Data?§?￡o U-Pb in situ por LA-ICPMS em zirc?μes detr?-ticos da Forma?§?￡o Cercadinho, Supergrupo Minas

摘要

In this paper, new geochronological data obtained for the detrital rocks of the Cercadinho Formation, basal unit of the Piracicaba Group, Minas Supergroup, are presented. U-Pb Laser Ablation Induced Coupled Mass Spectrometer (LA-ICPMS) analysis in detrital zircon from quartzite samples provided a new maximum depositional age for the Cercadinho Formation. The youngest zircon population, among the dated samples, provided an average age of 2680 ?± 24 Ma. These rocks have an expressive contribution of Meso- to Neoarchean zircons, with ages between 2812 ?± 19 and 2909 ?± 19 Ma, and older populations between 3212 ?± 18 and 3272 ?± 16 Ma, which occur mainly in the core of younger zircon grains. Comparing the U-Pb ages obtained in this work with previously published geochronological data for the basal units of the Minas Supergroup (Moeda Formation) an aging of the source for the detrital rocks of Cercadinho Formation can be observed, with a major contribution of zircons from TTG rocks crystallized between the Meso- and Neoarchean.