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Petrogenesis of Upper Paleozoic post-collisional peraluminous leucogranites, Sierra de Ancasti, northwest Argentina

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Abstract:

The Santa Rosa and Sauce Guacho plutons are two post-collisional peraluminous Late Devonian to Early Carboniferous leucogranites that intruded the banded schists of the Ancasti Formation. The leucogranites are composed of microcline phenocrysts along with quartz, plagioclase, muscovite, biotite, ilmenite, tourmaline, apatite, monazite and zircon. Their geochemical composition is consistent with S-type granites and mineralogically they belong to MPG granites (muscovite-peraluminous granites). It is proposed that granite magma generation was related to shear zones that concentrated fluids in the metasedimentary crust during a collision or transcurrent tectonics. U-Pb analyses on monazite gave an age of 369.8 ± 5.3 Ma, while Sm/Nd isotopic data yield εNd(t) values of −5.3 for Sauce Guacho and −5.7 for Santa Rosa indicating crustal provenance. Nd model ages between 1,544 and 1,571 Ma are within the range of magmatic rocks from the Lower Ordovician Famatinian Arc in the Central Sierras Pampeanas.

Spanish
Los plutones de Santa Rosa y Suace Guacho son granitos peraluminosos post-colisionales del Devónico superior al Carbonífero inferior, que intruyen en los esquistos bandeados de la Formación Ancasti. Ambos son leucogranitos compuestos por fenocristales de microclina, con cuarzo, plagioclasa, moscovita, biotita, ilmenita, turmalina, apatita, monacita y circón. La composición química corresponde a granitos tipo-S y la mineralogía permite su asignación a los granitos MPG (granitos peraluminosos con moscovita). La génesis se relacionaría con fusión en zonas de cizalla que concentran fluidos en la corteza metasedimentaria durante una tectónica de colisión o de transcurrencia. La edad U-Pb sobre monacita es de 369,8 ± 5,3 Ma, y las determinaciones Sm-Nd, dan para Sauce Guacho valores de εNdt de −5,3 y para Santa Rosa εNdt de −5,7, que evidencian proveniencia cortical. Las edades modelo de Nd de 1.544 a 1.571 Ma se corresponden con el rango del Arco Famatiniano de las Sierras Pampeanas Centrales.

Keywords: LEUCOGRANITES; PERALUMINOUS; POST-COLLISIONAL; SIERRAS PAMPEANAS; U-PB GEOCHRONOLOGY; UPPER-PALEOZOIC

Document Type: Research Article

DOI: http://dx.doi.org/10.1127/0077-7749/2011/0152

Publication date: August 1, 2011

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