中国中部河南省榴辉岩中柯石英的发现及其构造意义

DISCOVERY OF COESITE ECLOGITES IN HENAN PROVINCE, CENTRAL CHINA AND ITS TECTONIC IMPLICATION

本文报道了一项中美合作研究的新进展:笔者于1992年在河南省新县发现了柯石英榴辉岩。这些柯石英榴辉岩呈透镜体赋存于“大别群”长英质片麻岩中,由石榴石,绿辉石,蓝晶石,石英,和多硅白云母等矿物组成。柯石英及其假象呈包裹体产于石榴石和蓝晶石中。柯石英的显微拉曼光谱显示了在520cm^(-1)处的强峰和在270cm^(-1)处及在151cm^(-1)处的两个弱峰。初步研究表明,新县柯石英榴辉岩的高压变质峰期压力在3.0GPa时温度约为660℃。

Coesite eclogite was discovered by the authors in Xinxian County, Henan Province, central China in 1992. The coesite eclogite occurs as lenses or blocks in felsic gneiss called 'Dabie Group'. Mineralogically, the eclogite is composed of garnet, omphacite, kyanite, quartz, phengite and others. Coesite and its psuedomorphs are included by garnet and kyanite, with diagnose radial fractures. The micro-Raman spectra analysis shows a high peak at 520 cm^(-1), and two weak peaks at 270 cm^(-1) and 151 cm^(-1). The preliminary study indicates that the ultra-high-pressure metamorphism peak temperature is about 660℃ at 30 kbar. The P-T values are lower than those in the Dabie Mountains (700℃ at average), and much lower than those in the Su-Lu(East Shandong-North Jiangsu) region (770℃ at average), which implies a differantial tectonic unloading. The Qinling-Dabie orogenic belt uplifted and exposed its deep portion to the east (Su-Lu region) and shallow portion to the west(Qinling Mountains).