榴辉岩中金红石的矿物地球化学研究及其意义

Mineral Geochemistry of Rutile in Eclogite and Its Implications

金红石的微量元素分析在俯冲带地质作用示踪、榴辉岩原岩判别以及形成温度估算等的研究中具有重要指示作用,其U-Pb同位素和Hf同位素分析则对于确定高级变质岩的冷却时代以及探讨物质来源和壳幔作用过程具有重要意义.初步研究显示,苏鲁超高压变质地体及大陆科学钻探岩心中不同产状、不同类型的榴辉岩中的金红石具有不同的微量元素特征,对榴辉岩原岩及金红石形成温度具有很好的指示作用;3个金红石样品的Pb同位素组成在逐步淋溶分析的某个中间阶段和最后阶段均出现有相似规律的2次突变,其余阶段则相对平稳,有可能反映了金红石在其生长过程中构造环境背景的变化.进一步对金红石进行详细系统的矿物地球化学分析,有望在苏鲁地体大陆深俯冲-折返过程的地球动力学及榴辉岩型金红石矿床的研究中获得一些新的认识.

The study of rutile＇s mineral geochemistry can provide important information for the investigation of petrology and the geodynamics of a subduction zone. Rutile-bearing eclogite （eclogitic-rutile deposit） in Sulu UHPM terrane and the 〉5 000 m deep CCSD main hole provide a good opportunity for the geochemical investigation of rutile. Preliminary research has shown that eclogites of different occurrences and different types in Sulu UHPM terrane and CCSD main hole have different trace element contents, which indicate that trace elements in rutile can serve as a practical tool for provenance tracing of eclogite and for estimation of rutile mineralization temperature. Pb isotope composition of 3 rutile samples showed two abrupt changes during step-leaching analysis, which may be a reflection of tectonic condition variation during the growth history of rutile, and have potential use in tracing the process of continental subduction-exhumation. Further detailed studies on the geochemistry of rutile are needed to provide new knowledge on the geodynamics of the subduction-exhumation of Sulu terrane, and on the eclogitic rutile deposit.