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No.75 (2003/3) >

 
Title :Geology, structure and metamorphism of the Mai khola area, southwestern part of Ilam Bazaar, eastern Nepal
Authors :Chamlagain, Deepak
Rai, Santa Man
Hayashi, Daigoro
Authors alternative :林, 大五郎
Issue Date :Mar-2003
Abstract :The study area consists of three tectonic zones from south to north, they are the Siwalik, Lesser Himalayan Sequence and Higher Himalaya Crystalline thrust sheet. The Lesser Himalayan Sequence is composed of chlorite, biotite and garnet grade metasediments and augen gneiss. The Higher Himalayan Crystalline thrust sheet is composed of kyanite to sillimanite grade paragneiss, orthogneiss and quartzite. The area is affected mainly by two deformational episodes (i) Syn-MCT metamorphic ductile deformation and (ii) Post-MCT metamorphic deformation. Syn-MCT metamorphic ductile deformation is characterized by (a) development of bedding-parallel foliation and syn-metamorphic stretching lineations trending NNE- SSW and (b) development of S-C structure. Three sub phases of the post-MCT metamorphic deformation are observed in the study area viz. (a) development of folds, (b) new generation of foliation and extensional shearing features and (c) small-scale brittle fault, shear bands and cross-cut veins. The Lesser Himalayan Sequence has been metamorphosed to greenschist-amphibolite facies whereas the Higher Himalayan Crystalline thrust sheet has been metamorphosed to amphibolite to granulite facies. At least two metamorphic events could be recorded in the Lesser Himalayan Sequence. During Pre Himalayan metamorphic phase, the Lesser Himalayan Sequence might be metamorphosed up to anchizone grade prograde metamorphism(?). But Eo-Himalayan metamorphic phase could not affect the Lesser Himalayan Sequence. The Neo-Himalayan (Syn-MCT) metamorphic phase has been recorded on S-C fabric and is revealed by inverted metamorphic zonation in the Lesser Himalayan Sequence. The final phase in the Lesser Himalayan Sequence was retrograde phase shown by chloritization of garnet and biotite. At least three metamorphic events are recognized in the Higher Himalayan Crystalline thrust sheet of the study area. In the Eo-Himalayan (pre-MCT) metamorphic event kyanite grade prograde metamorphism has been occurred. This is followed by sillimanite grade retrograde metamorphism (lower P/high T) on the hanging wall of MCT and is assigned as Neo-Himalayan (Syn-MCT) metamorphic event. Finally the replacement of garnet and biotite by chlorite is the third (retrogressive metamorphic event) occurred during post MCT movement.
Type Local :紀要論文
ISSN :0286-9640
Publisher :琉球大学理学部
URI :http://hdl.handle.net/20.500.12000/2618
Citation :琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus no.75 p.55 -74
Appears in Collections:No.75 (2003/3)

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