Garnet- and omphacite-bearing biotite-muscovite schist, micaceous marble, black quartzite, and amphibolite in thin interlayers within a metamorphic sequence, described as allochthonous, garnet-bearing, quartz-biotite-muscovite schist and quartzite (Swainbank and Forbes, 1975; Brown and Forbes, 1986; Weber and others, 1992; Foster and others, 1994) and designated as the Chatanika assemblage by Robinson and others (1990). The Chatanika assemblage is primarily epidote-amphibolite facies rocks, but also includes eclogitic rocks and has some lithologic similarities with the structurally underlying quartz and pelitic schist (unit |<yqs). Protolith of eclogite was predominantly quartz-rich and pelitic to calcareous pelitic sedimentary rocks, impure limestone, and associated mafic volcanic and volcaniclastic rocks. Pressure and temperature conditions of 11 kbar and 600 to 700 °C were cited by Newberry and others (1996) on the basis of microprobe analyses and are supported by the high-pressure eclogite-facies mineral assemblage. Other estimates of pressure-temperature conditions range from 590 °C and 5.5 to 7.5 kbar (Swainbank and Forbes, 1975) to 600±50 °C and 13–15 kbar (Brown and Forbes, 1986) on the basis of mineral-pair geothermometers and geobarometers. Newberry and others (1996) inferred a Mississippian to Devonian protolith age from unspecified 40Ar/39Ar, K/Ar, and Pb-Pb studies; Forbes (1982) reported a questionable K/Ar protolith age of 478±35 Ma on low-potassium amphibole and K/Ar ages on mica that range from 166.±2.2 to 103.5±3.4 Ma, which he attributed to Mesozoic metamorphism. Includes parts of the Chatanika assemblage, units Pce and Pcu of Robinson and others (1990); unit PDe of Newberry and others (1996), unit Pzc of Weber and others (1992) in the Livengood quadrangle, and unit PzpCms of Foster and others (1983) in the Circle quadrangle