Convective removal of lower lithosphere beneath the Tibetan Plateau can account for a rapid increase in the mean elevation of the Tibetan Plateau of 1000 m or more in a few million years. Such uplift seems to be required by abrupt tectonic and environmental changes in Asia and the Indian Ocean in late Cenozoic time. The composition of basaltic volcanism in northern Tibet, which apparently began at about 13 Ma, implies melting of lithosphere, not asthenosphere. The most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere. The initiation of normal faulting in Tibet at about 8 (± 3) Ma suggests that the plateau underwent an appreciable increase in elevation at that time. An increase due solely to the isostatic response to crustal thickening caused by India's penetration into Eurasia should have been slow and could not have triggered normal faulting. Another process, such as removal of relatively cold, dense lower lithosphere, must have caused a supplemental uplift of the surface. Folding and faulting of the Indo-Australian plate south of India, the most prominent oceanic intraplate deformation on Earth, began between about 7.5 and 8 Ma and indicates an increased north-south compressional stress within the Indo-Australian plate. A Tibetan uplift of only 1000 m, if the result of removal of lower lithosphere, should have increased the compressional stress that the plateau applies to India and that resists India's northward movement, from an amount too small to fold oceanic lithosphere, to one sufficient to do so. The climate of the equatorial Indian Ocean and southern Asia changed at about 6–9 Ma: monsoonal winds apparently strengthened, northern Pakistan became more arid, but weathering of rock in the eastern Himalaya apparently increased. Because of its high altitude and lateral extent, the Tibetan Plateau provides a heat source at midlatitudes that should oppose classical (symmetric) Hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons. For the simple case of axisymmetric heating (no dependence on longitude) of an atmosphere without dissipation, theoretical analyses by Hou, Lindzen, and Plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal (monsoonlike) circulation than such a source centered on the equator, but only if heating exceeds a threshold whose level increases with the latitude of the heat source. Because heating of the atmosphere over Tibet should increase monotonically with elevation of the plateau, a modest uplift (1000–2500 m) of Tibet, already of substantial extent and height, might have been sufficient to exceed a threshold necessary for a strong monsoon. The virtual simultaneity of these phenomena suggests that uplift was rapid: approximately 1000 m to 2500 m in a few million years. Moreover, nearly simultaneously with the late Miocene strengthening of the monsoon, the calcite compensation depth in the oceans dropped, plants using the relatively efficient C4 pathway for photosynthesis evolved rapidly, and atmospheric CO2 seems to have decreased, suggesting causal relationships and positive feedbacks among these phenomena. Both a supplemental uplift of the Himalaya, the southern edge of Tibet, and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the Himalaya that, in turn, enhanced extraction of CO2 from the atmosphere. Thus these correlations offer some support for links between plateau uplift, a downdrawing of CO2 from the atmosphere, and global climate change, as proposed by Raymo, Ruddiman, and Froehlich. Mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts, but might also play an important role in altering regional and global climates.

Mantle dynamics, uplift of the Tibetan Plateau, and the Indian Monsoon

http://www2.ess.ucla.edu/~yin/05-Publications/papers/091-Yin-2006-ESR.pdf

Cenozoic tectonic evolution of the Himalayan orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation

A correlation of tectonic units of the Alpine-Carpathian-Dinaridic system of orogens, including the substrate of the Pannonian and Transylvanian basins, is presented in the form of a map. Combined with a series of crustal-scale cross sections this correlation of tectonic units yields a clearer picture of the three-dimensional architecture of this system of orogens that owes its considerable complexity to multiple overprinting of earlier by younger deformations.

/pdf/the-alpine-carpathian-dinaridic-orogenic-system-correlation-2gm3qeefzn.pdf

The Alpine-Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units

The Himalaya and Tibet provide an unparalleled opportunity to examine the complex ways in which continents respond to collisional orogenesis. This paper is an attempt to synthesize the known geology of this orogenic system, with special attention paid to the tectonic evolution of the Himalaya and southernmost Tibet since India-Eurasia collision at ca. 50 Ma. Two alternative perspectives are developed. The first is largely historical. It includes brief (and necessarily subjective) reviews of the tectonic stratigraphy, the structural geology, and metamorphic geology of the Himalaya. The second focuses on the processes that dictate the behavior of the orogenic system today. It is argued that these processes have not changed substantially over the Miocene–Holocene interval, which suggests that the orogen has achieved a quasi–steady state. This condition implies a rough balance between plate-tectonic processes that lead to the accumulation of energy in the orogen and many other processes (e.g., erosion of the Himalayan front and the lateral flow of the middle and lower crust of Tibet) that lead to the dissipation of energy. The tectonics of the Himalaya and Tibet are thus intimately related; the Himalaya might have evolved very differently had the Tibetan Plateau never have formed.

Tectonics of the Himalaya and southern Tibet from two perspectives

Potassic volcanism has been widespread and semi-continuous on the Tibetan plateau since ~13 Ma, post-dating the orogenic thickening of the India—Asia collision. Volcanism may have commenced slightly earlier (~16—20 Ma) in the southern portion of the plateau arid then ceased around 10 Ma. The dominant lavas are pyroxeneand plagioclase-phyric shoshonites with subordinate occurrences of dacites and rhyolites. Their mineralogy reflects crystallization from high-temperature (^1100°C) magmas which had elevated oxygen and water fugaciti.es. Geochemically, they are characterized by relatively low TiO2, AI2O3 and Fe^Os, and high .A&^Q coupled with variable abundances of compatible trace elements and very high contents of incompatible trace elements. Normalized incompatible element patterns have marked negative Nb, la and Ti anomalies whereas K^O appears to be buffered at ~4% over a wide range of SiO^. Isotope data show a relatively broad and enriched range of^Sr/^Sr (0-7076-0-7106) at more restricted (—5 2 to -8 1). Pb isotopes are characterized by a range of 204 ^Pb/^Pb (38-67-39 SO) /204 pb/20 pb (,5.51_15.72) 207pb/pb (

/pdf/post-collision-shoshonitic-volcanism-on-the-tibetan-plateau-46befoqush.pdf

Post-collision, shoshonitic volcanism on the Tibetan Plateau: implications for convective thinning of the lithosphere and the source of ocean island basalts

Tectonics and plate tectonics model for the Variscan belt of Europe

Accretionary history and crustal evolution of the Variscan belt in Western Europe

The main tectonometamorphic alpine events which occurred in the western part of the western Himalayan virgation at south of the main suture, in northern Pakistan, are dated by the 39Ar/40Ar method. These events are as follows: (1) the blueschist metamorphism (80 ± 5 Ma) present in tectonic/ophiolititic melanges along the suture (this event occurred during an early subduction or obduction stage) (2) the alpine barrovian metamorphism (50–30 Ma) developed in the sedimentary cover and orthogneisses of the Indian Plate during the postcollisional northward underthrusting of this plate below Asia, and (3) the emplacement of postmetamorphic leucogranites (23 Ma) resulting from the melting of the Indian crust during the climax of the alpine metamorphism.

Ages of Alpine tectonometamorphic events in the northwestern Himalaya (northern Pakistan) by 39Ar/40Ar method

New 39Ar−40Ar radiometric data are presented. They concern the metasedimentary series and the orthogneiss pluton of Kangmar. Ages as young as 13 Ma are found which may be related either to the metamorphism or to the resetting of the minerals during the emplacement of the numerous intrusive bodies into the North Himalaya Belt. Inherited excess argon is found in micas from the orthogneiss previously dated at 562 Ma. These bodies are constituted by leucogranitic magmas, the biotites and the muscovites of which the granites intrude (Lhagoi Kangri Massif). Same range of ages is found in the High Himalaya Belt for micas from leucogranites. Ages as young as 4 Ma are found on micas from the southern part of the cross section between Nyalam and Zham. The recent uplifts and/or the movement of recent normal faults may be related to these young ages.

Argon 39-argon 40 dating of metamorphic and plutonic events in the north and high Himalaya belts (southern Tibet-China)

Deep seismic reflection profiling (ECORS program vertical and wide-angle survey) coupled with field and subsurface geology are used to propose a complete NNE–SSW section of the Variscan Belt in western France from Belgium to southern Brittany. On this 800 km long profile, which probably crosses two Paleozoic sutures, the Variscan Belt appears as a broad fanlike orogen characterized by large (100 km) northward and southward overthrusts with polyphase deformation and metamorphism. The central part of the Belt (Central Armorican zone) suffered a simpler dextral shearing parallel to the strike of the belt with only green schist metamorphism. Deep reflection profiling shows that all the large thrusts visible at the surface root deeply in the lower crust or even crosscut the Moho. In the same way, all the large strike-slip faults parallel to the belt appear at depth as narrow discontinuities which crosscut the whole crust and, in some cases, the Moho. The seismically well-layered crust develops essentially at depth in the most deformed and metamorphic internal parts of the belt, in contrast with the relatively transparent Brabant foreland basement, which escaped the Variscan deformation. The Moho appears as a relatively flat boundary at an average depth of 35 km with different characters: It is sharp and strongly reflective both by wide angle and vertical seismics below the internal thrust zones, much less distinct in the central Armorican zone, and only defined by low frequency signals at wide angle below the Brabant foreland. All these characteristics led us to consider the layering of the lower crust and the Moho itself as initially tectonometamorphic features essentially produced by shearing and crust mantle decollement during the Variscan stacking of the crust by intracontinental lithospheric subduction.

Seismic signature and tectonic cross section of the Variscan Crust in western France

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