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TitleTectonometamorphic evolution of the tip of the Himalayan metamorphic core in the Jajarkot klippe, west Nepal
AuthorSoucy La Roche, RORCID logo; Godin, L; Cottle, J MORCID logo; Kellett, D AORCID logo
SourceJournal of Metamorphic Geology vol. 37, issue 2, 2018 p. 239-269, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20180197
Mediapaper; on-line; digital
File formatpdf
AreaHimalayas; Nepal
Lat/Long WENS 79.0000 95.0000 31.0000 26.5000
Subjectstectonics; geochemistry; geochronology; structural geology; mineralogy; crustal evolution; tectonic history; metamorphism; deformation; foliation; lineations; crustal thickness; accretion; bedrock geology; structural features; klippen; faults, thrust; folds; anticlines; synclines; lithology; modelling; phase relations; equilibrium; pressure-temperature conditions; radiometric dating; argon argon dating; metamorphic facies; greenschist facies; amphibolite facies; mineralogical analyses; Neogene; Miocene; Paleogene; Oligocene; Himalayan Metamorphic Core; Nepal Foreland; Jajarkot Klippe; Himalayan Orogeny; Main Central Thrust; South Tibetan Detachment; geological contacts; Phanerozoic; Cenozoic; Tertiary
Illustrationsgeoscientific sketch maps; cross-sections; tables; photomicrographs; profiles; phase diagrams; graphs; bar graphs
ProgramGEM: Geo-mapping for Energy and Minerals GSC Science Laboratory Network
Released2018 10 24
AbstractNew phase equilibrium modelling, combined with U-Th/Pb petrochronology on monazite and xenotime, and 40Ar/39Ar geochronology on white mica, reveal the style of deformation and metamorphism near the southern tip of the extruded Himalayan metamorphic core (HMC). In the Jajarkot klippe, west Nepal foreland, greenschist to lower amphibolite facies metamorphism is entirely constrained to the Cenozoic Himalayan orogeny, in contrast with findings from other foreland klippen in the central Himalaya. HMC rocks exposed in the Jajarkot klippe yield short-lived, hairpin pressure-temperature-time-deformation paths that peaked at 550-600°C and 750-1,200 MPa at 25 Ma. The Main Central thrust (MCT) and the South Tibetan detachment (STD) bound the base and the top of the HMC, respectively, and were active simultaneously for at least part of their deformation history. The STD was active at c. 27-26 Ma and possibly as late as c. 19 Ma, while the MCT may have been active as early as 27 Ma and was still active at c. 22 Ma. The tectonometamorphic conditions in the Jajarkot klippe are characteristic of crustal thickening and footwall accretion of new material at the tip of the extruding metamorphic orogenic core. Our new results reveal that collisional processes active in the middle to late Miocene at the base of the HMC now exposed in the hinterland were also active earlier, during the Oligocene, at the tip of the southward-extruding middle crust.
Summary(Plain Language Summary, not published)
The Himalayan orogen is an important study case for understanding continent-continent collisions. In this study, the temperature, pressure and geological timing of metamorphic in metamorphic rocks in the foreland of the mountain belt are investigated. The results show that in this region of the orogen, rocks do not preserve a pre-Himalayan (i.e. pre-Eocene) metamorphic history, although they were metamorphosed earlier (Oligocene) than in the hinterland (Miocene). These results allow us to reconstruct the metamorphic evolution of the orogen from its Eocene beginning to the present day.

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