Abstract

DAHLQUIST, Juan A et al. The El Chorro monzogranitic stock (Sierra de Ancasti, Catamarca): An example of S-type magmatism with igneous garnet. Rev. Asoc. Geol. Argent. [online]. 2011, vol.68, n.2, pp.195-204. ISSN 0004-4822.

The Ordovician granitic rocks of the Sierra de Ancasti represent one of the easternmost outcrops of the Famatinian orogenic belt of the Sierras Pampeanas. We report and describe a small granitic stock (named El Chorro) with distinctive garnet presence. Although the garnet is an uncommon accessory mineral, in igneous rocks is petrologically significant. El Chorro is an S-type monzogranite that contains an unusual amount of magmatic garnet (2.8 % modal). Combined petrology, chemistry/mineralogy and whole-rock geochemistry indicates that the magma was produced by partial melting of metasedimentary rocks with garnet and muscovite occurring throughout the crystallization. Our studies reveal that garnet formed by direct crystallization from peraluminous magma in equilibrium with mineral phases such as biotite and muscovite. Geothermobaric calculations reveal a crystallization temperature of 710-716 °C and a pressure of 3.8 + 0.8 kbar, indicating that the magma was emplaced at middle crustal depths (~ 14 km) at moderate to low magmatic temperature conditions.

Keywords : Garnet; Whole-rock geochemistry; Chemistry mineral; Geothermobarometry.

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