Three‐dimensional vorticity and time‐constrained evolution of the Main Central Thrust zone, Garhwal Himalaya (NW India)

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 approa...

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Bibliographic Details
Published in:Terra nova (Oxford, England) England), 2020-06, Vol.32 (3), p.215-224
Main Authors: Montemagni, Chiara, Carosi, Rodolfo, Fusi, Nicoletta, Iaccarino, Salvatore, Montomoli, Chiara, Villa, Igor M., Zanchetta, Stefano
Format: Article
Language:English
Subjects:
3D microCT
40Ar/39Ar geochronology
Computed tomography
Deformation
Dimensions
Himalayan Main Central Thrust zone
Kinematic vorticity RGN method
Kinematics
Micas
Shear flow
Shear zone
Tomography
Vorticity
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Summary: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. 40Ar/39Ar 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.
ISSN:0954-4879
1365-3121
DOI:10.1111/ter.12450