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The final closure time of the Paleo-Asian Ocean and the Permo-Carboniferous tectonic settings in the northern Alxa are very important but controversial tectonic issues. The geochronology and petrogenesis of mafic igneous rocks are superior in clarifying regional tectonic settings. Here, we report on zircon U-Pb-Hf isotopes, biotite 40Ar/39Ar geochronology and whole-rock geochemical data of the hornblende gabbro from the Baogeqi gabbro pluton in the northern Alxa. The LA-ICP MS U-Pb analysis of zircon grains from the hornblende gabbro yield a weighted mean age of 262.7 ± 2.3 Ma (2σ, MSWD = 0.74), manifesting that the Baogeqi gabbro pluton emplacement was during the late Middle Permian (Capitanian). The 40Ar/39Ar dating of biotite grains from the hornblende gabbro yields a plateau age of 231.3 ± 1.6 Ma (2σ, MSWD = 0.55), indicating that the Baogeqi gabbro pluton cooled to below 300 ℃ in the Triassic. The hornblende gabbro samples are calc-alkaline with metaluminous character, and show enrichment in large ion lithophile elements (e.g., Rb, Ba, Sr, and K) but depletion in Nb, Ta, P, Th, and Ti relative to primitive mantle. Combined with the positive zircon εHf(t) values (+4.9–+9.4), we suggest that the magmas formed from the partial melting of depleted mantle were metasomatized by slab-derived fluids. Together with regional geology, these geochemical data suggest that the Baogeqi gabbro pluton was formed in an intracontinental extension setting, further indicating that the Paleo-Asian Ocean in the northern Alxa was closed prior to the late Middle Permian (Capitanian), and this region was in a post-collision extensional setting during the Capitanian-Late Permian. In addition, the Triassic cooling of the gabbro pluton may be a record of the decline of the Capitanian-Late Permian post-collisional extension basin due to the far-field effect of subduction-collision during the closure of the Paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]

The Permian sedimentary rocks in the Turpan–Hami Basin are key records of the tectonic evolution in the Eastern Tianshan area, although their depositional ages and provenances remain relatively less studied. Here, we conducted detrital zircon U–Pb geochronology on subsurface samples collected from Well LN1 in the Turpan–Hami Basin to understand the depositional ages and provenances of the Permian rocks. In this study, detrital zircon U–Pb ages from the Late Carboniferous Sumuke Formation yielded a notable Permian age population with the youngest single‐grain age at 282.6 Ma. Compiling this result with a published dataset from the surrounding regions of the Turpan–Hami Basin, it shows that the Sumuke Formation was actually deposited in the Early Permian and the Late Carboniferous palynological assemblages within it are of recycled origin. The detrital zircon age spectra of the three Early–Middle Permian samples from Well LN1 define similar unimodal distribution, with prominent late Carboniferous age peaks and scarce Precambrian ages, further indicating that the zircon grains in these three samples should be ultimately sourced from the Jueluotag, the southern branch of the North Tianshan. Regionally, the Bogda, the northern branch of the North Tianshan, as catchment areas recorded interaction between southern and northern sources, and thus, there was a single greater Junggar–Turpan Basin during the Early–Middle Permian. During the latest Middle Permian to Late Permian, provenance shifts occurred at the Jueluotag and the southern piedmont of the Bogda, reflecting the uplift of the Central Tianshan and the Bogda and the isolation of the Junggar Basin and Turpan–Hami Basin. Integrating regional geological studies and provenance evolution trends, we suggest that the Turpan–Hami Basin and its surrounding regions were in a rift setting controlled by post‐collision extension during Early–Middle Permian. By contrast, tectonic contraction and inversion occurred during the latest Middle Permian to Late Permian as a part of the intraplate orogenic process in the Tianshan, which responded to the convergence between the Songpan–Ganzi terrane and palaeo‐Eurasian Plate. [ABSTRACT FROM AUTHOR]

The article focuses on a study which examined the paleoenvironmental conditions associated with the Middle Triassic Luoping Biota in Yunnan, China. Samples of major and trace elements were collected from the Dawazi section. Results of the study showed that the low magnesium oxide/calcium oxide ratio indicate a warm paleoclimate in the Luoping area. The study also observed a deep-sea environment and anoxic conditions in the area.