Schist, paragneiss, and marble

Unit symbol: DPxsgm
Age range Devonian to Neoproterozoic (1000 to 358.9 Ma)
Lithology: Metamorphic
Group name: Metasedimentary and metavolcanic rocks of the Central Belt and Northern Thrust assemblage of Till and others (2008a)
Spatially associated with the Arrigetch Peaks orthogneiss, this unit includes pelitic schist, metaquartzite, mafic schist, and rocks originally mapped as the Skajit Limestone and an orange dolomitic marble by (Nelson and Grybeck, 1980) in the Survey Pass quadrangle and banded schist by Dillon and others (1986) in the western Wiseman quadrangle. In the Survey Pass quadrangle the unit consists largely of granoblastic, massive, light-gray weathering, cream to very light-gray, fine- to medium-grained marble and orange-weathering, medium- to coarse-grained dolomitic marble. In the Wiseman quadrangle, unit is interlayered, locally gneissic, coarse-grained quartz-mica schist, quartzite, calcareous schist, marble, graphitic phyllite, and metabasite. “Upper greenschist facies rocks predominate, but includes amphibolite facies paragneiss, and local relict blueschist and eclogite facies metabasite” (Dillon and others, 1986). The informally named Ernie Lake pluton (unit Pxgn), an orthogneiss, intrudes this unit and has yielded a U/Pb zircon age of 971±5 Ma (McClelland and others, 2006), which indicates that at least part of this unit is early Neoproterozoic or older. Till and others (2008a) report that gneissic textures are particularly common where the unit is closest to metaplutonic rocks of the Arrigetch Peaks and Mount Igikpak orthogneiss (unit Dogn). Mafic rocks within the unit contain assemblages of the albite-epidote-amphibolite facies (Dusel-Bacon and others, 1989; Vogl, 2002); exposures west of the major orthogneiss bodies appear to be lower in grade (Nelson and Grybeck, 1980; Toro, 1998). Unit may, in part, represent a higher metamorphic grade equivalent of a number of units of the Brooks Range, including SCbs, Dbf, Degh, DCcs, and PzPxaqm

Source map information

Source map Till, A.B., Dumoulin, J.A., Harris, A.G., Moore, T.E., Bleick, Heather, and Siwiec, Benjamin, 2008, Bedrock geologic map of the southern Brooks Range, Alaska, and accompanying conodont data: U.S. Geological Survey Open-File Report 2008-1149, 88 p., 2 sheets, scale 1:500,000.
Symbol PzZem
Unit name Metamorphic rocks of the Ernie Lake area
Description Coarse crystalline marble, orange dolomitic marble, quartz-mica schist, metaquartzite, calcareous schist, graphitic metaquartzite, and metabasite exposed in eastern Survey Pass and western Wiseman quadrangles. Locally gneissic. This unit is part of the Central belt.
Lithology Metamorphic

Correlated geologic units

Label PzZel
Description Marble and intercalated gneissic rocks, early Paleozoic or preCambrian
Geologic age Neoproterozoic to Devonian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Marble < Metacarbonate < Metasedimentary < Metamorphic Major
Orthogneiss < Metaigneous < Metamorphic Indeterminate, major
Mica-schist < Schist < Metamorphic Indeterminate, major