volcanic, sedimentary, structural and metamorphic events in the Dananhu and adjacent areas were attributed to southward rollback of the subducted Kanguer oceanic slab. The long-time arc magmatism and regional crustal thickening before the Late Triassic led to the formation of an arclogite-bearing root beneath the Dananhu arc. The Late Triassic extension-related magmatism in the Dananhu arc, which was synchronous with or slightly younger than regional thickened crust-derived magmatism, was linked to the local root foundering of the long-lived Dananhu arc at the late stage of orogenesis. The episodic occurrence of geodynamic processes such as slab rollback, arc root foundering and ridge subduction/slab tearing, which were accompanied by massive input of juvenile materials into continental crust, contributed to multi-stage significant crustal growth in southern Altaids. [Display omitted] • Ferroan granite and two phases of dioritic dykes in Eastern Tianshan were identified. • End-Early Carboniferous to Late Carboniferous slab rollback occurred beneath Dananhu. • Late Triassic magmatism in Dananhu was related to local arc root foundering. [ABSTRACT FROM AUTHOR]