The Himalayan Mountain Ranges is the most complex system of mountain-building orogeny on Earth. Evidence of previous upper volcanic activity and lower magma uplifts are extensively present over the entire Himalaya Belt.
As the plates collided, the sinking Indian Plate generated extensive volcanoes in southern Tibet because the rock at the top of the plate melted from friction and huge pressures of the collision. Today, the tibetan Plateau is dotted with young volcanoes.
The High Himalayas consist of a continuous belt of thick crustal stacking of metasedimentary and metaigneous rocks and associated granites, with a very complex deformational history. The base of the High Himalayas is made up of metamorphic rocks: schists formed from muds and sands that crystallised as a result of the collision. These are predominantly clastic metasedimentary rocks. Gneisses in this base layer are overlain by a thick layer of amphibolite calcareous rocks in many areas of central Nepalese Himalayas. Higher up are two huge bands of granite. Nearer the top the rocks are sedimentary. Within a few hundred metres of the summit is a formation known to climbers as the ‘Yellow Band’. This layer of shale, sandstone and limestone is made up of marine silts, clays and animal remains from the bed of the Tethys Ocean.
The tectonostratigraphy of the Himalayan belt is divided into the Tibetan Himalaya, Greater Himalaya, Lesser Himalaya, and Subhimalaya zones. Separating the zones are major fault systems: the South Tibetan Detachment system (STDS) between the Tibetan Plateau and Higher Himalayas, the Main Central Thrust (MCT) between the Higher and Lesser Himalayas, and the Main Boundary Thrust (MBT) between the Lesser Himalaya and Subhimalaya. Other important structures include the Ramgarh and Main Frontal Thrusts (MFT) and the Lesser Himalayan duplex.
The two parallel granite belts span the Higher Himalayas running parallel to the South Tibetan Detachment system (STDS). It is thought that these granite belts were formed during the evolution of the Main Central Thrust (MCT) from the (STDS): a decollement thrust. The (MCT) separates the high-grade metamorphic rocks of the Higher Himalaya crystalline hanging wall from the weakly metamorphosed series of the Lesser Himalaya footwall. The Main Frontal Thrust (MFT) is also decollement thrust with no basement involvement at least as far north as the downdip projection of the Main Boundary Thrust system (MBT). The (MBT) separates the metapsammitic schists and phyllites of the Lesser Himalaya hanging wall from the conglomerates and sandstones of the Sub-Himalaya footwall. The (MFT) is a low-angle, basal thrust along which the Indian plate is subducted beneath the Himalaya and southern Tibet and into which the (MBT) and (MCT) system root. The basal Himalayan Sole thrust (HST) becomes basement north of the downdip projection of the (MCT), or approximately at the latitude of the Himalayan range crest.
(http://www.gsajournals.org/gsaonlin....1130/0091-7613(2003)031<0359:KMFTMC>2.0.CO;2)
The two seperate granite belts are thought to have been created by discontinuous melting reactions during the thrust surface slip that dips shallowly through the metamorphically stratified crust. Depending on the position of magma emplacement above the (STDS), the spacing approximates the distance between the two plates. The granites are embedded within Tethyan medasedimentary rocks and appear to have high melting temperatures.
http://sims.ess.ucla.edu/pdf/Harrison_et_al_GEOLOGY_1997.pdf
Hot-spring waters near the Main Central Thrust (MCT) in the Marsyandi River of central Nepal are caused by hydrothermal interactions with the tectonic metamorphic flux processes below, indicative of magma activity. This area is marked by thrusting and active uplifting. The Marsyandi River marks the transition from a region of rapid uplift in the Higher Himalayan ranges to a region of slower uplift to the south. http://www.geo.cornell.edu/geology/research/derry/publications/Evans_Geology_01.pdf
An active deformation of surface-rupture earthquakes, uplift of stream terraces, active foldinging and uplifting indicates that the Himalayan Frontal Thrust (HFT) and the Kunlun fault that divides the Tibetan Plateau are tectonically the most active zone areas across the whole of the Himalayas. (www.ias.ac.in/currsci/jun102004/1554.pdf)
Apart from the strike-slip faulting there are important variations in compressional structural. The Main Mantle Thrust (MMT) of Indian continental crust beneath the principal Tethyan suture zone now has a vertical attitude suggesting a strong buckling component associated with this thrusting. It seems most likely that uplift along the northern Indus valley section occurred by buckle folding and East-West flattening. The transition between the thrust-fold geometries at Liachar portion of the MMT and the kilometric buckle fold at Sassi apparently involves a series of ductile shear zones exposed along the Ramghat section.
http://earth.leeds.ac.uk/tectonics/nanga_parbat/parbatepsl.pdf
There are extensive igneous rock plutons formed from magma in the Northern Ignus-Tsangpo Suture Zone (ITSZ) formed due to melting of the crust during the terminal collision. the Main Central Thrust (MCT) brought the magma of the deep continental crust to lie on top of the Lesser Himalaya Zone (LHZ), Midland Formation in Nepal. This magma rose above the MCT lowering the solidus in the hot High Himalaya Crystalline Zone (HHCZ) and produced melts. The melt rose through the metamorphic piles along giant dykes and sills and emplaced at the contact between the HHCZ and High Himalaya Sedimentary Zone (HHSZ). Many of the Himalayan leucogranite plutons are indeed underlain and fed by giant dyke and sill complexes. However, there is no evidence of partial melting in the rocks occurring in the immediate hangingwall of the MCT, and the footwalls of the MCT is occupied by sedimentary or very low grade metamorphic rocks that do not appear to have given off large amount of fluid.
melting model for the Himalayan leucogranite. thrusting along MCT caused metamorphism in the footwall (LHZ) releasing H2O+CO2 fluid that triggered partial melting in the hangingwall (HHCZ). The melts emplaced at higher structural levels along giant dikes.
Following the collision, the continued convergence resulted in the frontal part of the Indian plate to get thrusted back onto itself (reverse folding). This detachment is referred to as the Main Himalayan Thrust (MHT).
The frontal part of the Indian continental crust thrusted back onto itself along a northerly dipping detachment. This detachment is also called Main Himalayan Thrust (MHT) that extends into south Tibet and possibly north of Indus-Tsangpo Suture Zone (ITSZ). The black line above the Indian Ocean Crust represents partially molten crust, as imaged in seismic profiling. The calculated thermal structure shown assumes a horizontal MHT at a depth of 30 km and a depth to mantle at 80 km.
Partial melting affects the thickened Himalayan crust, both along and across the orogen as well as at different depths. Depending on the values of heat-flow parameters, it is also possible for the transient geotherms to have steeper gradient than the initial (i.e., at the time of thrusting) geothermal gradient. Consequently, partial melting and emplacement of granitic magma may be continuing to the present day. Very young ages obtained from some of the plutons and high surface heat flow in Tibetan plateau supports this contention. This is also in conformity with the deduction from seismic data of a partial molten crust in southern Tibet.
Sources:
"A melting mechanism for the Himalayan leucogranite," by Dilip K. Mukhopadhyay, Journal of the Virtual Explorer, Vol. 11, 2003.
http://www.virtualexplorer.com.au/2003/11/05/
"Tectonics of the Himalaya and southern Tibet from two perspectives," K. V. Hodges, Geological Society of America Bulletin: Vol. 112, No. 3, pp. 324–350, 2000.
http://www.gsajournals.org/gsaonlin...0.1130/0016-7606(2000)112<324:TOTHAS>2.0.CO;2
As the plates collided, the sinking Indian Plate generated extensive volcanoes in southern Tibet because the rock at the top of the plate melted from friction and huge pressures of the collision. Today, the tibetan Plateau is dotted with young volcanoes.
The High Himalayas consist of a continuous belt of thick crustal stacking of metasedimentary and metaigneous rocks and associated granites, with a very complex deformational history. The base of the High Himalayas is made up of metamorphic rocks: schists formed from muds and sands that crystallised as a result of the collision. These are predominantly clastic metasedimentary rocks. Gneisses in this base layer are overlain by a thick layer of amphibolite calcareous rocks in many areas of central Nepalese Himalayas. Higher up are two huge bands of granite. Nearer the top the rocks are sedimentary. Within a few hundred metres of the summit is a formation known to climbers as the ‘Yellow Band’. This layer of shale, sandstone and limestone is made up of marine silts, clays and animal remains from the bed of the Tethys Ocean.
The tectonostratigraphy of the Himalayan belt is divided into the Tibetan Himalaya, Greater Himalaya, Lesser Himalaya, and Subhimalaya zones. Separating the zones are major fault systems: the South Tibetan Detachment system (STDS) between the Tibetan Plateau and Higher Himalayas, the Main Central Thrust (MCT) between the Higher and Lesser Himalayas, and the Main Boundary Thrust (MBT) between the Lesser Himalaya and Subhimalaya. Other important structures include the Ramgarh and Main Frontal Thrusts (MFT) and the Lesser Himalayan duplex.
The two parallel granite belts span the Higher Himalayas running parallel to the South Tibetan Detachment system (STDS). It is thought that these granite belts were formed during the evolution of the Main Central Thrust (MCT) from the (STDS): a decollement thrust. The (MCT) separates the high-grade metamorphic rocks of the Higher Himalaya crystalline hanging wall from the weakly metamorphosed series of the Lesser Himalaya footwall. The Main Frontal Thrust (MFT) is also decollement thrust with no basement involvement at least as far north as the downdip projection of the Main Boundary Thrust system (MBT). The (MBT) separates the metapsammitic schists and phyllites of the Lesser Himalaya hanging wall from the conglomerates and sandstones of the Sub-Himalaya footwall. The (MFT) is a low-angle, basal thrust along which the Indian plate is subducted beneath the Himalaya and southern Tibet and into which the (MBT) and (MCT) system root. The basal Himalayan Sole thrust (HST) becomes basement north of the downdip projection of the (MCT), or approximately at the latitude of the Himalayan range crest.
(http://www.gsajournals.org/gsaonlin....1130/0091-7613(2003)031<0359:KMFTMC>2.0.CO;2)
The two seperate granite belts are thought to have been created by discontinuous melting reactions during the thrust surface slip that dips shallowly through the metamorphically stratified crust. Depending on the position of magma emplacement above the (STDS), the spacing approximates the distance between the two plates. The granites are embedded within Tethyan medasedimentary rocks and appear to have high melting temperatures.
http://sims.ess.ucla.edu/pdf/Harrison_et_al_GEOLOGY_1997.pdf
Hot-spring waters near the Main Central Thrust (MCT) in the Marsyandi River of central Nepal are caused by hydrothermal interactions with the tectonic metamorphic flux processes below, indicative of magma activity. This area is marked by thrusting and active uplifting. The Marsyandi River marks the transition from a region of rapid uplift in the Higher Himalayan ranges to a region of slower uplift to the south. http://www.geo.cornell.edu/geology/research/derry/publications/Evans_Geology_01.pdf
An active deformation of surface-rupture earthquakes, uplift of stream terraces, active foldinging and uplifting indicates that the Himalayan Frontal Thrust (HFT) and the Kunlun fault that divides the Tibetan Plateau are tectonically the most active zone areas across the whole of the Himalayas. (www.ias.ac.in/currsci/jun102004/1554.pdf)
Apart from the strike-slip faulting there are important variations in compressional structural. The Main Mantle Thrust (MMT) of Indian continental crust beneath the principal Tethyan suture zone now has a vertical attitude suggesting a strong buckling component associated with this thrusting. It seems most likely that uplift along the northern Indus valley section occurred by buckle folding and East-West flattening. The transition between the thrust-fold geometries at Liachar portion of the MMT and the kilometric buckle fold at Sassi apparently involves a series of ductile shear zones exposed along the Ramghat section.
http://earth.leeds.ac.uk/tectonics/nanga_parbat/parbatepsl.pdf
There are extensive igneous rock plutons formed from magma in the Northern Ignus-Tsangpo Suture Zone (ITSZ) formed due to melting of the crust during the terminal collision. the Main Central Thrust (MCT) brought the magma of the deep continental crust to lie on top of the Lesser Himalaya Zone (LHZ), Midland Formation in Nepal. This magma rose above the MCT lowering the solidus in the hot High Himalaya Crystalline Zone (HHCZ) and produced melts. The melt rose through the metamorphic piles along giant dykes and sills and emplaced at the contact between the HHCZ and High Himalaya Sedimentary Zone (HHSZ). Many of the Himalayan leucogranite plutons are indeed underlain and fed by giant dyke and sill complexes. However, there is no evidence of partial melting in the rocks occurring in the immediate hangingwall of the MCT, and the footwalls of the MCT is occupied by sedimentary or very low grade metamorphic rocks that do not appear to have given off large amount of fluid.
melting model for the Himalayan leucogranite. thrusting along MCT caused metamorphism in the footwall (LHZ) releasing H2O+CO2 fluid that triggered partial melting in the hangingwall (HHCZ). The melts emplaced at higher structural levels along giant dikes.
Following the collision, the continued convergence resulted in the frontal part of the Indian plate to get thrusted back onto itself (reverse folding). This detachment is referred to as the Main Himalayan Thrust (MHT).
The frontal part of the Indian continental crust thrusted back onto itself along a northerly dipping detachment. This detachment is also called Main Himalayan Thrust (MHT) that extends into south Tibet and possibly north of Indus-Tsangpo Suture Zone (ITSZ). The black line above the Indian Ocean Crust represents partially molten crust, as imaged in seismic profiling. The calculated thermal structure shown assumes a horizontal MHT at a depth of 30 km and a depth to mantle at 80 km.
Partial melting affects the thickened Himalayan crust, both along and across the orogen as well as at different depths. Depending on the values of heat-flow parameters, it is also possible for the transient geotherms to have steeper gradient than the initial (i.e., at the time of thrusting) geothermal gradient. Consequently, partial melting and emplacement of granitic magma may be continuing to the present day. Very young ages obtained from some of the plutons and high surface heat flow in Tibetan plateau supports this contention. This is also in conformity with the deduction from seismic data of a partial molten crust in southern Tibet.
Sources:
"A melting mechanism for the Himalayan leucogranite," by Dilip K. Mukhopadhyay, Journal of the Virtual Explorer, Vol. 11, 2003.
http://www.virtualexplorer.com.au/2003/11/05/
"Tectonics of the Himalaya and southern Tibet from two perspectives," K. V. Hodges, Geological Society of America Bulletin: Vol. 112, No. 3, pp. 324–350, 2000.
http://www.gsajournals.org/gsaonlin...0.1130/0016-7606(2000)112<324:TOTHAS>2.0.CO;2
