The statherian anorogenic magmatism in the Paramirim Aulacogen, são Francisco-Congo paleoplate: New data, synthesis and regional correlations

Abstract

Fragmentation of continental masses is usually associated with anorogenic magmatism, and in this context, major silicic magmatic events may be associated with Large Igneous Provinces (LIPs). The Paramirim Aulacogen evolves between 1.77 and 0.67 Ga, filling anorogenic siliciclastic and acidic volcanic rocks with subordinate carbonates. A rhyolite from the Algodão Formation, the oldest unit of the Aulacogen, was dated in this work using the U–Pb method (LA-ICPMS), finding a crystallization age of 1777±1 Ma, with a model age (TDM) of 3.10 Ga and εNd (t) equals −10.4. The anorogenic plutonic magmatism is represented by the Lagoa Real Intrusive Suite, with over 5000 km2. New geochemical and geochronological data are presented, and the integration with the literature allowed the interpretation of four plutonic magmatism cycles: (i) Cycle 1: represented by Lagoa do Barro granitoids (1762 ± 9 Ma) and the metavolcanic rocks of the Algodão Formation (1775 ± 77–1777±1 Ma); (ii) Cycle 2: with the São Timóteo (1741 ± 4–1746 ± 5 Ma) and Caetité (1743 ± 5 Ma) granitoid and syenitoid, in addition to charnockitic rocks (1742±7 Ma); (iii) Cycle 3: is related to phonotephrite, tephriphonolite and phonolite. Trachyte, trachyandesite and trachydacite of São Simão Formation (1731 ± 5 Ma) and tuff layer of Ouricuri do Ouro Formation (1722 ± 13 Ma), as well as rhyolites and dacites that ocurr in the basement of Paramirim Aulacogen. The Caldeirão granitoid and syenitoid (1724 ± 5 Ma) is associated with this cycle; and (iv) Cycle 4: with the Suçuarana intusive rocks (1686 ± 6 Ma) and pyroclastic rocks of trachyandesitic composition. The Sm–Nd model ages (TDM) obtained in this work and the literature varies between 3.1 and 2.2 Ga, with values of εNd (t) between −15.8 and −8.6. The formation of the Statherian magmas possibly occurred by melting the enriched mafic mantle, followed by underplating in the continental crust and assimilation of Archean crustal rocks, with fractionation of hornblende, biotite, apatite, and Fe–Ti oxides during magma evolution. The Lagoa Real Intrusive Suite, and their volcanic correlates, represent part of a Statherian Silicic Large Igneous Province (SLIP) developed in a crust of the Archean-Rhyacian-Orosirian age of the São Francisco-Congo Paleoplate. This magmatism marks the attempt at the breakup of the Columbia supercontinent, with correlates in other regions of Brazil and the world.