subsequent extension-induced exhumation. Geochronological dating of
various Structural, thermobarometric, and geochronological data place
limits on the age and tectonic displacement along the Zanskar shear
zone, a major north-dipping synorogenic extensional structure separating
the high-grade metamorphic sequence of the High Himalayan Crystalline
Sequence from the overlying low-grade sedimentary rocks of the Tethyan
Himalaya, A complete Barrovian metamorphic succession, from kyanite to
biotite zone mineral assemblages, occurs within the I-km-thick Zanskar
shear zone. Thermobarometric data indicate a difference In equilibration
depths of 12 +/- 3 km between the lower kyanite zone and the garnet
zone, which is Interpreted as a minimum estimate for the finite vertical
displacement accommodated by the Zanskar shear zone. For the present-day
dip of the structure (20 degrees), a simple geometrical model shows that
a net slip of 35 +/- 9 km is required to regroup these samples to the
same structural level. Because the kyanite to garnet zone rocks
represent only part of the Zanskar shear zone, and because its original
dip may have been less than the present-day dip, these estimates fur the
finite displacement represent minimum values. Field relations and
petrographic data suggest that migmatization and associated leucogranite
intrusion in the footwall of the Zanskar shear zone occurred as a
continuous profess starting at the Barrovian metamorphic peak and
lasting throughout the subsequent extension-induced exhumation.
Geochronological dataing of various leucogranitic plutons and dikes in
the Zanskar shear zone footwall indicates that the main ductile shearing
along the structure ended by 19.8 Ma and that extension most likely
initiated shortly before 22.2 Ma.