Age and provenance of the Cryogenian to Cambrian passive margin to foreland basin sequence of the northern Paraguay Belt, Brazil

Abstract

The Paraguay Belt in central South America developed in response to the collision of the Amazonian craton, the São Francisco craton, and the Paranapanema block. The alleged "Brasiliano" age (ca. 620 Ma) of orogenesis has recently been questioned by paleo magnetic and radioisotopic ages that indicate the closing stages of orogenesis occurred well into the Cambrian. We investigated the timing of deposition and source areas for these sedimentary rocks overlying the Amazonian craton using integrated U-Pb and Hf isotope data of detrital zircons from within this sequence. In total, 742 detrital zircon U-Pb ages were analyzed from samples taken from the base to the top of this sedimentary succession. Maximum depositional ages from the uppermost part of this sequence of rocks, the Diamantino Formation, indicate that fi nal deposition began no earlier than 560 ± 13 Ma and possibly as young as the Cambrian. Given that zircon inheritance in these rocks continues up until this age and that known Amazonian craton ages are older than ca. 950 Ma, we considered other potential sources for these sediments. This was achieved by integrating the U-Pb detrital zircon data with Hf isotopic data from these zircons that have ε Hf values ranging from -18 to 12. The ε Hf signature is consistent, with a predominantly Amazonian source until the early Neoproterozoic, at which point the signal becomes signifi cantly more evolved. These data, when combined with other evidence discussed here, are consistent with an ocean to the east of the present-day Amazonian craton that did not close until the latest Ediacaran-Cambrian.

Identifying Laurentian and SW Gondwana sources in the Neoproterozoic to Early Paleozoic metasedimentary rocks of the Sierras Pampeanas: Paleogeographic and tectonic implications

“…4 the flat slab segment (including some in Patagonia) and in the Paraguay belt in central Brazil are largely covered by younger sedimentary and igneous units (see Tohver et al 2006Tohver et al , 2012Pankhurst et al, 2014;McGee et al, 2014). Several contrasting geodynamic models have been proposed for the evolution of this large sector, but there is a general consensus that crustal accretion mainly took place during two Early Paleozoic orogenic events, the Pampean (Ediacaran-Early Cambrian) and Famatinian (Ordovician-Silurian) orogenies (e.g., Toselli, 1976, 1981;Aceñolaza and Miller, 1982;Rapela, 2000;Schwartz et al, 2008;Dahlquist et al, 2008;Mulcahy et al, 2011Mulcahy et al, , 2014Escayola et al, 2011).…”

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.…”

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

“…B, the present authors suggest that the proto‐Paraguay Belt was created by such a peripheral bulge – signifying that the incipient stages of basin inversion began as oceanic crust connected to the Amazon Craton was underthrust beneath the Paranapanema Block and the Goiás Massif. A minor influence from volcanic arcs is interpreted in the Raizama Formation based on U–Pb ages reported by (McGee et al ., ). These arcs are now buried under the Paraná Basin, to the south‐east of the Paraguay Belt (Fig.…”

“…The 40 Ar/ 39 Ar analyses of white mica reported here complement recent detrital zircon studies (McGee et al ., ) by providing constraints on source regions and recognizing the age of lower temperature (<450°C) events in the northern Paraguay Belt. The maximum depositional ages here are based on the ages of the youngest concordant cluster of detrital muscovite grains for each respective formation.…”