LA-ICP-MS U-Pb zircon geochronology of the Neoproterozoic igneous rocks from Northern Guangxi, South China: Implications for tectonic evolution
LA-ICP-MS U-Pb zircon geochronology of the Neoproterozoic igneous rocks from Northern Guangxi, South China: Implications for tectonic evolution
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DOI：
10.1016/j.precamres.2005.11.014
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发表时间：
2006-03
影响因子：
3.8
通讯作者：
Xiaolei Wang;Jincheng Zhou;J. Qiu;W. Zhang;Xiaoming Liu;G. Zhang
中科院分区：
文献类型：
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作者：
Xiaolei Wang;Jincheng Zhou;J. Qiu;W. Zhang;Xiaoming Liu;G. Zhang
元古宙江南造山带西端位于华南北方桂北。区内新元古代花岗岩类占绝对优势（>90%），约占100%。8%为镁铁-超镁铁岩。这些火成岩的产生此前被认为与导致罗迪尼亚超大陆分裂的地幔柱（或超级地幔柱）事件有关。本文报道了广西北方火成岩的激光剥蚀-ICP-MS锆石U-Pb数据。寨滚岩体、本东岩体、东马岩体、三房岩体和天蓬岩体的年龄分别为835.8±2.5、822.7±3.8、824±13、804.3±5.2和794.2±8.1Ma，何家湾层状辉绿岩的年龄为811.5±4.8Ma。这些年龄表明了岩浆活动的广泛持续时间（约。这与羽流模型预测的大范围岩浆喷发和侵位在1- 500万年之间不一致。桂北方花岗岩类是典型的S型花岗岩，具有较高的ACNK值（1.10-1.87），在构造判别图解中一般都标绘在碰撞相关区。它们不应该是地幔柱活动的产物。相反，它们可能与扬子陆块和华夏陆块之间的陆-陆碰撞造山作用有关。通过对8个锆石岩心和2个单颗粒锆石捕虏体的现场分析，给出了新元古代早期的年龄，范围约为1000 - 2000年。870-950Ma。这些年龄可能记录了北方950- 870 Ma期间的俯冲或碰撞岩浆事件。结合前人的年代学和地球化学资料，新的测年结果支持桂北方835- 800 Ma花岗岩和基性岩的成因为碰撞后伸展，而不是地幔柱或超地幔柱模式。俯冲板片拆离和岩石圈拆沉引起的深地幔上涌，可能导致陆壳部分熔融，形成S型花岗岩。沿江南造山带沿着的陆-陆碰撞造山事件可能跨越约1000年。新元古代早期俯冲作用可能持续约7000万年。一亿三千万年。据此推测，华南在约8000年时可能位于罗迪尼亚超大陆的西缘。870-800Ma。
The western end of the Proterozoic Jiangnan orogen is located at the Northern Guangxi, South China. Neoproterozoic granitoids are dominant (>90%) in the area, with ca. 8% being the mafic-ultramafic rocks. The generation of these igneous rocks was previously considered to be related to a mantle plume (or superplume) event that led to the breakup of the Rodinia supercontinent. In this work, we present new laser ablation-ICP-MS U-Pb zircon data for the igneous rocks from Northern Guangxi. The ages for the Zhaigun, Bendong, Dongma, Sanfang and Tianpeng granitic plutons are 835.8±2.5, 822.7±3.8, 824±13, 804.3±5.2 and 794.2±8.1Ma, respectively, and the Hejiawan layered diabases are 811.5±4.8Ma. These ages indicate a broad duration of magmatic activities (ca. 35million years), inconsistent with plume models that predict widespread magmatic eruption and emplacement within period of 1–5million years. The granitoids in Northern Guangxi are typical S-type granites with high ACNK values (1.10–1.87), and are generally plotted in the collision-related areas in the tectonic discrimination diagrams. They should not be the products of the mantle plume activity. On the contrary, they might be related with the continent–continent collisional orogeny between the Yangtze and Cathysia blocks. A total of eight spot analyses of zircon cores and two from single zircon xenoliths gave early Neoproterozoic ages ranging from ca. 870–950Ma. These ages might record subduction or collision-related magmatic events during 950–870Ma in Northern Guangxi. Combined with previous geochronological and geochemical data, our new dating results support post-collisional extension, instead of mantle plume or superplume model, for the genesis of 835–800Ma granites and mafic rocks in Northern Guangxi. The upwelling of deep mantle due to the detachment of subducted slab and the delamination of the lithosphere might cause partial melting of the continental crust to generate S-type granites. The continent–continent collisional orogenic event along the Jiangnan orogen may have spanned ca. 70million years from 870 to 800Ma, and the early Neoproterozoic subduction might last for ca. 130million years. It is proposed that South China might have been located at the western margin in the Rodinia supercontinent during the period of ca. 870–800Ma.