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 chromium-garnet) from serpentinite is homogeneous in a single grain, covering compositions in the uvarovite-andradite solid solution series of Adr_58–66Uv_33–41, with few grossular components. Uvarovite from rodingites contain various Cr₂O₃ contents (1.7–17.9 wt%) and mineral compositions being in the range of Adr_21–31Uv_41–50Grs_22–37, Adr_52–90Uv_5–25Grs_0–21 and Adr_19–67Uv_3–63Grs_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.

中文翻译：

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大洋俯冲带超高压蛇纹岩和罗丁岩中紫云母的形成演化及其对铬迁移率的制约

紫云母-andradite 和紫云母-andradite-grossular 固溶体系列在自然界中很少见。天山西南部超高压变质带蛇纹岩和菱铁矿中发现紫云母-andradite，为研究其在俯冲带中的行为提供了机会。蛇纹岩中的紫云母（定义为铬石榴石）在单个晶粒中是均质的，覆盖了 Adr _58-66 Uv _33-41的紫云母-红霞石固溶体系列中的成分，几乎没有_粗粒成分。从rodingites钙铬榴石含有各种的Cr ₂ ö _3分含量（1.7-17.9重量％）和在阿霉素的范围内矿物成分_21-31紫外_41-50 GRS _22-37, Adr _52–90 Uv _5–25 Grs _0–21和 Adr _19–67 Uv _3–63 Grs _13–42. 铀矿从核到边缘不连续的化学变化表明，铀矿是通过消耗和菱镁矿和铬铁矿形成的，可以提供钙、铬、铝和铁。水的拉曼信号被鉴定为来自蛇纹岩和罗丁岩的 uvarovite，蛇纹岩中的 uvarovite 含水量高。高压矿物组合以及与钙钛矿的结合表明，所研究的蛇纹石和罗丁石的紫云母是在俯冲带蛇纹石化和罗丁石化过程中通过高压变质作用形成的。大洋俯冲带蛇纹石化或罗纹石化释放的高碱性和高度还原的流体促进了铬的迁移并使其能够长距离迁移。