Mafic schist and amphibolite

Unit symbol: Pzyms
Age range Devonian or older Paleozoic (541 to 358.9 Ma)
Lithology: Metamorphic
Group name: Gneiss, amphibolite, schist, quartzite, and marble (Yukon-Tanana crystalline complex)
“Green, quartz-chlorite-carbonate schist, commonly having abundant plagioclase porphyroblasts. Associated with amphibolitic schist and minor marble, quartzite, and pelitic schist. Thought to represent metamorphosed mafic pyroclastic rocks interbedded with schists of unit |<yqs” in the Circle quadrangle (Wilson and others, 1998; see also Foster and others, 1983). In the south-central Circle and adjacent Big Delta quadrangle unit varies from greenish-gray actinolitic greenschist to dark green, fine- to coarse-grained, schistose amphibolite of unit |<yqm, which is interlayered or interlaminated with muscovite-feldspar-quartz felsite (Smith and others, 1994). In the southeast Big Delta quadrangle, unit is similarly composed of dark-green, fine- to medium-grained, strongly foliated, hornblende-biotite amphibolite gneiss associated with augen gneiss of unit MDag or interlayered with foliated, medium-grained, equigranular calc-silicate schist and, locally, quartzite of unit |ymi (Day and others, 2007). In the southeastern Eagle quadrangle, unit consists of moderately- to nonfoliated, fine- to medium-grained hornblende metagabbro and metadiabase (Werdon and others, 2001).Unit also contains a green and white, medium- to coarse-grained, slightly- to nonfoliated metaigneous rock that has pseudomorphs after clinopyroxene and plagioclase of fine-grained actinolite, chlorite, epidote, clinozoisite, albite, and (or) sphene (Szumigala and others, 2002)

Source map information

Source map Foster, H.L., 1976, Geologic map of the Eagle quadrangle, Alaska: U.S. Geological Survey, Miscellaneous Investigations I-922, 1 sheet, scale 1:250,000.
Symbol MzPzg
Unit name Metagabbro
Description Dark greenish black, coarse- to fine-grained, metagabbro.
Lithology Metamorphic

Correlated geologic units

Label PzZms
Description Mafic schist
Geologic age Paleozoic to Devonian
Geologic setting Metamorphic, undivided
Lithology Form Importance
Calc-silicate-schist < Schist < Metamorphic Greenschist Major
Amphibole-schist < Schist < Metamorphic Greenschist Indeterminate, major
Marble < Metacarbonate < Metasedimentary < Metamorphic Greenschist Minor
Quartzite < Metaclastic < Metasedimentary < Metamorphic Greenschist Minor
Quartz-feldspar-schist < Schist < Metamorphic Greenschist Minor