扬子地台西南缘朱家坝辉绿岩地球化学特征及其地质意义

近年来在扬子西缘大量的早—中元古代岩浆岩证据显示扬子地台内形成的断陷盆地及早中元古代岩浆岩与全球性的Columbia超大陆裂解事件有着密不可分的联系。这种联系主要表现在区内早中元古代的岩浆岩地球化学特征上。为了探讨武定裂陷槽朱家坝辉绿岩的地球化学特征及其意义,以12块朱家坝辉绿岩的地球化学分析数据为基础,在分析了其主微量和稀土元素的特征之后发现朱家坝辉绿岩w(SiO_2)为44.16%～48.08%,w(K_2O+Na_2O)为3.54%～4.26%,在化学成分上属于钙碱性岩石;其稀土元素的总量为183.1×10^-6～206.91×10^-6,LREE/HREE=1.44～1.96,表明在其形成过程中发生了明显的地壳混然或者是岩浆分异作用,其化学成分基本可以反映出岩浆源区的化学组成特征。基于此,对朱家坝辉绿岩进行了源区性质、构造环境和可能的成因机制探讨,认为朱家坝辉绿岩形成于拉张环境之中,很有可能是在昆阳裂谷形成初期形成,其岩浆来源于较富集的地幔源区,形成过程中几乎没有地壳物质参与。

GEOCHEMICAL CHARACTERISTICS AND SIGNIFICANCE OF ZHUJIABA DIABASE IN THE SOUTHWEST MARGIN OF YANGTZE PLATFORM

The geochemical characteristics of early-middle Proterozoic igneous rocks in the west margin of Yangtze platform shows that the magmatic activity is closely related to the global Columbia supercontinent splitting event.12 diabase samples at Zhujiaba area of Wuding rift trough are collected and the characteristics of major trace elements and rare earth elements are analyzed and studied.It shows that the w(SiO2) content of Zhujiaba diabase is 44.16%~48.08%,w(K2O+Na2O) is 3.54%~4.26%.Total amount of REE is 183.1×10^-6~206.91×10^-6,LREE/HREE=1.44~1.96.Based on the geometrical characteristics,the Zhujiaba diabase is discussed in terms of its source area property,tectonic environment and possible genetic mechanism.It is considered that the Zhujiaba diabase is formed in the extensional environment and probably in the early stage during the formation of Kunyang rift.The magma is originated from the enriched mantle source area and almost no crustal material is involved in the formation process.