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-motionsfor the pre- and syn-collisionMovement historiesBulge

Indian oceansince mid-earlyCretaceous(Aptian)until present

From; www.geodynamics.no

(Patriat and Achache, 1984)

Le Pichon et al., 1993

70-80 Ma

50-60 Ma

Ca 50 Ma-present

2-D cartoon of plate - tectonic evolution, top speed of India at ca. 60 Ma.

30 km

Geological cross-section interpreted based on surface observation across the Himalayas,•THE FORELAND SEQUENCE

50 km

ITSMCTMBTMFT STDS

FORELAND FOLD- AND THRUST BELT: Notice thedecollement surface in the Eocambrian evaporitesequence. Notice also the negative Bouguer anomalyand 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 actingloads 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 plateinfill = density of material above the plateg = average gravityx = horizontal distance= flexural parameter given by:

D = flexural rigidity of the plate given by:

WhereE = Youngs Modulusv = Poisson's RatioTe= Elastic thickness of the lithosphere

Low Himalaya High Himalaya

LOW HIMALAYA

HIGH HIMALAYA

SOUTH TIBETANDETACHMENT

INDUS-TSANG POSUTURE

SEISMIC IMAGE OF THE CRUSTAL STRUCTURE

INDIAN CONTINENTAL CRUST

SCHEMATICN-S PROFILE ACROSS THE HIMALAYAS

MHT

ITS

MCT

MBT

MFT

STDS

High-Himalaya

NB! INTER-PLAY BETWEENCONTRACTION AND EXTENSION DURINGA LONG PERIOD OFCOLLISION

Low-Himalaya

MCT STDS

From: Hodges et al. 1997

THE TRANS-HIMALAYAN-BATHOLITHREMNANT OF THE ANDEAN MARGIN WHICH PRE-DATETHE CLOSURE OF TETHYAN OCEAN (AGE ≈ 95-45 Ma)

MHT

ITS

MCT

MBT

MFT

STDS

THB

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 OLDERMETAMORPHISMStaurolite

Kyanite

Sill-Musc

Sill-Kspar

Leucogranites

HIMALAYAN LEUCO-GRANITES AND PATIAL MELTING

THE SUTURE(S):INDUS -TSANG POKOHISTAN ARC

DEEP SUBDUCTIONOF CONTINETALLITHOSPHERE(SEISMIC EVENTS)AND REFRACTIONSTUDIES

SPONTANGOPIOLITE

THE KOHISTAN ARC, AN ALMOST COMPLETELY PRESERVED ISLAND ARC COMPLEX EXPOSED FROMBASE TO TOP!

NOT PRESERVED

CONTINUE WITH PRESENT DAY TECTONICS OF

THE HIMALAYAN TIBETAN COLLISION ZONE