TIMS TECHNIQUES FOR MEASURING STRONTIUM ISOTOPE RATIOS IN APATITE GRAINS AND APPLICATION TO IGNEOUS ROCK PETROLOGY

Whole-rock analyses of Sr composition by thermal ionization mass spectrometry (TIMS) require age calculations and Rb-Sr ratio determinations, which are expensive, high-time consuming, and susceptible to compositional heterogeneity. A significant knowledge gap exists in the development of alternative TIMS methods that provide accurate and representative Sr isotope data while addressing these challenges. This study explores the potential of Sr isotopic composition in apatite grains from magmatic rocks as a proxy for initial ⁸⁷Sr/⁸⁶Sr ratios. Understanding the isotopic composition of magmatic systems through apatite is crucial for deciphering magma origin, crustal contamination, and magmatic differentiation, especially in tectonically complex regions. Therefore, this research focuses on granitoid rocks from the Ribeira Orogeny, Brazil, which is shaped by pre-, syn-, and post-collisional magmatic events. The proposed TIMS-based method for analyzing Sr isotopes in apatite grains offers a reliable, cost-effective, and time-efficient alternative to traditional whole-rock analyses, with validation showing consistent results within an uncertainty of 0.5 %.