| dc.description.abstract | Yuli belt is a typical geologic province of high pressure minerals. Amphibolites with glaucophane inclusions contacting with metapillow is quite ynusual. In this study, we use petrography and mineral chemistry to construct these rocks and to define their evolutions.
According to the petrographic observation, mineral constructions of metabasite are epidote, chlorite, quartz, albite, actinolite, muscovite, calcite, and sphene. Mineral compositions of Garnet-Epidote Amphibolite are garnet, amphibole, epidote, quartz, calcite, chlorite, apatite, and albite. Some amphibole exhibits poikiloblastic textures with glaucophane inclusions. And these amphiboles also show polymetamorphism.
Bulk rock analysis is quite powerful to define the protolith of metabasite and garnet-epidote amphibolite. The results show that the metabasite came from island arc basalt; and the garnet-epidote amphibolite were mixed by volcanic ash, tuff and ocean floor sediment. Some metabasite were found in the garnet-epidote amphibolite. It implies that these two rocks were coexisting before metamorphism. In addition, these two rocks went through the same metamorphism.
Using SEM and EDS to perform qualitative and semi-quantitative analyses of the mineral chemistry are very effective. The amphiboles were classified to Alkali and Calcic amphiboles. The alkali amphiboles in this study were glaucophane. And the calcic amphiboles were classified to edenite, pargasite, actinolite, and hornblende. The amphiboles went through three stages metamorphism. The first stage was blueschist facies, then epidote-amphibolite facies, the last stage was greenschist facies. The glaucophane were overgrown by calcic amphiboles, and the least rimed by actinolite. When the rocks were uplifted, the hydrothermal alteration then occurred. Many minerals were replaced by quartz, and many grain surfaces were altered. In area altered by hydrothermal water chrome element can be found.
Combining mineral chemistry, petrography, and buck rock analysis, this rock includes metabasite, ocean floor sediment, and volcanic ash. When the protolith sub-ducted to blueschist facies, it grow glaucophane. Then it transferred to epidote-amphibolite facies and growth the calcic amphiboles. Finally, the rock was uplifted to greenschist facies to the surface.
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