摘要
The Lesser Himalaya in central Nepal consists of greenschist\|facies metasedimentary rocks, which are overthrust by the amphibolite\|facies rocks of the Higher Himalaya along the Upper Main Central Thrust (UMCT). Despite a number of works on metamorphism of the MCT zone and the Higher Himalaya, the low\|grade metamorphic rocks to the south of the MCT zone have not been studied yet.In the present study, an attempt was made to constrain the metamorphic events and thermal structure of the whole Lesser Himalaya by means of white mica (Ms) compositions. About 600Ms grains in 48 metapelitic samples from the Lesser Himalaya were analysed by the EPMA. Compositional zoning in individual Ms grains was checked by means of X\|ray compositional mapping. There exist wide intersample, intrasample and within grain compositional variations in Ms in the samples from the Lesser Himalaya. Sheared Ms phenocrysts in pegmatites and gneisses have compositions very close to that of the ideal muscovite. Detrital Ms show wide variation in phengite content, most of which are poor in phengite content, and are most probably derived from older higher\|grade metamorphic rocks.
The Lesser Himalaya in central Nepal consists of greenschist\|facies metasedimentary rocks, which are overthrust by the amphibolite\|facies rocks of the Higher Himalaya along the Upper Main Central Thrust (UMCT). Despite a number of works on metamorphism of the MCT zone and the Higher Himalaya, the low\|grade metamorphic rocks to the south of the MCT zone have not been studied yet.In the present study, an attempt was made to constrain the metamorphic events and thermal structure of the whole Lesser Himalaya by means of white mica (Ms) compositions. About 600Ms grains in 48 metapelitic samples from the Lesser Himalaya were analysed by the EPMA. Compositional zoning in individual Ms grains was checked by means of X\|ray compositional mapping. There exist wide intersample, intrasample and within grain compositional variations in Ms in the samples from the Lesser Himalaya. Sheared Ms phenocrysts in pegmatites and gneisses have compositions very close to that of the ideal muscovite. Detrital Ms show wide variation in phengite content, most of which are poor in phengite content, and are most probably derived from older higher\|grade metamorphic rocks.
出处
《地学前缘》
EI
CAS
CSCD
2000年第S1期51-52,共2页
Earth Science Frontiers
