A study of Pleistocene volcano Manantial Pelado, Chile: Unique access to a long history of primitive magmas in the thickened crust of the Southern Andes
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Textural and geochemical analysis of lavas and tephra from a poorly studied, glacially dissected, mafic, stratocone, Manantial Pelado, in the Southern Andean Volcanic Zone was collected to characterize the volcano’s petrogenesis and assess its primitive nature. Manantial Pelado lies within the transitional segment of the Southern Volcanic Zone (35.5°S) amidst thickened crust (~55 km) while surrounded by extensive silicic volcanism such as the Descabezado Grande-Cerro Azul Volcanic Complex. How mafic magmas reached the surface through thickened continental crust is a larger question at hand, but prior to addressing broader processes at work, initial geochemical characterization is necessary. Understanding the full extent of its primitive nature is crucial for broader insight of proximal vent interactions and relationships as well as insight towards magma genesis. A combination of the whole-rock and mineral-scale data reveals initial primitive characterization may not accurately represent the initial compositions and that their signature is truly primitive. Textural and zonation patterns of olivines, the presence of cr-spinels within olivine cores, and elevated Mg# and Ni content within olivine cores provided evidence toward a more primitive signature for these lavas. This led to further investigation of petrogenetic processes such as diffusive equilibration. Mineral-melt relationships also provided magmatic reservoir constraints through the use of geothermometers and hygrometers to estimate crystallization temperatures, oxygen fugacity, and initial water content of these lavas. A potential variation in source of melting was identified as well as varying water contents.