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 Foster, H.L., 1970, Reconnaissance geologic map of the Tanacross quadrangle, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigation Map I-593, 1 sheet, scale 1:250,000.
Symbol PzpCb
Unit name Biotite gneiss and schist unit
Description Biotite gneiss and schist unit. Includes quartz-feldspar-biotite gneiss and intrusions of fine-grained felsic and granite dikes
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