北秦岭新元古代花岗岩类成因与构造环境的地球化学研究

GEOCHEMICAL STUDY OF GENESIS AND TECTONIC SETTING FOR LATE PROTEROZOIC GRANITOIDS, NORTH QINLING, CHINA

花岗岩类地球化学特征和区域地质事件的综合分析结果表明,蔡凹岩体和黄柏峪岩体形成于活动陆缘或古岛孤环境,与古秦岭洋板块向北秦岭俯冲消减作用有关,属于Ⅰ型花岗岩,源岩来自于地幔派生物质;而德河岩体的形成可能是在板块俯冲作用早期,活动陆缘受板块俯冲作用的动力学影响,陆壳物质剪切改造所诱发岩浆的产物,属S型花岗岩,其源岩为陆壳碎屑物质。多种证据证明,北秦岭至少自新元古代就开始运行板块构造运动体制。

The Late Proterozoic granitic bodies in the North Qinling belt include the Dehe,the Caiao and the Huangbaiyu plutons. The biotite two-feldspar granites from the Dehe pluton are of S-type granite and derived from the source probably comprised of clastic sediments. The granodiorites from the Caiao and the Huangbaiyu plutons are all of Ⅰ-type granites and derived from the source of mantle chemical characteristics. Geochemical features of these granitoids, together with their regional geology, indicate an island-arc or active continental margin environment for the Caiao and the Huangbaiyu plutons, but the Dehe pluton, being older than the Caiao and the Huangbaiyu plutons,might have resulted from reworking of the continental crust in the active continental margin due to the subduction. Various lines of evidence suggest that the plate tectonics has operated in the North Qinling since at least the Late Proterozoic.