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Diagnostic features and processes in the construction and evolution of Oman-, Zagros-, Himalayan-, Karakoram-, and Tibetan-type orogenic belts

By
Michael P. Searle
Michael P. Searle
1
Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK
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Published:
January 01, 2007

The closing of the Tethys Ocean and continent-continent collision along the Alpine-Himalayan chain ultimately produced large Himalayan-type mountain belts and large plateaux, such as Tibet. Earlier stages in the collision process, however, can be seen in the Oman Mountains of eastern Arabia and the Zagros Mountains of SW Iran. In Oman, a large, intact ophiolite was emplaced onto a Mesozoic passive continental margin, largely by thin-skinned thrust processes, prior to continental collision. The ophiolite and a granulite-amphibolite-greenschist facies inverted metamorphic sole were formed in a subduction zone setting during the early stages of emplacement. Eclogites were formed by the attempted subduction of the continental margin, and its rapid expulsion back up the same subduction zone, during later stages of the orogeny. The early stages of continental collision are best seen in the Zagros Mountains where thick-skinned thrusting and simple folding has resulted in a relatively small amount of crustal shortening (50–70 km) with almost no metamorphic or magmatic consequences. Burial metamorphism may be occurring presently at deep levels of the internal zone and the Turkish-Iranian Plateau where the crust is thicker, but this remains unexposed at the surface.

The collision of the Indian plate with Asia since ca. 50 Ma resulted in formation of the Himalaya along the north margin of India, and the Karakoram–Hindu Kush Mountains along the south Asian margin. Together with renewed uplift and crustal thickening of the Tibetan Plateau, this was arguably the largest continental collision in the last 450 m.y. of Earth history. The Himalayan-type orogeny involved large amounts of crustal shortening (∼500–1000 km), early ultrahigh-pressure (UHP) coesite-eclogite facies metamorphism, peak Barrovian facies kyanite and sillimanite metamorphism, and mid-crustal anatexis resulting in garnet, tourmaline, muscovite-bearing migmatites, and leucogranites. Processes involved in the construction of the Tibetan Plateau include crustal shortening and doubling the thickness of the crust to 65–90 km. High-pressure (HP) eclogite and high-temperature/high-pressure (HT-HP) granulite metamorphism may be occurring at depth today in the lower crust beneath Tibet. Widespread ultrapotassic volcanism across Tibet indicates the presence of a hot subcontinental mantle, which was progressively shifted northwards as the cold, Indian lithosphere underthrust southern Tibet. Whereas Tibet shows mainly upper crustal sedimentary and volcanic rocks at the present surface, the Karakoram Range, along strike to the west, shows mostly deep crustal high-grade metamorphic rocks, multiple granite intrusions, and over 60 m.y. of high-temperature metamorphism. This paper reviews the salient geological features of Oman-, Zagros-, Himalayan-, Tibetan-, and Karakoram-type orogenic belts. These features can be used in studies of older orogenic belts to give indications of their tectonic origins.

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GSA Memoirs

4-D Framework of Continental Crust

Robert D. Hatcher, Jr.
Robert D. Hatcher, Jr.
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Marvin P. Carlson
Marvin P. Carlson
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John H. McBride
John H. McBride
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José R. Martínez Catalán
José R. Martínez Catalán
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Geological Society of America
Volume
200
ISBN print:
9780813712000
Publication date:
January 01, 2007

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