Contribution to the study of the Paleo and Mesoproterozoic magmatism of the SW Amazonian craton based on stable isotopes of O, H and S

Author(s)

Mauro Cesar Geraldes ^[1] ; Wilson Teixeira ^[2] ; Claudia Sayão Valladares ^[3]

Affiliation

^[1] UERJ. Faculdade de Geologia - Brasil

^[2] USP. Instituto de Geociências - Brasil

^[3] UERJ. Faculdade de Geologia - Brasil

• Document type: Journal article
• Source: Acta Amazonica; v. 38, n. 2, p. 297-306, 2008-00-00.
• Field of knowledge: Physical Sciences and Mathematics - Geosciences

Abstract

Stable isotopes of O, H and S were used to investigate the origin of magmatic rocks of the Jauru and the Pontes e Lacerda Terrains, SW portion of the Amazonian craton, Mato Grosso state, Brazil. Granitic rocks of the Alto Jauru Greenstone belt and Cachoeirinha Suite, Jauru terrain, present δ18O values between +9.0‰ and +6.3‰, indicative of derivation from juvenile magmas. The Rio Branco Intrusive Suite basic and felsic rocks' δ18O values fall, respectively, within +5.4‰ to +5.8‰ and +8.7‰ to +9.0‰ ranges; the intermediate rocks present δ18O between +7.3‰ and +8.3‰. The lower values of δ18O, obtained from basic rocks, are compatible with a mantle source, however the felsic rocks present δ18O values indicative of crustal source. The stable isotopes of hydrogen yielded δD values between - 83‰ and - 92‰, different from the δD signatures of metamorphic rocks and rain water. Sulphur isotopes in sulfides from basic and intermediate rocks of the Rio Branco suite presented δ34S values coherent with a mantle source (between + 0.7‰ and +3.8‰), whereas δ34S values between + 5.2‰ and + 6.1‰, obtained from the felsic rocks, suggest crustal participation in their genesis. For the Santa Helena Suite (Pontes e Lacerda Terrain) the δ18O values fall between +4.4‰ and +8.9‰. The present study confirms the advantages of using stable isotopes to understand magmatic processes and crustal evolution. (AU)