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Synorogenic extension in the Tethyan Himalaya documented by structural studies and the Kübler index, Lachung La area, NW India

Published online by Cambridge University Press:  09 July 2018

M. Girard ,
P. Thélin  and
A. Steck
M. Girard*
Affiliation:
Institut de Minéralogie et Petrographie, Université de Lausanne, BFSH2, CH-1015 Lausanne, Switzerland
P. Thélin
Affiliation:
Institut de Minéralogie et Petrographie, Université de Lausanne, BFSH2, CH-1015 Lausanne, Switzerland
A. Steck
Affiliation:
Institut de Minéralogie et Petrographie, Université de Lausanne, BFSH2, CH-1015 Lausanne, Switzerland
*
*E-mail: matthieu.girard@imp.unil.ch
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Abstract

Tectonic observations in the Tethyan Himalaya reveal an important extensional event that succeeds the emplacement of SW-verging nappes. A major thrust, called the Kum Tso Thrust, has been backfolded and reactivated by normal faulting associated with this event.

Measurements of the Kübler index, coupled with characterization of clay-size paragenesis show the effect of normal faulting on the regional metamorphic zonation and indicate that important extension zones, like the Sarchu-Lachung La Normal Fault Zone (SLFZ), exist within the Tethyan Himalaya. Diagenetic limestones from within the SLFZ are characterized by the occurrence of mixed-layered clay phases, kaolinite and an illite with a 001 peak >0.4 Δ°2θ. This zone is bordered by two anchizonal-to-epizonal zones, where illite peaks become narrower. Further to the NE the successive appearance of biotite, chloritoid, garnet and garnet-staurolite-kyanite assemblages testifies to an increase in metamorphic grade. The cataclastic samples from the normal faults contain kaolinite, smectite and a ‘broad’ illite, indicating that extension occurs under diagenetic conditions.

Keywords

Tethyan HimalayaKübler indexIndiamixed-layer clay phases
Type
Research Article
Information
Clay Minerals , Volume 36 , Issue 2 , June 2001 , pp. 237 - 247
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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