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Multi-stage Mesozoic thrust-nappe and extensional structures are distributed in the east segment of the Southeast Yangtze Block situated in the junction region of Zhejiang-Jiangxi-Anhui provinces. The features and genetic mechanism of the deformations were analyzed after a detailed field observation of their distribution, geometry, and kinematics. In addition, the time sequences of the thrust and extensional structures were determined by combining the results of the comparative analysis with the chronological evidence of strata and magmatic rocks cut by a fault or formed after a fault according to field facts. This study identified three stages of the nappe structures and at least two stages of the extensional structures during the Mesozoic. The geotectonic setting of the nappe and extensional structures was considered to be related to the different geodynamics in the study area including the Early Mesozoic geological event, i.e., N-S compression, forming Lantian fault, etc.; the Late Mesozoic flat-slab subduction, forming Xiaoxi thrust fault and tectonic window; and the roll-back of the paleo-Pacific Plate, forming extensional structures like basin marginal fault; the last compression, forming Wucheng-Shenxian fault. These findings provide additional evidence for remodeling the tectonic and geodynamic evolution of Southeast China. [ABSTRACT FROM AUTHOR]

Large-scale volcanism in the late Mesozoic was a prominent geological event in southeast China. The late Mesozoic volcanic sequences, named the Moshishan Group, are exposed in Zhejiang Province and are predominantly felsic in composition with subordinate mafic magma and rare andesites. To understand the late Mesozoic tectonic evolution of southeast China, we present zircon U–Pb dating, major and trace element analyses, and Hf isotopic compositions from felsic volcanic rocks of the Moshishan Group. Zircon U–Pb dating shows that the Moshishan Group formed between 145 and 129 Ma. The εHf(t) of the analysed zircons ranges from −16.58 to +6.89, and theTDM2age ranges from 753 to 2238 Ma with a major peak at ca. 1870 Ma. Hf isotopic compositions of zircons in Early Cretaceous volcanic rocks are more radiogenic than that of the metamorphic basement rocks, indicating a juvenile component in these magmas. Major element concentrations show that the volcanic rocks mainly belong to the high-K calc-alkaline series. Both zircon saturation temperatures and the εHf(t) values of zircons gradually increased with the evolution of the magma. Trace element data indicates that neither magmatic differentiation of mantle-derived magma nor mixing of magmas from different sources were the predominant magmagenetic processes. Earlier studies suggest that contemporaneous underplating contributed to the heat source that induced crustal melting and to the material origin that inconsistently mixed with the local crustal melts. Magmatic underplating is likely to have occurred because of the southwestward subduction of the Pacific plate with episodic slab rollback. The data obtained in this study suggest that the crust–mantle interaction under the influence of slab rollback played a progressive role in the formation of Early Cretaceous felsic volcanic rocks in southeast China. [ABSTRACT FROM AUTHOR]

• Source region of the Ordovician sandstones suffered stronger weathering than that of the Cambrian sandstones. • Baoshan block was located at Indian margin of East Gondwana in the early Paleozoic. • Subduction initiation of the Proto-Tethys Ocean was at 540-500 Ma. • A shift in the tectonic setting occurred at East Gondwana margin. • Subduction of the Proto-Tethys Ocean and formation of the peripheral orogens provided the driver for ecological evolution. The effect of plate interactions on surface processes, environmental changes of the earth and their contributions to biodiversification during Gondwana assembly has been hotly debated in the last decades. The late Neoproterozoic-early Paleozoic was a key period in the tectonic assembly of Gondwana, global climate change and metazoan evolution. During this interval, the amalgamation of Greater Gondwana was succeeded by the subduction initiation of oceanic slabs in the Proto-Tethys Ocean. Here, we use whole-rock geochemical data, detrital zircon U-Pb and Hf isotopic of Cambrian and Ordovician sedimentary rocks from the Baoshan block in the Southeastern Tibetan Plateau combined with existing data in the literature to constrain the timing of subduction initiation of the Proto-Tethys Ocean at 540-500 Ma. The results show that the Baoshan block, adjacent to the Pinjarra Orogen on the northern margin of India, witnessed the transition from passive to active continental margin in East Gondwana. After the subduction initiation, the source of the sedimentary rocks experienced more intense weathering, causing a higher sediment flux. Contemporaneously, the Cambrian Explosion and stepwise increase in atmospheric oxygen accompanied the Greater Gondwana assembly at the late Neoproterozoic-early Paleozoic boundary. Subduction of the Proto-Tethys Ocean and occurrence of peripheral orogens further increased atmospheric O 2 content, transported nutrients to the ocean and reduced the greenhouse effect, which provided major propulsion for biological evolution. [ABSTRACT FROM AUTHOR]