Jurassic sedimentary features and tectonic settings of southeastern China |
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Authors: | LiangShu Shu Yan Wang JinGeng Sha ShaoYong Jiang JinHai Yu YanBin Wang |
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Institution: | (1) Present address: Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou, 510640, Peoples Republic of China |
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Abstract: | Two types of the Jurassic basins are distinguished in SE China based on their geodynamic features: the Late Triassic-Early
Jurassic post-orogenic basins and the Middle Jurassic intra-continental extensional basins. The Lower Jurassic sequence shows
a change from coarse- to fine-grained accumulation, suggesting a gradually deepening depositional environment from river to
shore-lake and to deep-water lake. In contrast, the Middle Jurassic accumulation was changed from claystone to conglomerate
along the coastal provinces in SE China, indicative of an initial crustal uplift. The Wuyi Mountains have been a paleogeograghic
separating zone since the Middle Jurassic. The Late Jurassic strata are absent in most areas of SE China. A large-scale bimodal
intra-continental rift-type volcanism occurred during the Middle Jurassic along a 40–60 km wide and 200 km long area in western
Fujian and southern Jiangxi provinces, which is most likely the strongest volcanism in SE China since the Cambrian. The SHRIMP
zircon U-Pb analyses on the rhyolite from the Dongkeng basin in the southern Jiangxi area yield a concord U-Pb age of 160±0.5
Ma, providing an upper age limit for the bimodal volcanic eruption. The analyses of the basin features indicate a change of
the depositional environment during the interval from Middle Triassic to Late Triassic from a shallow-sea to an intra-continent
in SE China in response to the strong collision between the Yangtze and North China Blocks. Sedimentary structures record
a southward direction of Early Jurassic paleo-currents, reflecting that their source areas were to the north side. We propose
that the Wuyi region was uplifted as early as Middle Jurassic, followed by a wide E-W-trending extended depression and bimodal
volcanism in the western foot of the Wuyi Mountains. Presumably the uplift of the Wuyi domain changed the Middle Jurassic
paleogeographic outline and formed the transformational tectonic regime from compression to extension as a tectonic response
to the Pacific plate subduction. |
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