Crystallization conditions and petrogenetic characterization of metaluminous to peraluminous calc-alkaline orogenic granitoids from mineralogical systematics: The case of the Cambrian magmatism from the Sierra de Guasayán (Argentina)

PRISCILA ZANDOMENI; JUAN MORENO; SEBASTIÁN VERDECCHIA; EDGARDO G. BALDO; JUAN DAHLQUIST; MATÍAS MORALES CÁMERA; CATALINA BALBIS; MANUELA BENÍTEZ; SAMANTA SERRA-VARELA; CARLOS I. LEMBO WUEST

Minerals

MDPI

Lugar: Basel; Año: 2021

2075-163X

.Abstract: The Sierra de Guasayán (Eastern Sierras Pampeanas, Argentina) is formed by low to medium grade metamorphic rocks intruded by Cambrian metaluminous (La Soledad quartz-diorite), slightly peraluminous (Guasayán, El Escondido and El Martirizado plutons) and strongly peraluminous (Alto Bello granodiorite) granitoids of the Pampean magmatic arc. Chemical compositions of amphibole, plagioclase, biotite, and titanite indicate that these granitoids were emplaced at low-pressure (mostly < 3 kbar), temperature lower than 770 ºC, and oxidizing conditions (high fO2), which are similar to the emplacement conditions reported for other granites of the Pampean magmatic arc. The mafic mineral assemblage and the obtained mineral chemistry of the granitoids from the Sierra de Guasayán are consistent with the available whole-rock chemistry and indicate an I-type affinity for the La Soledad quartz-diorite (amphibole, biotite, titanite), S-type affinity for the Alto Bello granodiorite (biotite, muscovite, cordierite, sillimanite) and a hybrid nature for the main Guasayán and El Escondido plutons (biotite, monazite, magnetite). This hybrid nature is supported by the presence of abundant mafic enclaves and possible rapakivi texture (K-feldspar phenocrysts mantled by plagioclase) along with the published zircon Hf-isotope data (εHfi ranging from -4,76 to -0,12). This suggests in turn the involvement of assimilation and/or magma mixing processes in the genesis of these granitoids, which seem to be distinctive mechanisms operating in the Pampean magmatic arc.