Abstract

Garnet with complex, discontinuous zoning is a common occurrence in metamorphic terrains, and the relationship between major and trace element zoning can provide insight into the metamorphic evolution of the host rock. Mylonitic micaschists along the Posada-Asinara Shear Zone in the Axial Zone of the Sardinia Variscan chain contain garnet porphyroblasts, enveloped by the S2 schistosity, with distinct core and rim domains. A large garnet porphyroblasts was investigated by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICPMS) mapping. The major element compositional variation follows a bell-shaped zoning, with Ca and Mn contents progressively decreasing, and Fe and Mg increasing, from the core to the outer rim. LA-ICPMS mapping revealed a thin and sharp annular enrichment zone in Y, Sc, Dy, Ho, Er, Tm at the mantle-rim boundary. The trace element (TE) compositional profiles show a central enrichment area for HREE (Tm, Yb, Lu). This enrichment decreases progressively, as a function of atomic number, for Er, Ho and Dy. Elements with even lower atomic number (Tb, Gd, Eu and Sm), are depleted in this central domain, but their content increases in broad shoulders towards the garnet rim. The position of these lateral shoulders migrates progressively rimwards with decreasing atomic number. The REE distribution, trend and behavior in the growth zones of the garnet is an example of TE control during a continuous growth ruled by diffusion-limited REE uptake. The Y + HREE annular enrichment zone, interpreted as resulting from a decrease in the garnet growth rate, reflects a short-lived episode in the garnet growth history.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.