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Tectono-metamorphic evolution of a convergent back-arc; the Famatinian Orogen, Sierra de Quilmes, Sierras Pampeanas, NW Argentina

Melanie A. Finch, Roberto F. Weinberg, Pavlina Hasalova, Raul Becchio, M. Gabriela Fuentes and Allen Kennedy
Tectono-metamorphic evolution of a convergent back-arc; the Famatinian Orogen, Sierra de Quilmes, Sierras Pampeanas, NW Argentina
Geological Society of America Bulletin (December 2017) 129 (11-12): 1602-1621

Abstract

Back-arcs are hot regions of enduring weakness in the hinterland of subduction zones that are commonly sites of strain localization, forming mobile belts that, in some cases, develop into mountain belts. Their evolution results from their strength, a function of thickness, heat flux, and stresses. Contractional back-arcs may be too weak to form thick crusts, whereas in other cases, they can thicken considerably and lead to mountain building. The stress and thermal histories of back-arcs can be retrieved from investigation of the relationships between deformation and metamorphism. The 490-430 Ma Famatinian orogen of the Sierras Pampeanas is associated with a back-arc that has a complex development. We focus on the Sierra de Quilmes within the northern section of the back-arc and present new structural data tied to anatexis and constrained by geochronology. We find that low-pressure-high-temperature conditions prevailed over an approximately 35 m.y. thermal peak between 497 and 461 Ma, as indicated by U/Pb ages of monazite. Anatexis coincided with thrusting to the west and northwest, as evidenced by leucosomes in axial planes of folds and in thrust planes. As rocks were thrust upward, they cooled, melt solidified, and deformation localized into two major thrust zones. These record the same thrust-to-the-west or northwest kinematics as the earlier syn-anatectic deformation and ultimately placed hot rocks over cold ones. Continuous thrusting during cooling from peak metamorphism, accompanied by strain localization, is consistent with a number of shear zones in the northern Sierras Pampeanas. The low-pressure metamorphic assemblages indicate that shortening was not accompanied by pronounced crustal thickening, suggesting that the lithosphere was too hot, and the partially melted crust was too weak for substantial stacking.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 129
Serial Issue: 11-12
Title: Tectono-metamorphic evolution of a convergent back-arc; the Famatinian Orogen, Sierra de Quilmes, Sierras Pampeanas, NW Argentina
Affiliation: Monash University, School of Earth, Atmosphere and Environment, Clayton, Victoria, Australia
Pages: 1602-1621
Published: 201712
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 81
Accession Number: 2018-020380
Categories: Structural geologyIgneous and metamorphic petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2017188
Illustration Description: illus. incl. sects., 2 tables, geol. sketch maps
S26°19'00" - S26°10'00", W66°00'00" - W66°00'00"
Secondary Affiliation: Czech Geological Survey, CZE, Czech RepublicNational University of Salta, ARG, ArgentinaCurtin University, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 201805
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