Two end member models of how the high elevations in Tibet formed are (i) continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and (ii) time-dependent, localized shear between coherent lithospheric blocks. Recent studies of Cenozoic deformation, magmatism, and seismic structure lend support to the latter. Since India collided with Asia ∼55 million years ago, the rise of the high Tibetan plateau likely occurred in three main steps, by successive growth and uplift of 300- to 500-kilometer-wide crustal thrust-wedges. The crust thickened, while the mantle, decoupled beneath gently dipping shear zones, did not. Sediment infilling, bathtub-like, of dammed intermontane basins formed flat high plains at each step. The existence of magmatic belts younging northward implies that slabs of Asian mantle subducted one after another under ranges north of the Himalayas. Subduction was oblique and accompanied by extrusion along the left lateral strike-slip faults that slice Tibet's east side. These mechanisms, akin to plate tectonics hidden by thickening crust, with slip-partitioning, account for the dominant growth of the Tibet Plateau toward the east and northeast.

http://science.sciencemag.org/content/sci/294/5547/1671.full.pdf

Oblique Stepwise Rise and Growth of the Tibet Plateau

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

Geological atlas of western and central Europe

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Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism

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

The new tectonic map of the Alps is based on the combination of purely structural data with criteria regarding paleogeographical affiliation and/or tectono-metamorphic evolution. The orogenic evolution of the Alps is discussed using a combination of maps and paleogeographical reconstructions. It is proposed that the Alps are the product of two orogenies, a Cretaceous followed by a Tertiary one. While the former is related to the closure of an embayment of the Meliata ocean into Apulia, the latter is due to the closure of the Alpine Tethys between Apulia and Europe. The along-strike changes in the overall architecture, as for example revealed by geophysical-geological transects, are by far more substantial than hitherto believed. It appears that the Alps are still far from being over-investigated, as is demonstrated by many surprising recent findings based on field geology, laboratory results and geophysical methods of deep sounding.

/pdf/tectonic-map-and-overall-architecture-of-the-alpine-orogen-23efh3jp0j.pdf

Tectonic map and overall architecture of the Alpine orogen

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

Major and trace element, Sr–Nd–Pb–O isotope and mineral INTRODUCTION chemical data are presented for post-collisional ultrapotassic, silicic The high plateau of Tibet, the Himalaya and the Kapotassic and high-K calc-alkaline volcanic rocks from SW Tibet, rakoram Ranges are the product of the continuing colwith Ar/Ar ages in the range 17–25 Ma. The ultrapotassic lision of India with the southern margin of Eurasia during lavas contain mantle xenocrysts (olivine ± rutile/armalcolite). the past 50 my (e.g. Klootwijk & Radhakrishnamurty, Their initial Sr/Sr (0·7172–0·7220) and Nd/Nd 1981). Despite numerous studies of the region, the pro(0·51190–0·51200) ratios suggest that they originated from cesses responsible for the formation of the plateau and lithospheric sources enriched in Rb with low Sm/Nd ratios. Initial the surrounding mountain ranges are still controversial. Pb isotopic compositions ( Pb/Pb = 18·41–18·51; Pb/ Three hypotheses have been suggested to explain the Pb = 15·68–15·72; Pb/Pb = 39·42–39·60) and crustal thickening and altitude of Tibet. In the first geochemical features such as high Th/Ta, low Sr/Nd, low Ce/ (e.g. Argand, 1924; Powell & Conaghan, 1975; Ni & Pb and negative Eu anomalies are consistent with a recycled crustal Baranzagi, 1983), virtually the entire Tibetan plateau is component. Nd depleted mantle model ages range from 1·3 to 1·9 underthrust by Indian lithosphere. In the second (e.g. Ga, whereas Pb model ages record an Archaean event, suggesting Zhao & Morgan, 1985, 1987), thickening is by inflow of that the source had a complex multi-stage evolution. In contrast, material from India. In the third, the crust of Tibet is the high-K calc-alkaline dacites and rhyolites have less enriched interpreted as having thickened by shortening (e.g. Dewey initial Sr (0·7091–0·7097) and Nd (0·51213–0·51225) iso& Burke, 1973). Quantitative analysis of the third model, topic compositions. The presence of zircon xenocrysts with a Pbassuming a vertically average lithosphere rheology, preevaporation age of 471 ± 33 Ma documents the importance of dicts lithospheric thickening and additional uplift of the crustal anatexis in their genesis. Processes responsible for the partial entire plateau by convective thinning of the lower conmelting of metasomatized lithospheric mantle and post-collisional tinental lithosphere (e.g. England & Houseman, 1988, magmatism in the Lhasa block could be a consequence of (1) 1989). Molnar et al. (1993) argued that a sudden increase convective removal of the lower lithosphere or (2) of slab breakoff. in uplift occurred at ~8 Ma and that the start of post-

Post-Collisional Potassic and Ultrapotassic Magmatism in SW Tibet: Geochemical and Sr–Nd–Pb–O Isotopic Constraints for Mantle Source Characteristics and Petrogenesis

Tectonic units of the Alpine collision zone between Eastern Alps and western Turkey

In addition to the well-known Variscan and Alpine orogenic cycles, a Permian thermal event occurred in the European Alps. The geodynamic background of this event is not well understood. Here we suggest that the event is a reflection of lithospheric thinning accompanied by magmatic underplating causing partial melting of the lower crust and low-pressure–high-temperature metamorphism. The event was terminated by Early Triassic opening of the Meliata ocean and was followed by sag-stage subsidence during slow lithospheric cooling. This last stage of the evolution allowed the onset of the Mesozoic marine evolution with the orogen-wide formation of Triassic carbonate platforms well known from the Dolomites and the Northern Calcareous Alps. The combined evidence for magmatism, metamorphism, and late subsidence identifies the Permian event of the Alps as an excellent example of underplating events suggested as a cause for low-pressure–high-temperature terrains worldwide.

Ralf Schuster

Papers

Tectonic map and overall architecture of the Alpine orogen

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

Post-Collisional Potassic and Ultrapotassic Magmatism in SW Tibet: Geochemical and Sr–Nd–Pb–O Isotopic Constraints for Mantle Source Characteristics and Petrogenesis

Tectonic units of the Alpine collision zone between Eastern Alps and western Turkey

Permian metamorphic event in the Alps