The Tonian Embu Complex in the Ribeira Belt (Brazil): revision, depositional age and setting in Rodinia and West Gondwana

Abstract

The Embu Complex in the Neoproterozoic Ribeira Belt of Brazil provides a record of sedimentation associated with the Rodinia supercontinent and its subsequent deformation and metamorphism during assembly of West Gondwana. It is composed of a succession of variably migmatized pelitic schists and paragneisses, as well as minor calcsilicate rocks with quartzite intercalations, and orthogneiss. Detrital zircon U-Pb (LA-ICP-MS and SHRIMP) determinations for key samples of the Embu Complex in its type-area (West and Southwest of São Paulo City), and samples from neighboring units (Votuverava and São Roque groups) indicate distinct provenance histories and in combination with other data, discrete times of sediment accumulation. Detrital zircons from the Embu Complex are characterized by ages in the range 1500-1000 Ma and 2000-1700 Ma, with a very minor number of older ages. The youngest detrital grain is dated at 974 ± 12 Ma. Metamorphic zircon overgrowths range from 850 to 570 Ma with age peaks at ca. 820-790 and 650-570 Ma. Thus, the depositional age of the Embu Complex is constrained to 970-850 Ma. The detrital zircons of the Votuverava and São Roque groups are dominated by ages in the range 2200-2000 Ma, along with minor Paleoproterozoic and Archean ages. The youngest detrital grains are ~1400 Ma (Votuverava Group) and ~1750 Ma (São Roque Group). Metamafic rocks from the Votuverava Group have crystallization ages of ca. 1300 Ma, with a higher metamorphic grade amphibolite showing a range of discordant ages with upper and lower intercepts of 1300 Ma and ~800 Ma, respectively. These results demonstrate that the Embu Complex was probably accreted to the Apiaí Terrane during a Tonian (820-790 Ma) orogenic event, prior to final development of the Ediacaran Ribeira belt arc-related magmatism and a transcurrent shear zone system. The main source area for detrital zircons of the Embu Complex is likely to be the Grenville-Sveconorwegian-Sunsás orogen or time-equivalent regions rather than the central portions 2 of the neighboring cratons. The Embu Complex geological context is consistent with accumulation on the margin of the Rodinia supercontinent.

Breaking the Grenville–Sveconorwegian link in Rodinia reconstructions

“…Late Meso‐ and early Neoproterozoic accretionary orogens are found on most continents (e.g., Campanha et al, , Cawood et al, ) and although the allochthonous North Atlantic Neoproterozoic successions can be correlated based on similarities in stratigraphy, metamorphic and magmatic history, and provenance (e.g., Cawood et al, , Kirkland et al, , Strachan et al, ), it is likely that there were several other coeval active margins with broadly similar tectonic and temporal evolution. Thus, unless the allochthons show some unique feature that allows them to be correlated, for example, age of deposition, metamorphic and magmatic events, one could argue that they are not correlative (Figure f,i; Corfu, Roberts, Torsvik, Ashwal, & Ramsay, ).…”

Comment on “Tectono Metamorphic Evolution of the Central Ribeira Belt, Brazil: A Case of Late Neoproterozoic Intracontinental Orogeny and Flow of Partially Molten Deep Crust During the Assembly of West by Meira et al.

“…In the Socorro and Embu-Paraíba do Sul terranes of southern Ribeira belt, the study area of the commented article, many plutonic rock bodies display expanded calcalkaline signatures with U-Pb zircon ages of ca. 780 Ma and 660 to 620 Ma, with mixed Mesoproterozoic T DM Nd model ages and slightly negative ε Nd and Hf values typical for continental arc signatures (Alves et al, 2013(Alves et al, , 2016Campanha et al, 2019;Cordani et al, 1973;Ebert et al, 1996;Figueiredo & Campos Neto, 1993;Hackspacher et al, 2003;Heilbron et al, 2017;Vinagre et al, 2014). In Central Ribeira belt (Rio de Janeiro and adjacent Minas Gerais states), available data point to a more complex pre-collisional scenario, where two magmatic arcs have been described: an inner continental arc system (Serra da Bolívia, Marceleza, Muriaé, Valentim batholiths) developed between ca.…”

Chronostratigraphy of a 1.5±0.1 Ma composite sedimentary record from Colônia basin (SE Brazil): Bayesian modeling based on paleomagnetic, authigenic 10Be/9Be, radiocarbon and luminescence dating

“…1c-d). The Colônia basin is inserted in the tectonicstratigraphic domain of the Neoproterozoic Embu Complex in the Ribeira Belt (Campanha et al, 2019). Accordingly, the main rock types in the region are gneisses, migmatites, diorites, mica schists, quartzites, mylonites, amphibolites, metabasites, granites and granodiorites, all of which are intensively weathered (Riccomini et al, 1991).…”