ew high-precision Ar-40/Ar-39 ages for the Serra do Mar alkaline magmatism in the Sao Sebastiao Island, SE Brazil, and implication

Author(s)

Giraldo-Arroyave, Maria Isabel ^[1] ; Vlach, Silvio Roberto Farias ^[1] ; Vasconcelos, Paulo Marcos ^[2]

Affiliation

^[1] Univ Sao Paulo, Inst Geosci, Sao Paulo, SP - Brazil

^[2] Univ Queensland, Sch Earth & Environm Sci, Brisbane, Qld - Australia

• Document type: Journal article
• Source: BRAZILIAN JOURNAL OF GEOLOGY; v. 51, n. 4 2021.
• Web of Science Citations: 0

Abstract

We present new high-resolution Ar-40/Ar-39 ages for alkaline layered gabbros and cross-cutting mafic-ultramafic and felsic dykes from the Sao Sebastiao Island, in the northern sector of the Serra do Mar Alkaline Province, Sao Paulo, Brazil. Duplicate analysis of single kaersutite crystals yielded plateau ages of 88 +/- 1 and 87.9 +/- 0.8 Ma for a gabbro and 87 +/- 1 and 86.0 +/- 0.8 Ma for a picrite dyke. Two biotite aliquots from a trachyte yielded ages of 86.0 +/- 0.5 and 86.2 +/- 0.5 Ma, while an alkali feldspar concentrate yielded ages of 86.0 +/- 0.5 Ma. The similar ages obtained for minerals with contrasting closure temperatures suggest that the results are crystallization ages and that the rocks were emplaced at shallow crustal levels. Our results, along with available high-resolution data, point to a relatively narrow time span (ca. 88-85 +/- 0.6 Ma) for the entire alkaline magmatism on the island. Other alkaline occurrences both nearby and in the continent's interior reveal similar ages, reinforcing the hypothesis that mantle decompression and upwelling of heterogeneous mantle sources led to crustal extension and fast ascension of a variety of alkaline magma types in this segment of South America. (AU)

• FAPESP's process: 12/06082-6 - The Paraná-Etendeka magmatic province in Brazil: temporal and petrologic relationships between the tholeiitic and alkaline magmatism and geodynamic implications
• Grantee: Excelso Ruberti
• Support Opportunities: Research Projects - Thematic Grants