摘要
笔者在近年来的中国东南沿海花岗岩成因研究中，注意到下地壳之下的岩石圈地幔与下地壳之间必然有着十分密切的关系，认识到壳幔作用的重要形式是发生于壳幔接口的玄武岩浆的底侵作用，它涉及地幔对地壳在“成分”和“热”两方面的贡献。研究表明，本区底侵作用十分发育，是中国东南大陆边缘陆壳演化的重要过程。中国东南部晚中生代早期形成的花岗岩多为 Ｓ型花岗岩，它们主要是板块强烈挤压作用导致地壳增厚，陆壳重熔形成的岩石。而且这期大规模花岗岩浆活动是与弧后拉张、岩石圈减薄、软流圈上涌作用直接有关，早期太平洋板块向欧亚大陆板块俯冲对大陆裂解起了诱导作用。中国东南部晚中生代缝合带的年龄为１００ ～１１０ Ｍａ ，可能代表了晚中生代构造岩浆作用由“挤压地壳增厚○陆壳重熔”向“拉张岩石圈减薄双峰式岩浆作用”机制的转变年龄。
Granitoids are the main component of the continental crust, and the key problem for understanding the structure, composition and evolution of the continental lithosphere. Late Mesozoic calc alkaline magmatism is well developed in the coastal area of southeastern China, and is similar to the magmatism developed in the Basin and Range of North American. During the previous studies on the granites in the coastal area of southeastern China, however, little attention has been paid to the temporally and spatially coexisted A type granite, gabbroic stocks or dikes, as well as the bimodal volcanic rocks (basalt rhyolite composite lavas). The authors have been studying the granites in the coastal area for many years and noticed recently that this region experienced extensive crust mantle interaction at the crust mantle boundary, and underplating was the important process which involved in the chemical and thermal contributions from the mantle to the crust. The petrography, geochemistry and isotope studies for the gabbroic granulite xenoliths from Qilin basaltic pipe in the same region, and integration with the regional geophysical data indicate that gabbroic granulites were formed by underplating of basaltic magmas at the bottom of the crust at ca 112 Ma. This is consistent with the extensive granitic magmatism in the late Mesozoic time along the coastal area of southeastern China. Therefore, underplating plays an important part in the evolution of the continental crust of southeastern China. Most of the granites formed in the earlier stage of late Mesozoic time in southeastern China are S type granites. They might be generated from the partial melting of the deeper crust material under the compressive tectonic setting. While the extensive I type and A type granitic magmatism in the coastal area of southeast China is closely related with back arc extension, lithosphere thinning and asthenosphere upwelling, which may have been induced by the earlier stage subduction of the Pacific plate towards the Eurasian continent. In fact, the late Mesozoic magmatisms along the coastal area have an essentially extension related bimodal character, and apparently, the genesis of granites in the coastal area of southeastern China is directly related with the basaltic magma underplating. The suture age of 100～110 Ma of southeast China may represent the transition age of tectono magmatism from “compression crust thicking continental crust re melting” to “extension lithosphere thinning bimodal magmatism”.
出处
《高校地质学报》
CAS
CSCD
1999年第3期240-250,共11页
Geological Journal of China Universities
基金
国家自然科学基金
