An investigation on the evolution of a Himalayan gneiss dome

详细信息    An investigation on the evolution of a Himalayan gneiss dome

• 出版日期：2000.
• 页数：135 p. :
• 第一责任说明：David A. Schneider.
• 分类号：a383.4
• ISBN：0599892692(ebk.) :

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02h0023593 20110629092915.0 cr un||||||||| 110414s2000 xx ||||f|||d||||||||eng | AAI9982858 0599892692(ebk.) : CNY371.35 NGL NGL NGL a383.4 Schneider, David A. An investigation on the evolution of a Himalayan gneiss dome [electronic resource] : Nanga Parbat-Haramosh massif, western syntaxis / David A. Schneider. 2000. 135 p. : digital, PDF file. Source: Dissertation Abstracts International, Volume: 61-08, Section: B, page: 4045. ; Adviser: P. K. Zeitler. Thesis (Ph.D.) -- Lehigh University, 2000. Localized high-grade metamorphic terranes exposed within orogenic belts offer a unique opportunity to examine rocks which were once at great depths and which have enjoyed the various orogenic phases. Many of these terranes are thought to have developed rapidly, exhumed during the late- to post-orogenic stages. The Nanga Parbat-Haramosh massif, western Himalayan syntaxis, exemplifies such a feature. A multidisciplinary approach, with an emphasis on geo- and thermochronology and field observations, allows the tectonic evolution of the massif to be tightly constrained.;The Indian plate rocks which constitute the Nanga Parbat massif initially underwent Eocene metamorphism and Miocene anatexis as a result of collision between India, a juvenile island are, and Asia at about 60 Ma. Indian plate metasedimentary rocks across the western syntaxial region, near Nanga Parbat and Hazara, yield Oligocene mica cooling ages suggesting these rocks were in the shallow crust by that time. Crustal-scale transpression as a result of India-Asia collision and dextral slip along the Karakourm fault created a series of off-stepping domes in the western syntaxial region, upwarping Indian crust and forming the beginnings of the present-day massif. Not only manifested as structural domes, the Late Miocene occurrence is also observed in isotopic signatures. U-Th-Pb crystallization ages on accessory minerals from metamorphic and plutonic sequences along the flanks of Nanga Parbat and at Haramosh indicate heating and related anatexis from 13 Ma to 9.5 Ma. Ar-Ar analyses on medium-closure temperature silicates indicate cooling was concurrent with doming; these patterns are preserved at Haramosh and in the Karakorum, to the north and east. The Nanga Parbat massif, however, has been subsequently overprinted by a distinct high-grade petrologic and structural event. This Plio-Pleistocene episode appears to be spatially restricted to Nanga Parbat (sensu stricto) and has resulted in the formation of 3 Ma migmatites, 1 Ma granites, and recent, rapid exhumation and cooling. Granites are suggested to have formed by vapor-absent crustal melting as a result of this rapid decompression as well as local melting via fluid infiltration through shear zones. Exhumation is dominated by erosion, with an apparent lack of any crustal-scale, normal-motion detachment. Structural modification of Nanga Parbat is primarily accomplished through a pair of conjugate thrust-displacement shear zones, defining a crustal scale antiformal “pop-up structure”, consistent with models predicting doubly-vergent orogen structures/geometries. The shear zones have a spatial and temporal association with magmatism, beginning probably with the Late Miocene doming event and continuing today.;The evolution suggested here for Nanga Parbat indicates that, although the most recent episode has significantly overprinted signatures of previous events, the massif has had a protracted tectonic history, characterized by at least three episodes involving melting and deformation, and is not the product of a single, late-orogenic event. Other gneiss dome-type structures in orogenic belts may have an analogous evolution and should be evaluated in a similar manner. Gneiss Himalaya Mountains. Lehigh University. aCN bNGL http://168.160.16.198/umi/detail_usmark.jsp?searchword=pub_number%3DAAI9982858&singlesearch=no&channelid=%CF%B8%C0%C0&record=1 NGL Bs183 rCNY371.35 ; h1 bs1104