Some aspects of collision tectonics in the Indus Suture Zone, Ladakh

In the Indus Suture Zone, five tectonic zones can be recognized, which are from N to S: (i) the Ladakh or Trans-Himalayan Batholith (103-25 Ma) and the Dras Volcano-plutonic Group; (ii) the Indus Detrital Group with marine formations of Aptian to Ilerdian age (103-45 Ma) and continental formations of Oligocene-?Miocene age; (iii) the Nindam (Cretaceous) and Lamayuru (Ladinian-Dogger) Flysch Nappes; (iv) the Zanskar Structural Nappe Complex (Upper Palaeozoic-Ilerdian) resting on a metamorphic 'basement'; and (v) the Spongtang-Photaksar Ophiolitic Nappe. Several folding phases affect these tectonic units; analyses of mesoscopic and microscopic structures show a polyphase tectonic history with a syn-metamorphic cleavage (S-1 or S1-2, striking 090-120 degrees) which is axial planar to recumbent folds associated with a N-S mineral lineation, a fracture cleavage (striking 120 degrees) which varies in dip and this is cut by a still later steeply dipping fracture cleavage striking 030-040 degrees. The tectonic contacts, the kinematics, relative chronology and structural evolution are discussed. We propose that the structural sequence results from continuous N-S compression occurring during collision.