同位素地球化学填图与化学地球动力学在东秦岭造山带研究中的应用

APPLICATION OF ISOTOPIC MAPPING AND CHEMICAL GEODYNAMICS TO STUDYING THE EAST QINLING OROGENIC BELT

总结了应用同位素地球化学填图和化学地球动力学研究东秦岭造山带的初步经验，并以较成功的实例来说明，内容包括：（１）华北和扬子克拉通幔源和壳源岩石化学和Ｎｄ、Ｐｂ同位素组成及壳幔演化差异的确定；（２）南秦岭前寒武纪基底应归属于扬子陆块构造－地球化学省的地球化学论证；（３）关于东秦岭蛇绿岩铅同位素的Ｄｕｐａｌ型特征及其同三江地区（属古特提斯范围）蛇绿岩的相似性的揭示；（４）北秦岭元古宙基底可能为古洋岛型微陆块的地球化学证据；（５）东秦岭新元古代和早古生代洋壳俯冲消减及聚汇带壳－幔再循环的地球化学证据；（６）关于陆－陆碰撞过程中杨子陆块边缘（南秦岭）俯冲于华北陆块边缘（北秦岭）之下，从碰撞型花岗质岩浆源区地球化学研究获得的直接证据。这些初步成果说明同位素填图与化学地球动力学在造山带研究中是具有重要前景的技术途径。

This paper summarizes the preliminary experienoe in our recent study of the East Qinling Orogenic Belt on isotopic mapping and chemical geodynamics with several successful examples. The contents include:(1)determining the difference in chemical and isotopic (Nd and Pb)compositions of the mantle-and crust-derived rocks and in the crust -mantle evolution between the North China and Yangtze cratons,(2)geochemical evidence for classifying the Proterozoic basement of the South Qinling belt to the Yangtze tectonic-geochemical province;(3)revealing the Dupal type of Pb isotopic composition of the ophiolites in the East Qinling and the similarity of the Qinling ophiolites in Pb isotopic features to the ophiolites in the Sanjiang area being part of the paleotethys,(4)geochemical evidence for inferring the Proterozoic basement of the North Qinling belt probably to be an ancient oceanic island ,amicrocontinent;(5)geochemically proving subduction of the ancient Qinling oceanic crust during the Neoproterozoic and the Early Paleozoic times,and the crust-mantle recycling at the subduction zone;(6)geochemical evidence provided by the study of source of the collision type granitic magma for directly affirming the subduction of the margin of Yangtze continental block (South Qinling belt) beneath the margin of North China continental block(North Qinling belt )during the continent -continent collision.Theseachievements indicate that isotopic mapping and chemical geodynamics are significant and perspective approaches to researches on orogenic belts.