Orogen-parallel deformation of the Himalayan midcrust: Insights from structural and magnetic fabric analyses of the Greater Himalayan Sequence, Annapurna-Dhaulagiri Himalaya, central Nepal

Autor: Michael P. Searle, Eric C. Ferré, A. J. Parsons, G. E. Lloyd, Richard J. Phillips, Richard D. Law
Rok vydání: 2017
Předmět:
ISSN: 0278-7407
Popis: The metamorphic core of the Himalaya (Greater Himalayan Sequence, GHS), in the Annapurna-Dhaulagiri region, central Nepal recorded orogen-parallel stretching during mid-crustal evolution. Anisotropy of magnetic susceptibility (AMS) and field-based structural analyses suggest that mid-crustal deformation of the amphibolite facies core of the GHS occurred under an oblate/sub-oblate strain regime with associated formation of low-angle northward-dipping foliation. Magnetic and mineral stretching lineations lying within this foliation from the top of the GHS record right-lateral orogen-parallel stretching. We propose that oblate strain within a mid-crustal flow accommodated oblique convergence between India and the arcuate orogenic front without need for strain partitioning in the upper-crust. Oblate flattening may have also promoted orogen-parallel melt migration and development of melt-depleted regions between km3-scale leucogranite culminations at ~50-100 km intervals along orogen-strike. Following cessation of flow, continued oblique convergence led to upper-crustal strain partitioning between orogen-perpendicular convergence on thrust faults and orogen-parallel extension on normal and strike-slip faults. In the Annapurna-Dhaulagiri Himalaya, orogen-parallel stretching lineations are interpreted as a record of transition from mid-crustal orogen-perpendicular extrusion to upper-crustal orogen-parallel stretching. Our findings suggest that mid-crustal flow and upper-crustal extension could not be maintained simultaneously and support other studies from across the Himalaya, which propose an orogen-wide transition from mid-crustal orogen-perpendicular extrusion to upper-crustal orogen-parallel extension during the mid-Miocene. The 3D nature of oblate strain and orogen-parallel stretching cannot be replicated by 2D numerical simulations of the Himalayan orogen.
Databáze: OpenAIRE
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