amphibole in belt , ceniral Shikoku , Japan : with the Seba eclogitic basic schists , Sambagawa implications for timing ofjuxtaposition of the the non-eclogite Sambagawa schists 183 metamorphic eclogite body

Content Provider	Semantic Scholar
Author	Fazle, Kabir Md Akira, And T. A. K. A. S. U.
Copyright Year	2014
Abstract	The Seba eclegitic basic schists in the Sambagawa metarnorphic belt of the Besshi distrjct in central Shikoku, southwest japan, preserve evidence of two distinct metamorphic events. These are a first cclogitic metamorphic evcnt, and a second glaucophane-barroisitic metamorphic event. The peak metamorphjc conditions of the first eclogitic metamoxphic event are deduced ftom the mineral assemblage of schistosityforming minerals of the eclogite facies (T!610-640 and P==12-24 kbar; Aoya 2001). The peak eclogitic conditiens were fbllowed by a clockwise decompression P-Tpath, with retrogression into the epidote amphibolite facies at 7!=400-535 OC and P==6-7 kbar, These cenditions were obtained from phases replacing thc minerals of the peak metamorphic conditions. The second glaucophalle-barroisitic mctamorphic event is defined by distinctly zoned amphiboles which suggest a prograde path from the epidote-blueschist facies to the epidote a:nphibolite facies, The prograde path is similar to that of surrounding llon-eclogitic Sambagawa schists. The Seba eclogitic basic schists wcre juxtaposed with non-eclogitie Sarnhagawa sehists during thc prograde metamorphism of the non-eclogitic Sambagawa schists. These amalgamatcd metamorphic sequences subsequently underwent prograde metamorphism reaching the epidote-amphibolite facies, and were then exhumed to shallow crustal levels, Kby Words : Seba eclogite, glaucophane,SambagawaCSanbagawa) metamorphic belt lntroduction The Sambagawa metarnorphic belt ofsouthwest Japan is a typical example of a higb-pressure interrnediate-type metamorphic belt (Miyashiro 1961) . In the Besshi distnct of central Shikoku, the Sambagawa belt is divided jnto fbur mineral zones bascd on index minerals in pelitic schists (Fig. 1; e.g, Enami 1983; Higashino 1990). These are the chlorite zone (T = 300-360 °C , P = 5,5-6.5 kbar), garnet zone (T = 425-470 °C , P = 7-8.5 kbar), albite-biotite zone (T = 470-590 °C , P = 8-9.5 kbar) and oligoclase-biotite zollc (T = 585-635 °C , P = 9-Il kbar) (Enami 1983; Enami et al. 1994) . The metamorphic grade ofthe albite-biotite and oligoclase-biotite zones is equivalent to that of the epidote-amphibelite facies (Enami et a!. 1994; Wallis et al. 2000), Several eclogitc occunences are prcscnt within thc albite-biotite arid oligoclase-biotite zones ih the Besshi district, These are mainly found within block-like bodies of varying size and lithology (Fig. 1; e.g. Banno et al. 1976; Kunugiza et al. 1986; Aoya 2001; Ota ct al. 2004) . Pclitic and basic schists exposed around these block-like eclogitc bodies partly preserve the residuaL pressure comparal)le to that in the eclogites based on the Raman spectrometty for quartz inclusions in the garnets within these schists (Enami et al, 2007; Mouri and Enami 2008; Kouketsu and Enami 2010; Kouketsu et al. 2010) . Ill the Seba area of the Besshi district the basjc and pelitic schjsts occur within the albite-biotite zone. and eclogitic mineral assemblages are sporadically preserved within the Seba eclogitic basic schists (Takasu 1984; Naohara 1995; Naohara and Aoya 1997; Aoya and Wallis 1999), Aoya (2001) has reported a P-T path ofthe eclogites occurring in the Seba eclogitic basic schists. The cclogites first attained peak pressure conditions, then decompressed with continuously increasing temperature until they reached their peak temperature cenditions (T = 610-640 °C at P =: 12-24 kbar). According to Aoya (2001) and Zaw et al. (2005) 2010 e3A 2 HeeN. 2010 ai 8A 21 Heeny. * Department ofGeoscience, Faeulty ofScience and Engineering, ShimaneUniversitx1060Nishikawatsu,Matsue690-8504,Japan Corresponding author. Ibl, & Fax: + 8I 852 32 6461 M, E KABiR: faztekabir@gmail,com A. TAKASU: takasu@riko.shimane-u.ae.jp (5)
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