The Musters Stock: a hybrid quartz monzogabbro-to granodiorite, west of Valcheta, Río Negro

LÓPEZ DE LUCHI, M. G.; MARTÍNEZ DOPICO, C.; RAPALINI, A.E.

San Luis

Simposio; Segundo Simposio sobre Petrología Ígnea y Metalogénesis Asociada, PIMA2013; 2013

Universidad de San Luis

The Musters stock which is located 20 km west of Valcheta town is a broadly elongated but curved 30 km2 unit with a major NNE trending branch (Figure 1a). This stock was considered as part of the Naverrete Plutonic Complex (Caminos, 2001; López de Luchi et al. 2008b) based on lithological affinities. Two chemical data of the quartz monzogabbro /monzodiorite are available. Based on the TAS classification of Middlemost (1985) they are quartz diorites (SiO2 59.29-59.60%) which belong to a high-K calc-alkaline series with ASI between 0.95-1.01. The samples display similar chondrite-normalized REE patterns that are characterized by LREE enrichment with (La/Sm)N=2.37- 3.40 and weakly fractionated HREE with (Tb/Yb)N=1.40-1.50, suggesting garnet-free sources. Moderate but very consistent negative Eu anomalies (Eu/Eu*=0.66-0.71) were calculated (Figure 1C). In primitive-mantle normalized trace element patterns light-REE enrichment, positive Pb anomaly and the Nb-Ti troughs are observed which are typical of calc-alkaline magmatism in active continental margins.