Andalusite and Na- and Li-rich cordierite in the La Costa pluton,udSierras Pampeanas, Argentina: textural and chemical evidenceudfor a magmatic origin

摘要

The La Costa pluton in the Sierra de Velascoud(NW Argentina) consists of S-type granitoids that can beudgrouped into three igneous facies: the alkali-rich SantaudCruz facies (SCF, SiO2 *67 wt%) distinguished by theudpresence of andalusite and Na- and Li-rich cordieriteud(Na2O = 1.55–1.77 wt% and Li2O = 0.14–0.66 wt%), theudAnillaco facies (SiO2 *74 wt%) with a significant proportionudof Mn-rich garnet, and the Anjullo´n facies (SiO2ud*75 wt%) with abundant albitic plagioclase. The petrography,udmineral chemistry and whole-rock geochemistry ofudthe SCF are compatible with magmatic crystallization ofudNa- and Li-rich cordierite, andalusite and muscovite fromudthe peraluminous magma under moderate P–T conditionsud(*1.9 kbar and ca. 735C). The high Li content of cordieriteudin the SCF is unusual for granitic rocks of intermediateudcomposition.