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 Kubler 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 Delta degrees2 theta. 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 assemblapes 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.