New hints on the evolution of the Eastern Magmatic Belt, Puna Argentina. SW Gondwana margin: Zircon U-Pb ages and Hf isotopes in the Pachamama Igneous-Metamorphic Complex

Abstract

There are various geotectonic interpretations of the origin of the Eastern Magmatic Belt as part of the Lower Paleozoic Orogen at the Southwestern Gondwana margin in the Puna, NW Argentina. In this research paper, we obtained zircon U-Pb and Lu-Hf in key rocks from the Pachamama Igneous Metamorphic Complex in order to further constrain the evolution of the Eastern Magmatic Belt. We contribute to the understanding of magmatic sources, processes, and the emplacement of magmas during Lower Paleozoic times in this sector of the Puna. These will allow improving the reconstruction of the geotectonic setting that controlled the Eastern Magmatic Belt. A monzogranite from the mentioned complex yielded concordant zircon U-Pb ages from ∼530 Ma and ∼490 Ma, with the magmatic activity summit at ∼515-510 Ma. In addition to the monzogranite, the wall rocks (schist and gneiss), revealed zircon isotope ɛHf(t) values between +2 and −3 and whole rock ɛNd(t) values between +2 and −5, with TDM ages between 1.3 and 1.6 Ga. These indicate that the rocks from the Pachamama Igneous Metamorphic Complex, derived from a mixture of a reworked Mesoproterozoic crustal source and juvenile mantle-derived magmas. The combined data obtained in this contribution together with previous work, allow us to suggest that a long-lived magmatic event formed the granitoids in the Eastern Magmatic Belt from ∼540 Ma until ∼440 Ma. This event was represented by periods of low-level magmatic activity, interrupted periodically by short bursts of high-volume magmatism, triggered by repeated magmatic underplating.