Dating minerals by ID-TIMS geochronology at times of in situ analysis: selected case studies from the CPGeo-IGc-USP laboratory

Abstract

Since 1964, the Center for Geochronological Research -CPGeo, one of the interdepartmental centers of the Instituto de Geociências (IG) of São Paulo University, has developed studies related to several geological processes associated with different rock types. Thermal Ionization Mass Spectrometry Isotopic Dilution (ID-TIMS) has been the technique widely used in the CPGeo U-Pb Laboratory. It provides reliable and accurate results in age determination of superposed events.However, the open-system behavior such as Pb-loss, the inheritance problem and metamictization processes allow and impel us to a much richer understanding of the power and limitations of U-Pb geochronology and thermochronology. In this article, we present the current methodology used at the CPGeo-IGc-USP U-Pb laboratory, the improvements on ID-TIMS method, and report high-precision U-Pb data from zircon, monazite, epidote, titanite, baddeleyite and rutile from different rock types of several domains of the Brazilian south-southeast area, Argentina and Uruguay.

U-Pb Zircon Dating of Ash Fall Deposits from the Paleozoic Paraná Basin of Brazil and Uruguay: A Reevaluation of the Stratigraphic Correlations

“…One additional age determination was performed at the Institute of Geosciences, University of São Paulo, with the ID-TIMS U-Pb technique, according to the procedures described by Passarelli et al (2009). The sample was an AFL in the basal part of the Corumbataí Formation, the uppermost unit in the state of São Paulo, below the Piramboia Formation of Mesozoic age.…”

Crystallization ages of the A-type magmatism of the Graciosa Province (Southern Brazil): Constraints from zircon U-Pb (ID-TIMS) dating of coeval K-rich gabbro-dioritic rocks

“…The procedures for fraction dissolution, spiking, and determination and treatment of the isotopic ratios followed protocols in use at the Centro de Pesquisas Geocronológicas (CPGeo, Universidade de São Paulo), described in detail by Passarelli et al (2009). Data correction was performed using PbDAT (Ludwig, 1993).…”

High T/P evolution and metamorphic ages of the migmatitic basement of northern Sierras Pampeanas, Argentina: Characterization of a mid-crustal segment of the Famatinian belt

“…The isotopic dilution method ID-TIMS (Isotope Dilution e Thermal Ionization Mass Spectrometry) was applied. Monazite concentrates were obtained using standard crushing and sieved, and separated using a vibrating table, magnetic separation and heavy liquids treatment (for details see Passarelli et al, 2009). Complete, translucent, clear and crack-free monazite crystals were handpicked under alcohol from this concentrate using a stereoscope that is coupled with an imaging system.…”