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Shoshonitic and ultrapotassic Proterozoic intrusive suites in the Cachoeirinha-Salgueiro belt, NE Brazil: a transition from collisional to post-collisional magmatism

1993; Elsevier BV; Volume: 62; Issue: 3 Linguagem: Inglês

10.1016/0301-9268(93)90028-z

1872-7433

Adejardo Francisco da Silva Filho, Ignez P. Guimarães, R. N. Thompson,

earthquake and tectonic studies

The Cachoeirinha-Salgueiro belt is located in the Borborema Province, NE Brazil. It has been intruded by several syenitic and granitic plutons and by dykes, which can be grouped into four magma series. This study deals with the petrology, geochemistry and the tectonic setting of two Neoproterozoic and one Cambrian intrusive suite from the Cachoeirinha-Salgueiro belt, namely the Terra Nova, Salgueiro and Serra do Livramento plutons, and associated dyke swarms. They belong to three distinct magma series: high-K calc-alkaline, shoshonitic and ultrapotassic. They show high LIL/HFS ratios. Increase in initial 87Sr86Sr and RbSr ratios, with decreasing age of the intrusives, fits a genetic model in which crustal thickening occurred in the belt at the end of the Proterozoic. The intrusive rocks studied in this investigation show a clear overall geochemical signature of a subduction-related origin, although there are also some subtle differences. The authors believe these plutons both to represent the last major magmatic stage and to record a transitional tectonic setting between the collisional and post-collisional phases in the evolution of an active continental margin, now represented in part by the Cachoeirinha-Salgueiro belt.