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TitleThermo-kinematic evolution of the Annapurna-Dhaulagiri Himalaya, central Nepal: The composite orogenic system
AuthorParsons, A J; Law, R D; Lloyd, G E; Phillips, R J; Searle, M P
SourceGeochemistry, Geophysics, Geosystems (G3) vol. 17, 2016 p. 1511-1539, https://doi.org/10.1002/2015GC006184
Year2016
Alt SeriesEarth Sciences Sector, Contribution Series 20160285
PublisherAGU Publications
Documentserial
Lang.English
Mediaon-line; digital
File formatpdf
AreaAfghanistan
Lat/Long WENS -84.0000 -83.5000 28.7500 28.2500
Subjectsstructural geology; Himalayan orogen; wedge extrustion; thrust stacking; optical microscopy analyses; Electron Backscatter Diffractin (EBSD); deformation temperature profiles; thermokinematic evolution
Illustrationslocation maps; tables; photomicrographs; stereograms; diagrams
ProgramWestern Cordillera, Redefinition of crustal blocks, GEM2: Geo-mapping for Energy and Minerals
AbstractThe Himalayan orogen represents a "Composite Orogenic System" in which channel flow, wedge extrusion, and thrust stacking operate in separate "Orogenic Domains" with distinct rheologies and crustal positions. We analyze 104 samples from the metamorphic core (Greater Himalayan Sequence, GHS) and bounding units of the Annapurna-Dhaulagiri Himalaya, central Nepal. Optical microscopy and electron backscatter diffraction (EBSD) analyses provide a record of deformation microstructures and an indication of active crystal slip systems, strain geometries, and deformation temperatures. These data, combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the GHS. The profiles define a three-stage thermokinematic evolution from midcrustal channel flow (Stage 1, >700°C to 550-650°C), to rigid wedge extrusion (Stage 2, 400-600°C) and duplexing (Stage 3, <280-400°C). These tectonic processes are not mutually exclusive, but are confined to separate rheologically distinct Orogenic Domains that form the modular components of a Composite Orogenic System. These Orogenic Domains may be active at the same time at different depths/positions within the orogen. The thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya describes the migration of the GHS through these Orogenic Domains and reflects the spatial and temporal variability in rheological boundary conditions that govern orogenic systems.
Summary(Plain Language Summary, not published)
The Himalaya represents a 'Composite Orogenic System' in which multiple tectonic processes operate in different parts of the crust. We analyze 104 samples from the metamorphic core (Greater Himalayan Sequence, GHS) of the Annapurna-Dhaulagiri Himalaya, central Nepal. Optical and electron microscopy provide a record of grain-scale deformation. These data, combined with existing constraints are used to construct deformation profiles for the GHS which define a three-stage evolution from mid-crustal to upper-crustal deformation. Tectonic processes at each stage are confined to separate 'Orogenic Domains' that form the components of a Composite Orogenic System. Orogenic Domains may be active at the same time at different positions within the mountain belt. The tectonic evolution of the Annapurna-Dhaulagiri Himalaya describes the movement of the GHS through these Orogenic Domains and reflects the spatial and temporal variability in the conditions that govern mountain belt formation.
GEOSCAN ID299471