Age, provenance and tectonic setting of the high-grade Jequitinhonha Complex, Araçuaí Orogen, eastern Brazil

Abstract

ABSTRACT:The Jequitinhonha Complex of the northeastern Araçuaí orogen is an extensive sedimentary unit metamorphosed in the amphibolite-granulite facies transition around 580-545 Ma. The unit consists of Al-rich (kinzigitic) paragneisses with decametric intercalations of graphite gneisses and quartzites, and centimetric to metric lenses of calcsilicate rocks. A new detrital zircon U-Pb age spectrum is reported for a sample of quartzite, and whole-rock geochemical (major and trace elements, 9 samples) and Sm-Nd isotope data (10 samples) for Jequitinhonha Complex paragneiss. Together with published data these show that: (1) the geochemistry of paragneiss samples of the Jequitinhonha Complex are similar to those of passive margin sedimentary protoliths; (2) detrital zircon data yield U-Pb age populations between ca. 0.9 and 2.5 Ga; and (3) Sm-Nd T DM model ages range from 1.6 to 1.8 Ga and εNd (575 Ma) around -7.5. The data reveal a mixture of Cryogenian to Mesoproterozoic rift-related igneous rocks with the Palaeoproterozoic-Archaean basement rocks of the São Francisco-Congo palaeocontinent as the main source areas, and also support the correlation between the Jequitinhonha Complex and the passive margin units of the upper Macaúbas Group, constituting the precursor basin of the orogen. Our results, with the absence of ophiolites in the Jequitinhonha Complex, reinforce the interpretation that the São Francisco-Congo palaeocontinent was not divided to the north of the focused region, suggesting an ensialic termination of a gulf during the Neoproterozoic.

Hot Versus Cold Orogenic Behavior: Comparing the Araçuaí‐West Congo and the Caledonian Orogens

“…This has been documented by a variety of geothermometers applied to stable mineral parageneses in granulites and migmatites of the orogen, as discussed in detail by Moraes et al (), who found temperature values around 850°C in the northern part of the hot internal domain. This is consistent with other results, which generally show peak metamorphic temperatures in excess of 750°C for this domain, as illustrated in Figure c (Belém, ; Dias et al, ; Gradim et al, ; Gonçalves et al, ; Moraes et al, ; Munhá et al, ; Uhlein et al, ). A rather well‐studied portion of this internal hot part of the orogen is the Carlos Chagas anatectic domain (CC in Figure ), where vast amounts of crustal melt have been produced and deformed in the nonsolid state at midcrustal levels during the orogeny (Cavalcante et al, , ).…”

“…Several estimates of paleopressures associated with the metamorphic peak in the internal part of the orogen have been presented in the literature, generally varying between 0.5 and 0.7 GPa. (Belém, ; Dias et al, ; Gradim et al, ; Gonçalves et al, ; Moraes et al, ; Munhá et al, ; Petitgirard et al, ; Uhlein et al, ). The highest pressure (0.8 GPa) for the main Araçuaí‐West Congo orogeny was found in the southernmost part of the Araçuaí belt (Bento dos Santos et al, ).…”

Reviewing the puzzling intracontinental termination of the Araçuaí-West Congo orogenic belt and its implications for orogenic development

“…Paragneisses showing evidence of partial melting are widespread in the internal domain (blue unit 3 in Fig. 3), and are at least in part considered to represent partially molten Macaúbas Group (e.g., Dias et al, 2016), but also synorogenic metasediments (Nova Venécia Group; Richter et al, 2016).…”

The Vazante and Canastra groups revisited: Sm-Nd and Sr isotopes - evidence for contribution from Tonian intraplate magmatism during passive margin development along the SW São Francisco margin, Brazil

“…8). Compared to the Vazante and Canastra groups, Gonçalves- Dias et al (2016) interpreted the provenance patterns of the Jequitinhonha Complex, located on the SE border of the SFC, in the Araçuaí Orogen, as resulted from the mixture between cratonic and Tonian rift-related volcanic rocks of the West Congo belt (Tack et al 2001). Caxito et al (2014a) reached the same conclusion for the Canabravinha Formation, in the Rio Preto Fold Belt, northwestern margin of the SFC.…”