T33F-2997
The Temporal Relationship Between Alkaline and Tholeiitic Magmatism in the Paraná-Etendeka Igneous Province: ID-TIMS U-Pb Ages of the José Fernandes Gabbro and Dykes of the Ponta Grossa Arch, Brazil

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Vidyã Vieira de Almeida1,2, Larry M Heaman3, Barry Shaulis4, Valdecir A Janasi1 and Frederico Meira Faleiros1, (1)USP University of Sao Paulo, São Paulo, Brazil, (2)CPRM Geological Survey of Brazil, São Paulo, Brazil, (3)University of Alberta, Earth and Atmospheric Sciences, Edmonton, AB, Canada, (4)Lunar and Planetary Institute, Houston, TX, United States
Abstract:
The Ponta Grossa Arch (PGA) region in S-SE Brazil hosts prominent NW-oriented lineaments with hundreds of tholeiitic dykes of the Ponta Grossa Dyke Swarm (PGDS) and also alkaline intrusions concentrated between the Guapiara and São Jerônimo-Curiúva lineaments. Many of these intrusions lack more robust geochronological data; the alkaline intrusions appear to be both coeval with (e.g. Jacupiranga, Juquiá with ~130 Ma) and much younger than (e.g. Tunas, Cananéia with ~85 Ma) the adjacent Paraná basaltic lavas.

We present in this work the first ID-TIMS U-Pb baddeleyite-zircon ages for diabase dykes of the Guapiara Lineament and for an alkaline intrusion (José Fernandes Gabbro) in order to determine more precisely the space-time relation between alkaline and tholeiitic magmatism in the PGA.

The dated diabase dykes show high TiO2 (up to 4.5 wt%) and variable Sr (405-890 ppm). Baddeleyite-zircon concordia ages are 130.3 ± 0.5 Ma (all uncertainties reported at 2σ) and 131.3 ± 0.7 Ma, within the range of previously reported step-heating 40Ar/39Ar ages (133.1 ± 0.5 to 130.8 ± 0.4 Ma), confirming a good coherency between crystallization and cooling ages.

Three distinct samples of the José Fernandes Gabbro were investigated (melagabbro, banded gabbro and quartz monzogabbro). Preliminary baddeleyite U-Pb ages obtained for a crust-contaminated quartz monzogabbro (52-56% SiO2; ~4% K2O; δ18O= +6.7 to +7.5‰; eNd(T)= -10) yielded a weighted mean 206Pb/238U data of 133.56 ± 0.31 Ma as the age for the intrusion. The age is about 2 m.y. older than the U-Pb ages obtained for the diabase dykes of the PGA.

FAPESP proc. 2012/06082-6; CNPq 202043/2014-2