Dados da Submissão

Título

U–Pb GEOCHRONOLOGY OF DETRITAL RUTILE AND ZIRCON UNRAVELS SEDIMENTARY PROVENANCE AND TECTONIC EVOLUTION IN THE SÃO FRANCISCO CRATON/ ARAÇUAÍ OROGEN THRUST ZONE, SERRA DO CIPÓ, BRAZIL

Texto do resumo

The knowledge about craton/orogenic belts transition zones has become increasingly an important object of study in tectonics over the past few years. The Araçuaí Orogen, located in southeastern Brazil, is a component of a Neoproterozoic orogenic system that developed between the São Francisco and Congo cratons, inserted in the context of Western Gondwana. Here we present new detrital zircon and rutile U–Pb geochronology data from Lapinha da Serra and Serra do Cipó (MG) areas, where deformed and metamorphosed quartzites of the Mesoproterozoic Espinhaço Supergroup and the Neoproterozoic Macaúbas Group overthrust marbles and metapelites of the Ediacaran/Cambrian Bambuí Group during the collisional stage of the Brasiliano Orogeny. The zircon grains analyzed in the quartzite rocks of the Matão-Duas Barras Formation (Macaúbas Group), the micaceous quartzites considered as the Macaúbas Group (undivided) and the Santa Rita Formation (Espinhaço Supergroup) record a sedimentary provenance that ranges from 625 to 3748 Ma. However, Archean and Paleoproterozoic grains are predominant in the analyzed samples, which indicates, as in most provenance studies in the Araçuaí Orogen, a great contribution from the São Francisco-Congo cratonic basement and the Paleoproterozoic complexes. The occurrence of Mesoproterozoic grains (1.2 and 1.6–1.5 Ga) correlates with the main magmatic phases of the rift-sag system of the Espinhaço basin. The data obtained in the U–Pb geochronology of detrital rutiles show Paleoproterozoic contributions, except for the Mesoproterozoic peaks, which means both the formation of metamorphic terrains during the Rhyacian orogeny and Archean greenstone-TTG formation, and the absence of important Mesoproterozoic metamorphic events, retracing the evolution of the Espinhaço rift-sag basins. Ediacaran grains (ca. 620 Ma) in a sample of micaceous quartzite mapped as Macaúbas Group (undivided) restrict their maximum depositional age as contemporary with the syn-orogenic stage of the Araçuaí Orogen, characterized by the evolution of the Rio Doce Arc. Therefore, this sample cannot be interpreted as part of this rift I and/or rift II sequence. The variability in the source areas and the occurrence of syn-orogenic units interspersed in the pre-orogenic metasedimentary rocks highlight the need to carry out studies to better understand and support the context for tectonic, stratigraphic and paleogeographical interpretations in the boundary between the Araçuaí Orogen and the São Francisco Craton. The sedimentary provenance records found in detritic rutile and zircon data indicate a low-grade metamorphism and hydrothermalism and in the shear zone, which together were not able to restart the U–Pb system of rutile grains and metassomatize or create new zonings in zircon grains, causing these grains to record only their source ages. On the other hand, deformation ages obtained by the Rb-Sr method allows to observe a metamorphism capable of resetting micas but not the U-Pb system in zircons and rutiles, which allows to infer a deformation temperature between approximately 400 to 300 ºC. Further metamorphic studies are necessary to confirm the specific temperature which these rocks were subjected during the deformational event in the thrust fault.

This work is supported by Instituto Serrapilheira (Serra-1912-31510) and CNPq (Process 408815/2021–3).

Palavras Chave

Neoproterozoic; Araçuaí orogen; U-Pb geochronology; shear zones