Investigations on Features and Genesis of Higher Himalayan Crystallines
详细信息
- 责任者：Yang Yongxin (State Key Laboratory of Earthquake Dynamics ; Institute of Geology ; China Earthquake Administration ; Beijing 100029 ; China) ; Yang Xiaosong
- 刊名：Seismology and Geology
- 出版年：2013
- 卷期：35(2)
- 关键词：混合岩 ; migmatites ; 喜马拉雅山 ; Himalayas
- 页码：p.261-277
- 图表：illus., 3 tables, 23 refs.
- 分类号：0802
- issnNo：ISSN0253-4967
- isbnNo：CN11-2192/P
摘要
The widely distributed migmatites in Higher Himalayan Crystallines( HHC) are an important clue to investigate the anatexis,crustal rheology,origins of Higher Himalayan leucogranites ( HHL) and evolution of orogenic belts. We studied in detail the petrographic,petrologic and geochemical features of three basic constituent units of the migmatites,i. e. leucosome,mesosome and melanosome,collected from Nyingchi and Nyalam regions in Tibet. In order to study the chemical features of each migmatite unit,the major,trace elements and rare-earth elements of leucosomes,mesosomes and melanosomes separated from migmatites have been analyzed. Our studies indicate that leucosome is the product of crystallization of migrated melt,and mesosome is regarded as source rocks of migmatites or as a reactant of unsegregated melt and restite at source region. The melanosome represents the aggregation of melanocratic minerals crystallized from melt or the products of retro-metamorphic reaction between segregated melt and mesosome. Leucosomes and melanosomes are usually characterized by igneous textures,coarse grain size and isotropic fabric,which are important identifications to distinguish them from mesosomes. Positive Eu anomaly of leucosomes may be attributed to partially melting of plagioclase significantly and /or early crystallization of plagioclases from primary melt in nearby source region. In contrast,leaving feldspars behind source region and crystallization differentiation of plagioclase during melt aggregation contributed to negative Eu anomaly displayed by leucograintes. It seems that the existence of minerals formed in dehydration melting cannot be regarded as judgment standard about partial melting because the diagnostic minerals of dehydration melting may disappear during retrograde reactions.
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