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 unusually 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 c. 735 ºC). The high Li content of cordierite in the SCF is unusual for granitic rocks of intermediate composition and is reported here for the first time