浙江陈蔡群斜长角闪岩的地球化学特征及其大地构造背景探讨

陈蔡群斜长角闪岩的基本组成矿物是斜长石和角闪石,不同样品中还可出现透辉石、黑云母、石英和碱性长石等。大多数斜长角闪岩显示石英拉斑和橄榄拉斑系列的特征,个别属于钙碱性系列。其稀土元素配分曲线显示不同程度的LREE富集特征,指示斜长角闪岩原岩在成岩过程方面的多样性。根据微量元素蛛网图的斜率和Nb、Ta异常情况以及Zr-TiO₂相关性,斜长角闪岩主要分成岛弧和洋岛两种类型,指示陈蔡群的原岩形成于洋内俯冲或洋陆俯冲的环境。龙游八都群斜长角闪岩呈MORB的地球化学特征,与陈蔡群斜长角闪岩形成鲜明的对比

GEOCHEMISTRY OF THE AMPHIBOLITES FROM CHENCAI GROUP, ZHEJIANG PROVINCE: IMPLICATIONS FOR THE TECTONIC SETTINGS

The basic assemblage of the amphibolites is consisted of amphibole and plagi oclase. Other phases include diopside, biotite, quartz and alkali feldspar. Most amphibolites show an iron rich trend, typical of the tholeiitic series, few is in calc alkaline series. The amphibolites are either quartz normative or olivi ne normative. Though in various degrees, LREE rich is a common feature of the am ph ibolites from Chencai Group. The petrogeneses of the provenances are also variab le. Nb and Ta anomalies, the slope of the incompatible element distribution patt erns and the correlation between Zr and TiO 2 show island arc and oceanic islan d signatures, suggesting two sources for the amphibolites in Chencai Group. The co existence of IAB and OIB is indicative of a tectonic setting of ocean ocean or o cean continent subduction. The geochemistry of the amphibolite from Badu Group, southwestern Zhejiang province, has an MORB signature, suggesting a different t e ctonic setting from the central Zhejiang province.