Fluid inclusions hidden in coesite-bearing zircons from ultrahigh-pressure metamorphic rocks in southwestern Sulu terrane, eastern China
【摘要】：正 Primary fluid inclusions, together with coesite mineral inclusions, are identified in the same zircon domains by Laser Raman spectroscopy, cathodoluminescence (CL) image and micro-texture analysis in paragneiss and retrogressive eclogite from the main drilling hole of Chinese Continental Scientific Drilling Project, southwestem Sulu terrane. Most fluid inclusions are characterized by CO_2 (gas) - H_2O (liquid) two-phase; a few by H_2O one-phase liquid inclusions. These features indicate that the eclogite and its country-rocks may not be located in the "dry system", but in the "Wet system" circumstance, when the Sulu terrane occurred ultrahigh-pressure metamorphism. The SHRIMP U-Pb dating suggests that the time for fluid and coesite inclusions trapped in metamorphic recrystallized zircon domains is about 230-236 Ma (the weighted mean = 233.7±4.3 Ma); this age is in agreement with many reported Triassic UHP metamorphic ages of 230-245 Ma from eclogites and gneissic rocks in Sulu-Dabie terrane. This research not only shows important significance for an in-depth study of the fluid property and evolutional feature, and fluid-rock interaction mechanism in Sulu-Dabie UHP terrane, but also provides a new method for exactly identifying the primary fluid inclusions preserved in zircons from the ultrahigh-pressure metamorphic rocks in the world.