摘要
The uvarovite-andradite and uvarovite-andradite-grossular solid-solution series are rare in nature.The discovery of uvarovite-andradite in serpentinite and rodingite from the ultra-high pressure(UHP)metamorphic belt in southwestern Tianshan provided an opportunity to investigate its behavior in the subduction zone.Uvarovite(defined as chromiumgarnet)from serpentinite is homogeneous in a single grain,covering compositions in the uvarovite-andradite solid solution series of Adr_(58-66)Uv_(33-41),with few grossular components.Uvarovite from rodingites contain various Cr_(2)O_(3) contents(1.7-17.9 wt%)and mineral compositions being in the range of Adr_(21-31)Uv_(41-50)Grs_(22-37),Adr_(52-90)Uv_(5-25)Grs_(0-21) and Adr_(19-67)Uv_(3-63)Grs_(13-42).Discontinuous chemical variation of uvarovite from core to rim indicates that uvarovite formed by consuming andradite and chromite,which could provide Ca,Cr,Al and Fe.Raman signals of water were identified for uvarovite from both serpentinite and rodingite,with high water content in uvarovite from serpentinite.The high pressure mineral assemblage,as well as the association with perovskite,indicated that the studied uvarovite from serpentinite and rodingite was formed through high pressure metamorphism,during the subduction zone serpentinization and rodingitization.High alkaline and highly reduced fluids released from serpentinization or rodingitization in the oceanic subduction zone promote the mobility of chromium and enable its long-distance migration.
基金
financially supported by the National Natural Science Foundation of China(Grant Nos.41872067,41972064,41630207,41720104009,41703053)
Project of the Chinese Geological Survey(Grant Nos.DD20190006,DD20190060)
the Foundation of the Chinese Academy of Geological Sciences(Grant Nos.J1901-9,J1901-31,J1903)。
作者简介
Corresponding author:SHEN Tingting,female,born in 1985 in Shandong Province,Ph.D.,graduated from Peking University,China,associate professor at the Institute of Geology,Chinese Academy of Geological Sciences.She is interested in the metamorphic geology of subduction zone serpentinites and associated rodingites and eclogites(e.g.,the Chinese southwest Tianshan area),high pressure petrology and the microstructure of HP-UHP minerals,water in mantle nominally-anhydrous minerals and DHMS phases.E-mail:ttshen@pku.edu.cn;ZHANG Cong,male,born in 1983 in Liaoning Province,Ph.D.,graduated from Peking University,China,associate professor at the Institute of Geology,Chinese Academy of Geological Sciences,Scientific board member of the International Geoscience Program.He is interested in metamorphic geology,petro-tectonics,Tibetan Plateau,high-ultrahigh pressure metamorphic rocks and Raman spectroscopy.E-mail:congzhang@pku.edu.cn.
