Multiple tectono-magmatic cycles in the Ediacaran Campo Alegre-Corupá Basin revealed through zircon U-Pb-Hf isotopes link volcanism and tectonics during the consolidation of Western Gondwana

The late-convergent to post-collisional tectonic stages associated with the consolidation of Western Gondwana resulted in multiple volcano-sedimentary episodes in the Ediacaran Campo Alegre-Corupá Basin (CACB). At least two main stages of volcano-sedimentary infilling have been recognized through detailed stratigraphic and lithofaciological studies combined with whole-rock geochemistry and U-Pb-Hf analysis. During the initial Basin Stage (605-590 Ma), the development of the CACB occurred as a syn-orogenic rift (impactogene) in response to the regional collisional tectonics. The sedimentary cycle progressed from alluvial fans at the northern limit of the basin to braided rivers and into a lake to the south. Supported by U-Pb geochronology and Lu-Hf isotopic signatures of the detrital zircon crystals, the provenance of the sedimentary sequences indicates the participation of the Paleoproterozoic basement that constitutes the Luis Alves Terrane as the main source. Furthermore, the nearby Neoproterozoic Piên Magmatic Arc and the Curitiba Terrane also acted as subordinated sources for the sediments. Bimodal volcanic activities register the ending of the Basin Stage, progressively covering the sedimentary strata with OIB-like, mildly alkaline basalts interbedded with subordinate trachydacites and surge-like pyroclastic deposits. Conversely, the second stage of infilling of the CACB results in the Caldera Stage (583-577 Ma), constituted mainly by large volumes of widespread, densely-welded to rheomorphic ignimbrite sheets. The Caldera Stage initiates with the outpouring of trachytic and very subordinated IAB-like basalts at ~583 Ma, followed by the production of pumiceous fallouts during an early Plinian-like period of decompression of shallow magma chambers at ∼580 Ma and culminating with the collapse of a graben-like caldera. Compositional and isotopic signatures suggest lithospheric mantle sources for the magmas from both volcanic stages and support a cogenetic nature between the silicic rocks from the Caldera Stage and the A-type granitoids from the nearby plutonic Graciosa Province. The CACB also records an intense “resurgent” volcanic stage at ∼ 563 Ma, with an expressive formation of pyroclastic fall- and flow-deposits and a widespread hydrothermal imprint at ∼ 565 Ma to ∼ 550 Ma. Additionally, this volcanic activity may have been crucial for the preservation of the oldest macrofossils in this region of West Gondwana at the Itajaí Basin.