北祁连九个泉蛇绿岩及其上覆岩系的岩石地球化学特征和地球动力学意义

Lithogeochemical Characteristics of Jiugequan Ophiolite and its Overlying Rock Suites,North Qilian:The Geodynamic Significance

本文通过对北祁连九个泉蛇绿岩及其上覆岩系的详细的野外、岩石学和地球化学的研究表明:该区火山岩由多个火山角砾岩—块状玄武岩—凝灰岩的旋回所组成;蛇绿岩之上整合覆盖着一套火山岩—沉积岩组合(蛇绿岩的上覆岩系)。蛇绿岩中玄武岩为典型的N-MORB,其上覆岩系中玄武岩为E-MORB。剖面从下到上,玄武岩中LREE,HFSE含量递增。火山岩的地球化学和沉积岩的岩相学反映了洋壳从扩张中脊向大陆方向迁移的动力学过程,蛇绿岩从形成到侵位的时间间隔较短。

Detailed field, petrological and geochemical studies of the Jiugequan ophiolite and its overlying rock suites, North Qilian, are reported in this paper. The volcanic rocks are made up of cycles of pyroclastic rocks, basalts and tuffs. The ophiolite is covered conformably with a suite of volcanic-sedimentary rocks, namely the ophiolite's overlying rock suites (OORS). The basalts from the ophiolite are typical N-type MORBs, whereas those from the OORS are E-type MORBs. The highly/moderately incompatible trace elements are more and more enriched up wards within the OORS. Geochemisty of the basalts and petrography of the sediments both record the geodynamic processes during the oceanic crust's moving from the spreading axis to the continental margin. It is inferred that the time interval was relatively short between the birth of the Jiugequan ophiolite and its obduction.