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Calc-alkaline magmatism at the ArcheanProterozoic transition: The caico complex basement (NE Brazil)

Abstract : The Paleoproterozoic metaplutonic rocks of the Caico* Complex Basement (Serido* region, NE Brazil) provide important and crucial insights into the petrogenetic processes governing crustal growth and may potentially be a proxy for understanding the Archean^ Proterozoic transition. These rocks consist of high-K calc-alkaline diorite to granite, with Rb^Sr, U^Pb, Pb^Pb and Sm^Nd ages of c. 225^215 Ga. They are metaluminous, with high YbN, K2O/Na2Oand Rb/Sr, low ISr ratios, and are large ion lithophile elements (LILE) enriched. Petrographic and geochemical data demonstrate that they belong to differentiated series that evolved by low-pressure fractionation, thus resulting in granodioritic liquids.We propose a model in which the petrogenesis of the Caico* Complex orthogneisses begins with partial melting of a metasomatically enriched spinel- to garnet-bearing lherzolite (with high-silica adakite melt as the metasomatic agent), generating a basic magma that subsequently evolved at depth through fractional crystallization of olivine, followed by low-pressure intracrustal fractionation. A subduction zone setting is proposed for this magmatism, to account for both negative anomalies in high field strength elements (HFSE) and LILE enrichment. Mantle-derived juvenile magmatism with the same age is also known in the SaÐ o Francisco andWest Africa cratons, as well as in French Guyana, and thus the Archean^Proterozoic transition marks a very important continental accretion event. It also represents a transition from slab-dominated (in the Archean) to wedge-dominated post-Archean magmatism.
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Submitted on : Friday, December 14, 2007 - 2:44:42 PM
Last modification on : Tuesday, August 16, 2022 - 2:32:23 PM

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Z.S. Souza De, Hervé Martin, Jean-Jacques Peucat, Emanuel Ferraz Jardim de Sa, M.H. Freitas Macedo De. Calc-alkaline magmatism at the ArcheanProterozoic transition: The caico complex basement (NE Brazil). Journal of Petrology, Oxford University Press (OUP), 2007, 48 (11), pp.2149-2185. ⟨10.1093/petrology/egm055⟩. ⟨insu-00197194⟩



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