SHRIMP U-Pb zircon dating of Pedras Grandes Suite, southern Santa Catarina State, Brazil

Andréa R Jelinek,Artur C Bastos-Neto,Jayme A.D Leite,Neal J Mcnaughton,Léo A Hartmann

doi:10.1590/s0001-37652005000100010

Abstract

Two major magmatic pulses of the granitic Florianópolis Batholith in Santa Catarina State, southern Brazil, occurred between 613±5Ma and 595±5 Ma, during the Neoproterozoic Brasiliano Cycle. These ages were obtained by U-Pb isotopic determinations with the sensitive high mass-resolution ion microprobe on igneous zircons from Pedras Grandes Suite in Santa Catarina State. Euhedral zircons remained unaltered close to a fluorite vein deposited at 180?C or more. These ages suggest a northern limit for the Pedras Grandes Suite, explaining the spatial relationship between the fluorite veins and the source rock.

Highlights

The extensive Neoproterozoic granitic magmatism of the Brasiliano Cycle in the Precambrian/Cambrian shield of Santa Catarina State in southern Brazil (Fig. 1) is poorly known from a geochronological point of view
The zircons were analyzed for U, Th and Pb using the sensitive high resolution ion microprobe (SHRIMP II) at Curtin University, Western Australia, using methods originally published by Compston et al (1984) and more recently stated by Smith et al (1998)
Twenty-one SHRIMP spots were analyzed in fifteen zircon grains for this sample (Table II) and the U-Pb isotopic data plotted in a concordia diagram (Fig. 3)

Summary

Introduction

The extensive Neoproterozoic granitic magmatism of the Brasiliano Cycle in the Precambrian/Cambrian shield of Santa Catarina State in southern Brazil (Fig. 1) is poorly known from a geochronological point of view. The southern part of the Florianópolis Batholith consists mostly of the Pedras Grandes Suite, which is poorly known geochronologically (Sallet et al 2000). Two zircon SHRIMP U-Pb ages are known for rocks exposed tens of kilometers to the north of the area studied here (Silva et al 2002) points to the need of additional investigations to establish the timing of intrusion age of the major granitic suites. The granitic rocks in the southernmost part of the batholith have been included either in the Pedras Grandes Suite or in the Tabuleiro Suite, an issue that requires clarification

Methods

Results

Conclusion