Abstract The analysis of trace elements (TE) in geological materials is a valuable tool to understand geological processes, including studies in geochemistry and petrology. Among the methods applied to determine TE, Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) detects TE contents in the μg/g and ng/g range. The aim of this paper is to validate, at Laboratório de Geologia Isotópica (LGI) — Centro de Estudos em Petrologia e Geoquímica/Universidade Federal do Rio Grande do Sul (CPGq/UFRGS), a high-precision method for LA-ICP-MS analyses of TE in geological materials. Samples used in this work were reference Max-Planck-Institut für Chemie — Dingwell (MPI-DING) glasses. The method is used in tandem with the Electron Probe Microanalyzer — Wavelength Dispersive X-ray Spectrometer (EPMA-WDS) technique to determine the major and minor elements of the samples and check for homogeneity. Analyses were conducted in a Thermo® Element2 Inductively Coupled Mass Spectrometer (ICP-MS) coupled to a New Wave Research® Neodymium-Doped Yttrium Aluminum Garnet (Nd:YAG) (213nm) laser ablation system. 43Ca and 29Si were used as internal standards (IS). Glitter® software and in-house spreadsheets were utilized for reduction treatments. The results using 29Si as IS present a high degree of fractionation errors compared to the results using 43Ca. Uncertainties caused by matrix interferences and fractionation effects can be corrected applying a correction factor. The obtained results demonstrate an effective recovery of TE content for the analyzed reference materials. Moreover, these silicate glasses proved to be robust to create an internal database of matrix matching standards in routine silicate analyses.

ABSTRACT: The Ibaré Lineament is a shear zone that sections the Western portion of Sul-riograndense Shield, affecting the orthogneissic rocks of Santa Maria Chico Granulitic Complex, acting as a conduct for hydrothermal fluids. The studied hydrothermal mineralogy reflects a propylitic alteration paragenesis that is composed of Fe-clinochlore, epidote, albite, calcite and quartz, typical low-pressure paragenesis (< 2,000 bar). This mineral association reflects an equilibrium in a neutral to slightly alkaline pH. Using the new approach for chlorite geothermometry, an average formation temperature of 274°C was obtained, compatible with the stability of polytype IIb chlorite and with the irregular textures of twinning in calcites. The fluid inclusions in quartz establish a low-salinity system (2.45 wt.% NaCl eq.) and an average temperature of 175°C. The obtained temperatures are interpreted as a continuum cooling model with meteoric fluids entrance. The system pressure is evaluated from isochores, reaching an average value of 1,560 bar. This is the first temperature and pressure estimate to the Ibaré Shear Zone, which enabled the establishment of a shallow hydrothermal system (epithermal) with fluid interaction from magmatic and meteoric sources, confirmed by the behavior of carbon and oxygen stable isotopes, which indicated an the origin from mixed sources.