牡丹江地区蓝片岩的地球化学特征及其大地构造意义

牡丹江地区的蓝片岩分布于牡丹江东部的椅子圈、磨刀石等地。野外调研表明:牡丹江蓝片岩主要呈透镜体状或构造残片状发育在长英质片岩中,并部分可见变余枕状构造和气孔状构造;主量元素岩石化学分析得到这些蓝片岩为亚碱性玄武岩组合;稀土元素标准化配分曲线与洋中脊环境(E-MORB)配分曲线一致;微量元素蛛网图曲线也与E-MORB一致,部分易活动元素(Ba,Sr等)一定程度的分异应与海相玄武岩形成时遭受海水蚀变或后期绿片岩相变质有关。代表性蓝片岩的地球化学特征表明,牡丹江地区蓝片岩的原岩形成于大洋板块内的洋中脊环境。因此,黑龙江蓝片岩应为佳木斯地体向西与松嫩地块之间碰撞拼贴而形成的具有蛇绿岩性质的高压变质带;而目前保存下来的蓝片岩带应为遭受高压变质作用并仰冲到佳木斯地块之上的大规模增生杂岩带的残余部分。结合作者近年取得的牡丹江地区蓝片岩SHRIMP锆石年龄210～250 Ma和变质云母等单矿物180～190 Ma的年代学证据,证明它们为晚二叠世—晚三叠世的玄武岩经过印支期前后高压变质而形成。黑龙江蓝片岩带的形成是印支期前后古亚洲构造域向环太平洋构造域转换的结果,即黑龙江杂岩带为典型的构造转换带——古亚洲洋构造拼合的结束和环太...

Geochemical Characteristics of the Mudanjiang Blueschists in the NE China and Its Tectonic Implications

The Mudanjiang blueschists are the typical outcrop of the Heilongjiang high pressure metamorphic rocks in NE China.The Mudanjiang blueschists occur as tectonic lenses and/or tectonic fragments which mainly distributed in the area of Yiziquan and Modaoshi along the Mudanjiang fault.The protolith of the blueschists is the subalkali-basalt according to their geochemical characteristics.Both the REE patterns and spidergrams of trace elements for these basalts are similar to that of the typical E-MORB.This study...