Eclogite and associated rocks

Unit symbol: Pze
Age range Paleozoic (541 to 252.2 Ma)
Lithology: Metamorphic
Group name: Eclogite and associated rocks (Yukon-Tanana crystalline complex)
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

Source map information

Source map Weber, F.R., Wheeler, K.L., Rinehart, C.D., Chapman, R.M., and Blodgett, R.B., 1992, Geologic map of the Livengood quadrangle, Alaska: U.S. Geological Survey Open-File Report 92-562, 19 p., scale 1:250,000.
Symbol Pzc
Unit name Chatanika unit
Description Fairbanks-White Mountains area: Allochthonous, quartz-biotite-muscovite schist, garnet-bearing; and quartzite. Primarily epidote-amphibolite facies rocks, but also includes eclogitic rocks. Age of rocks in Chatanika allochthon is problematical. Pattern of ages suggests varied overprinting or older rocks during early Cretaceous metamorphism
Lithology Metamorphic

Correlated geologic units

Label Pze
Description Chatanika unit, allochthonous garnet-bearing qtz-bio-mus schist and quartzite, Paleozoic
Geologic age Paleozoic
Geologic setting Metamorphic, undivided
Lithology Form Importance
Quartzite < Metaclastic < Metasedimentary < Metamorphic Amphibolite, epidote-amphibolite Major
Mica-schist < Schist < Metamorphic Amphibolite, epidote-amphibolite Major
Quartz-feldspar-schist < Schist < Metamorphic Eclogite Incidental