青藏高原内部三条磨拉石带的确定及其构造意义

造山带地球化学研究的目标主要是为重建古板块构造格局服务，其次是探讨古造山带不同演化阶段岩石的形成、演化、变质及其所反映的大陆动力学和深部地幔过程。造山带演化分为5个阶段，各个阶段的火成岩具有不同的特征，地球化学研究的任务就是要识别出各个阶段岩石产物的特征、来源、成因和形成环境。文中着重讨论了造山带火成岩的若干地球化学问题。笔者指出：蛇绿岩主要分为岛弧拉斑玄武岩（IAT）和MORB两种，最近的研究发现，蛇绿岩中有来自富集地幔的信息。岛弧火山岩突出的地球化学特征是富集大离子亲石元素、ω（Th）＞ω（Ta）和Nb，Ta亏损，这是由于消减带物质加入的结果，本质上是一个（深源）陆壳混染的问题。花岗岩可能是幔源与壳源之间混合的连续谱系，花岗岩成因类型的控制因素主要是不同类型的源岩而不是构造环境。双峰式火山岩的成因比原先想象的要复杂，可以产于各种构造环境。文中还讨论了造山带地球化学研究方法的问题。

造山带火成岩地球化学研究

The geochemical study of orogenic belts is aimed at reconstructing the tectonicregime of paleo-plates, and discussing the formation, evolution and metamorphism of rocks invarious evolutionary phases and corresopding continental geodynamics as well as deep mantleprocess. The purpose of geochemical study on different igneous rocks in orogenic belts is to i-dentify the significance, source, genesis and environment of the rocks in the evolutionary histo-ry of orogenic belts, which is generally divided into five phases. This paper is mainly concernedabout the geochemical study of igneous rocks in orogenic belts. It is suggested that (1) ophio-lites have two main types, island-arc tholeiite(IAT) and mid-oceanic ridge basalt(MORB) andthey may also be derived from the enriched mantle; (2) island-arc volcanic rocks are character-ized by enriched large ion lithophile elements(LILE), ω(Th) >ω(Ta) and depleted Nb, Ta,which are caused by the mixture of slab-derived components, but actually as a result of hy-bridization in deep continental crust; (3) granites may be in the mixed continuous spectrumranging from rmantle to crust source, and the genetic types of granites are mainly controlled bydifferent source rocks, not by tectonic environments; (4) the genesis of bimodal volcanic rocksis much more comlicated than that has been learnt before, and they can be developed in vari-ous geological settings. Additiondly, the geochemical methods on the research of orogenic beltsare also discussed in the paper.