Journal of Mineralogical and Petrological Sciences,
Vol. 106, No. 5; pp. 255-260, 2011,
ISSN: 1349-3825.
IMPACT FACTOR= 0.677
Petrology and geochemistry of chromian spinel-bearing serpentinites in the Hida
Marginal Belt (Ise area, Japan): characteristics of their protoliths
Mohamed Zaki Khedr ** and Shoji Arai *
*
Department of Earth Sciences, Graduate School of Natural Science and Technology,
Kanazawa University, Kakuma, Kanazawa 920-1192, Japan
**
Department of Geology, Faculty of Science, Kafrelsheikh University, Egypt
ABSTRACT
The Ise area is located in the western part of the Hida Marginal Belt (central Japan), which
includes several sporadic exposures of ultramafic rocks, sometimes forming a serpentinite
mélange of the Paleozoic age. Ultramafic rocks in the Ise area, enveloped by PaleozoicMesozoic sedimentary rocks, are completely serpentinized; however, the abundance of bastite
after orthopyroxene suggests harzburgite protoliths. The bastite- and mesh-textured
serpentines are distinguished from each other in Al2O3, Cr2O3 and NiO contents. The bastitetextured serpentine is high in Al2O3 (up to 4.0 wt%) and Cr2O3 (up to 1.2 wt%), but low in
NiO (<0.3 wt%) relative to the mesh-textured one. Relic chromian spinel, vermicular in
shape, shows an inter-grain chemical homogeneity and is sometimes altered to ferritchromite
at the margin. It has a narrow range of Cr# [= Cr/(Cr + Al) atomic ratio] from 0.38 to 0.51
and low YFe [=(Fe3+/(Cr + Al + Fe3+) atomic ratio, <0.03)], similar to chromian spinel in
Kotaki and Oeyama ultramafic masses. It is also similar in chemistry to spinels in forearc and
abyssal peridotites, suggesting two possibilities for the derivation of the Ise serpentinite’s
protoliths. The degree of melting using Cr# versus TiO2 of chromian spinel is  2025%,
which is in accordance with the harzburgite protoliths obtained by whole-rock chemistry
models. We found that Cr, Al, Ni and Ca, preserved in bastite and mesh-textured serpentine,
are conservative during serpentinization, confirmed from the similarity in the whole-rock A1
and Ca of the Ise serpentinites to Horoman harzburgites. The occurrence of dolomite can
stabilize the Ca and limited its mobility to escape outside the serpentinites. The harzburgite
protoliths were