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Título

GEOLOGY, PETROLOGY AND GEOCHRONOLOGY OF 2.03 TO 1.96 GA MAGMATIC ARC GRANITES FROM JURUENA MINERAL PROVINCE, BRAZIL: IMPLICATIONS FOR THE AMAZONIAN CRATON TECTONIC EVOLUTION.

Texto do resumo

New petrological, geochemical, U–Pb, and Sm–Nd isotopic data allow us to propose a new petrogenetic model for the granite production in the southernmost portion of Amazonian Craton, Brazil, here called Novo Mundo complex. This region is located in the extreme north of the Juruena Mineral Province and the south of Tapajós-Parima Province. The rock facies include monzonite, monzogranite, biotite granodiorite and syenogranite. Andesitic dikes occur by cutting the granitic body. Biotite from the granites is classified as annite, with characteristics of biotite formed in a volcanic arc environment. The I-type, meta to peraluminous, calc–alkaline to alkali–calcic granites have petrographic, lithogeochemical, mineral chemistry and isotopic characteristics of volcanic arc, with different degrees of crustal contribution. Magmatic zircon crystals revealed U–Pb LA–ICP–MS ages of 2032 ± 6 Ma for monzonite, 2029 ± 4 Ma for monzogranite, 1989 ± 6.2 Ma for biotite granodiorite and 1987 ± 7.4 Ma to 1964 ± 1 Ma for syenogranite. The granites exhibit TDM Nd model ages of 2.52–2.15 Ga and ɛNd(t) from −2.0 to +1.81, indicating that the parental magma of the granites originated from the mantle or melting of the juvenile Orosian crust. The weak positive ɛNd(t) anomalies suggest an upwelling asthenospheric mantle that supplied heat to remelt the lower continental crust and the isotopic data highlights different levels of crustal reworking during arc evolution. These ages can be correlated with the data evolution of the Paleoproterozoic Cuiú–Cuiú Magmatic Arc emplaced during the main phase of the arc subduction evolution in the region (2.05–1.99 Ga). The monzonite and monzogranite are associated with the initial stages of arc evolution. The monzogranite has locally primary muscovite. The granodiorite shows the contribution of juvenile sources correlating with mafic magma inflow events while the syenogranite represents the final stages of the arc formation, indicating a predominance of crustal contribution. The obtained data, together with recent studies, allow suggest the existence of a continuous magmatic arc in the Paleoproterozoic at the south part of the Amazonian craton, which was responsible for the formation of the Tapajós and Juruena mineral provinces main granitic rocks, instead of the interpretation of individual tectonic provinces as responsible for the different ages of granite formation in the region. They are also crucial to expanding our knowledge for the magma generation and granite-related mineral deposits and in south Amazonian Craton.

Palavras Chave

Amazonian Craton; Paleoproterozoic Granite; Magmatic arc; Petrology.