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Deciphering the tectono‐metamorphic evolution of Precambrian terranes can be difficult due to reworking by later superimposed events. Whole‐rock elemental and isotopic geochemistry and zircon U–Pb geochronology are often employed in those studies, but these approaches are often not sensitive to the presence of multiple events and medium‐grade metamorphic episodes. The Rio Apa Terrane (RAT), an allochthonous fragment of the Amazonian Craton, is a crustal block with a well‐characterized crustal evolution but with no detailed thermal constraints for its tectono‐metamorphic evolution. In contrast to previous studies, we show the existence of four tectono‐metamorphic events at c. 1,780, c. 1,625, c. 1,420–1,340, and c. 1,300–1,200 Ma on the basis of apatite, titanite, and rutile U–Pb, in situ white‐mica Rb–Sr, and in situ garnet Lu–Hf geochronology combined with mineral chemistry and phase‐equilibria modelling. The c. 1,780 Ma event is recorded in the basement of the Western domain, representing an extensional event coeval with the development of its Eastern domain in response to the retreat stage of the accretionary system. This is followed by juxtaposition of the Western and Eastern domains along a major crustal boundary at c. 1,625 Ma, which is defined by the magnetic profiles and zircon U–Pb–Hf data across the boundary. The third and fourth events correspond to progressive high‐pressure/medium‐temperature (HP/MT) metamorphism, characterized by an anticlockwise P–T path, suggesting a convergent‐to‐collisional tectonic setting. The RAT was accreted to the adjoining Paraguá Terrane at c. 1,420–1,340 Ma under an isobaric P–T evolution spanning ~530°C to 600°C and ~10.0 kbar. Subsequently, the combined Rio Apa and Paraguá terranes collided with the SW Amazonian Craton at c. 1,300–1,200 Ma, reaching P–T conditions of ~560–580°C and ~10.9–11.7 kbar during crustal thickening. This study reveals for the first time the existence of a HP/MT metamorphic evolution related to the growth of the SW Amazonian Craton as part of an accretionary orogenic system during Rodinia assembly in the Palaeoproterozoic to Mesoproterozoic. [ABSTRACT FROM AUTHOR]

The Embu Complex is one of the most expressive and unknown geotectonic units of the Ribeira Belt (SE Brazil), and its evolutionary history has important implications for the reconstruction of West Gondwana. The Embu Complex is dominated by an amphibolite facies metasedimentary rock assemblage composed of micaschist and migmatitic paragneiss with intercalations of quartzite and calc-silicate, metaultramafic and metamafic rocks. The objectives of this work consist in constraining the P-T-t conditions to the peak of the main regional metamorphic event recorded in the Embu Complex and assess the regional implications of these data in the context of available geochronological and petrological data and large-scale tectonic processes. We present new petrological, phase equilibria modelling and zircon U/Pb SHRIMP and LA-MC-ICP-MS data obtained in key samples of migmatitic paragneiss and associated quartzite from the Embu Complex. Detailed petrological data indicate that the peak of the main regional metamorphic event recorded in the Embu Complex is represented by a migmatitic paragneiss constituted by a sillimanite + garnet + biotite + quartz + K-feldspar + plagioclase residual assemblage, which reached high-grade metamorphism. Quartzo-feldspathic layers that occur in the area are interpreted as granitic neosomes formed during the anatexis. The presence of granitic leucosome, K-feldspar and sillimanite indicate the fluid-absent muscovite breakdown melting reaction was crossed. X-ray mapping garnet analyses are consistent with the rim-core -rim analytical chemical profiles, both showing a very weak to absent composition zonation from to the core to the rim, interpreted as diffusional zoning of garnet, suggesting that thermodynamic equilibrium had possibly been achieved within the peak mineral assemblages at the metamorphic peak stage. Biotite modes on calculated pseudosection modeling in the NCKFMASHTO system using the Perple_X technique constrained the peak P-T conditions to 780 to 808ºC at 5.1 to 10 kbar. Metamorphic zircon overgrowths yielded oldest Concordia ages of 825 ± 14, 792 ± 5 and 788.9 ± 8.5 Ma, interpreted as the time of near peak metamorphism and regional anatexis, which indicate that the main regional metamorphism recorded in the westernmost portion of the Embu Complex occurred in the Tonian. Available geochronological and petrological data and the existence of coeval 810-780 Ma granitic plutons with S-type collisional affinities strongly support the existence of a major Tonian accretionary-to-collisional event in the southern and central Ribeira Belt, which was probably responsible for accretion of Mesoproterozoic exotic terranes to the margin of the Paranapanema Craton. Metamorphic zircon overgrowths with Concordia ages of 566.7 ± 3.7 Ma and 615.2 ± 5.8 Ma were heterogeneously developed, in high-grade and low-grade samples, corroborating the existence of an Ediacaran to Cryogenian metamorphism described for the Ribeira Belt and indicating a complex multiphase metamorphic history for the Embu Complex. [ABSTRACT FROM AUTHOR]