The coexistence of jadeite and omphacite in an eclogite-facies metaquartz diorite from the southern Sesia Zone, Western Alps, Italy
スポンサーリンク
概要
- 論文の詳細を見る
An association of jadeite and omphacite has been newly found in an eclogite-facies metaquartz diorite collected from the Orco Valley area, southern part of the Eclogitic Micaschist Complex of the Sesia Zone, Western Alps, Italy. Both the jadeite and omphacite occur as idiomorphic to subidiomorphic grains in the matrix, and some of them are in contact with each other with a sharp grain boundary. Most of the jadeite shows faint and irregular zoning, with a chemical variation of Xjd (AlVIjd /(Na + Ca)) = 0.75-0.90. Half of the omphacite grains is homogeneous, and the remainder shows various zoning patterns. Some omphacite grains exhibit prograde zoning with an increase in Xjd from 0.31 to 0.55 and a decrease in Xaeg (= Fe3+/(Na + Ca)) from 0.14 to 0.04 from the core to the rim. The rim composition of the zoned omphacite is similar to that of homogeneous omphacite (Xjd = 0.40-0.56). The average rim composition of the jadeite-omphacite pairs in direct contact shows an apparent miscibility gap between Xjd = 0.50 ± 0.06, Xaeg = 0.09 ± 0.03, and Xaug (= Ca/(Na + Ca)) = 0.41 ± 0.05 in omphacite, and Xjd = 0.79 ± 0.04, Xaeg = 0.08 ± 0.03, and Xaug = 0.13 ± 0.03 in jadeite. Application of Powell (1985) garnet-clinopyroxene geothermometer gives T = 470 ± 30°C at P = 12 kbar and application of Waters and Martin (1993) garnet-omphacite-phengite geobarometer gives P = 12.4 kbar at T = 440°C and P = 12.0 kbar at T = 500°C as peak metamorphic conditions. Composition data of the pyroxene P2/n and C2/c compositional fields obtained from both this study and the literature suggest that: (1) the shape of two miscibility gaps between jadeite and omphacite and between omphacite and augite in the jadeite-augite-aegirine phase diagram of Carpenter (1983) is more concordant with the natural data than that of Holland (1990), (2) the miscibility gap between omphacite and augite closes at T ∼ 500°C and P = 15 kbar, but the miscibility gap between jadeite and omphacite may still exist, and (3) the miscibility gap between jadeite and omphacite closes at T = 700-850°C and P =15-45 kbar.
- 2005-04-01
著者
-
HIRAJIMA Takao
Department of Geology and Mineralogy, Graduate School of Science, Kyoto University
-
Hirajima Takao
Kyoto Univ. Kyoto Jpn
-
Hirajima Takao
Department Of Geology And Mineralogy Division Of Earth And Planetary Sciences Graduate School Of Sci
-
MATSUMOTO KEISAKU
Department of Geology and Mineralogy, Graduate School of Science, Kyoto University
-
Matsumoto Keisaku
Department Of Geology And Mineralogy Graduate School Of Science Kyoto University
関連論文
- The coexistence of jadeite and omphacite in an eclogite-facies metaquartz diorite from the southern Sesia Zone, Western Alps, Italy
- Sr-sulphate and associated minerals found from kyanite-bearing eclogite in the Moldanubian Zone of the Bohemian Massif, Czech Republic
- Pseudosection analysis for talc-Na pyroxene-bearing piemontite-quartz schist in the Sanbagawa Belt, Japan
- Analysis of Mn-bearing lawsonite occurring in meta-siliceous rocks in Hakoishi serpentinite melange of Kurosegawa Belt, Central Kyushu, Japan
- Pseudosection analysis for the Sanbagawa pelitic schist and its implication to the thermal structure of high-pressure intermediate type of metamorphism
- Chemical characteristics and trapping P-T conditions of fluid inclusions in quartz veins from the Sanbagawa metamorphic belt, SW Japan
- Preservation and retrogression of ultra high pressure (UHP) rocks: case studies of UHP metagranitoids in Western Alps and Su-Lu region
- Equilibration temperature of the Kobe meteorite
- Age determination of thorianite in phlogopite-bearing spinel-garnet peridotite in the Gfohl Unit, Moldanubian Zone of the Bohemian Massif
- An ultra-high-pressure metamorphic condition and isothermal decompression path obtained from a garnet-pyroxenite in the Horni Bory granulite of the Bohemian Massif
- Fluid inclusions with high Li/B ratio in a quartz vein from the Besshi area of the Sambagawa metamorphic belt : implications for deep geofluid evolution
- Effect of Jadeite-content on the Garnet-clinopyroxene Geothermometer for an Ultrahigh-pressure Eclogite Complex
- Preiswerkite and hogbomite within garnets of Aktyuz eclogite, Northern Tien Shan, Kyrgyzstan
- Finding of prehnite-pumpellyite facies metabasites from the Kurosegawa belt in Yatsushiro area, Kyushu, Japan
- Annular fluid inclusions from a quartz vein intercalated with metapelites from the Besshi area of the Sanbagawa belt, SW Japan
- Analysis of Mn-bearing lawsonite occurring in meta-siliceous rocks in Hakoishi serpentinite melange of Kurosegawa Belt, Central Kyushu, Japan
- Eclogitized Metagranitoid from the Su-Lu Ultra-High Pressure (UHP) Province, Eastern China.