Abstract
Five different groups of granitoids intruded phyllites and schists of the SW/NE-trending Cachoeirinha-Salgueiro Foldbelt (CSF) and adjacent basement migmatites in northeastern Brazil during the Brasiliano cycle. K-calc-alkalic batholiths intruded the northern CSF boundary at a depth of about 13 km about 580 Ma. Calc-alkalic tonalites to granodiorites with four textural types of magmatic epidote intruded the central CSF at about 19 to 23 km. Leucocratic, epidote-bearingtonalites to granodiorites, with continental trondhjemitic affinities, are restricted to the area of higher grade metamorphics of the Salgueiro Group, in the cores of two ring-structures, with oversaturated peralkalic rocks towards the margins. Ultra-potassic peralkalic syenites with subordinate pyroxenite developed a syenitoid line about 580 Ma following pull-apart opening of fractures along 150 km of the southern boundary of the CSF. In its northern extension, peralkalic rocks are replaced by shoshonitic granitoids. Three granitoid groups display δ 18O values between 9–10 permil SMOW. The epidote-bearing calc-alkalic group, however, has values mostly between 12 and 13 permil, while “pyroxene corrected” whole-rock δ 18O values for rocks in the syenitoid line cluster around 8 permil. The high δ 18O values for the epidote-bearing calc-alkalic plutons were probably inherited from their source rocks, and this isotope behavior cannot be generalized for plutons of the same kind in the world. All groups have positive δ 34S, usually higher than +66 permil CDT. Values for the ultrapotassic syenites and pyroxenite range from 6 to 12 permil. The Sr, O, and S isotope signatures of this ultrapotassic province, and their LILE-enrichment, suggest an anomalous mantle source th at may have existed beneath northeastern Brazil and part of West Africa since Archeans times.
Published Version
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