Mineral chemistry of high-pressured metamorphic rock and their tectonic implications in Northern Qilian, China

• Main Authors: Yung-Ching Huang, 黃永清
• Other Authors: Wei-Min Donald Chen
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/64337043075479852359

碩士 === 國立中央大學 === 應用地質研究所 === 87 === This research presents a series field geology, petrology and mineral chemistry of high-pressured metamorphic rocks in northern Qilian. Study area near Qilian Country, from west to east was Chre Creek, Chse Creek, Wayu River, Sia Creek and Bejin Creek. The petrology show assemblages are Gln + Grt + Chl + Epi + Phe + Omp + Ab. The garnets are major Almandine and show apparent chemical zonation. The contents of almandine (Xalm) and pyrope (Xpy) increase from core to rim with a decrease in spessartine (Xsp) content. That maybe occurred by prograde metamorphism. The chemistry indicates that the main amphiboles found in this study include glaucophane, crossite, and actinolite (Leake, 1978). The Na(M4) versus Al(IV) diagram (Brown,1977) show the pressure at least 7 Kbar in alkali-amphibole and below 4 Kbar in calcic-amphibole. The P, T estimates from thermobarometry for the garnets with growth zoning in the eclogites yield 344 。, 8.8 kbar for the cores and 462 。, 10.8 kbar for their rims. In contrast, the estimates for the glaucophane schists are 380 。 for the cores and 410 。 for the rims. Study of petrology, mineral chemistry and thermobarometry, The P-T paths derived from garnets for the eclogites and glaucophane schists systematically show increases in pressure and temperature from core to rim. These probably reflect the deep burial process for the protoliths of eclogites and glaucophane schists. In terms of tectonic framework, the deep burial process may be related to a paleo-subduction event.