Investigating mid‐Ediacaran glaciation and final Gondwana amalgamation using coupled sedimentology and ⁴⁰Ar/ ³⁹Ar detrital muscovite provenance from the Paraguay Belt, Brazil

Abstract

Understanding the evolution of the northern Paraguay Belt, Brazil, is critical in two current controversies: (i) the number, timing and significance of Ediacaran glaciations; and (ii) the timing of amalgamation of South American Gondwana. The Neoproterozoic Alto Paraguay Group forms much of the northern Paraguay Belt. The Serra Azul Formation, within this Group, contains unequivocal evidence for a glacial influence on sedimentation, including multi‐directional striations on sandstone clasts and striated, polished and bullet‐shaped mudstone clasts. However, the age of the Serra Azul Formation is not well‐constrained. The northern Paraguay Belt also formed after the traditionally accepted time for amalgamation of South American Gondwana. If the orogen represents closure of an ocean, then this traditional view is incorrect. A significant number of single grain 40Ar/39Ar detrital muscovite cooling ages (ca 120) from the Alto Paraguay Group are presented. The three youngest grains from the Serra Azul Formation yield a weighted mean age of 640 ± 15 Myr, providing a robust maximum depositional age for this formation. This age, when considered with other data, suggests that the Serra Azul Formation developed in a mid‐Ediacaran glaciation consistent with that expressed in the Gaskiers Formation of Newfoundland, Canada. Cryogenian 40Ar/39Ar detrital muscovite ages from the Alto Paraguay Group are hard to reconcile with the known geology of Amazonia and are interpreted as being sourced from the evolving orogen to the east – from an arc terrane, possibly the Goiás–Paranapanema Massif. Detrital muscovites in the upper part of the Alto Paraguay Group are as young as 544 ± 7 Myr, consistent with mounting evidence that indicates a Cambrian age for orogenesis within the Paraguay Belt during the final amalgamation of Gondwana. This article suggests that the data best support a model where ocean closure in the region continued until Ediacaran/Cambrian times, with final ocean closure represented by orogenesis in the Paraguay–Araguaia orogen.

Paleomagnetism of the Amazonian Craton and its role in paleocontinents

“…Meanwhile, pelitic and fine sandstone deposits of Diamantino Formation (Upper Formation from Paraguay Group) are associated with the molassic phase. U-Pb detrital zircons dating of rocks from the basal part of this formation indicates that the deposition of Diamantino Formation occurred after 541 ± 7 Ma (Bandeira et al 2012, 2015a, 2015b. Furthermore, the recent sedimentological and radiometric studies of glaciogenic rocks from Serra Azul Formation (Alto Paraguay Group) indicate that they are probably associated with the 580 Ma Gaskiers event (McGee et al 2013(McGee et al , 2015a.…”

“…Recently, sedimentologic and provenance studies of rocks from two geological formations of Alto Paraguay Group (Paraguay Belt) showed that their evolutions are associated with the Clymene Ocean closure (Bandeira et al 2012, 2015a, 2015b. According to these studies, the top unit of Alto Paraguay Group represents the last transgressive deposits of the Paraguay Basin, resulting from the last stage of marine incursion of this ocean.…”

Western Paraná suture/shear zone and the limits of Rio Apa, Rio Tebicuary and Rio de la Plata cratons from gravity data

“…A major advance in understanding the Neoproterozoic to Cambrian tectonic history of the SW Gondwana supercontinent evolution has been achieved in the last decade with the acquisition of new geochronological data (Ar-Ar and U-Pb ages) and isotope geochemistry studies of igneous and metamorphic rocks of the exposed basement of cratons and ancient terranes (Cordani et al, 2001;Rapela et al, 2007;Cordani et al, 2010;Oyhantçabal et al, 2010;Escayola et al, 2011;Rapela et al, 2011;Casquet et al, 2012). Together with a few paleomagnetic (Trindade et al, 2006;Tohver et al, 2010;Rapalini et al, 2013) and sediment provenance studies using zircon detritus ages and the geochronology of Neoproterozoic Pampean back-arc basins (Rapela et al, 1998, Rapela et al, 2007, Escayola et al, 2007, Rapela et al, 2011, Ramos et al, 2015 and of the Paraguay orogenic belt (Bandeira et al, 2012;Babinski et al, 2013;McGee et al, 2015), a new view of the final amalgamation of the SW Gondwana is emerging.…”

Early extensional detachments in a contractional orogen: coherent, map-scale, submarine slides (mass transport complexes) on the outer slope of an Ediacaran collisional foredeep, eastern Kaoko belt, Namibia

“…Deformation and exhumation of the CKz at 580-570 Ma (Goscombe et al 2005;Jung et al 2014) was broadly coeval with a transition from subduction-related to slab-failure magmatism and exhumation in the DF-R arc (Oyhantçabal et al 2009(Oyhantçabal et al , 2011Faleiros et al 2011;Tupinambá et al 2012;Alves et al 2013;Heilbron et al 2013). Closure of the Adamastor paleocean, situated at this latitude between the rifted Congo margin and DF-R arc, occurred 20-30 Myr after abortive continental subduction of the opposite (eastward) polarity in the West Gondwana belt ( (Fuck et al 2008;Bandeira et al 2012;McGee et al 2015a, b).…”