Deformation of a pervasively molten middle crust: insights from the neoproterozoic Ribeira‐Araçuaí orogen (SE Brazil)

Abstract

Pervasive melting of the middle crust, as inferred in Tibet and the Altiplano, probably influences the deformation of the lithosphere. To constrain strain distribution in a pervasively molten crust, we analysed the deformation in an eroded analogue of these orogens. The Ribeira‐Araçuaí orogen (SE Brazil) comprises a stack of allochthons containing large volumes of anatectic and magmatic rocks. The upper allochton (∼300 km long, 50–100 km wide and >10 km thick) involves peraluminous diatexites and leucogranites resulting from partial melting of the middle crust. It overlies another allochthon containing huge early‐ to syn‐collisional plutons intruding metasediments. Both anatexites and magmatic intrusions display a pervasive strain‐induced magmatic fabric. Homogeneous strain distribution suggests inefficient localization. U–Pb ages of ∼575 Ma imply that anatexite melting was synchronous to the early‐ to syn‐collisional magmatism. Similarity in ages magmatic and solid‐state fabrics indicates that intrusions and anatexites deformed coherently with solid‐state rocks while still molten, in response to a combination of gravity‐driven and collision‐driven deformation.

Magmatic garnet in the Cordilleran-type Galiléia granitoids of the Araçuaí belt (Brazil): Evidence for crystallization in the lower crust

“…1b and c), previously investigated by Gonçalves et al (2014), Mondou et al (2012), Nalini (1997), Nalini et al (2000Nalini et al ( , 2005Nalini et al ( , 2008 and Vauchez et al (2007). The study area covers ca.…”

“…600 km, almost the entire length of the Araçuaí orogen, covering an area of approximately 30,000 km 2 (Fig. 1a) (Gonçalves et al, 2014;Pedrosa-Soaeres et al, 2011;Pedrosa-Soares et al, 2001;Vauchez et al, 2007). Based on field evidence, mineral textural studies and geochemical features, Gonçalves et al (2014) have recently further subdivided the Galiléia batholith into a suite of enclave-rich tonalitegranodiorite rocks and a suite of enclave-poor tonalitic to granitic rocks.…”

“…Different tectono-stratigraphic schemes have been proposed to describe the architecture of this orogen. PedrosaSoares et al (2001) and Pedrosa-Soares and Wiedemann-Leonardos (2000) proposed its subdivision into external, internal and northern domains, while Mondou et al (2012) and Vauchez et al (2007) adopted another subdivision (Fig. 1b) defining a Western Domain (or Western Mylonitic Unit), a Central Domain (or Central Plutonic Unit) and an Eastern Domain (or Anatectic Unit).…”

“…1b; e.g. Vauchez et al, 2007). The Western Domain, which has been thrust over the eastern São Francisco Craton (mostly made up of gneiss and Al-quartzites), consists of hightemperature (~750°C) and relatively low-pressure (~0.6 GPa) metasedimentary mylonites crosscut by abundant syn-kinematic garnet-cordierite-bearing leucocratic veins (570-580 Ma, LA-ICP-MS U-Pb zircon and monazite ages; Petitgirard et al, 2009).…”

“…These include: the garnet-epidote bearing dikes cropping out in the Front Range, Colorado (Dawes and Evans, 1991;Evans and Vance, 1987); the Dehnow pluton, north east Iran (Samadi et al, 2014); the Bushy Point Granites, south eastern Alaska (Arth et al, 1988;Hammarstrom, 1984a, 1984b); the Jinshan Intrusion associated with the Dabie Orogenic belt, China (e.g. Xu et al, 2013) and the subject of this study, the 30,000 km 2 Neoproterozoic Cordilleran-type Galiléia Batholith, located within the Araçuaí Orogen, Brazil (Mondou et al, 2012;Nalini, 1997;Nalini et al, 2000Nalini et al, , 2005Nalini et al, , 2008Vauchez et al, 2007). Garnet and epidote-bearing assemblages have been reported throughout the Galiléia batholith but the origin of both minerals has not been accurately constrained.…”