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Calc-Alkaline Magmatism at the Archean Proterozoic Transition: the Caico Complex Basement (NE Brazil) |
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| Authors: | De Souza Zorano Sergio; Martin Herve; Peucat Jean-Jacques; Jardim De Sa Emanuel Ferraz; Macedo Maria Helena De Freitas |
| Institution: | 1Pós-GraduaÇão Em Geodinâmica E Geofísica And Departamento De Geologia, Ccet-Ufrn, Caixa Postal 1502, Cep 59078-970, Natal/Rn, Brazil 2Laboratoire Magmas Et Volcans, Opgc, Cnrs, Ird, Université Blaise Pascal, 5, Rue Kessler, 63038, Clermont-Ferrand Cedex, France 3Géosciences Rennes, Cnrs, Université De Rennes 1, 35042, Rennes Cedex, France |
| Abstract: | The Paleoproterozoic metaplutonic rocks of the CaicóComplex Basement (Seridó region, NE Brazil) provide importantand crucial insights into the petrogenetic processes governingcrustal growth and may potentially be a proxy for understandingthe Archean–Proterozoic transition. These rocks consistof high-K calc-alkaline diorite to granite, with Rb–Sr,U–Pb, Pb–Pb and Sm–Nd ages of c. 2·25–2·15Ga. They are metaluminous, with high YbN, K2O/Na2O and Rb/Sr,low ISr ratios, and are large ion lithophile elements (LILE)enriched. Petrographic and geochemical data demonstrate thatthey belong to differentiated series that evolved by low-pressurefractionation, thus resulting in granodioritic liquids. We proposea model in which the petrogenesis of the Caicó Complexorthogneisses begins with partial melting of a metasomaticallyenriched spinel- to garnet-bearing lherzolite (with high-silicaadakite melt as the metasomatic agent), generating a basic magmathat subsequently evolved at depth through fractional crystallizationof olivine, followed by low-pressure intracrustal fractionation.A subduction zone setting is proposed for this magmatism, toaccount for both negative anomalies in high field strength elements(HFSE) and LILE enrichment. Mantle-derived juvenile magmatismwith the same age is also known in the São Franciscoand West Africa cratons, as well as in French Guyana, and thusthe Archean–Proterozoic transition marks a very importantcontinental accretion event. It also represents a transitionfrom slab-dominated (in the Archean) to wedge-dominated post-Archeanmagmatism. KEY WORDS: calc-alkaline; magmatism; NE Brazil; Paleoproterozoic; petrogenesis |
| Keywords: | : calc-alkaline magmatism NE Brazil Paleoproterozoic petrogenesis |
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