Macrostructural and microstructural architecture of the Karakoram fault: Relationship between magmatism and strike-slip faulting

Phillips, R. J. and Searle, M. P. (2007) Macrostructural and microstructural architecture of the Karakoram fault: Relationship between magmatism and strike-slip faulting. Tectonics, 26 (3). TC3017, doi:10.1029/2006TC001946. ISSN 0278-7407 DOI 10.1029/2006TC001946.

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Abstract

A key factor in interpreting the significance of large-scale strike-slip faults in models of continental deformation is an understanding of the temporal relationship between faulting and magmatism. Knowledge of when a strike-slip fault initiated is essential in order to determine its long-term slip rate and its significance in accommodating strain. We review key structural criteria that identify whether magmatism is prekinematic or synkinematic with faulting and apply these criteria to a major Tibet-bounding strike-slip fault. Along the Karakoram fault, in western Tibet, opinion is divided between (1) those advocating that magmatism and shearing were coeval, in which case the youngest U-Pb crystallization age provides a minimum age of shear, and (2) those advocating that magmatism preceded strike-slip shearing, in which case the youngest U-Pb crystallization age provides a maximum age of shear. Fault zone rocks within the central segment of the fault are variably deformed, displaying high- to low-temperature solid-state fabrics. Mylonites indicate subsolidus noncoaxial deformation at temperatures that have not exceeded greenschist–lower amphibolite facies. There is no evidence for submagmatic deformation, and there are no textural or structural indicators that suggest synkinematic magmatism. Consequently, magmatism preceded shearing suggesting that the U-Pb age of proximal leucogranites sets a maximum age for shear. Coupled with a limited offset (<150 km), these data confirm a low long-term slip rate for the Karakoram fault (3–10 mm/yr). Consequently, the fault is unlikely to have played a significant role in accommodating strain during the Indo-Asian collision, and thus its role in suggested extrusion models of deformation is limited.

Item Type: Article
Uncontrolled Keywords: IA45 2007 P
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Tectonics
Volume: 26
Page Range: TC3017, doi:10.1029/2006TC001946
Identification Number: 10.1029/2006TC001946.
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:03
Last Modified: 23 Jul 2013 10:08
URI: http://eprints.esc.cam.ac.uk/id/eprint/595

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