Abstract
This article presents new lithochemical and geochronological data obtained from gneisses and granites occurring in the region located to the east of the Rio Doce calc-alkaline arc (630 - 580 Ma), which corresponds to the back-arc basin of the Aracuai orogen. The Nova Venecia Complex, represents the most fertile source of peraluminous granitic melts in the studied back-arc zone. It mostly consists of migmatitic Al-rich paragneisses, ranging from biotite-rich gneisses to biotite-free cordierite-rich granulites, whose main protoliths were graywacky sediments. An EW-oriented section across the northern back-arc region reveals a zone rich in cordierite granulites of the Nova Venecia Complex at the base, followed by migmatites that gradually pass to the Ataleia foliated granites rich in metasedimentary enclaves, which in turn lay beneath the Carlos Chagas batholith. To the south of the Carlos Chagas batholith, orthopyroxene-bearing rocks often occur in both the Nova Venecia Complex and the Ataleia Suite, suggesting a deeper crustal level. Our U-Pb data suggest that melting processes started on the Nova Venecia Complex during the late development of the Rio Doce arc, around 590 Ma, forming autochthonous peraluminous melts related to the Ataleia Suite. Progressive anatexis and melt accumulation attained the climax around 575 Ma, leading to the development of the syn-collisional Carlos Chagas batholith. Around 545 - 530 Ma, a late to post-collisional anatectic episode formed garnet-cordierite leucogranites, mostly from the re-melting of the Ataleia and Carlos Chagas granites. A remarkable post-collisional plutonism caused widesperead re-heating of the back-arc domain from ca. 520 Ma to 480 Ma. This long lasting history (ca. 110 Ma) of granite generation in the back-arc zone requires distinct heat sources, such as asthenosphere ascent under the back-arc region in the pre-collisional stage, thrust stacking of the hot arc onto the back-arc, radiogenic heat release from the collisional thickened crust and, finally, asthenosphere uprising during the gravitational collapse of the Aracuai orogen.
Highlights
The Araçuaí orogen and its counterpart located in Africa, the West Congo belt, make up an orogenic edifice edged by the São Francisco-Congo craton (Fig. 1)
Back-arc basins related to active subduction zones and orogens develop over thin and hot lithospheric domains
Even when associated with continental magmatic arcs, back-arc domains can receive important heat inputs related to asthenosphere ascent and heat renewed by convection during the pre-collisional stage of the orogeny (Hyndman et al 2005)
Summary
The Araçuaí orogen and its counterpart located in Africa, the West Congo belt, make up an orogenic edifice edged by the São Francisco-Congo craton (Fig. 1) This confined orogenic system developed inside an end-branch (a gulf ) of the Adamastor Ocean, shaped into the São Francisco-Congo paleocontinent in Neoproterozoic time (Pedrosa-Soares et al 2001, 2008, 2011; Cordani et al 2003; Alkmim et al 2006). Together with a carefully fieldchecked compilation of the previous maps published by Féboli (1993a,b), Signorelli (1993), Silva (1993), Vieira (1993), Tuller (1993), Baltazar (2009), and Baltazar and Silva (2009) resulted in the regional map of the studied back-arc zone (Fig. 2) This solid field basis allowed us to select the appropriate samples from the regional rock units for petrographic, lithochemical and geochronological studies presented here. 630 – 480 Ma) succession of granite production events (Pedrosa-Soares et al 2011) These plutonic rocks have been grouped into five supersuites, namely G1–G5 (Fig. 1, Tab. 1). Despite its volcanic arc chemical signature, the G1 rocks show hybrid isotopic attributes (negative epsilon Nd values from -5 to -13, TDM model ages from 1.2 to 2.2 Ga, inherited zircons mostly from a late Rhyacian continental crust), suggesting interaction between mantle derived magmas and the Paleoproterozoic continental basement
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