Horoman peridotite (lherzolite) - serpentinization

For a general description of the Horoman peridotite body, see the post of July 2, 2013: "Horoman Peridotite ... - olivine microfabfric".

Although the Horoman ultramafic complex is usually described as an extremely fresh peridotite body with very little serpentinization, there were several small occurrences of serpentinized olivine in part of the thin section from which this image was made. The edge of this specimen was apparently adjacent to or near a fracture, as indicated by the jagged contour. Thus, it was more exposed to metasomatising fluids than other parts of the thin section.

Click on image to enlarge.          Photo © Daniel R. Snyder

This image depicts a large, partially-serpentinized olivine grain. The relict olivine shows orange interference colors, grading to red and violet due to deformation. A little yellow-green is visible on the right. The remainder of the grain has been altered to serpentine, here showing olive green interference colors. Grains in various shades of gray are pyroxene. A small symplectite nodule is at lower right. Horoman peridotite body, Hokkaido, Japan. XPL Digital mosaic. Imaged area 5.7 mm by 11.5 mm.

For an image of the full thin section, see post of July 11, 2013: "Horoman peridotite (lherzolite) - full thin section".

REFERENCES

Niida,  K., (1975), Textures and Olivine Fabrics of the Horoman Ultramafic Rocks, Japan; Jour. Japan. Assoc. Min. Petr. Econ, Geol.; 70, p. 265-285. (In English with Japanese abstract)

Niida, K., (1984), Petrology of the Horoman Ultramafic Rocks in the Hidaka Metamorphic Belt, Hokkaido, Japan, Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy, 21(2):197-250. (In English)