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 S Zandomeni,Carlos I Lembo Wuest,Edgardo G Baldo,Manuela Benítez,Samanta Serra-Varela,Sebastián O Verdecchia,Juan A Dahlquist,Juan A Moreno,Catalina Balbis,Matías M Morales Cámera

doi:10.3390/min11020166

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 granodiorite 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) and temperature (<770 °C) under oxidizing conditions (QFM + 1 and QFM + 2), which are similar to the emplacement conditions reported for other granites of the Pampean magmatic arc. Mineral assemblages and whole-rock and mineral chemistry of the granitoids from the Sierra de Guasayán indicate an I-type affinity for the La Soledad quartz-diorite (amphibole, biotite, and titanite), S-type affinity for the Alto Bello granodiorite (biotite, muscovite, cordierite, and sillimanite), and a hybrid nature for the main Guasayán and El Escondido plutons (biotite, monazite, and magnetite). This hybrid nature is supported by the presence of abundant mafic microgranular enclaves and rapakivi texture and by published zircon Hf-isotope data (εHfi ranging from −4.76 to −0.12). This suggests, in turn, the involvement of hybridization in the genesis of these granitoids, which seems to be a common mechanism operating in the Pampean magmatic arc.

Highlights

Granites sensu lato are the most abundant magmatic rocks of the continental crust; their study represents a main topic in igneous petrology (e.g., [1,2,3])
The combined study of mineral assemblages, textural evidence, and mineral chemistry with the available geochemical and isotope data for the granitoids from the Sierra the Guasayán allow us to subdivide them into three groups with distinctive characteristics: 1
The obtained P-T crystallization conditions suggest that these magmas were emplaced at shallow structural levels (

Summary

Introduction

Granites sensu lato are the most abundant magmatic rocks of the continental crust; their study represents a main topic in igneous petrology (e.g., [1,2,3]). 80 wt.% SiO2 (e.g., [4]), their mineralogy is relatively simple with a predominance of quartz, plagioclase, and alkali feldspar with varying modal proportions of varietal minerals (e.g., micas, amphiboles, pyroxenes, garnet, cordierite, and aluminosilicates) and variable amounts of accessory minerals (e.g., apatite, rutile, Fe–Ti oxides, zircon, titanite, monazite, epidote, and allanite). The study of these major and accessory minerals can be used to assess the geochemical affinities of the host granitoids (e.g., I- or S-type signature) as well as to establish their crystallization/emplacement conditions. Several geobarometers and geothermometers based on amphibole, amphiboleplagioclase, biotite, and titanite compositions are widely used in the literature (e.g., [15,16,17,18,19,20,21,22,23,24]), whilst the oxygen fugacity of the magmas can be roughly estimated using Fe/(Fe + Mg) ratios of amphibole and biotite (e.g., [25,26,27])

Objectives

Discussion

Conclusion