In situ Sr isotope analyses by LA-MC-ICP-MS of igneous apatite and plagioclase from magmatic rocks at the CPGeo-USP

ALVES A.; MORANO S.; MUÑOZ P. M.; CORDENONS P. D.; DE SOUZA S.; AZZONE R. G.; SPROESSER W.

Brazilian Journal of Geology

Zeppelini Editorial

Lugar: São Paulo; Año: 2016 vol. 46 p. 227 - 243

2317-4889

ABSTRACT: This contribution describes the successful implementationof in situ Sr isotope analyses by LA-MC-ICP-MS at the CPGeo--USP. The choice for an analytical configuration using measurements ofhalf-masses allows the accurate assessment of lanthanide interferences,permitting the determination of Sr isotopes in important REE-richaccessory phases, such as apatite. Likewise, the on-peak-zero methodeffectively corrects the background contribution (both from Kr and residualSr contributions from previous ablations) to the signals of theunknown samples. The analytical campaigns resulted in an accuracy, inrespect to reference TIMS values, better than 57 ppm (~ ±0.000057 2σSD) for a modern coral and the Batjberg clinopyroxene which impartsignificant quality to our data. Similarly, the majority of the stable Srisotope ratios are close to the accepted values, which also confirms theeffectiveness of the method. The achieved accuracy allows the identificationand investigation of spatially-controlled isotopic heterogeneitieson the micrometric scale in several Sr-rich minerals (apatite, carbonates,plagioclase, and clinopyroxene) with important implications to the understandingof relevant geochemical processes, particularly AFC, sourcegeochemical heterogeneities and magma-mixing