黑龙江省完达山造山带东方红蛇绿岩的成因、时代及构造意义

The Dongfanghong Ophiolite, located in the Wandashan Orogen of eastern Heilongjiang Province, is an important product of Paleo-Pacific subduction. However, its origin and formation and accretion ages are still unknown, restricting its function of recovering oceanic-continental framework and tectonic evolution. This project studies the meta- peridotite, pyroxenite, gabbro and basalt in the Dongfanghong ophiolite based on field geological survey, mineralogical and petrological studies, major and trace element and Nd-Hf isotopic analyses. The framework of the ophiolite will be reconstructed and the mantle signature and origin type of the ophiolite will be determined. The formation age of the ophiolite will be constrained based on zircon U-Pb dating and whole rock and mineral Lu-Hf and Sm-Nd isochrone dating on the mata- ultramafic-mafic rocks. The accretion time of the ophiolite against the continental margin will also be constrained based on Ar-Ar dating for the amphiboles of the meta-gabbro. Finally, the tectonic processes of the Dongfanghong ophiolite from formation to accretion will be reconstructed , providing reference for studying the effect of Paleo-Pacific subduction towards eastern China.

黑龙江省完达山造山带的东方红蛇绿岩是古太平洋板块俯冲的重要产物，然而其成因类型及形成和侵位时代尚不清楚，限制了其恢复洋陆格局及大地构造演化的作用。本项目以东方红蛇绿岩内的变橄榄岩、变辉石岩、变辉长岩、变玄武岩等岩石为研究对象，拟通过详实的野外地质调查、细致的岩石-矿物学研究、全岩主量、微量及Nd-Hf同位素分析，恢复蛇绿岩原始岩石组合序列，厘定地幔源区特征，判断蛇绿岩成因类型；利用锆石U-Pb及全岩-单矿物Lu-Hf和Sm-Nd等时线年代学方法测定变镁铁-超镁铁质岩石的岩浆结晶年龄，厘定该蛇绿岩的形成时代；对变辉长岩中变质成因的角闪石进行Ar-Ar年代学研究，测定角闪岩相变质年龄，限定蛇绿岩在大陆边缘就位的时代。在上述研究基础上，重建东方红蛇绿岩从形成到就位的构造演化过程，为揭示古太平洋俯冲对中国东部大地构造演化的影响提供参考。

东方红蛇绿岩位于黑龙江省东部完达山造山带，发育层状堆晶岩体，并经历了低角闪岩相变质，原岩岩性包括橄榄岩、辉橄岩、辉石岩、(层状)辉长岩、闪长岩等。通过野外地质调查、岩石-矿物学研究、全岩主量、微量及同位素分析，恢复了东方红蛇绿岩原始岩石组成，明确了蛇绿岩属于SSZ型，并具有堆晶体从下往上逐渐同位素变富集的特征，符合Whattam & Stern在2011年提出的“俯冲起始定律”；利用锆石U-Pb年代学方法测定变镁铁-超镁铁质岩石的岩浆结晶年龄，厘定该蛇绿岩的岩浆侵位时代为~275 Ma。在上述研究基础上，重建东方红蛇绿岩从形成到就位的构造演化过程，指出东方红蛇绿岩形成于古太平洋向中国东北俯冲的起始阶段。