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Direct shear fabric dating constrains early Oligocene onset of the south Tibetan detachment in the western Nepal Himalaya

Renaud Soucy La Roche, Laurent Godin, John M. Cottle and Dawn A. Kellett
Direct shear fabric dating constrains early Oligocene onset of the south Tibetan detachment in the western Nepal Himalaya
Geology (Boulder) (April 2016) Pre-Issue Publication

Abstract

A newly identified and dated segment of the South Tibetan detachment in the Karnali klippe, western Nepal Himalaya, constrains initiation of mid-crustal tectonically driven exhumation to the early Oligocene. The folded top-to-the-northeast high-temperature ( approximately 600 degrees C) shear zone separates amphibolite-facies rocks with a ca. 36-30 Ma prograde metamorphic history in the footwall from weakly to non-metamorphosed upper crustal rocks in the hanging wall. In-situ dating of syn-kinematic-post-metamorphic peak monazite indicates that the base of the shear zone was active from ca. 30-29 to <24 Ma, and a post-deformation muscovite cooling age implies that ductile shearing had ceased by ca. 19 Ma. Deformation along the South Tibetan detachment in western Nepal was thus synchronous with thrust-sense shearing along the lower boundary of a zone of migmatitic rocks, compatible with tectonic models involving mid-crustal channelized flow during the Oligocene. Along with other published data from the Himalayan range, this suggests that the South Tibetan detachment actively exhumed the middle crust for almost 20 m.y.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: Pre-Issue Publication
Title: Direct shear fabric dating constrains early Oligocene onset of the south Tibetan detachment in the western Nepal Himalaya
Affiliation: Queen's University, Department of Geological Sciences and Geological Engineering, Kingston, ON, Canada
Published: 20160419
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 22
Accession Number: 2016-054096
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2016132
Illustration Description: illus. incl. geol. sketch map
N27°00'00" - N37°00'00", E72°00'00" - E97°00'00"
N27°00'00" - N30°15'00", E80°00'00" - E88°00'00"
Secondary Affiliation: University of California at Santa Barbara, USA, United StatesGeological Survey of Canada, CAN, Canada
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: 201626
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