Petrogenesis and tectonic setting of mafic magmatism within the Laguna Amarga Metamorphic Complex, Andes of Catamarca, Argentina: Insights into the opening of the Cuyania/Precordillera terrane from the Ouachita rift

Abstract

Neoproterozoic crystalline basement rocks are exposed as fault-bounded blocks over the high Andes of Catamarca. The crystalline basement is stratigraphically grouped into the unique Laguna Amarga Metamorphic Complex and represents the northern extension of the Cuyania/Precordillera terrane. Tabular bodies of meta-mafic rocks are widespread in the basement interspersed within a thick sequence of meta-sedimentary rocks derived from siliciclastic, calc-silicate, and limestone protoliths. Overall, the geochemical characteristics of meta-mafic rocks are in the compositional range of Normal-Mid Ocean Ridge Basalt (Normal-MORB), reflecting a common depleted-mantle source with varying degrees of partial melting. While preserving the typical bulk chemistry of MORB magmatism, some mafic magma underwent differentiation at emplacement, leading to the development of high-Ti mafic rocks. New U-Pb zircon geochronology reveals three distinct age peaks, with two coinciding with ages identified in the metasedimentary host rocks. The dominant Mesoproterozoic age cluster is linked to inherited zircon crystals assimilated within a single meta-mafic rock. In contrast, zircon ages from the late Ordovician to early Devonian are attributed to metamorphic overgrowths. Notably, the third age cluster, delineates a Late Neoproterozoic magmatic event, indicating the temporal span of mafic magmatism. The finding agrees with the best available age (576 ± 17 Ma) for mafic magmatism on the Precordillera Mafic-Ultramafic Belt. Stratigraphic relationships and geochemical fingerprints enable correlation among the meta-mafic rocks from Laguna Amarga, tracing a belt of mafic magmatism with an oceanic affinity that extends southward. Building upon previous works, this study reaffirms that the rift-drift transition of the Cuyania/Precordillera terrane, linked to the Ouachita rift opening from southeastern Grenville, evolved during the latest Neoproterozoic.