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Source map Wilson, F.H., and Hults, C.P., 2010, Unpublished data.
Symbol Pzmsm
Unit name Mixed Schist and Marble
Description Interlayered gray marble, orange dolomitic marble, magnetite bearing chlorite schist, and garnet biotite quartz schist with small calcsilicate skarns containing amphibole near the Arrigetch pluton. Intermediate amount of interlayered marble distinguishes these rocks from marble unit, DSso (more marble), and the schist unit Pzsch (less marble); however, they may be equivalent in age.
Lithology Metamorphic

Correlated geologic units

Label DZsm
Description Orange weathering chloritic marble Brooks Range schist belt
Geologic age Silurian to Devonian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Marble < Metacarbonate < Metasedimentary < Metamorphic Major
Schist < Metamorphic Minor