The aragonite, an index mineral of glaucophane schist facies, has not been confirmed in the Dabie Mountains high pressure and ultrahigh pressure metamorphic belts. The Mulanshan glaucophane schist in Huangpi County,...The aragonite, an index mineral of glaucophane schist facies, has not been confirmed in the Dabie Mountains high pressure and ultrahigh pressure metamorphic belts. The Mulanshan glaucophane schist in Huangpi County, Hubei Province is located in the southwestern Dabie Mountains, Central China. The micron sized intergranular aragonite is confirmed with optical microscope (OM) and electron probe microanalysis (EPMA) in the glaucophane schist. The submicrometer sized ellipse aragonite inclusion is observed by using bright field image (BFI), X ray energy damage spectrograph (EDS) and selected area electron diffraction (SAED) with transmission electron microscope in the quartz lens of glaucophane albite epidote chlorite schist from Mulanshan. The presence of aragonite indicates not only the average geothermal gradient of the Mulanshan glaucophane schist less than 10 ℃/km, which is very close to that of eclogite in the Dabie Mountains metamorphic belts, but also the relatively higher concentration of CO2 during the metamorphic process. In addition, the glaucophane schist free of such index minerals as lawsonite, prehnite and pumpellyite, has been attributed to the effect of CO2 on the stability of calcium aluminum silicate minerals during the low grade metamorphism. EDS and SAED analysis results show that the host of aragonite inclusion is amorphous SiO2. The occurrence of amorphous SiO2 indicates a quick cooling process during the exhumation of the Mulanshan glaucophane schist. These results suggest that the rapid exhumation mechanism of the glaucophane schist, the same as that of eclogite in the Dabie Mountains metamorphic belts, occurred in the geodynamic context of subduction obduction.展开更多
基金theNationalNaturalScienceFoundationofChina (No .4980 2 0 0 4)
文摘The aragonite, an index mineral of glaucophane schist facies, has not been confirmed in the Dabie Mountains high pressure and ultrahigh pressure metamorphic belts. The Mulanshan glaucophane schist in Huangpi County, Hubei Province is located in the southwestern Dabie Mountains, Central China. The micron sized intergranular aragonite is confirmed with optical microscope (OM) and electron probe microanalysis (EPMA) in the glaucophane schist. The submicrometer sized ellipse aragonite inclusion is observed by using bright field image (BFI), X ray energy damage spectrograph (EDS) and selected area electron diffraction (SAED) with transmission electron microscope in the quartz lens of glaucophane albite epidote chlorite schist from Mulanshan. The presence of aragonite indicates not only the average geothermal gradient of the Mulanshan glaucophane schist less than 10 ℃/km, which is very close to that of eclogite in the Dabie Mountains metamorphic belts, but also the relatively higher concentration of CO2 during the metamorphic process. In addition, the glaucophane schist free of such index minerals as lawsonite, prehnite and pumpellyite, has been attributed to the effect of CO2 on the stability of calcium aluminum silicate minerals during the low grade metamorphism. EDS and SAED analysis results show that the host of aragonite inclusion is amorphous SiO2. The occurrence of amorphous SiO2 indicates a quick cooling process during the exhumation of the Mulanshan glaucophane schist. These results suggest that the rapid exhumation mechanism of the glaucophane schist, the same as that of eclogite in the Dabie Mountains metamorphic belts, occurred in the geodynamic context of subduction obduction.
