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TitleAnatexis, cooling, and kinematics during orogenesis: Miocene development of the Himalayan metamorphic core, east-central Nepal
AuthorLarson, K P; Kellett, D AORCID logo; Cottle, J MORCID logo; King, J; Lederer, G; Rai, S M
SourceGeosphere vol. 12, no. 5, 2016, 19 pages, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20160109
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
AreaHimalayas; Tama Kosi; Mahabharat Range; Nepal
Lat/Long WENS 85.7500 86.3333 28.1167 26.9167
Subjectsigneous and metamorphic petrology; tectonics; structural geology; geochemistry; geochronology; Miocene; Oligocene; Eocene; crustal evolution; orogenesis; plate tectonics; plate boundaries; metamorphism; deformation; accretion; anatexis; partial melting; crystallization; recrystallization; thermal history; crustal shortening; strain analysis; lithology; metamorphic rocks; orthogneisses; igneous rocks; intrusive rocks; leucogranites; kinematic analysis; models; radiometric dating; uranium lead dating; zircon dates; thorium lead dates; monazite; argon argon dating; mica; structural features; faults, thrust; whole rock analyses; x-ray fluorescence; trace element analyses; major element analyses; rock analyses, rare earth elements; spectrometric analyses; temperature; Himalyan orogen; Suri Dobhan orthogneiss; Melung-Salleri orthogneiss; Phanerozoic; Cenozoic; Tertiary
Illustrationsgeological sketch maps; location maps; photomicrographs; schematic cross-sections; ternary diagrams; geochemical plots; diagrams; tables; Concordia diagrams; models
ProgramScience laboratory network
Released2016 08 23
AbstractThe exposed mid-crustal rocks of the Himalayan orogen provide a natural laboratory for constructing the kinematic evolution of the midcrust during a large-scale continental collision. Kinematic models provide testable, geometrically valid, internally consistent, integrated solutions for diverse geological data from deformed regions. We investigated the Tama Kosi region of east-central Nepal with structural, geochemical, and geochronological methods to refine a detailed kinematic model for the Miocene Epoch, during which the mid-crust was pervasively deformed, translated southward, and progressively stacked via basal accretion. Geochemical and U-Pb zircon data demonstrate that two similar orthogneiss bodies were derived from different protoliths, one formed through vapor-absent melting at 1940 ± 16 Ma and the other via vapor-present melting at 1863 ± 14 Ma, respectively, indicating that they do not reflect structural repetition. In situ Th-Pb monazite petrochronology from the Mahabharat Range links the orogenic foreland to the exposed mid-crust of the High Himalaya via a coeval, protracted metamorphic growth-crystallization and/or recrystallization record spanning late Eocene or early Oligocene to early Miocene. Differential cooling of white mica, evidenced by 40Ar/39Ar cooling ages across the studied area, may outline a previously unrecognized out-of-sequence thrust, the occurrence of which is coincident with the location of a sharp break previously recognized from quartz crystallographic fabric deformation temperatures. Together with previous work, these data form the basis for a new, internally consistent kinematic model for rocks of the Tama Kosi region during the Miocene Epoch that tracks the transition from distributed ductile deformation in the mid-crust to deformation along discrete surfaces during their exhumation.
Summary(Plain Language Summary, not published)
This study uses a multi-disciplinary approach including microstructural analysis, geochronology and geochemistry to investigate the structural and tectonic history of a section of the Himalayan mountain belt. This mountain belt is studied as the type example of a continent-continent collision, and used to understand older, less well preserved mountain belts formed from continent-continent collision such as the Trans-Hudson orogen in Canada. The new datasets presented indicate a previously unidentified out-of-sequence thrust and are used to test and refine a model for stacking of the rocks during their exhumation in the critical Miocene evolution of the mountain belt.

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