Towards an integrated tectonic model for the interaction between the Bambuí basin and the adjoining orogenic belts : evidences from the detrital zircon record of syn-orogenic units.
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2020
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The Sao ̃ Francisco craton and its surrounding orogens are some of the most important tectonic elements of South
America, and key regions to understanding the assembly of Western Gondwana in the Proterozoic-Palaeozoic
transition. During this major tectonic event, diachronic collisions between small continents developed an
intricated orogenic system, where several orogens evolved in unique paths through time and space. In such
collisional settings, there are some tectonic processes that promote subsidence, thus controlling the formation of
orogenic-related sedimentary basins. Furthermore, the tectonic activity in collisional orogens generates dynamic
landscapes that usually favor increased erosion and sediment generation to feed these basins, making them key
places to seek for clues about the tectonic evolution of their surroundings. On the S ̃
ao Francisco craton, the
Bambuí Group records a complex foreland system, which evolved in response to the lithospheric overload
exerted by the uplift of both Brasília belt and Araçuaí orogen. In turn, both Salinas Formation and Ibia ́ Group
comprise orogenic deposits resting within the Araçuaí orogen and Brasília belt, respectively, whose tectonic
significance is still under debate. Here we present new U–Pb (LA-ICP-MS and SHRIMP) and Lu–Hf isotopic an-
alyses on a great amount of detrital zircon grains extracted from the rocks of the Bambuí Group and Salinas
Formation, together with a thorough data compilation from the literature. The two units present similar prov-
enance patterns, sharing the major detrital zircon age peaks (550–650 Ma, 950–1050 Ma, 1750–2000 Ma,
2600–2800 Ma) and maximum depositional age in c. 550 Ma. The Ediacaran zircons recovered from the Bambuí
Group show a wide range of the εHf(t), ranging from c. − 17 to +15, which suggest the existence of multiple late
Neoproterozoic sources, some of them juvenile and some with a long crustal residence. The variation in detrital
zircon age patterns and εHf(t) values from different units within the Bambuí Group provided additional clues of
provenance changes occurred during the evolution of the basin. The new data obtained for the Salinas Formation
constrain its deposition between 548 and 500 Ma, which have an important implication on its tectonic signifi-
cance. We propose that in both Brasília belt and Araçuaí orogen sides, the early foredeep deposits of the Bambuí
basin should have been incorporated to the orogenic domains, which could explain the apparent lack of deposits
recording the climax of the Brasilia belt uplift (c. 630 Ma) within the cratonic area. In this same direction, we
consider that both Salinas Formation and Ibi ́
a Group could represent remnants of these early foreland deposits
related to the uplift of Brasília belt and Araçuaí orogen, respectively, incorporated to the orogenic wedges due to
the advance of the deformational fronts. Therefore, what we know as Bambuí Group is in fact the remaining
record of an advanced stage of the foreland system, when subsidence was already influenced by the two evolving orogens. Altogether, the analyses of the stratigraphic, structural and geochronological data converge towards an
integrated tectonic model for the interaction between the Bambuí basin and the surrounding orogens during West
Gondwana amalgamation.
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Gondwana, São Francisco craton, Araçuaí orogen, Brasília belt, Bambuí foreland system
Citação
AMARAL, M. H. K. do. et al. Towards an integrated tectonic model for the interaction between the Bambuí basin and the adjoining orogenic belts: evidences from the detrital zircon record of syn-orogenic units. Journal of South American Earth Sciences, v. 104, 2020. Disponível em: <https://www.sciencedirect.com/science/article/pii/S0895981120303746>. Acesso em: 29 abr. 2022.