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Himalayan gneiss dome formation in the middle crust and exhumation by normal faulting; new geochronology of Gianbul Dome, northwestern India

Forrest Horton, Jeffrey Lee, Bradley Hacker, Meilani Bowman-Kamaha'o and Michael Cosca
Himalayan gneiss dome formation in the middle crust and exhumation by normal faulting; new geochronology of Gianbul Dome, northwestern India
Geological Society of America Bulletin (July 2014) 127 (1-2): 162-180

Abstract

A general lack of consensus about the origin of Himalayan gneiss domes hinders accurate thermomechanical modeling of the orogen. To test whether doming resulted from tectonic contraction (e.g., thrust duplex formation, antiformal bending above a thrust ramp, etc.), channel flow, or via the buoyant rise of anatectic melts, this study investigates the depth and timing of doming processes for Gianbul dome in the western Himalaya. The dome is composed of Greater Himalayan Sequence migmatite, Paleozoic orthogneiss, and metasedimentary rock cut by multiple generations of leucogranite dikes. These rocks record a major penetrative D2 deformational event characterized by a domed foliation and associated NE-SW-trending stretching lineation, and they are flanked by the top-down-to-the-SW (normal-sense) Khanjar shear zone and the top-down-to-the-NE (normal sense) Zanskar shear zone (the western equivalent of the South Tibetan detachment system). Monazite U/Th-Pb geochronology records (1) Paleozoic emplacement of the Kade orthogneiss and associated granite dikes; (2) prograde Barrovian metamorphism from 37 to 33 Ma; (3) doming driven by upper-crustal extension and positive buoyancy of decompression melts between 26 and 22 Ma; and (4) the injection of anatectic melts into the upper levels of the dome-neutralizing the effects of melt buoyancy and potentially adding strength to the host rock-by ca. 22.6 Ma on the southwestern flank and ca. 21 Ma on the northeastern flank. As shown by a northeastward decrease in (super 40) Ar/ (super 39) Ar muscovite dates from 22.4 to 20.2 Ma, ductile normal-sense displacement within the Zanskar shear zone ended by ca. 22 Ma, after which the Gianbul dome was exhumed as part of a rigid footwall block below the brittle Zanskar normal fault, tilting an estimated 5 degrees -10 degrees SW into its present orientation.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 127
Serial Issue: 1-2
Title: Himalayan gneiss dome formation in the middle crust and exhumation by normal faulting; new geochronology of Gianbul Dome, northwestern India
Affiliation: University of California, Santa Barbara, Department of Earth Science, Santa Barbara, CA, United States
Pages: 162-180
Published: 20140716
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 85
Accession Number: 2015-002421
Categories: Structural geologyIgneous and metamorphic petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
N07°00'00" - N37°00'00", E68°00'00" - E97°00'00"
Secondary Affiliation: Central Washington University, USA, United StatesU. S. Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201502
Program Name: USGSOPNon-USGS publications with USGS authors
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