Tectono-magmatic cycles and the volcanic-plutonic evolution of the Campo Alegre-Corupá Basin SC, Brazil

• Ano de defesa: 2023
• Autor(a) principal: Santos, Lucas Martins Lino Aguiar dos
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Bimodal magmatism; Geochemistry; Magmatic plumbing systems; não disponível; Volcanic-plutonic connection; Western Gondwana assembly
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/44/44143/tde-04082023-072802/

At least two main stages of filling and subsidence have been identified in the Campo AlegreCorupá Basin (CACB), namely the Basin and the Caldera Stages. In the Basin Stage, the regional collisional tectonics triggered the far-field stress resulting in a local extension at ~605 ± 5 Ma through the reactivation of NNW-SSE inherited basement structures. The deposition of the sedimentary basin finishes with the Initial Volcanic Activity, corresponding to a bimodal mildly alkaline, predominantly mafic and effusive volcanism. The basaltic rocks are transitional to mildly alkaline, exhibiting OIB-like trace element enrichment patterns, with depletion in Nb and Ta, however, and crustal-like Sr-Nd isotopic signatures, suggesting that they were derived from low degrees (~5%) of partial melting of an enriched lithospheric mantle source. The silicic rocks are transitional to mildly alkaline trachydacites and minor rhyolites, with trace element compositions typical of A2-type granitoids, produced by fractional crystallization of the coeval basalts at the Moho. After the transition to a post-collisional setting, probably at ca. 595 Ma, regional extension led to the Caldera Stage of the basin, which had its volcanic peak at ca. 583-580 Ma, contemporaneous with the intrusive A-type magmatism of the nearby Graciosa Province. The Main Volcanic Activity, corresponding to the volcanic rocks from the Caldera Stage, is constituted by alkaline trachytes and rhyolites, occurring primarily as pyroclastic sequences with minor effusive lava flows, also exhibiting trace element compositions typical of A2-type granitoids. They are associated with minor transitional to mildly alkaline basalts exhibiting IAB-like trace element signatures. The basalts from the Caldera Stage result from the partial melting of ~15% of enriched lithospheric-mantle sources during the lithospheric root collapse of a cratonic terrane, and the silicic rocks are derived from their fractional crystallization at the Moho. However, an additional stage of differentiation in the upper crust is required to explain their silica-enriched compositions. The products from both volcanic activities were raised to the surface mainly through NNW-SSE and ENE-WSW oriented conduits, respectively reactivated and neo-formed during the collisional process. The crustal-scaled discontinuities associated with the development of the sedimentary basin have further controlled the subsidence of the caldera structure, which might be the main mechanism of preservation for these ancient volcano-sedimentary sequences. Lu-Hf isotopes from detrital zircon suggest an Andean arc-type tectonic setting during the Paleoproterozoic (~2,185 Ma) history of the Luis Alves Terrane (LAT) basement. This tectonic setting was responsible for the arc-like signatures of the intraplate lithospheric-derived rocks of both bimodal volcanic sequences. Crustal-like Sr-Nd-Hf isotopic characteristics result from a protracted isotope evolution of their mantle sources, and each tectono-magmatic stage results from a different extensional setting, which has implications for the metacratonization of the LAT. Finally, the CACB consists of a rare and excellent exposure of both caldera-forming pyroclastic rocks and their cogenetic underlaying plutons. Zircon trace element data for the volcanic rocks from all stages of the CACB indicate that the silicic volcanic rocks from the Caldera Stage represent highly evolved compositions extracted from a crystal-mush solidified as a syenitic intrusion (the Corupá pluton). During the evolution of the volcanic-plutonic system, zircon crystals were able to track compositional changes associated with the extraction of residual silicic liquids from crystal mushes and the formation of intermediate-silicic cumulates. Such a connection is revealed by the complementary behavior of Eu/Eu*, Zr/Hf, and Th/U ratios between volcanic and plutonic rocks, and interpreted to result from crystal-melt segregation processes.