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A structural model for the South Tibetan Detachment system in northwestern Bhutan from integration of temperature, fabric, strain, and kinematic data

Sean P. Long, Connor L. Mullady, Jesslyn K. Starnes, Stacia M. Gordon, Kyle P. Larson, Laura S. Pianowski, Robert B. Miller and Emmanuel Soignard
A structural model for the South Tibetan Detachment system in northwestern Bhutan from integration of temperature, fabric, strain, and kinematic data
Lithosphere (April 2019) 11 (4): 465-487

Abstract

Despite playing a fundamental role in all models of Himalayan tectonics, minimal data constraining the structural evolution, metamorphic history, and offset magnitude of the South Tibetan detachment system (STDS) are available. Here, we integrate petrofabric, finite strain, and kinematic data with metamorphic and deformation temperatures to generate a structural model for the STDS in northwestern Bhutan. We divide the STDS into an approximately 2-km-thick lower level that accommodated approximately 6-13 km of thinning via > or =30-76 km of simple shear-dominant displacement within Greater Himalayan rocks, and an approximately 3-km-thick upper level that accommodated > or =21 km of displacement via an upward decrease (from 44% to 2%) in transport-parallel lengthening within Tethyan Himalayan rocks. Peak metamorphic temperatures in the lower level are approximately 650-750 degrees C, and two distinct intervals of telescoped isotherms in the upper level define a cumulative upward decrease from approximately 700 to approximately 325 degrees C. These intervals are separated by an abrupt upward increase from approximately 450 to approximately 620 degrees C, which we interpret as the result of post-STDS thrust repetition. Above the upper telescoped interval, temperatures gradually decrease upward from approximately 325 to approximately 250 degrees C through a 7-km-thick section of overlying Tethyan Himalayan rocks. Telescoped isotherms lie entirely above the high-strain lower level of the STDS zone, which we attribute to progressive elevation of isotherms during protracted intrusion of granite sills. This study demonstrates the utility of using gradients in fabric intensity and thin section-scale finite strain to delineate shear zone boundaries when field criteria for delineating strain gradients are not apparent.


ISSN: 1941-8264
EISSN: 1947-4253
Serial Title: Lithosphere
Serial Volume: 11
Serial Issue: 4
Title: A structural model for the South Tibetan Detachment system in northwestern Bhutan from integration of temperature, fabric, strain, and kinematic data
Affiliation: Washington State University, School of the Environment, Pullman, WA, United States
Pages: 465-487
Published: 20190416
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 149
Accession Number: 2019-036120
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., 4 tables, geol. sketch maps
N27°30'00" - N28°04'60", E89°15'00" - E89°40'00"
Secondary Affiliation: University of Nevada at Reno, USA, United StatesUniversity of British Columbia Okanagan, CAN, CanadaSan Jose State University, USA, United StatesArizona State University, Leroy Eyring Center for Solid State Science, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, 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: 201919
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