Publication: Petrología, geoquímica y vinculación regional de las unidades neoproterozoicas-cámbricas de la
Sierra de Guasayán, Sierras Pampeanas
Orientales, Noroeste de Argentina
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Publication Date
2020
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Fundación Miguel Lillo
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Abstract
La Sierra de Guasayán forma parte de las Sierras Pampeanas Orientales, en la provincia de Santiago del Estero, NW Argentino, y está conformada por varios cuerpos graníticos que intruyen en un basamento metamórfico de bajo grado, el cual está representado al norte de la sierra por pizarras y filitas, mientras que al sur predominan los esquistos bandeados con inyecciones cuarzo-feldespáticas. Sobre la base de sus caracteres sedimentarios, petrológicos y relaciones estratigráficas generales, las unidades metasedimentarias del sector norte se asocian al contexto estratigráfico de la cuenca de Puncoviscana. En la zona de contacto granito-metamorfitas se han reconocido corneanas cordieríticas desarrolladas por metamorfismo térmico. Los granitoides constituyen un cinturón elongado de Norte a Sur, de composición mayoritariamente tonalítica-granodiorítica al norte y granítica-granodiorítica al sur. Los granitoides son predominantemente de textura porfírica y tamaño de grano medio, y es común la presencia de pequeños xenolitos de forma redondeada a alargada. Geoquímicamente son rocas calcoalcalinas de alto K2O, de carácter débilmente peraluminoso con valores del índice de saturación en alúmina (ASI) entre 1 y 1,09. La uniformidad petrográfica y geoquímica que presentan los cuerpos aflorantes indicaría una posible génesis en común. Comparativamente, son similares a los granitoides cámbricos presentes en el Batolito de Tastil, en el norte, en el ámbito de la Cordillera Oriental y en parte a los de la Sierra de Ischilín y del Batolito Sierra Norte-Ambargasta, que afloran hacia el sur. Todos ellos constituyen el Arco Magmático Pampeano desarrollado en el margen occidental de Gondwana durante el Neoproterozoico tardío - Cámbrico inferior. Sin embargo, los granitoides de la Sierra de Guasayán no presentan las características petrográficas y geoquímicas de los típicos granitos calcoalcalinos metaluminosos de Tipo I. La participación de material cortical en la génesis de los magmas parentales sería responsable de la signatura geoquímica e isotópica de las rocas estudiadas.
“Petrology, geochemistry and regional relationship of the Neoproterozoic-Cambrian units of the Sierra de Guasayán, Sierras Pampeanas Orientales, Northwest Argentina”. The Sierra de Guasayán is part of de Eastern Sierras Pampeanas, in the province of Santiago del Estero, NW Argentina, being mainly formed by several granite bodies emplaced in a regional low-grade metamorphic basement. The latter is represented by slates and phylites in the northern part of the range, whereas in the southern part, banded schists with quartz-feldspar veins are predominant. On the basis of their sedimentary, petrological and general stratigraphic relations, the metasedimentary units of the northern sector are related here to the Puncoviscana basin. Cordieritic hornfelds developed by thermal metamorphism have been recognized in the granitemetamorphites contact zone. The composition of the granitoids is mainly tonaliticgranodioritic to the north, and granitic-granodioritic to the south. They are mainly medium grained porphyritic textures, while there is common occurrence of small rounded to elongated xenoliths. Geochemically, granitoids are high-K2O calc-alkaline, weakly peraluminous with ASI values between 1.00 and 1.09. Normal trends of evolution are shown in the Harker diagram. The petrographic and geochemical uniformity of the granitic rocks suggests a common genetic source. Comparatively, the granitoids of Sierra de Guasayán are similar to the Cambrian-age Batolito de Tastil granitoids exposed to the north, in Cordillera Oriental, and partly to those of the Sierra de Ischilín and the Batolito Sierra Norte-Ambargasta, to the south. All of them constitute the Pampean Magmatic Arc, developed on the western margin of Gondwana during the Late Neoproterozoic - Lower Cambrian. Nevertheless, the granitoids of the Sierra de Guasayán do not present the petrographic and geochemical characteristics of the typical I-Type metaluminous calc-alkaline granites. The participation of crustal material in the source of the parental magmas would be responsible for the geochemical and isotopic signature of the studied rocks.
“Petrology, geochemistry and regional relationship of the Neoproterozoic-Cambrian units of the Sierra de Guasayán, Sierras Pampeanas Orientales, Northwest Argentina”. The Sierra de Guasayán is part of de Eastern Sierras Pampeanas, in the province of Santiago del Estero, NW Argentina, being mainly formed by several granite bodies emplaced in a regional low-grade metamorphic basement. The latter is represented by slates and phylites in the northern part of the range, whereas in the southern part, banded schists with quartz-feldspar veins are predominant. On the basis of their sedimentary, petrological and general stratigraphic relations, the metasedimentary units of the northern sector are related here to the Puncoviscana basin. Cordieritic hornfelds developed by thermal metamorphism have been recognized in the granitemetamorphites contact zone. The composition of the granitoids is mainly tonaliticgranodioritic to the north, and granitic-granodioritic to the south. They are mainly medium grained porphyritic textures, while there is common occurrence of small rounded to elongated xenoliths. Geochemically, granitoids are high-K2O calc-alkaline, weakly peraluminous with ASI values between 1.00 and 1.09. Normal trends of evolution are shown in the Harker diagram. The petrographic and geochemical uniformity of the granitic rocks suggests a common genetic source. Comparatively, the granitoids of Sierra de Guasayán are similar to the Cambrian-age Batolito de Tastil granitoids exposed to the north, in Cordillera Oriental, and partly to those of the Sierra de Ischilín and the Batolito Sierra Norte-Ambargasta, to the south. All of them constitute the Pampean Magmatic Arc, developed on the western margin of Gondwana during the Late Neoproterozoic - Lower Cambrian. Nevertheless, the granitoids of the Sierra de Guasayán do not present the petrographic and geochemical characteristics of the typical I-Type metaluminous calc-alkaline granites. The participation of crustal material in the source of the parental magmas would be responsible for the geochemical and isotopic signature of the studied rocks.