Diversity of Siderian magmatic pulses revealed by intracrustal melting of oceanic crust in the Mineiro Belt, southern São Francisco Craton

Abstract

The early Paleoproterozoic Era has been largely recognized as a period of global magmatic slowdown (∼2.3–2.2 Ga). The Lagoa Dourada Suite, located in the Mineiro Belt – southern São Francisco Craton - Brazil, is a juvenile high‑aluminum 2350 Ma TTG suite and spatially associated with a network of dykes that received little attention in the literature. Based on field features, petrography, whole-rock geochemistry, U-Th-Pb, and Hf isotopes in zircons, we propose that these dykes represent three different magmatic pulses produced via intracrustal melting of oceanic crust. Pulse 1 (<2347 Ma) is syn-plutonic with low-SiO₂, high-Mg# and HREE, moderate [La/Yb]_N, and low Ba+Sr contents. Pulse 2 (ca. <2330 Ma) shows high-SiO₂, low-Mg# and HREE, moderate [La/Yb]_N, and high Ba+Sr. Pulse 3 (ca. <2325 Ma) has intermediate-SiO₂, low-Mg#, high HREE, moderate to high [La/Yb]_N, and high Ba+Sr values. Their Hf compositions are broadly similar to those of the host rock, with positive εHf_(t) values and the Hf-T_DM model ages ranging from 2.65 to 2.46 Ga, attesting to their juvenile nature. These characteristics, coupled with their homogeneous Hf signature (¹⁷⁶Hf/¹⁷⁷Hf = 0.281382 to 0.281481), suggest that all these magmatic pulses came from a similar source. However, the whole-rock chemical diversity of the dykes and host rock suggests chemical heterogeneities within this source rock and/or the different magmatic pulses were generated by variable degrees of partial melting of a tholeiitic metabasaltic source throughout approximately 25 Ma. These findings reveal a wide compositional diversity of magmas that gave rise to a network of dykes crosscutting the Lagoa Dourada Suite and, consequently, to the framework of a juvenile continental crust on the southern margin of the São Francisco Craton. Furthermore, these rocks constitute a singular example of juvenile magmatism and contribute to a better understanding of the tectono-magmatic lull and potential petrological processes during this period.