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The Nova Monte Verde metamorphic core complex is an arched structure located in the southern portion of the Rio Negro-Juruena geochronological Province and is part of a belt of metamorphic rocks containing gneiss and migmatite domes exhumed during Statherian extension of rifted Ventuari-Tapajós crust. This metamorphic core is bordered, both to the north and south, by felsic volcanic and plutonic rocks intensely foliated near the metamorphic core and becoming progressively undeformed as one moves away from the metamorphic core. U-Pb analyses of zircon and monazite from migmatites exposed in the core of the complex, coupled with a detailed structural analysis, enlighten the timing and duration of migmatite crystallization, indicating that crystallization, extensional deformation and exhumation of the core-complex were coeval. Analysis of a high melt fraction from migmatites outcroping near Bacaeri Farm suggest that the Nova Monte Verde metamorphic core complex records a history of neosome formation spanning at least 37 Ma, as indicated by 206Pb/238U ages (1800-1763Ma) for new zircon growth attributed to migmatization. Monazite from two samples yielded U-Pb ages of 1798 ± 29 Ma for the aluminous metatexite and 1754 ± 11 Ma for sillimanite-biotite metatexite. The former is interpreted as the metamorphic peak and main generation of leucosomes, and the latter as the second phase of partial melting or as an alternative, the timing of cooling and exhumation of metamorphic core complex. Crystallization of the Nova Monte Verde migmatites was therefore coeval in part with upper crustal extension and ductile flow of the mid-crust, suggesting that crustal anatexis was widespread over much of the mid-crust during Statherian time (∼1800-1760Ma). Therefore, the tectonic history of the Nova Monte Verde core complex involved regional extension and exhumation of high-grade metamorphic rocks by transtensional tectonics. The following results are at least more compatible with, if not suggestive of, a continental rift setting than the traditionally accepted continental arc setting. • Migmatites and the Statherian felsic magmatism is related to thermal perturbations in the upper mantle and mafic underplating. • Nova Monte Verde complex is a dome not related to subduction, and was exhumed during Statherian extension of rifted crust. • The crystallization, extensional deformation and exhumation of the Nova Monte Verde core-complex were coeval. • Migmatites of metamorphic core complex records a history of neosome formation spanning at least 37 Ma. [ABSTRACT FROM AUTHOR]

A major Mesoproterozoic paleo-plate boundary in the southwestern Amazonian Craton, the Guaporé Suture Zone, is investigated by U–Pb zircon geochronology, Sr–Nd isotope geochemistry and aeromagnetic data. This suture zone is constituted dominantly by ophiolitic mafic–ultramafic rocks of the Trincheira Complex, and minor proportion of tonalites of the Rio Galera and São Felipe complexes, Colorado Complex, amphibolites of the Rio Alegre Terrane and syn- to late-kinematic mafic to felsic plutonic rocks. The ophiolitic Trincheira Complex formed during an accretionary phase from 1470 to 1430Ma and was overprinted by upper amphibolite–granulite facies metamorphism during the collisional phase of the Ectasian followed by syntectonic emplacement of gabbro and granite plutons (1350–1340Ma). The ophiolites were intruded by syntectonic tonalitic–plagiogranitic plutons ca. 1435Ma. Mafic–ultramafic rocks of the Trincheira ophiolites show moderate to highly positive initial epsilon Nd (t =1.46Ga) values (+2.6 to +8.8) and very low initial 87Sr/86Sr ratio (0.7013–0.7033). It is suggested that these magmas originated from a depleted mantle source in an island-arc–back-arc setting. The identification of a fossil ophiolite in the Guaporé Suture Zone early as 1470–1435Ma and later collisional phase, as late as 1350Ma, marks the impingement of the proto-Amazonian Craton against the Paragua Block, before the formation of the Rodinia supercontinent. The results provide important insights into the geodynamic history of the SW Amazonian Craton, with evidence for both accretionary orogen and subduction of oceanic lithosphere in the Mesoproterozoic, and provide information that allows other workers to evaluate the configuration of supercontinents. [ABSTRACT FROM AUTHOR]

Abstract: We document the first-known Mesoproterozoic ophiolite from the southwestern part of the Amazon craton, corresponding to the Trincheira Complex of Calymmian age, and propose a tectonic model that explains many previously enigmatic features of the Precambrian history of this key craton, and discuss its role in the reconstruction of the Columbia supercontinent. The complex comprises extrusive rocks (fine-grained amphibolites derived from massive and pillowed basalts), mafic–ultramafic intrusive rocks, chert, banded iron formation (BIFs), pelites, psammitic and a smaller proportion of calc-silicate rocks. This sequence was deformed, metasomatized and metamorphosed during the development of the Alto Guaporé Belt, a Mesoproterozoic accretionary orogen. The rocks were deformed by a single tectonic event, which included isoclinal folding and metamorphism of the granulite–amphibolite facies. Layered magmatic structures were preserved in areas of low strain, including amygdaloidal and cumulate structures. Metamorphism was pervasive and reached temperatures of 780–853°C in mafic granulites and 680–720°C in amphibolites under an overall pressure of 6.8kbar. The geochemical composition of the extrusive and intrusive rocks indicates that all noncumulus mafic–ultramafic rocks are tholeiitic basalts. The mafic–ultramafic rocks display moderate to strong fractionation of light rare earth elements (LREE), near-flat heavy rare earth element (HREE) patterns and moderate to strong negative high field strength element (HFSE) anomalies (especially Nb), a geochemical signature typical of subduction zones. The lowest units of mafic granulites and porphyroblastic amphibolites in the Trincheira ophiolite are similar to the modern mid-ocean ridge basalt (MORB), although they locally display small Ta, Ti and Nb negative anomalies, indicating a small subduction influence. This behavior changes to an island arc tholeiite (IAT) signature in the upper units of fine-grained amphibolites and amphibole rich-amphibolites, characterized by progressive depletion in the incompatible elements and more pronounced negative Ta and Nb anomalies, as well as common Ti and Zr negative anomalies. Tectono-magmatic variation diagrams and chondrite-normalized REE and primitive mantle normalized patterns suggest a back-arc to intra-oceanic island arc tectonic regime for the eruption of these rocks. Therefore, the Trincheira ophiolite appears to have originated in an intraoceanic supra-subduction setting composed of an arc-back-arc system. Accordingly, the Trincheira Complex is a record of oceanic crust relics obducted during the collision of the Amazon craton and the Paraguá block during the Middle Mesoproterozoic. Thus, the recognition of the Trincheira ophiolite and suture significantly changes views on the evolution of the southern margin of the Amazon craton, and how it can influence the global tectonics and the reconstruction of the continents. [Copyright &y& Elsevier]

The Peixoto de Azevedo domain (PAD) is the southernmost portion of the Tapajós-Parima province in the Amazonian craton. It is constituted by Paleoproterozoic rocks (2.05–1.85 Ga) of the Cuiú-Cuiú magmatic arc (CCMA), and by post-orogenic to anorogenic granitoids. The rocks with magmatic arc signature in the PAD are correlated with those of the Mundurucus orogeny (2.04–1.96 Ga) in the Tapajós domain, where several authors propose the evolution of at least three magmatic arcs. However, in this work, the rocks of PAD are interpreted as part of a single magmatic arc of Orosirian age, the CCMA. Geochronological, geochemical and petrographical data suggest that CCMA has evolved within a continuous long-lived subduction process, in the approximate range of 2.05–1.95 Ga, at the border of an Archean terrain. This older basement is represented by the Gavião gneiss, an inlier whose U-Pb LA-ICP-MS zircon age is 2825 ± 9 Ma. Additionally Nd-T DM data (2.76–2.5 Ga) and some Archean inherited and detrital zircon crystals indicate that CCMA developed on an Archean basement. The CCMA is divided into: Cuiú-Cuiú complex (CCC; 2050–1990 Ma), which marks the main phase of subduction in the evolution of CCMA and is represented by migmatitic orthogneisses, quartz diorites, tonalites and granodiorites; metaplutonic Pé Quente suite and volcanic rocks of the Jarinã formation (2000–1970 Ma), which both form an expanded calc-alkaline serie, typical of continental margin arcs, of tonalitic, granodioritic, monzo- and syenogranitic composition; and Nhandu intrusive suite (1970–1950 Ma), composed of high-K calc-alkaline to shoshonitic syeno- and monzogranites, whose isotopic data (ϵNd from −0.95 to −7.6) indicate strong participation of crustal sources in its generation. Nhandu intrusive suite shows chemical characteristics of magma generated in late to post-tectonic setting and marks the final phase of the CCMA evolution. The metamorphic peak in the area reached high amphibolite facies, probably between 2015 Ma and 1990 Ma (main age range of the migmatitic gneisses). After the orogenic compressive phase, the region experienced tectonic quiescence, which was followed by post-orogenic to anorogenic extension, approximately between 1905 and 1850 Ma. This later event is represented by expressive acid plutonism of Guarantã do Norte and Matupá granitoid suites, and subordinately by basic rocks of Flor da Serra intrusive suite. • Peixoto de Azevedo domain is the southernmost portion of the Tapajós-Parima province in the Amazonian craton. • The Orosirian Cuiú-Cuiú magmatic arc in Peixoto de Azevedo domain originated during a single long-lived subduction process. • The Cuiú-Cuiú magmatic arc shows continental margin arc signature, developed at the border of an Archean terrain. • Archean basement inlier represented by Gavião gneiss (2825 ± 9 Ma). [ABSTRACT FROM AUTHOR]

The Western Amazonia Igneous Belt (WAIB) occupies the northern part of South American continent, and a total area close to 125,000 km2. The belt is composed dominantly by volcano-plutonic felsic rocks (Juruena supersuite, Teles Pires suite and Colíder group) and has dominant alkali-calcic, metaluminous to peraluminous, ferrous, geochemical characteristics, similar to A-type granites. The Silicic members are represented by granites and rhyolitic-rhyodacitic volcanic rocks, mafic members by gabbroic rocks and diabase dykes. Intermediate rocks are rare. Local magma mingling and hybridization are present in several areas. The assemblage of silicic and basic rocks of WAIB was formed between c. 1825 and 1757 Ma. The presence of inherited zircons, from 1875 to 2050 Ma, as well as some Archean ages in the granitic and volcanic rocks from the WAIB, are suggestive of derivation by melting of pre-existing crustal basement (Ventuari-Tapajós Province). This hypothesis is also corroborated by bimodal magmatism and by several model-ages of granites, felsic volcanic rocks and mafic plutonic rocks, with T DM ranging from 2.0 to 2.3 Ga, and ε Nd value, varying from −3.90 to +2.52. The preferred model of formation of the WAIB envisages the emplacement of large volumes of hot mantle-derived melts into the lower crust. These processes resulted in partial melting of lower-crustal material, mixing with the mantle-derived melts and formation of granitic melts. The timing and spatial features and interpreted petrogenetic mechanisms of WAIB are suggestive of a continental rift setting. In addition, this volcano-plutonic province is similar to silicic igneous provinces (Silicic Large Igneous Province-SLIP) in areal extent, eruptive volume and petrogenetic characteristics. • The WAB occupies the south portion of Rio Negro-Juruena Province. • The igneous belt is predominantly formed by felsic rocks, ferroan, alkali-calcic, metaluminous to slightly peraluminous rocks. • Magmatic underplating involving dehydration melting of intermediate-felsic deep crust. [ABSTRACT FROM AUTHOR]