• 责任者：Yang Xiaoqiang (Department of Earth Sciences ; Zhejiang University ; Hangzhou 310027 ; China) ; Li Zilong
• 刊名：Acta Petrologica Sinica
• 出版年：2013
• 卷期：29(10)
• 关键词：麻粒岩 ; granulite ; 流体包裹体 ; fluid inclusions ; 阿尔泰山 ; Altai Mountains
• 页码：p.3446-3456
• 图表：8 illus., 3 tables, 56 refs.
• 分类号：0802
• issnNo：ISSN1000-0569
• isbnNo：CN11-1922/P

     The Late Paleozoic ultrahigh-temperature （UHT） granulite from the Altay orogenic belt, northwestern China contains UHT diagnostic mineral assemblages of spinel ＋ quartz and orthopyroxene ＋ sillimanite ＋ quartz. Its retrograde metamorphism is characterized by the formation of cordierite through typical decompression reaction. Newly discovered primary and pseudosecondary fluid inclusions in garnet together with primary fluid inclusions in quartz were studied in terms of petrography and microthermometry as well as laser Raman spectroscopy analyses in detail. Melting temperatures of inclusions obtained indicated that the trapped fluid phase is dominantly carbonic. Raman probe confirmed a near pure CO2 composition with only minor dilutant of N2. The homogenized temperatures of fluid inclusions both from the quartz in matrix and enclosed in garnet porphyroblasts range from 10. 1℃ to 29. 0℃with the corresponding densities of 0. 631 ～0. 861g/cm^3. The distance values of Fermi doublet from the pseudosecondary and secondary fluid inclusions trapped in garnets are around 104. lcm^-1 , smaller than those from quartz （ ～ 104. 7cm^-1 ）, indicating the lower density nature of the fluids in garnets. The range of CO2 isochores computed from density measurements in fluid inclusions passed below the retrograde stage of the P-T trajectory. We inferred that the Altay UHT granulite probably formed in an extensional setting, with the underplating of mantle-derived magma, which provided not only heat, but also sufficient CO2 to dilute the H2O activity. The consistent low-density carbonic fluids are probably a reflection of significant density reversal owing to modification of inclusion cavity volume by rapid decompression of the Ahay UHT granufite along a clockwise P-T path.