The Chon Aike magmatic province: an active margin origin?

Abstract

A combination of the geochemical and isotopic compositions of the Jurassic igneous rocks exposed along the Antarctic Peninsula and Patagonia suggest that they may have formed in a continental arc setting without a significant input of a mantle plume, as presented in Bastias et al. (2021). This interpretation revises previous interpretations (e.g. Pankhurst et al., 2000; Riley et al., 2001) that suggested the early deposits of the Chon Aike magmatic province in eastern and central Patagonia formed by the coupled action of an active margin and the peripheral thermal effect of the Karoo mantle plume. We present a tectono-magmatic evolution for the Chon Aike magmatic province following the argument of Bastias et al. (2021). Furthermore, we argue that a supra-subduction zone origin is supported by: (i) enriched LILE and LREE, with negative Nb, Ta, Sr and Ti anomalies in all of the Jurassic igneous rocks, which are typical of slab-dehydration reactions and thus active margins, (ii) the trace element compositions of Jurassic igneous rocks in Patagonia and the Antarctic Peninsula are indistinguishable throughout the region, and thus it is likely that they evolved via the same magmatic processes, (iii) the whole rock Nd and Sr, and zircon Hf isotopic compositions of Late Triassic-Jurassic igneous rocks show that the magmas formed from mixed sources that resided within the continental crust and (iv) numerical modelling. Therefore, unlike the igneous units of the Karoo and Ferrar LIPs, the involvement of a mantle plume is not necessary to generate any of the chronological, geochemical or isotopic characteristics of the Chon Aike magmatic province. This contribution serves as further information on the debate searching for the responsible mechanism generating the Chon Aike magmatic province: active margin vs. mantle plume.