Desenvolvimento de técnicas de análise isotópica de Nd e Sr por espectrometria de massas por termo-ionização (TIMS): aplicação a materiais de referência de rochas e à análise de apatita

Abstract

This study aimed to develop and optimize analytical procedures for measuring the Sm-Nd and Sr-Sr isotopic ratios in whole rock and in the mineral apatite. The research involved the implementation of advanced methods to ensure precise and reproducible measurements, contributing to the understanding and refinement of data used in the study of the genesis and evolution of rocks. Two papers were produced, highlighting the importance of reference materials for obtaining reliable data and the efficiency of Sr analysis in apatite by TIMS, a relatively low-cost, and high-precision technique. The first paper presents Sm-Nd and Sr isotopic ratios of the BRP-1 (“Basalto Ribeirão Preto”) reference material based on repeated TIMS measurements over twelve years carried out by the LAGIR laboratory. The measured Nd and Sr isotopic ratios of BRP-1 are: ¹⁴³Nd/¹⁴⁴Nd = 0.512408 ± 0.000010 (2s) and ⁸⁷Sr/⁸⁶Sr = 0.706011 ± 0.000017 (2s). The accuracy of these results was evaluated through the measurement of well-characterized reference materials, such as AGV-1, BCR-1, BHVO-1, G-2, and GSP-1 by USGS. The second paper investigates the use of Sr isotopic composition in apatite grains from magmatic rocks as a proxy for the initial ⁸⁷Sr/⁸⁶Sr ratios. Sr analysis in apatite is essential for understanding magma origin, crustal contamination, and magmatic differentiation. The study focuses on granitoid rocks from the Ribeira Orogeny, Brazil, and proposes a lower-cost, more efficient approach compared to traditional whole-rock analyses. The method, validated with 0.5% uncertainty, represents a reliable and efficient alternative. Both papers converge in enhancing analytical methods, resulting in more efficient and validated procedures for isotopic analyses. The methodological refinement developed throughout this work provides a more reliable and precise approach, essential for petrogenetic studies.