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ABBREVIATIONS: Ab, albite; Ac, acmite; Act, actinolite; Alm, alEclogites, blueschists, clinopyroxene-rich rocks and epidote ammandine; Aln, allanite; Ap, apatite; Aug, augite; Bar, barroisite; Bt, biotite; phibolites occur interlayered on a millimetre to decimetre scale in a Cc, calcite; Chl, chlorite; Cpx, clinopyroxene; Crs, crossite; Czo, clinozoisite; mafic unit interbedded with calcareous and quartz mica schists in Dol, dolomite; Ep, epidote; Fe-Ox, Fe-oxides; Gln, glaucophane; Gross, NE Oman. These rocks constitute part of the continental margin grossularite; Gt, garnet; Hm, haematite; Jd, jadeite; Kln, kaolinite; Kspar, of Oman subducted during the Cretaceous. Petrological data indicate K-feldspar; Mgt, magnetite; Oxychl, oxychlorite; Pg, paragonite; Ph, that they evolved through a clockwise P–T path and attained peak phengite; Qz, quartz; Pyrp, pyrope; Rt, rutile; Spess, spessartine; Tc, talc; conditions at T ~560°C, P >12 kbar, where the mineral Ttn, titanite; Win, winchite; Zrn, zircon. assemblages of the blueschists, eclogites and clinopyroxene-rich rocks were all stable. Whole-rock major, trace and rare earth element data indicate that the mineralogical differences between these rock types resulted from the metamorphism of interlayered basaltic flows INTRODUCTION and tuffs of variable compositions possibly reflecting different degrees Interlayered blueschists, eclogites and/or greenschists are of magmatic differentiation. The interlayered epidote amphibolites common in several areas such as Cazadero, California are chemically similar to the blueschists and appear to have formed (e.g. Oh et al., 1991), the Shuksan suite, Washington from the eclogites and blueschists during unroofing aided by fluid State (Dungan et al., 1983; Owen, 1989), the Tauern infiltration. Oxygen isotope data for minerals and whole rocks Window, Eastern Alps (e.g. Selverstone et al., 1992) and indicate low fluid:rock ratios during metamorphism and unroofing. several Cycladic islands (e.g. Okrusch & Brocker, 1990). The data also suggest that different layers may have interacted with This interlayering has been attributed to: (1) differences fluids of different isotopic signatures throughout their history. These in the P–T conditions of equilibration in the different results are similar to data reported for other areas of continent– layers (e.g. Reinsch, 1979; Ridley, 1984); (2) original continent collision or continental crust subduction. differences in the chemical compositions of the layers before metamorphism (e.g. Dungan et al., 1983; Oh et al., 1991); or (3) differences in the extent of retrograde overprinting as a result of variable fluid infiltration (e.g. Schliestedt & Matthews, 1987; Brocker, 1990; Barrientos & Selverstone, 1993).