Experimental constraints on the genesis of Jadeite quartzite from Shuanghe, Dabie Mountain ultra-high pressure metamorphic terrane

摘要: Jadeite quartzite, essentially a two-phase rock made up of jadeite and quartz, is one the most important UHP lithologies occurring in Dabie Mountain ultrahigh pressure metamorphic belt forms layers biotite-plagioclase gneiss. High pressure-high temperature studies on natural albite from country gneiss were undertaken to reveal the—in parts—complex mineralogical changes that occur quartzite during prograde metamorphism. Experiments conducted at 800-1200℃, range 2.0-3.5 GPa. One intriguing results shows low boundary jadeite+coesite stability field located between about 3.2 GPa 1000℃ 3.4 1200℃, thus (0.2-0.3)±0.1 higher than quartz-coesite transition curve, given uncertainty present study. Minor amounts sodium aluminum entering structure quartz intimate intergrowth texture run products may contribute observed shift. Combined petrological rocks yield following reaction sequence have occurred: The protolith jadeite-quartzite an albitized siltstone/greywacke characterized by albite+quartz assemblage. During metamorphism breaks down form jadeite+quartz this stage two types can be distinguished whereas type-I-quartz already existed protolith, type-Ⅱ-quartz represents newly formed product albite. further P - T -increase pure was transformed coesite, (together with jadeite) still as stable phase because its impurities Na Al. At later subduction, also decomposes coesite. These represent puzzlement for better understanding evolution continental crust subduction more complete knowledge formation orogenic general.