So close and yet so far: U–Pb geochronological constraints of the Jaibaras Rift Basin and the intracratonic Parnaíba Basin in SW Gondwana

Abstract

Several sag-type basins apparently developed from rift systems, but there is no consensus about how and if these grabens influenced the sedimentation of the post-rift thermal subsidence phase. The Ediacaran Jaibaras Rift Basin is one of the best-exposed sedimentary records among the NE Brazil late Precambrian – early Cambrian rift system, cropping out at the eastern margin of the intracratonic Parnaíba Basin and extending below it towards the west. Here we present detrital zircon U–Pb ages of rocks from the Jaibaras (Aprazível Formation) and Parnaíba (Ipu Formation) basins, in order to understand the provenance patterns, maximum depositional ages (MDA) and age relationship between these units. The MDA for the Aprazível Formation (c. 499 ± 5 Ma) indicates a Cambrian age for the upper part of the Jaibaras Basin. The bulk U–Pb data indicate that the Ipu Formation started to deposit during late Cambrian and/or Early Ordovician time, despite its MDA (c. 528 ± 11 Ma) being older than that of the Aprazível Formation. Detrital zircon provenance suggests that the primary source areas for the early deposits of the Parnaíba Basin were mountains related to the Brasiliano Orogeny to the south and SE (e.g. Rio Preto and Riacho do Pontal metamorphic belts). Finally, our data emphasize the key change in source areas from the rift to the initial deposition of the intracratonic phase, indicating major depositional style changes between both basins after the Gondwana assembly.

The hidden passive margins from the birth of SW Gondwana

“…8) indicates similar erosional terrains during the Upper Ediacaran-Cambrian and Ordovician (Fig. 9), suggesting regional readjustment and maintenance of the drainage pattern and catchment areas after the final consolidation of Gondwana (see similar interpretation in Cerri et al 2021).…”

“…Recently, efforts based on a multi-proxy approach (Cerri et al 2020(Cerri et al , 2021 in accordance with the integrated model (Klein 1995, Allen andArmitage 2012) have found evidence that the first basins of Gondwana initiated as flooded ramps opened to adjacent oceanic areas tens of millions of years after the formation of the initial Ediacaran-Cambrian rift basins. Thus, contrary to the notion that the intracontinental basins from SW Gondwana evolved from an NW-SE-oriented Neoproterozoic rift system (Fulfaro 1982, Tankard et al 1995, the updated models postulate that the continental lithosphere stretching and cooling occurred long after the final consolidation of Gondwana supercontinent (Cerri et al 2020).…”