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vol.48 issue2Melanite-bearing nepheline syenite fragments and 40Ar/39Ar age of phlogopite megacrysts in conduit breccia from the Poços de Caldas Alkaline Massif (MG/SP), and implications author indexsubject indexarticles search
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Brazilian Journal of Geology

Print version ISSN 2317-4889On-line version ISSN 2317-4692

Abstract

GOMES, Celso de Barros et al. New age determinations for the Banhadão and Itapirapuã complexes in the Ribeira Valley, southern Brazil. Braz. J. Geol. [online]. 2018, vol.48, n.2, pp.403-414.  Epub Mar 08, 2018. ISSN 2317-4889.  http://dx.doi.org/10.1590/2317-4889201820170094.

New age determinations by Ar-Ar and U-Pb SHRIMP for the alkaline complexes of Banhadão and Itapirapuã that occur in the Ribeira Valley are in agreement with the previously radiometric K-Ar ages available in literature. Ar-Ar ages on biotite for Banhadão range in the 106-110 Ma interval, and suggest a minimum age of 106 Ma for the complex. Ar-Ar data on biotite for Itapirapuã are more uniform, indicating an age of 102 Ma for the complex. U-Pb SHRIMP determinations on titanite from Itapirapuã melanite syenitic rocks yielded an age of ~106 Ma. Thus, the age interval of 100 and 110 Ma does exist indeed, suggesting an intermediate magmatic pulse between the already well-defined peaks of 80-90 Ma and 130-140 Ma for the alkaline rocks in southern Brazil, confirming the periodicity of the magmatism.

Keywords : Alkaline rocks; Ponta Grossa Arch; Geochronology.

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