MECHANISM FOR KOSMOCHLOR SYMPLECTITE AND COMPOSITIONAL VARIATION ZONING IN JADEITE JADE
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摘要: 翡翠中钠铬辉石是在变质作用高峰期与硬玉同时形成的变晶矿物，还是钠长石交代铬铁矿所形成的产物？就此争议问题，主要采用岩相学和EPMA分析测试技术，重点对矿物做相、显微组构及微区化学成分特征进行研究。研究表明，钠铬辉石主要是后成合晶形式取代或包绕翡翠中原生矿物铬铁矿，部分与硬玉相邻的铬铁矿经交代分解而形成销铬辉石+钙质钠铬辉石+钙铬榴石三层同心环状后成合晶域，并发育化学成分变异环带。由此显示了不平衡交代变质及应的多阶级性和复杂性。研究结果认为，变质作用高峰期后，铬铁矿与硬玉矿物粒间或晶内离子的扩散双交代与流体诊游交代的耦合作用，由剪切应力作用所致的晶粒破碎与晶内边缘份错密度的增大，是导致钠铬辉石等后成合晶及成分变异环带形成的主要缘由。Abstract: At present, different views on the compositional variation and origin of the kosmochlor, a new mineral, are held out. In this paper，the petrographic and EPMA analytical testing technologies are employed with an emphasis on the investigation into mineral microfacies，m icrofabric and microscopic chemical elements. The research indicates that kosmochlor is mainly in the form of symplectite substi- tutes or surrounds chromite, a primary mineral in jadeite. Part of kosmochlor is metasomatized with chromite adjacent to jadeite ，resulting in the three-layer symplectitic zoning of kosmochlor-calcic kos- mochlor-uvarovite. In this way, the chemical com positional variation zoning occurs ，revealing the mul- ti-stages and complexity of the imbalanced metasomatic reaction. It can be concluded that the coupling of ion diffusing bimetasomatism with flow percolating metasomatism between the mineral particles is the major cause of kosmochlor symplectite and compositional variation zoning.
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Keywords:
- kosmochlor /
- symplectite /
- compositional zoning /
- metasomatic reaction
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