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The changing origins of the late Paleozoic calc-alkaline magmatic rocks in the Bogda tectonic belt (BTB) during the Late Carboniferous–Early Permian bring new insights into the subduction-collision processes in the eastern Tianshan region. Based on the geochronological, geochemical and Sr–Nd–Hf isotopic data, a systematic study was conducted on the Late Carboniferous andesite and the Early Permian diabase dyke and MME-bearing granite porphyry from the Dalonggou area in the northern BTB. The ~310 Ma andesites are featured by low initial 87Sr/86Sr ratios, positive ε Nd (t) (+4.4 to +5.3) and ε Hf (t) (+10.2 to +13.6) values, enrichment in light rare earth elements and large ion lithophile elements, and depletion in Nb and Ta. They are interpreted as the products of partial melting of a metasomatized depleted mantle wedge in an extensional arc environment. The ~290 Ma diabase dykes exhibit a nearly flat REE pattern, low Fe/Mn ratios (53–59), and high TiO 2 and Zr contents and mantle potential temperatures (1471–1480 °C). They were derived from a sub-slab asthenospheric mantle with the involvement of the lithospheric mantle. The MMEs were produced by fractional crystallization of the diabase magmas, and the host granite porphyries were formed by magma mixing between melts derived from the newly-formed lower crust and mantle. These results indicate that the BTB represented a backarc/intra-arc rift during the Late Carboniferous that was transitioned to a post-collisional rift in the Early Permian, witnessing a dynamic switch from rollback to detachment of the subducted North Tianshan oceanic slab. Combined with the variation of magma sources with time, we propose that the collision between the Dananhu-Harlik arc and the Central Tianshan arc and the closure of the North Tianshan Ocean occurred at ca. 310–302 Ma. Such a scenario agreed well with coeval tectonics in the Karamaili area, shedding light on the late Paleozoic spatio-temporal tectonic evolution in the eastern Tianshan. • Late Carboniferous and Early Permian magmatic rocks in the BTB display diverse origins. • Two stages of rift events were recognized in the BTB during the late Paleozoic. • The BTB underwent a tectonic switch from backarc/intra-arc to post-collisional setting. • The closure of the North Tianshan Ocean took place in the late Carboniferous. [ABSTRACT FROM AUTHOR]

Rare earth mining can cause ecological problems as a result of soil erosion and water pollution in local areas. Thus assessing the development trends of ecological safety is crucial in formulating the environmental protection policies in rare earth area. Rare earth mining is a long and complicated process in which the state values of evaluation indicators for ecological safety are dynamic and continual interplay. Hence, conventionally measured indicators are inadequate in this context. An evaluation method based on the theory of quantitative scenario analysis was proposed in this study to analyze ecological safety development trends in rare earth mining areas. First, according to the PSR model framework, six indicators including "mining technology", "mining intensity", "water environment", "soil environment", "waste water, waste gas and waste residue management technologies" and "environmental protection policy", were selected to reveal the ecological safety in mining areas. Second, the crossover probability algorithm, Markov chain and nonlinear programming were utilized to construct a quantitative scenario analysis model for ecological safety development trends. Lastly, the model was verified using the data on Lingbei rare earth mining area located in Ganzhou City, China. Results showed that the quantitative scenario analysis model could be used to calculate the changes in various indicators, their cross impacts in the development process and the occurrence probability of scenario combinations for ecological safety development that were composed of the state changes of each indicator. These findings indicate that the proposed model can effectively and accurately forecast the ecological safety development trends in rare earth mining areas. The conclusions can provide a theoretical basis for environmental protection work in rare earth mining areas. [ABSTRACT FROM AUTHOR]

The tectonic–sedimentary environment of the Upper Yangtze Basin in China underwent significant changes from the Late Ordovician to Early Silurian. The widely distributed shale formed during this interval has recorded key information about paleo-ocean conditions. Analysis of major, trace and rare earth elements was conducted on 135 shale samples collected from five wells in the study area. The covariation of the Mo U enrichment factors indicates that the Upper Yangtze Basin in the Wufeng stage was characterized by sedimentary differentiation. The southern basin was dominated by a reducing bottom water environment under euxinic conditions. The northern and central basins were dominated by a suboxic–anoxic environment. Up to the early Longmaxi stage, the Upper Yangtze Basin formed a relatively uniform sedimentary environment with gradually increasing oxygen content in the bottom water. The paleoproductivity index indicates that marine organisms flourished in the Wufeng to early Longmaxi stages, making an important contribution to the siliceous content in organic-rich shale; subsequently, terrestrial siliciclastics gradually dominated. Analysis of paleogeography, rare earth elements, and weathering indicates that Chuanzhong and Qianzhong uplifts in the Wufeng stage were the provenance area of the Upper Yangtze Basin, with a relatively high weathering degree. Weathering decreased in the beginning of the Longmaxi stage and then gradually increased, with the Xuefeng Uplift becoming the main provenance areas after the early Longmaxi stage. Controlled by stress transfer from the continuous syn–Caledonian Kwangsian Orogeny in eastern South China, the Upper Yangtze Basin and Xiangzhong Basin were squeezed and pushed up successively. The uplift separated the open shallow sea and formed a relatively limited deep-water shelf environment, resulting in a relatively euxinic bottom water environment, which was favorable for organic matter accumulation. The tectonic–sedimentary evolution of the Upper Yangtze Basin in the Late Ordovician to Early Silurian proposed in this study indicates that the formation of organic-enriched shale was not only related to glacio-eustatic change but also strongly controlled by tectonic activities in South China. • The uppermost Ordovician and lowermost Silurian shale were formed in different sedimentary environments. • The organic-enriched black shale was formed in a relatively euxinic bottom water environment. • The Xuefeng Uplift became the main provenance area for basin in the later Longmaxi stage. • The formation of shale were controlled by the global sea-level changes and tectonic activities. [ABSTRACT FROM AUTHOR]