Orthogneiss and amphibolite of igneous origin

Unit symbol: Pzymi
Age range Mississippian, Devonian, and older? (541 to 323.2 Ma)
Lithology: Metamorphic
Group name: Gneiss, schist, and amphibolite (Yukon-Tanana crystalline complex)
Most common lithologies are granitic to trondhjemitic orthogneiss and lesser amphibolite. Includes quartz-biotite ┬▒ garnet gneiss, amphibolite, and minor pelitic gneiss, quartzite, schistose gneiss, augen gneiss, and quartz-mica schist (Weber and others, 1978; Foster, 1992; Dusel-Bacon and others, 2006). Unit is most extensive in the northern Alaska Range in the Tanacross quadrangle and sparsely exposed in the Yukon-Tanana Upland. Largely metamorphosed to amphibolite facies (Dusel-Bacon and others, 1993), locally unit has been retrograded to greenschist facies in the Mount Hayes quadrangle (Nokleberg and others, 1992a). Whole-rock trace-element data indicate a within-plate origin for most amphibolite (Dusel-Bacon and Cooper, 1999). Where possible, augen gneiss mapped separately as unit MDag. This unit is gradational with unit |<ygs, which is largely of metasedimentary origin, but includes some metaigneous components

Source map information

Source map Day, W.C., Aleinikoff, J.N., Roberts, Paul, Smith, Moira, Gamble, B.M., Henning, M.W., Gough, L.P., and Morath, L.C., 2003, Geologic map of the Big Delta B-2 quadrangle, east-central Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Series I-2788, scale 1:63,360.
Symbol Pzg
Unit name Biotite gneiss
Description Medium-gray, medium-grained, layered, foliated biotite-muscovite┬▒garnet quartzofeldspathic biotite gneiss. Southern part of unit dominated by medium-gray, equigranular, massive biotite-muscovite orthogneiss(?) of similar granodioritic composition as groundmass of augen gneiss (unit Dag). Equivalent with to unit PzpCg of Weber and others (1978)
Lithology Metamorphic

Correlated geologic units

Label PzZymi
Description Gneiss and amphibolite of igneous origin of the Yukon-Tanana Upland
Geologic age Paleozoic to Mississippian
Geologic setting Metaigneous, high-grade
Lithology Form Importance
Amphibolite < Metamorphic Major
Biotite-gneiss < Gneiss < Metamorphic Indeterminate, major
Hornblende-gneiss < Gneiss < Metamorphic Indeterminate, major
Greenstone < Metaigneous < Metamorphic Indeterminate, major
Metaintrusive < Metaigneous < Metamorphic Indeterminate, major
Metavolcanic < Metaigneous < Metamorphic Indeterminate, major