Neoproterozoic sequences along the Dexing-Huangshan fault zone in the eastern Jiangnan orogen, South China: Geochronological and geochemical constrains

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• 作者：Xianbing Xu ; Dejie Xue ; Yuan Li ; Peng Hu ; Nengsong Chen
• 关键词：Detrital zircon ; U&ndash ; Pb geochronology ; Dexing&ndash ; Huangshan fault zone ; Jiangnan orogen ; South China
• 刊名：Gondwana Research
• 出版年：January, 2014
• 年：2014
• 卷：25
• 期：1
• 页码：368-382
• 全文大小：2712 K

文摘

The Neoproterozoic Xikou Group is unconformably overlain by the Heshangzhen Group in the eastern Jiangnan orogen, South China. Samples from the Xikou and Heshangzhen Groups have generally intermediate to high SiO₂ (53.14-77.48 wt.%, average 65.33 wt.%) and Al₂O₃ (11.53-27.14 wt.%, average 18.96 wt.%) contents, typical of immature lithic varieties. Compared to the Xikou Group, the Heshangzhen Group has higher Al₂O₃ (average 21.19 wt.% for the Heshangzhen Group and 18.33 wt.% for the Xikou Group, respectively) and Fe₂O₃* + MgO (average 9.38 wt.% and 8.86 wt.%) contents, but lower SiO₂ (average 59.79 wt.% and 66.91 wt.%) content, suggesting that the Heshangzhen Group has more mafic components. The Chemical Index of Alteration (69-81) and the high Th/U ratios (> 3.8) indicate moderate weathering of the source area. Rare earth element patterns suggest that the source rocks came from an upper continental crust composed chiefly of felsic rocks. Discrimination diagrams reveal a mixed provenance of granitic and felsic volcanic components with minor old sedimentary component.

Detrital zircon U-Pb ages and previous geochronological data of granitic plutons indicate that the Xikou and Heshangzhen Groups were deposited at 840-820 Ma and 810-780 Ma, respectively. The Xikou Group was deposited in a back-arc basin and its source rocks came mainly from the Yangtze Block. The Heshangzhen Group formed in a post-orogenic setting with a provenance of the Yangtze Block and the Shuangxiwu arc. The Jiangnan orogen was built at 820-810 Ma after the final suturing between the Yangtze and the Cathaysia Blocks. This orogen collapsed shortly following the collision (within 10-20 million years) and formed the Dexing-Huangshan normal fault zone.