Age and duration of acid magmatism in the Paraná Magmatic Province from 40Ar-39Ar sanidine and U-Pb zircon and baddeleyite dating

Abstract

The small time interval (2-4 Ma) in which the impressive volume of volcanic rocks of the Paraná Magmatic Province (~800,000 km3) was formed requires the use of high precision geochronological techniques (> 0.5 Ma) to determine its chronostratigraphy and, thus, the correct establishment of its geological history. Among the best available temporal markers are volcanic rocks of silicic character (> 65% SiO2), with dacitic, trachydacitic and rhyolitic composition, occurring at different stratigraphic positions throughout most of the history of the Province. Unlike the largely predominant basalts, silicic rocks of higher crystallinity can provide sanidine, an ideal mineral for high precision 40Ar/39Ar dating due to its high K content, and zircon and/or baddeleyite, which can generate U-Pb ages with uncertainties better than 0.5 Ma when using the ID-TIMS methodology. To this project, twelve samples from key areas studied in detail by collaborating researchers from USP and UNESP were selected, thus enabling the dating of all types and subtypes of silicic volcanics from the Province: Ourinhos and Guarapuava subtypes from the Chapecó type (64-68% SiO2; 0,95-1,59% TiO2), and Clevelândia, Santa Maria, Anita Garibaldi, Barros Cassal, Caxias do Sul subtypes from the Palmas type (64-72% SiO2; 0,57-1,23% TiO2). The 40Ar/39Ar analyses in sanidine will be performed at the Argon-Argon Laboratory (CPGeo, USP), while U-Pb ID-TIMS analyses of samples supplying zircon and/or baddeleyite will be conducted at the Radiogenic Isotope Facility (University of Alberta, Canada). In this way, it is intended to refine the complete chronostratigraphy of the silicic volcanic rocks of the PMP, and thus contribute to identify the age and duration of the magmatic events that constitute it, with direct implications for the understanding of the processes responsible for the rupture of Gondwana and opening of the South Atlantic Ocean. (AU)