Geochemical discussion on Paleo-Mesoproterozoic basement crust of Yangtze and Cathaysia cratons in southern China: Using trace elements as tracers
Geochemical discussion on Paleo-Mesoproterozoic basement crust of Yangtze and Cathaysia cratons in southern China: Using trace elements as tracers
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发表时间：
2000
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通讯作者：
Chen Ying-jun
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作者：
Chen Ying-jun
大陆地壳的起源和生长是地质学家研究的热点之一。大量资料表明，早期大陆地壳是在地幔部分熔融产生的岩浆侵入或挤压作用下逐渐长大的。但后期地壳的横向生长是在早期垂直分异生长的基础上的部分调整。因此，相近相容元素的地球化学行为追踪了岩石圈同一区域内各种地质体的物质来源和后期过程。遵循这一思路，以华南扬子克拉通和华夏克拉通变质基底衍生的相似岩石（陆相碎屑岩、变基性火山岩和晋宁期花岗岩）为研究对象，选取7对相容性密切的元素（Rb/Cs、Sr/Ba、Th/U、Nb/Ta、Zr/Hf、Pd/Pt、Cr/Ni）作为示踪元素。对华南大陆古中元古代基底物质来源及后期发育特征的讨论表明：（1）扬子—华夏克拉通古中元古代基底陆源碎屑岩高场强元素整体表征的相似性，揭示了两地古元古代克拉通初始地壳物质组成的相似性。但晋宁期两个克拉通花岗岩的高场强元素比例与基底陆源碎屑岩的高场强元素比例基本一致，这或许表明高场强元素对于追溯陆源物质的继承具有重要意义。 (2)华夏克拉通基底陆源碎屑岩和晋宁期花岗岩中大离子亲石元素的含量和比例变化与扬子克拉通存在明显差异,这可能与①扬子克拉通和华夏克拉通所处的构造位置不同;②华夏克拉通较扬子克拉通经历了更强的后期叠印和改造作用;③同一地区不相容元素的块体效应有关。岩石圈区域值得进一步研究。
The origin and growth of continental crust is one of the hot points for geologists. A vast amount data discloses that early stage continental crust grew up gradually by the intrusion or extrusion of the magma that results from mantle partial melting. However, the crosswise growth of the later stage crust is the partly adjustment based on the early growth of vertical differentiation. Therefore, the geochemical conduct of the close compatibility elements traces the material-source and later process of various geologic bodies in the same area of lithosphere. Following this idea, the similar rocks (terrigeous clastic rocks, meta-basic volcanic rocks and Jinning period granitoid) that derived from the metamorphism basement of southern China Yangtze craton and Cathaysia craton were considered as objects of study, and seven couples of close compatibility elements (Rb/Cs, Sr/Ba, Th/U, Nb/Ta, Zr/Hf, Pd/Pt and Cr/Ni) are selected as tracer elements. The discussion of characterization of the material-source and later growth of the Paleo-Mesoproterozoic basement of southern China continent indicates that (1) the similarity of overall characterization of high field strength elements of terrigeous clastic rock of the paleo-Mesoproterozoic basement of Yangtza-Cathaysia cratons traces the similar material composition of the initial crust of the two cratons of Paleoproterozoic. However, the ratio of high field strength elements of granite of the two cratons of Jinning period is nearly consistent with that of terrigeous clastic rocks of the basement, maybe indicates that high field strength elements are significant to trace the inheritance of continent source material. It also indicates that (2) the change of the content and ratio of the large ion lithophile elements of Cathaysia craton in the basement continent-derived clastic rocks and Jinning period granitoid, evidentially differs from that of Yangtze craton, which possibly traces that① Yangtze and Cathaysia cratons occupy different structural position;② Cathaysia craton experienced stronger later overprint and reformation compared with Yangtze craton;③ the block effect of the incompatible elements in the same area of lithosphere is worthy of further study.