Produção Nacional
Provenance of heavy-minerals in the Piranhas-Acu River, Northeastern Brazil
2000; Sociedade Brasileira de Geologia; Volume: 30; Issue: 3 Linguagem: Inglês
10.5327/rbg.v30i3.850
ISSN2317-4889
AutoresMárcia Gomes da Silva, Helenice Vital,
Tópico(s)Paleontology and Stratigraphy of Fossils
ResumoClino-amphibole, epidote, garnet, sillimanite, tourmaline, staurolite, andalusite, zircon, rutile, augite, ilmenite, hematite and magnetite are the heavy-minerals recorded in the Piranhas-Acu River. Six assemblages were identified: (i) Garnet-hornblende-tourmaline with sillimanite, when cutting rocks of the Serido Formation; (ii) Hornblende-garnet-zircon, when crossing rocks of the Caico gneiss-migmatite Complex; (Hi) Hornblende-zircon-epidote-staurolite, when in rocks of the Jucurutu Formation; (iv) Hornblende-zircon-epidote, when rocks of the Acu Formation; (v) Hornblende-zircon-staurolite, when the lowermost Agu River channel cuts limestones of the Jandaira Formation, and (vi) Zircon-tourmaline-staurolite in the Acu River mouth (Cenozoic rocks) where coastal dynamics dominate. Mineral ratios that reflect differences in grain shape, density, and selective chemical decomposition were used to isolate the effects of source and as controls of mineral variability. The reworking of the sediments was regionally effective in selective sorting; the more equant minerals (e.g. epidote) and heavier minerals (e.g. opaques) had a higher probability of being selected for permanent deposition during reworking. The process of selective decomposition dominates at the river mouth.
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