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Three‐dimensional vorticity and time‐constrained evolution of the Main Central Thrust zone, Garhwal Himalaya (NW India)
Author(s) -
Montemagni Chiara,
Carosi Rodolfo,
Fusi Nicoletta,
Iaccarino Salvatore,
Montomoli Chiara,
Villa Igor M.,
Zanchetta Stefano
Publication year - 2020
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/ter.12450
Subject(s) - mylonite , geology , vorticity , shear zone , shearing (physics) , shear (geology) , simple shear , kinematics , seismology , geometry , geodesy , petrology , mechanics , vortex , physics , geotechnical engineering , tectonics , classical mechanics , mathematics
Abstract Vorticity estimates based on porphyroclasts analysis are limited by the extrapolation to three dimensions of two‐dimensional data. We describe a 3D approach based on the use of X‐ray micro‐computed tomography that better reflects the real 3D geometry of the porphyroclasts population. This new approach for kinematic vorticity analysis in the Munsiari Thrust mylonites, the lower boundary of the Main Central Thrust zone (MCTz) in Indian Himalaya, indicates a large pure shear component during non‐coaxial shearing. 40 Ar/ 39 Ar ages of micas along the mylonitic foliation of the Munsiari and Vaikrita thrusts (the upper boundary of the MCTz) constrain thrust activity to 5–4 and 8–9 Ma, respectively. Available kinematic vorticity analyses of the Vaikrita mylonites suggest the dominance of a simple shear component. Combining these data, we suggest that the southward and structurally downward shift of deformation along the MCTz was accompanied by a progressive increase in the pure shear component in a general shear flow.