Evolução estrutural e térmica de um batólito sin-cinemático no orógenos Neoproterozóico Araçuaí (leste do Brasil)

Abstract

AcknowledgementsMy first acknowledgments are for my two co-directors, Marcos Egydio-Silva, and Alain Vauchez, which permitted me to realize this work. I thank them to took me in a country that I enjoyed discover with them, especially during the field missions. And a special thank for their patience and their disponibility during the preparation of this manuscript and for their comments and reflexions in general.A great thank to Maria Irene Raposo who initiate me to the rock magnetism and help me to complete most of the experiments. Thank you for the discussions about sciences and other.I thank the correctors Ricardo Trindade and Jean-Luc Bouchez for accepting to criticize this work, and the others board members Jérôme Bascou, Maria-Helena Hollanda and Andréa Tommasi for their participation to the reflexion.I also thank all those who participated to this work, people from Geoscience Montpellier and from the Instituto de Geociências.Of course, I thank my family who supported me in my choices. My friends, from Brazil and France, for the precious moments of relaxation. And finally, thank you Lara, your support during this experience has been the greatest help I received. AbstractThe allochtonous domain of the Neoproterozoic Araçuaí belt involves large amounts of magma, widespread partial melting, granulitic facies and high geotherm, characterising this belt as a hot orogen. The Galiléia tonalitic suite, emplaced within host metasediments and deformed at magmatic state, represents a huge batholith that strongly influenced the mechanical behaviour of this middle crust. The anisotropy of magnetic susceptibility (AMS) measured through this batholith and used as a petrofabric proxy, combined to a detailed magnetic mineralogy investigation, permitted to characterize the paramagnetic behaviour of the Galiléia suite and therefore to highlight a complex 3D strain deformation. The observed structures developed within the viscous magma resulted from a combination of tangential tectonics induced by the compression, and gravitational forces arising from the load of the overlying crust. The kinematics of the batholith is compatible with that already described for ductile rocks of hot orogens. U/Pb dating on zircons and monazites together with 40 Ar/ 39 Ar dating on amphiboles, muscovites and biotites permitted to define the thermal evolution of the Galiléia batholith and its host metasediments and constrain the timing of the deformation. The Galiléia batholith emplaced during an important magmatic, tectonic and thermal event at ~580 Ma. Temperature remained high during the first ~50 Ma of the thermal evolution, promoting a seemingly constant deformation of the batholith at magmatic state during several tens of millions years. Such high temperature conditions and stable deformation kinematics during protracted periods of time are supposed to be characteristic of hot orogen. The slow cooling rate of ~10°C/Ma evidenced after ~500 Ma probably indicate a very slow exhumation probably only conducted by erosion. ResumoA faixa Araçuaí, ...

Deformation regime variations across the Neoproterozoic Araçuaí hot orogen (SE Brazil): insights from structural and magnetic fabric analyses

“…However, even if there is evidence of the breakup of Rodinia, the fact that there is no obvious identification of oceanic crust in the northern portion of the Ribeira belt and in the southern portion of the Araçuaí belt causes the subduction hypothesis to be considered with caution. The Paramirim Aulacogen indicates that the rift was aborted in the northern portion of the San Francisco craton and this suggests that a more southern oceanic spread occurred, resulting in an extension not large enough to initiate subduction and generate a magmatic arc during the convergence between the cratons (Mondou, 2010;Cavalcante et al, 2019).…”

“…Rocks of the Rio Doce Group (Figure 10, #7) host magmatic units in the study area. It is characterized by a metavolcanosedimentary succession that encompasses the supracrustal rocks of the Rio Doce magmatic arc (Vieira, 2007;Tedeschi et al, 2016;Novo et al, 2018 Craton (Vauchez et al, 2007;Mondou et al, 2010;Vieira et al, 2007;Novo et al, 2018).…”

“…The texture is typical of slow cooling rocks. Four U-Pb zircon ages of 585 ± 4 Ma (Mondou et al, 2010), 615 ± 6 Ma, 584 ± 8 Ma, 594 ± 5 Ma (Pinto, 2015) are reported for the São Vitor Tonalite in the study region (appendix B). The EAU is a large area dominated by anatectic rocks, formed by partial melting of the middle crust and deformed predominantly in the magmatic state (Cavalcante et al, 2013).…”