东昆仑造山带(西段)青白口纪辉石闪长岩的发现及其地质意义

The Discovery and Geological Significance of the QingbaikouPeriod PyroxeneDiorite in the East Kunlun Orogenic Belt(Western Section)

东昆仑造山带内元古代蓟县纪一青白口纪的岩石构造组合保留较少,蛇绿岩组合和洋岛一海山组合是中元古代昆中洋存在的直接依据,代表中元古代旋回的开始,而青白口纪碰撞型花岗片麻岩组合的成带分布和蓟县一青白口纪稳定陆表海环境的沉积代表元古代构造岩浆旋回的结束,但无准确的同位素资料和岩石化学数据证明中新元古代俯冲环境岩石组合的存在。青白口纪辉石闪长岩为本次工作中在金水口岩群新解体出的变质侵入体。本文通过对分水岭北地区青白口纪辉石闪长岩岩石学、岩石地球化学、锆石U-Pb同位素年代学以及成因类型和构造环境进行分析,进而为东昆仑造山带西段青白口纪所处造山阶段提供有力证据。

In the East Kunlun orogenic belt,there are few rock structural associations in Proterozoic Jixian and QingbaikouPeriod,the ophiolite assemblage and the oceanic island-seamount assemblage are the direct evidences for the existence of the Middle Proterozoic Kunzhong Ocean,which represents the beginning of the Mesoproterozoic cycle.The zonation distribution of collisional granitic gneisses in the QingbaikouPeriod and the deposition of stable epicontinental sea environment in the Jixian-QingbaikouPeriod represent the end of the proterozoic tectonic magmatic cycle.However,there is no accurate isotopic data and petrochemical data to prove the existence of rock assemblages in Mesoproterozoic subduction environment.Qingbaikoupyroxene diorite is a newly discovered metamorphic intrusion disintegrated from JinshuikouGroup.In this paper,the petrology,petrogeochemistry,U-Pb isotope chronology,genetic type and tectonic environment of the Qingbaikou Periodpyroxene diorite in the north area of the watershed are analyzed,which provide strong evidence for the orogenic stage of the QingbaikouPeriod in the western part of the East Kunlun orogenic belt.