Abstract
This study presents LA-ICP-MS U-Pb detrital zircon ages on a migmatitic paragneiss of the Jaguaretama Complex, northern Borborema Province, NE-Brazil. This metasedimentary rock comprises a stromatic migmatite with alternating layers of metapelite, metapsammite, and garnet-tourmaline-bearing leucosome. The paleosome displays a well-developed schistosity, with fine to medium-grained textures, and locally garnet porphyroblasts. Backscattered electron images show that many of the zircon grains display metamorphic overgrowths (recrystallization) and cores with igneous oscillatory zoning. The detrital zircon grains show 207Pb/206Pb ages clustering from 2.51 to 2.12 Ga (with 90% conc.), evidencing that the igneous sources were generated mostly during the Transamazonian/Eburnean orogeny. The age of 2137±9 Ma of the youngest and most concordant detrital zircon (core) is interpreted as the maximum depositional age of the protolith. The youngest and most concordant (conc. 99%) 207Pb/206Pb apparent age obtained in a metamorphic zircon overgrowth was 2046±6 Ma, which is interpreted as the age of high-grade metamorphism. This age of metamorphism is similar to other records of Paleoproterozoic high-grade metamorphic events in the Borborema Province and other cratonic domains (e.g. Sao Francisco and West Africa cratons). This age also represents the minimum depositional age of the protolith. Therefore, the depositional age of the studied supracrustal rock may be bracketed between ca. 2.14 and 2.05 Ga.
Highlights
The record of Paleoproterozoic high-grade metamorphism in the central Atlantic cratonic domains (e.g. São Luís-West Africa and São Francisco-Congo cratons) are commonly reported in the literature (e.g. Oliveira and Melo 2002; Oliveira et al 2010; Teixeira et al 2017)
We present U-Pb (LA-ICP-MS) ages of detrital zircons from a high-grade metasedimentary sample of the Jaguaretama Complex, which record the effects of the Paleoproterozoic high-grade metamorphism in zircon overgrowths and provide some provenance information from zircon cores
The analyzed sample from the Paleoproterozoic Jaguaretama metasedimentary sequence, indicates that this sequence is Paleoproterozoic in age, and the detrital zircon ages mimic the ages of many Rhyacian orthogneisses dated in basement rocks of the northern Borborema Province (e.g., Fetter et al 2000; Souza et al 2007; Martins et al 2009; Hollanda et al 2011; Silva et al 2014; Costa et al 2015; Souza et al 2016; Costa et al 2018)
Summary
The record of Paleoproterozoic high-grade metamorphism in the central Atlantic cratonic domains (e.g. São Luís-West Africa and São Francisco-Congo cratons) are commonly reported in the literature (e.g. Oliveira and Melo 2002; Oliveira et al 2010; Teixeira et al 2017). The Jaguaretama Complex is located in the northern portion of the Borborema Province between the Senador Pompeu and Tatajuba-Jaguaribe shears zones, according to Oliveira and Medeiros (2018) (Fig. 1C). This complex is mainly composed of tonalitic to granodioritic orthogneisses and high-grade metasedimentary rocks with variable degree of migmatization (Cavalcante et al 2003). Similar U-Pb ages and unradiogenic Nd signatures are found in other Paleoproterozoic orthogneisses across the northern Borborema Province, such as the Caicó Complex (Fetter et al 2000; Souza et al 2007; Hollanda et al 2011; Medeiros et al 2012; Sá et al 2014; Oliveira and Medeiros 2018)
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