Andalusite and Na- and Li-rich cordierite in the La Costa pluton, Sierras Pampeanas, Argentina: textural and chemical evidence for a magmatic origin |
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Authors: | Pablo H Alasino Juan A Dahlquist Carmen Galindo Cesar Casquet Julio Saavedra |
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Institution: | 1. UNLaR, CRILAR-CONICET, Entre Ríos y Mendoza, 5301, Anillaco, Argentina 2. UNLaR, CICTERRA-CONICET-UNC, Av. Vélez Sarsfield 1611, Pab. Geol., X5016CGA, Córdoba, Argentina 3. Dpto. Petrología y Geoquímica, UCM, Universidad Complutense, IGE (CSIC), 28040, Madrid, Spain 4. CSIC, Instituto de Agrobiología y Recursos Naturales, 37071, Salamanca, Spain
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Abstract: | 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. |
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