四川盐边元古代蛇绿岩中辉石的成因矿物学及其大地构造意义

本文用电子探针分析了岩浆型残余辉石的化学成分，建立了辉石组分之间的相关关系和定量的类质同象交换式，并讨论了母岩浆成分、结晶条件（压力、冷凝速度）对辉石成分的影响。深成岩和火山岩中辉石的标型元素含量和相关参数十分相近，说明深成─火山岩系为同源岩浆成因。尽管一些火山岩样品中辉石的Ａｌ，Ｔｉ因快速冷凝而富集，但总体化学成分仍明显显示拉斑玄武岩特征，与世界上典型的显生宙蛇绿岩熔岩及现代洋中脊玄武岩中的辉石相似，但与岛弧有关的火山岩明显不同。这说明。盐边元古代蛇绿岩很可能形成于一个继大陆裂谷之后的海洋扩张环境。本文提供的成因矿物学资料有助于理解和重建扬子板块西缘元古代造山带的地质历史。

GENETIC MINERALOGY OF PYROXENES FROM THE YANBIAN PROTEROZOIC OPHIOLITES(SICHUAN,CHINA),AND ITS GEOTECTONIC IMPLICATIONS

In this paper,relics of magmatic pyroxenes have been analyzed by microprobe. Thecorrelation between their components and the quantita tive sustitution formulas have been stab-lished.The effects of compositions of parent magma and crystallization condition(including pres-sure, cooling rate)on those of magma have also been discussed. The indicator-elements and ratiosof the pyroxenes in plutonic and volcanic sequences are very similar,suggesting a co-magmatic o-rigin for them. In spite of an enrichment in Al and Ti caused by high cooling rate in some sam-ples from the volcanics, the overal chemical compcoitions of the pyroxenes disptay a tholeiiticaffinity,comparable to those of pyroxenes of typical high-Ti Phanerozoic ophiolite volcanics andmodern mid ocean ridge basalts. Meanwhile, they are quite different from those of pyroxenes inthe rocks related to an island arc,implying that the Yanbian Proterozoic ophiolites would havebeen formed in an oceanic sprcading setting after continental rifting.This work provides some ge-netic mineralogical arguments helpfuI to understandi8 and reconstruction of the geological historyof Proterozoic orogenic belt on the western border of the Yangtze Plate.