Boron isotope compositions of antigorite-grade serpentinites in the Itoigawa-Omi area of the Hida-Gaien Belt, Japan

Abstract

The antigorite-grade serpentinite and Late Paleozoic high-pressure schists are main components of a serpentinite-matrix melange in the Itoigawa-Omi area, Hida-Gaien Belt, Japan. Based on the petrologic characteristics of the high-pressure schists, the melange is divided into two units, namely an šeeclogitic unitšf and a šenon-eclogitic unitšf. Our preliminary in-situ boron isotope analyses of five serpentinites using a laser-ablation multiple-collector inductively-coupled-plasma mass spectrometry (LA-MC-ICPMS) found a systematic difference of boron isotopic trends among the two units in the same melange. The šeeclogitic unitšf serpentinites from Yunotani and Kotagi-gawa are characterized by lower δ11B value (mostly lower than +10‰), whereas the non-eclogitic unit serpentinite from Omi-gawa is higher than +1‰. Although the δ11B value of <0‰ was not measured from the eclogitic unit serpentinites, the relatively low δ11B values of