Journal of Mineralogical and Petrological Sciences
Online ISSN : 1349-3825
Print ISSN : 1345-6296
ISSN-L : 1345-6296
ORIGINAL ARTICLES
Compositional variation of olivine related to high–temperature serpentinization of peridotites: Evidence from the Oeyama ophiolite
Toshio NOZAKA
Author information
JOURNAL FREE ACCESS
Supplementary material

2018 Volume 113 Issue 5 Pages 219-231

Details
Abstract

Compositional variation of olivine in serpentinized peridotites provides a significant constraint on modeling the redox conditions of serpentinization and the tectonothermal history of ophiolites. Here I report the variations of Fe, Mg, Mn, and Ni contents of olivine from the Oeyama ophiolite, SW Japan and show textural and chemical evidence for compositional modification of olivine related to high–temperature (T) serpentinization. The Fe–enrichment of olivine adjacent to antigorite without significant magnetite formation indicates a reducing condition for high–T serpentinization. Systematic variations of forsterite (Fo) component with distance from antigorite suggest Mg–Fe volume diffusion took place in olivine porphyroclasts under the conditions of high–T serpentinization. In addition, a similar diffusion pattern of Mn to Fe results in a retrograde trend in MnO–Fo diagram, which could be a useful indicator of high–T serpentinization. Retrograde antigorite is different from prograde antigorite in having a shape of elongated blade, lacking a significant amount of magnetite inclusion, and being more ferrous than lizardite. The existence of retrograde antigorite provides another piece of evidence for high–T serpentinization even if olivine has been decomposed by intense low–T serpentinization. Approximate estimation of time required for the observed Mg–Fe diffusion profiles of olivine porphyroclasts reveals that a cooling duration under the conditions of high–T serpentinization was much longer than that of amphibolite–facies metasomatism previously reported. This suggests a long residence time of the forearc peridotites within the serpentinized mantle wedge following rapid exhumation immediately after the amphibolite–facies metasomatism.

Content from these authors
© 2018 Japan Association of Mineralogical Sciences
Next article
feedback
Top