The India - Eurasia collision, Himalaya and the Tibetan plateau. Some important characteristics: Very long duration of continental collision and shortening Thickest crust and highest topography on earth Active tectonics include both reverse, normal and strike-slip deformation on a large scale Well-constrained plate-motions for the pre- and syn-collision Movement histories Bulge

Indian ocean since mid-early Cretaceous (Aptian) until present From; www.geodynamics.no

(Patriat and Achache, 1984)

Le Pichon et al., 1993

2-D cartoon of plate - tectonic evolution, top speed of India at ca. 60 Ma. 70-80 Ma 50-60 Ma Ca 50 Ma-present

Geological cross-section interpreted based on surface observation across the Himalayas, THE FORELAND SEQUENCE ITS MFT MBT MCT STDS 30 km 50 km

FORELAND FOLD- AND THRUST BELT: Notice the decollement surface in the Eocambrian evaporite sequence. Notice also the negative Bouguer anomaly and the infilling of Tertiary molasse. Thrust loading Pb (see next page)

The flexure of a broken plate is given by : Where Pb = applied line load / unit width (downward acting loads are negative - upward acting loads are positive). The load is applied at the end of the plate, at the break. y = flexure(negative downwards, positive upwards) m = density of material beneath the plate infill = density of material above the plate g = average gravity x = horizontal distance = flexural parameter given by: D = flexural rigidity of the plate given by: E = Youngs Modulus v = Poisson's Ratio Te= Elastic thickness of the lithosphere

Low Himalaya High Himalaya

SEISMIC IMAGE OF THE CRUSTAL STRUCTURE INDIAN CONTINENTAL CRUST HIGH HIMALAYA LOW HIMALAYA SOUTH TIBETAN DETACHMENT INDUS-TSANG PO SUTURE INDIAN CONTINENTAL CRUST SEISMIC IMAGE OF THE CRUSTAL STRUCTURE

SCHEMATIC N-S PROFILE ACROSS THE HIMALAYAS STDS ITS MBT MCT MFT MHT

NB! INTER-PLAY BETWEEN CONTRACTION AND EXTENSION DURING A LONG PERIOD OF COLLISION MCT STDS Low-Himalaya High-Himalaya From: Hodges et al. 1997

THE TRANS-HIMALAYAN-BATHOLITH REMNANT OF THE ANDEAN MARGIN WHICH PRE-DATE THE CLOSURE OF TETHYAN OCEAN (AGE ≈ 95-45 Ma) STDS ITS MBT THB MCT MFT MHT

HIMALAYAN REGIONAL METAMORPHISM, NORMAL AND INVERTED METAMORPHIC GRADIENTS “HOT-IRON” (HOT ON COLD) HYPOTHESIS TRANSPORTED OLDER METAMORPHISM HYPOTHESIS FRICTIONAL HEATING HYPOTESIS

FOLDED METAMORPHIC ISOGRADS INDICATING TRANSPORTED OLDER METAMORPHISM Staurolite Kyanite Sill-Musc Sill-Kspar Leucogranites

HIMALAYAN LEUCO-GRANITES AND PATIAL MELTING

THE SUTURE(S): INDUS - TSANG PO KOHISTAN ARC DEEP SUBDUCTION SPONTANG OPIOLITE DEEP SUBDUCTION OF CONTINETAL LITHOSPHERE (SEISMIC EVENTS) AND REFRACTION STUDIES

THE KOHISTAN ARC, AN ALMOST COMPLETELY PRESERVED ISLAND ARC COMPLEX EXPOSED FROM BASE TO TOP! NOT PRESERVED

CONTINUE WITH PRESENT DAY TECTONICS OF THE HIMALAYAN TIBETAN COLLISION ZONE