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: Berlín.; 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. 735ºC). The high Li content of cordierite in the SCF is unusual for granitic rocks of intermediate composition.