Origin and pre-eruptive conditions of felsic volcanic rocks from the Pinturas River, Patagonia: representatives of the last volcanic episodes of the Jurassic Chon Aike SLIP

Abstract

The Chon Aike Silicic Large Igneous Province (SLIP), formed during the Jurassic break-up of Gondwana, is one of Earth’s major silicic provinces. This study presents new whole-rock, mineral chemistry, and Nd isotopic data from phenorhyolitic to phenodacitic volcanic and pyroclastic rocks of the Chon Aike Formation in the Pinturas River area, western Deseado Massif, southern Argentina. These high-potassium, calc-alkaline, peraluminous ignimbrites and lavas contain oligoclase-andesine, sanidine, and magnetite-ulvöspinel, with pre-eruptive temperatures ranging from 760°C (magnetite-ulvöspinel) to ~950°C (feldspars), under high oxygen fugacity (−10 to −13). Estimated water contents (0.1–3%) are consistent with explosive volcanism. Isotopic data recalculated to 155 Ma indicate εNdi values between −2.26 and −0.03, pointing to a mixed crustal-mantle source with Mesoproterozoic (Grenvillian) derivation ages (TDM 0.98–1.16 Ga). When integrated with ~600 existing analyses from the Chon Aike SLIP, results support that geochemical differences are more spatial than temporal, shaped by tectonic setting and crustal architecture. While most domains exhibit strong crustal signatures, εNdi values near 0 in the Central domain suggest greater influence of metabasaltic components, consistent with petrogenetic models involving varying melting degrees and minor mantle input. These findings refine understanding of magmatic evolution in the Chon Aike SLIP.