飛騨外縁帯，小滝地域の超苦鉄質岩：大江山オフィオライトかんらん岩とその変成作用について

Abstract

Serpentinite hornfelses that formed by later contact metamorphism vary in their mineral assemblages, defined by atg, ol cpx, ol tr, ol tr talc, and ol tr opx zones that are arranged from west to east. The zones indicate that metamorphic temperatures generally increased toward the east. This finding suggests that the hornfelsic metamorphism of previously serpentinized peridotites of Type and Type was caused by a concealed plutonic intrusion beneath the Ishizaka rhyolite, which is exposed to the east. Abstract

Early Paleozoic jadeitites in Japan: An overview

“…In ultramafic rocks along the Omi-gawa River, the protolith of antigorite-dominant serpentinite is mainly dunite and harzburgite with rare chromitite; high Cr/(Cr + Al) atomic ratio (0.70 − 0.77) of chromian spinel in the chromitite contains abundant igneous pargasite, suggesting a mantle-wedge peridotite origin (Tsujimori, 2004). In contrast, those along the Kotaki-gawa River have both lherzolitic and harzburgitic protolith (Machi and Ishiwatari, 2010); relict chromian spinel exhibits vermicular intergrowth with clinopyroxene, which is the most common petrographic features in the residual peridotite of the Oeyama belt (e.g., Arai, 1980;Matsumoto et al, 1997). Ultramafic bodies have been partly overprinted by contact metamorphism during the intrusion of Cretaceous or Cenozoic granitic plutons (e.g., Machi and Ishiwatari, 2010), although some ultramafic bodies had undergone a regional metamorphism before contact metamorphism (Nakamizu et al, 1989;Nozaka 2005;Khedr and Arai, 2010).…”

“…Although jadeitite-hosted ultramafic rocks in the HDM are highly serpentinized or recrystallized, the chemical compositions of relict chromian spinel (or chromite) and bulk-rock compositions of serpentinite suggest a mostly harzburgite and subordinate dunite protolith (e.g., Machi and Ishiwatari 2010;Arai, 2010, 2011). In ultramafic rocks along the Omi-gawa River, the protolith of antigorite-dominant serpentinite is mainly dunite and harzburgite with rare chromitite; high Cr/(Cr + Al) atomic ratio (0.70 − 0.77) of chromian spinel in the chromitite contains abundant igneous pargasite, suggesting a mantle-wedge peridotite origin (Tsujimori, 2004).…”

Petrology and geochemistry of chromian spinel-bearing serpentinites in the Hida Marginal Belt (Ise area, Japan): characteristics of their protoliths

“…5). The examined chromian spinel seems to have intermediate spinel composition between Oeyama group (Cr#= ~ 35) and Tari -Ashidachi group (Cr#= ~ 50) of lherzolites -harzburgites from the Kotaki area (Machi and Ishiwatari, 2010) (Table 3; Fig. 5b).…”

“…The relic chromian spinel (Cr#= 0.38 -0.51) in the Ise serpentinites is similar to spinels in Oeyama harzburgites from the Tari -Misaka complex (spinel Cr#=0.5; Arai, 1980), confirming the harzburgite protoliths as inferred from the whole -rock chemisty and the texture. It has intermediate composition between spinels (Cr#= ~ 35) in Oeyama group and Tari -Ashidachi group (Cr#= ~ 50) from the Kotaki area (Machi and Ishiwatari, 2010) (Fig. 5b), possibly providing a missing link between the two groups, which may have been originally continuous.…”

“…Considering the tectonic setting of the HMB peridotites (cf., , the Ise . Fields of chromian spinel in forearc peridotites (Ishii et al, 1992), Alpinetype as well as abyssal peridotites (Dick and Bullen, 1984), lherzolites -harzburgites from the Kotaki area (Machi and Ishiwatari, 2010), mantle harzburgites in the Oeyama ophiolite (Arai, 1980;Kurokawa, 1985) and Omi serpentinites (Tsujimori, 2004) are shown for comparison. The grey arrowed line indicates a trend of spinel composition change during retrograde transition, lower amphibolite -to greenschist -facies (Müntener et al, 2000).…”