Andalusite and Na- and Li-rich Cordierite in the La Costa pluton, Sierras Pampeanas, Argentina: Textural and chemical evidence for a magmatic origin

ALASINO, P.H., DAHLQUIST, J.A., GALINDO, C., CASQUET, C., SAAVEDRA, J.

INTERNATIONAL JOURNAL OF EARTH SCIENCES

Springer

Lugar: Keil, Alemania; Año: 2010 vol. 99 p. 1051 - 1065

1437-3254

The La Costa pluton in the Sierra de Velasco (NW Argentina) consists of S-type granitoids that can be grouped into three igneous facies: the alkali-rich Santa Cruz facies (SCF, SiO2 ~67 wt%) distinguished by the presence of andalusite and Na- and Li-rich cordierite (Na2O = 1.55?1.77 wt% and Li2O = 0.14?0.66 wt%), the Anillaco facies (SiO2 ~74 wt%) with a significant proportion of Mn-rich garnet, and the Anjullón facies (SiO2 ~75 wt%) with abundant albitic plagioclase. The petrography, mineral chemistry and whole-rock geochemistry of the SCF are compatible with magmatic crystallization of Na- and Li-rich cordierite, andalusite and muscovite from the peraluminous magma under moderate P?T conditions (~1.9 kbar and ca. 735°C). The high Li content of cordierite in the SCF is unusual for granitic rocks of intermediate composition.