HR: 0800h
AN: V41C-0725    [Abstracts]
TI: The coexistence of jadeite-omphacite-diopside/hedenbergite in an albite-omphacite rock from the Kurosegawa zone, southwest Japan.
AU: * Miyazoe, T
EM: tomozoe@es.sci.kumamoto-u.ac.jp
AF: Graduate School of Science and Technology, Kumamoto University, 2-39-1, Kurokami, Kumamoto, 860-8555, Japan
AU: Nishiyama, T
EM: tadao@sci.kumamoto-u.ac.jp
AF: Graduate School of Science and Technology, Kumamoto University, 2-39-1, Kurokami, Kumamoto, 860-8555, Japan
AU: Uyeda, K
EM: oozuhs@edu-c.pref.kumamoto.jp
AF: Ohzu High school, Kumamoto, Japan, 1340, Ohzu, Ohzu, 869-1233, Japan
AU: Mori, Y
EM: mori@kmnh.jp
AF: Kitakyushu Museum of Natural History and Human History, 2-4-1, Higasida, Yahatahigashi-ku, Kitakyushu, 805⁰071, Japan
AU: Miyazaki, K
EM: kazu-miyazaki@aist.go.jp
AF: Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1, Higashi, Tsukuba, 305-8567, Japan
AB: Two miscibility gaps in the system jadeite - aeigirine - diopside/hedenbergite, one between jadeite and omphacite and the other between omphacite and hedenbergite were examined based on the coexistence of jadeite, omphacite and hedenbergite in an albite-omphacite rock which occurs within serpentinites of the Kurosegawa Zone in the middle Kyusyu, southwest Japan. Identification of simultaneous equilibrium of three pyroxenes is based on the following observation. A.Hedenbergite occurs as a core of omphacite or as a rim of omphacite in contact with K-feldspar vein. B.Omphacite is euhedral and overgrows hedenbergite or taramite. C.Jadeite occurs as euhedral crystals, overgrowing omphacite. D.Taramite is in contact with jadeite or overgrown by omphacite. Mineral chemistry of these minerals indicates miscibility gaps between jadeite and omphacite and between omphacite and hedenbergite in the albite-omphacite rock at the same metamorphic condition. The miscibility gap between omphacite and hedenbergite is similar to that of the earlier studies (Carpenter, 1980; Enami and Tokonami, 1983 etc) and that between omphacite and hedenbergite is narrower than that of Tsujimori(1997). The miscibility gaps in the ternary system are asymmetric (Holland, 1990) rather than symmetric (Carpenter, 1980). The albite-omphacite rock lacks mineral assemblages indicative of P-T condition. Therefore, we use a lawsonite blueschist and an epidote blueschist to estimate the metamorphic condition, which occurs in the same serpentinite melange zone. The lawsonite blueschist indicates schistose textures consisting of Na amphibole, lawsonite, pumpellyite, chlorite and augite, with small amounts of omphacite, quartz and albite. Omphacite occurs as a rim of augite. This occurrence is similar to that in the albite-omphacite rock. The epidote blueschist occurs as a thin horizon in the schistose lawsonite blueschist. This rock includes aegirine, Na amphibole, chlorite, epidote, muscovite, albite and quartz. The metamorphic condition of lawsonite blueschist was inferred from P-T pseudosection. The pseudosection indicates that the metamorphic pressure of the lawsonite blueschist is more than 5kbar and the temperature is not more than 400 Celsius. The metamorphic condition of the epidote blueschist was inferred from average P-T method. These results indicate that the metamorphic condition of lawsonite blueschist and epidote blueschist is 7.3kbar and 383 Celsius.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3651 Thermobarometry
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting