Late Paleoproterozoic and Mesoproterozoic magmatism of the Nico Perez Terrane (Uruguay): Tightening up correlations in southwestern Gondwana

Abstract

New geochronological, isotopic and geochemical data were obtained from the late Paleoproterozoic and Mesoproterozoic magmatic units of the Nico Perez Terrane (Uruguay). A U-Pb LA-ICP-MS zircon age of 1768 ± 11 Ma confirms the Statherian age for the Illescas rapakivi intrusion, being thus comparable with the age of the Campanero Unit felsic orthogneisses. Though both the Illescas and Campanero intrusions exhibit dominantly granitic, meta- to peraluminous compositions, the first shows a dominant shoshonitic and ferroan composition, whereas high-K calc-alkaline and magnesian to ferroan compositions characterize orthogneisses of the Campanero Unit. Additionally, Sm/Yb and LaN/YbN ratios indicate that both suites were emplaced in a thickened crust, whereas Lu-Hf zircon data of the Illescas granite together with available Sm-Nd data of the Campanero Unit point to significant recycling of an older, Archean and/or Paleoproterozoic crust of the Nico Perez Terrane. Results suggest a common origin for both the Illescas and Campanero magmatism, probably related to a post-collisional/post-orogenic setting. On the other hand, metagabbros of the Zanja del Tigre Complex present U-Pb LA-ICP-MS zircon ages of 1479 ± 4 and 1482 ± 6 Ma and tholeiitic gabbroic compositions. Geochemical and Sm-Nd isotopic data show similarities with LIP-related intracontinental mafic magmatism, suggesting a mixed magma source derived from depleted asthenosphere and fertile subcontinental lithospheric mantle contributions. Emplacement of the metagabbros was related to lithospheric extension in a continental rifting setting and, therefore, fertilization of the lithospheric mantle probably took place during older Paleoproterozoic subduction-related events. Coeval late Paleoproterozoic and early Mesoproterozoic magmatism is also recorded in the northern Nico Perez Terrane of southernmost Brazil, and in basement inliers of the Kaoko Belt and the Angolan Shield (southwestern Congo Craton), thus suggesting a common evolution of these blocks prior to the Neoproterozoic.