Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike-slip
shear zone: The case of the right-lateral Karakorum fault


Emmanuelle Boutonnet 1, P. H. Leloup 1, N. Arnaud, 2 J.-L. Paquette 3,  W. J. Davis 4, and K. Hattori 5

1 LGL-TPE Laboratoire de Géologie de Lyon: Terre, Planètes, Environnement, UMR CNRS 5276, Université Claude Bernard Lyon 1–ENS, Lyon, France.
2 Géosciences Montpellier, UMR CNRS 5243, Université de Montpellier, Montpellier, France.
3 Laboratoire Magma et Volcans, UMR CNRS 6524, Université Blaise Pascal, Université de Clermont-Ferrand, Clermont-Ferrand, France.
4 ESS/GSC-CNCB/GSC-CC/GEOCHRON, Geological Survey of Canada, Ottawa, Ontario, Canada.
5 Department of Earth Sciences, University of Ottawa, Ottawa, Ontario,
Canada.

Abstract:
New structural observations coupled with 15 U/Pb and 24 Ar/Ar new ages from the Karakorum shear zone (KSZ) constrain the timing and slip rate of the right-lateral Karakorum fault zone (KFZ), one of the great continental Asian strike-slip faults. In the Tangtse-Darbuk area, the Tangtse (SW) and Muglib (NE) mylonitic strands of the KSZ frame the less deformed Pangong Range. Inherited U/Pb ages show that granitic protoliths are mostly from the Karakorum and Ladakh batoliths, with a major Miocene melting event lasting from ≥21.5 to 13.5 Ma. Some of the Miocene granitic bodies show structural evidence for intrusion synkinematic to the KSZ. The oldest of these granitoids is 18.8 ± 0.4 Ma old, implying that deformation started prior to ~19 Ma. Microstructural data show that right-lateral deformation pursued during cooling. Ar/Ar data show that ductile deformation stopped earlier in the Tangtse (~11 Ma) than in the Muglib strand (~7 Ma). Deformation ended at ~11 Ma in the Tangtse strand while it is still active in the Muglib strand, suggesting a progressive localization of deformation. When merged with published observations along the KFZ, these data suggest that the KFZ nucleated in theNorth Ayilari range at least ~22 Ma ago. The long-term fault rate is 0.84 to 1.3 cm/yr, considering a total offset of 200 to 240 km. The KSZ collected magma produced within the shear zone and/or deeper in crust for which the producing mechanism stays unclear butwas not the lower crustal channel flow.

Citation: Boutonnet, E., P. H. Leloup, N. Arnaud, J.-L. Paquette, W. J. Davis, and K. Hattori (2012), Synkinematic magmatism,
heterogeneous deformation, and progressive strain localization in a strike-slip shear zone: The case of the right-lateral Karakorum
fault, Tectonics, 31, TC4012, doi:10.1029/2011TC003049. 

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The Karakorum fault zone