Abstract
The geological evolution of the Araguaia Belt (AB), an important Neoproterozoic orogen located in central-north Brazil, is marked by different stages in its tectonic evolution. These stages are characterized by various magmatic events represented by felsic alkaline plutons, ophiolitic suites, mafic-ultramafic intrusions, S-type granites, diabase dykes and tholeiitic basalts distributed along its 1200 km N–S long. One of these events was identified in the Xambioá region, in the NW of Tocantins/SE of Pará state, in which dozens of bodies of scapolite metagabbros and amphibolites were identified through mapping and fieldwork, which were gathered in the Xambica Gabbroic Suite (XGS). Field relations and structural observations reveal that they were intrusive bodies in the sedimentary successions of the Estrondo Group before metamorphism. We present complementary studies involving detailed petrographic, lithochemical and geochronological analyses to characterize these rocks and contextualize this magmatic event in AB evolution. The petrographic study allowed to classify the rocks of the XGS into metagabbros with plagioclase and clinopyroxenes relicts, scapolite-hornblende metagabbro, garnet-scapolite metagabbro, amphibolites, and rarely listwanite and steatite. Geochronological dating of zircon crystals from this suite of rocks was performed using two different techniques. Single zircon Pb-evaporation dating of a metagabbro (XL-02) yielded the age of 819 ± 5 Ma. U–Pb zircon dating by LA-MC-ICP-MS of a metagabbro (BV-01) and an amphibolite (XL-09) gave 822 ± 2 Ma and 826 ± 26 Ma, respectively. Two other metagabbro samples (XL-02 and XB-08) yielded concordant ages of 861 ± 21 Ma and 873 ± 15 Ma. The younger concordant ages are interpreted as the crystallization of the gabbroic protoliths in the Tonian, while the older concordant ages are related to the presence of inherited zircon. The geochemical signature of metagabbros and amphibolites is similar to that of ocean island basalts (OIB) related to an intraplate tectonic environment, characterizing an extensional tectonic phase in AB evolution, which differs from other mafic events already recognized in AB of a MORB or tholeiitic signatures. Similar Tonian age are reported in basic to intermediate volcanic secession in the Goiás Magmatic Arc representing a contemporary collisional tectonic event, which reveals a link in the evolution between these two geotectonic units.
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