Crustal shortening, exhumation, and strain localization in a collisional orogen: The Bajo Pequeño Shear Zone, Sierra de Pie de Palo, Argentina

Joshua M Garber; Sarah M Roeske; Jessica Warren; Sean R Mulcahy; William C McClelland; Lauren J Austin; Paul R Renne; Graciela I Vujovich

doi:10.1002/2013TC003477

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Crustal shortening, exhumation, and strain localization in a collisional orogen: The Bajo Pequeño Shear Zone, Sierra de Pie de Palo, Argentina

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Crustal shortening, exhumation, and strain localization in a collisional orogen: The Bajo Pequeño Shear Zone, Sierra de Pie de Palo, Argentina

Joshua M Garber, Sarah M Roeske, Jessica Warren, Sean R Mulcahy, William C McClelland, Lauren J Austin, Paul R Renne and Graciela I Vujovich

Tectonics, Vol.33(7), pp.1277-1303

07/2014

DOI: 10.1002/2013TC003477

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Abstract

The Bajo Pequeño Shear Zone (BPSZ) is a lower‐crustal shear zone that records shortening and exhumation associated with the establishment of a new plate boundary, and its placement in a regional structural context suggests that local‐ to regional‐scale strain localization occurred with progressive deformation. A kilometer‐scale field and analytical cross section through the ~80 m thick BPSZ and its adjacent rocks indicates an early Devonian (405–400 Ma) phase of deformation on the western margin of Gondwanan continental crust. The earliest stages of the BPSZ, recorded by metamorphic and microstructural data, involved thrusting of a hotter orthogneiss over a relatively cool pelitic unit, which resulted in footwall garnet growth and reset footwall white mica 40Ar/39Ar ages in proximity to the shear zone. Later stages of BPSZ activity, as recorded by additional microstructures and quartz c‐axis opening angles, were characterized by strain localization to the center of the shear zone coincident with cooling and exhumation. These and other data suggest that significant regional tectonism persisted in the Famatinian orogenic system for 60–70 million years after one microplate collision (the Precordillera) but ceased 5–10 million years prior to another (Chilenia). A survey of other synchronous structures shows that strain was accommodated on progressively narrower structures with time, indicating a regional pattern of strain localization and broad thermal relaxation as the Precordillera collision evolved. Key Points BPSZ deformation is associated with the establishment of a new plate boundary Strain localization in the BPSZ overprints an early inverted thermal gradient Structures in the Famatinian system show strain localization over ~70 Myr

convergent margin

Pie de Palo

collisional orogen

ductile shear zone

lower crust

Details

Title: Subtitle: Crustal shortening, exhumation, and strain localization in a collisional orogen: The Bajo Pequeño Shear Zone, Sierra de Pie de Palo, Argentina
Creators: Joshua M Garber - University of California
Sarah M Roeske - University of California
Jessica Warren - Stanford University
Sean R Mulcahy - University of California
William C McClelland - University of Iowa
Lauren J Austin - University of Oregon
Paul R Renne - Berkeley Geochronology Center
Graciela I Vujovich - Universidad de Buenos Aires
Resource Type: Journal article
Publication Details: Tectonics, Vol.33(7), pp.1277-1303
DOI: 10.1002/2013TC003477
ISSN: 0278-7407
eISSN: 1944-9194
Number of pages: 27
Language: English
Date published: 07/2014
Academic Unit: Earth and Environmental Sciences
Record Identifier: 9983984520902771

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