The Mineral Chemistry and Classification of New Ordinary Chondrites Collected in Antarctica

摘要

Petrography and mineral chemistry of ninety-eight ordinary chondrites from Grove Mountains, Antarctica, have been studied, in order to assign their chemical-petrographic types. The chemical-petrographic types of these meteorites are presented below: 36 H-groups (21 H4, 9 H5, 6 H6) and 62 L-groups (25 L5, 37 L6). The compositions of olivines and low-Ca pyroxenes in the all these ordinary chondrites have similar composition, respectively, reflecting some degree thermodynamics equilibration in them. The weathering degrees of all the ordinary chondrites, consisting of predominant weathering degrees of W1, suggest lightly weathered among them. More than 30% meteorites experienced severe shock metamorphism, as indicated by the presences of shock-induced melt veins and pockets. These heavily shocked meteorites provide us with natural samples for study of high-pressure polymorphs of minerals. Antarctica is the most concentrated region with meteorites. Since 9 different types were found in Yamato Mountains in 1969, Japan, USA, some countries of Europe have been searching for meteorites with the results of total more than 30000 meteorites. In 1998, Chinese Antarctic Research Expedition (CHINARE) had found the first 4 meteorites in Grove Mountains. Subsequently, CHINARE has carried out 4 expeditions in the region in order to look for meteorites in 1999/2000, 2002/2003, 2005/2006, 2009/2010 austral seasons with the big collection of more than 11000 meteorites which makes China to be one of the biggest countries with Antarctic meteorites. This work focuses on mineral chemistry and petrology of 98 meteorites collected in Grove Mountains, then further to classify them and discuss the features of weathering and shock metamorphism of these meteorites.