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Geochemistry of the eocretacic basalt magmatism in the Piraju-Ourinhos region, SE Brazil, and implications to the stratigraphy of the Serra Geral Formation

2007; Sociedade Brasileira de Geologia; Volume: 37; Issue: 01 Linguagem: Inglês

10.25249/0375-7536.2007371148162

2177-4382

Valdecir de Assis Janasi, Francisco de Assis Negri, Tarcísio José Montanheiro, Vivian Azor de Freitas, Brenda Chung da Rocha, Pedro Morais Reis,

Geological formations and processes

The Serra Geral Fm. in the Piraju-Ourinhos region (SW of the State of São Paulo) is made up of initial flows of acidic composition which were deposited over the sandstones of the Botucatu Fm., and were covered by basalt flows which crop out north of the Paranapanema river. Geochemical analyses of a suite of extrusive and intrusive basic rocks reveal significant variations that can be used as tools for stratigraphic correlation. All the rocks from flows and a significant proportion of the intrusive rocks show affinity with the Pitanga basalt type. A set of dike rocks, however, shows lower Ti/Y ratios and weakly fractionated primitive mantle-normalized incompatible element patterns, and are interpreted as conduits of younger basalt flows, now eroded, and equivalent to the Paranapanema type. Samples from one sill, on the other hand, are characterized by more fractionated incompatible element patterns and high Sr contents, indicative of the presence of Urubicitype magmas, previously unknown in this region.