INGEIS   05370
INSTITUTO DE GEOCRONOLOGIA Y GEOLOGIA ISOTOPICA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Middle Devonian magmatism of the Sierra de San Luis.
Autor/es:
MÓNICA G. LÓPEZ DE LUCHI; NOELIA FLAVIA IANNIZZOTTO; SIEGFRIED SIEGESMUND; KLAUS WEMMER; ANDRE STEENKEN
Lugar:
Neuquén
Reunión:
Congreso; 18 Congreso Geológico Argentino; 2011
Institución organizadora:
Universidad del Comahue
Resumen:
Middle Devonian batholiths which intruded the basement of the Eastern Sierras Pampeanas during the Achalian orogeny  are located along a belt almost parallel to the trend of the Ordovician Famatinian orogen from the Sierra de San Luis (SL) in the south, to the Sierra de Córdoba (SC) in the north. This magmatism could continue farther north in the Early Carboniferous granitoids of the Sierra de Velasco. In SL voluminous Middle Devonian batholiths are made up by a I-type to A-type hybrid monzonite?granite suite with metaluminous magnesian alkali-calcic (393-385 Ma) porphyritic to equigranular monzonite- quartz monzonite? granodiorite±calc-alkalic monzogranite and mildly peraluminous magnesian to ferroan alkali-calcic equigranular monzogranites. Middle Devonian crystallization ages of the batholiths, structural features and geochronological constraints on the activity of the crustal scale shear zones of the Sierra de San Luis (López de Luchi et al.  2004, 2007 and references therein) indicate that at a regional scale the emplacement of the Devonian batholiths is syn-kinematic. A continuum from magmatic to high temperature solid-state microstructural features indicates the involvement of regional shear zones in the emplacement process of the batholiths. Deformation features are indicated by well-developed magmatic foliation, sometimes accompanied by solid-state deformation, as well as microstructures such as chessboard pattern in quartz, and recrystallized feldspars. Ar/Ar muscovite ages of 375 to 351 Ma constrain the activity of the NNE-SSW Río Guzmán shear zone. The contemporaneous activity of NNW-SSE sinistral transtensional and NNE-SSW strike-slip systems led to a NNE-SSW directed extension allowing the formation of magma conduits. Subsequent inflation of the batholiths follows the direction of space creation and is associated with dominant NNE-SSW lineations The presence of an external stress field, even if a weak one, may have favoured contamination and hybridization between coeval granitic and mafic magmas and also have provided conduits for mafic magmas arising from the previously enriched mantle and have controlled the ascent of a segment of the crust. Therefore, the Middle Devonian magmatism would not be post-tectonic regarding the Famatinian orogeny but would result from another compressive event, the Achalian orogeny, during which an episode of crustal growth by mafic magma input was developed. Middle Devonian crystallization ages of the batholiths, structural features and geochronological constraints on the activity of the crustal scale shear zones of the Sierra de San Luis (López de Luchi et al.  2004, 2007 and references therein) indicate that at a regional scale the emplacement of the Devonian batholiths is syn-kinematic. A continuum from magmatic to high temperature solid-state microstructural features indicates the involvement of regional shear zones in the emplacement process of the batholiths. Deformation features are indicated by well-developed magmatic foliation, sometimes accompanied by solid-state deformation, as well as microstructures such as chessboard pattern in quartz, and recrystallized feldspars. Ar/Ar muscovite ages of 375 to 351 Ma constrain the activity of the NNE-SSW Río Guzmán shear zone. The contemporaneous activity of NNW-SSE sinistral transtensional and NNE-SSW strike-slip systems led to a NNE-SSW directed extension allowing the formation of magma conduits. Subsequent inflation of the batholiths follows the direction of space creation and is associated with dominant NNE-SSW lineations The presence of an external stress field, even if a weak one, may have favoured contamination and hybridization between coeval granitic and mafic magmas and also have provided conduits for mafic magmas arising from the previously enriched mantle and have controlled the ascent of a segment of the crust. Therefore, the Middle Devonian magmatism would not be post-tectonic regarding the Famatinian orogeny but would result from another compressive event, the Achalian orogeny, during which an episode of crustal growth by mafic magma input was developed.
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