Continental contribution to the marinoan cap carbonate of Tangará da Serra – MT, Brazil: further evidence from Sr-Nd-Pb isotope geochemistry

Abstract On the southern edge of the Amazonian Craton, the Mirassol d’Oeste and Guia formations constitute the cap carbonate of the Araras Group. Petrography, X-ray diffraction, and quantification of terrigenous material allowed the identification of detrital grains (e.g., mica, quartz, and feldspar...

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Bibliographic Details
Published in:	Brazilian journal of geology Vol. 54; no. 1
Main Authors:	Souza, Nayra Michelly das Chagas, Lafon, Jean Michel, Milhomem Neto, João Marinho, Soares, Joelson Lima
Format:	Journal Article
Language:	English
Published:	Sociedade Brasileira de Geologia 01-01-2024
Subjects:	Amazonian Craton Cap carbonate GEOLOGY GEOSCIENCES, MULTIDISCIPLINARY Marinoan Sr-Nd-Pb isotopes Sr-Nd-Pb isotopes Marinoan Amazonian Craton Cap carbonate
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Summary:	Abstract On the southern edge of the Amazonian Craton, the Mirassol d’Oeste and Guia formations constitute the cap carbonate of the Araras Group. Petrography, X-ray diffraction, and quantification of terrigenous material allowed the identification of detrital grains (e.g., mica, quartz, and feldspar) in different proportions and diagenetic features. The sequential leaching of carbonates along a section of the upper portion of the Guia Formation yielded 87Sr/86Sr ratios increasing from 0.7070 to 0.7077, which is considered the primary Sr isotopic signature of seawater. The increasing continental influx of dissolved Sr from freshwater accounts for the increase in 87Sr/86Sr along the section. Such abrupt change toward more radiogenic values is also observed in carbonate layers soon after the Marinoan glaciation, elsewhere in the world. The same samples provided Nd-TDM model ages (1.84–2.54 Ga) comparable with those of the continental crust of the Paleoproterozoic provinces of the Amazonian Craton, which forms the basement of the Araras Group. The ԐNd(635Ma) values between -4.7 and -11.1, probably indicate the presence of Nd from the suspended material transported by continental waters to the ocean where the carbonates precipitated. The random variations of Nd-TDM ages and ԐNd values suggest important and rapid variations in the continental contribution to the post-Marinoan oceans.
ISSN:	2317-4889 2317-4692 2317-4692
DOI:	10.1590/2317-4889202420230015