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In the Su-Lu ultrahigh-P terrane, eastern China, many coesite-bearing eclogite pods and layers within biotite gneiss occur together with interlayered metasediments now represented by garnet-quartz-jadeite rock and kyanite quartzite. In addition to garnet + omphacite + rutile + coesite, other peak-stage minerals in some eclogites include kyanite, phengite, epidote, zoisite, talc, nyboite and high-Al titanite. The garnet-quartz-jadeite rock and kyanite quartzite contain jadeite + quartz + garnet + rutile f zoisite f apatite and quartz + kyanite + garnet + epidote + phengite + rutile f omphacite assemblages, respectively.Coesite and quartz pseudomorphs after coesite occur as inclusions in garnet, omphacite, jadeite, kyanite and epidote from both eclogites and metasediments. Study of major elements indicates that the protolith of the garnet-quartz jadeite rock and the kyanite quartzite was supracrustal sediments. Most eclogites have basaltic composition; some have experienced variable 'crustal' contamination or metasomatism, and others may have had a basaltic tuff or pyroclastic rock protolith.The Su-Lu ultrahigh-P rocks have been subjected to multi-stage recrystallization and exhibit a clockwise P-T path. Inclusion assemblages within garnet record a pre-eclogite epidote amphibolite facies metamorphic event. Ultrahigh-P peak metamorphism took place at 700-890" C and P > 28 kbar at c. 210-230 Ma. The symplectitic assemblage plagioclase + hornblende f epidote f biotite + titanite impIies amphibolite facies retrogressive metamorphism during exhumation at c. 180-200 Ma. Metasedimentary and metamafic lithologies have similar P -T paths. Several lines of evidence indicate that the supracrustal rocks were subducted to mantle depths and experienced in-situ ultrahigh-P metamorphism during the Triassic collision between the Sino-Korean and Yangtze cratons.

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The mineral assemblages of hematite-bearing basic schists in intermediate high-pressure metamorphism are temperature dependent. For assemblages with excess hematite. albite, muscovite and quartz, the paragenetic relations can be dealt with in terms of a fourcomponent system, without omitting or grouping major components.In the Sanbagawa belt in central Shikoku, the dominant amphibole in the hematite-bearing basic schists changes from winchite, via crossite and barroisite to hornblende. The stability of amphibole is described chemographically within a pseudoternary system with another excess phase, epidote. Many amphiboles are chemically heterogeneous owing to retrograde reactions which produced low-TIP amphibole around the prograde amphibole. The examination of amphibole zoning makes it possible to draw a retrograde P-T trajectory which passes on the lower pressure side of the prograde one.

Deformation in the Sanbagawa Belt is characterized by ductile flow in an east-west direction sub-parallel to its length. The east-west flow (D1) caused large-scale recumbent folding of the metamorphic sequence in central Shikoku, which can explain the inverted thermal structure of this region. Chemical zoning of metamorphic minerals associated with D1 microstructures also suggest that the east-west flow developed under retrograde conditions. D1 is therefore related to exhumation rather than subduction processes. A variety of kinematic indicators show that during the east-west flow, deformation was partitioned into structurally continuous domains with opposed senses of shear. This suggests that bulk deformation was not simple shear but included a component of flattening.1985; Higashino 1990) have been proposed. The Asemigawa route cross-cuts the inverted thermal structure of Central Shikoku (Fig. 2). There is good exposure along this traverse that affords good structural control across this section making it ideal for studying the structures responsible for the inverted metamorphic zonation.

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The higher-grade region of the Sanbagawa metamorphic belt in Shikoku and the Kii peninsula contains metagabbro, peridotite, and serpentinite. These rocks occur exclusively in the garnet, albite-biotite, and oligoclase-biotite zones, and tend to have equilibrium mineral assemblages stable with respect to the mineral zones where they occur. Thermal histories of previous equilibrium stages can be discerned through not only the mineralogy of relics, but also the texture, megascopic structure, and bulk composition of the rocks. The protoliths were layered gabbro, cumulate and residual peridotites, and garnet clinopyroxenite. Some of these rocks were in the eclogite facies before emplacement into the Sanbagawa schists and others were in the granulite facies. They were emplaced into the metamorphic regime by solid intrusion during a later stage of the schistosity formation, that is, emplacement was syntectonic. Some peridotites were serpentinized before attaining equilibrium assemblages of the Sanbagawa metamorphism; their emplacement was during an earlier stage of the metamorphism, but not at the sedimentary stage. The source region of those exotic blocks may have been a lower crust-upper mantle region of an island arc.

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