History of plate motions:

• India broke free of Antarctica before 70 Ma (part of continued break-up of Gondwana Land) and moved toward Asia at rate of 10 cm/yr.
• collision initiated some 42 Ma (plus or minus several Ma), but some debate.
• rate of motion after collision circa 5 cm/yr which gives 2000 km of crustal overlap to look for
• diagram to right showing the northward movement of India, and collision with the Asian Continent. Image source: http://pubs.usgs.gov/gip/dynamic/himalaya.html .

Simple map view of the orogen. Note the distinctive curvature of the Himalayas, and the two distinct ends. Image source: http://pubs.usgs.gov/gip/dynamic/understanding.html .

Map from USGS showing earthquake distribution in the region.

USGS showing the epicenter of an earthquake in China. Much of the topography depicted here is actively tectonically generated topography. Along with the earthquake map above, they remind the viewer that the deformation associated with the India-Asia collision penetrates deeply into the Asian continent. Image source: http://neic.usgs.gov/neis/last_event/world_china.html .

Some major components of the Himalayas:

• Image of the area in thewestern Himalayas where the UNO GLIMS project had done work on the interplay of erosion, glaciers, climate and tectonics in shaping these mountains. Image source: http://visibleearth.nasa.gov/view_rec.php?id=155 .
• MFT: main frontal thrust, changes with time, deforms Quaternary river terraces .
• MBT: Plio-Pleistocene in age with Triassic Megalodon linestone in hanging wall, stacked passive margin sediments.
• MCT: main central thrust: large basement-involved thrust with > 100 km displacement and folded by underlying thrusts. Overlying basement are Cambrian thorugh Eocene passive margin sediments. Thrust intruded by granites.
• Siwaliks:
  • mid Miocene to Pleistocene (15 Ma-0 ma) molasse sediments.
  • derived from the foreland fold-thrust belt (i.e. the Himalayas).
  • involved in thrusts, which in places ride out over their own sedimentary debris.
  • well known terrestrial vertebrate fauna
• Indus-Tsangbo suture zone: 2 belts of ophiolites with 70 Ma old attached sediments. Glaucophane schists also indicate previous subduction zone metamorphism.
• 15-30 Ma leucogranites (anatectic melts).
• Kohistan arc found on W side, K batholiths and metamorphism, crustal cross section exposed, built on Lhasa block.
• Lhasa block: an accreted terrane with K age deformation.
• Bangong-Nujiang suture: ophiolite thrust onto Middle-Upper Jurassic clastics,but overlain by Middle K volcanic redbed unit -> Lower Cretaceous suturing of Lhasa block.
• Tien Shan Range in NE Tibet - flat lying marine strata from 200-40 Ma.

Visible earth field trip to Himalayas:

• Mountain range flyover .
• Central portion of front range.
• Eastern end.
• Tibetan plateau.
• Strike-slip Kunlun fault.
• More detailed false-color image of Kunlun fault.
• Hindu Kush and W end of Himalayas.
• Sulaiman Mountains in Pakistan (spectacular deformation).
• Of course - Mt. Everest.
• Cal Tech Field Trip to Tien Shan range.

There is about 300 km of shortening in the Himalayas plus 600-700 km to form the crustal thickness observed within the Tibetan plateau. Different workers have somewhat different numbers, but all result in a deficit considering how much plate motion has occurred between the two continents since initial collision. How was the rest accomodated?

Escape tectonics:

• on W side: dextral Herat fault and sinistral Quetta-Chaman fault bound one edge.
• on E side: many more strike-slip faults, more complex, treated as a free boundary to the east, Altyn Tagh sinistral fault and red River dextral fault bount one wedge.
• more information on escape tectonics.

Gravitational collapse: pile it on and it will fail.

Summary:

• A look at the whole thing by Liu, Z., & P. Bird [2008] Kinematic modelling of neotectonics in the Persia-Tibet-Burma orogen, Geophys. J. Int., 172(2), 779–797; doi: 10.1111/j.1365-246X.2007.03640.x, + 3 digital file appendices.
• Summary mechanisms from University of Arizona researcher.