Mafic igneous rocks, central and northeast Alaska

Unit symbol: PzPxmi
Age range early Paleozoic and (or) late Proterozoic (635 to 387.7 Ma)
Lithology: Igneous - Plutonic
Group name: Mafic and ultramafic rocks in central, western, and northern Alaska
Unit consists primarily of gabbro and diabase sills(?) and serpentinite exposed in a linear belt in the Livengood and northwest Circle quadrangles. Gabbro and diabase are dark olive green and greenish-gray to dark greenish-black, medium- to coarse-grained, and very fine-grained on outer margins of sills; locally grades into diorite. These rocks are associated with greenstone and basalt, interbedded slate, siliceous shale, chert, argillite of the Amy Creek unit of Weber and others (1992) (unit D_kb, here). Serpentinite is intruded by dikes of clinopyroxene gabbro, microgabbro, and diorite. Attempts to date these rocks have yielded 40Ar/39Ar (high temperature fraction) and K/Ar ages that range from 643 to 390 Ma (Weber and others, 1988, 1992; Reifenstuhl and others, 1998a; Athey and others, 2004). Unit also includes very small outcrops of poorly known, dense, dark-grayish-green, chloritized, locally schistose dikes and sills reported by (Reiser and others, 1980) in the Demarcation Point quadrangle, whose occurrence is restricted to within the Cambrian phyllite unit (included in CPxwn, here)

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 CZum
Unit name Ultramafic and mafic rocks
Description Livengood area: Serpentinite, light to dark yellowish-green, grayish-green, greenish-black an black, weathers to shades of medium to dark brown, reddish-brown and grayish-brown, derived from clinopyroxene peridotite, dunite, and lesser clinopyroxenite; and clinopyroxene-plagioclase metabasalt, medium to dark green,yellowish-green, grayish-green, and greenish-gray; diabase and minor metatuff, weather to darker shades of yellow, yellowish-brown, reddish-brown, olive gray or greenish-gray. Serpentinite intruded by dikes of clinopyroxene gabbro, microgabbro and diorite, green or olive gray, yellowish gray to gray weathering
Lithology Igneous

Correlated geologic units

Label CZum
Description Ultramafic and mafic rocks and greenstone, Cambrian and/or preCambrian
Geologic age Ediacarian to Cambrian
Geologic setting Intrusive, peridotite
Lithology Form Importance
Greenstone < Metaigneous < Metamorphic Greenschist Major
Serpentinite < Metaigneous < Metamorphic Greenschist Major
Peridotite < Ultramafic < Plutonic < Igneous Indeterminate, major