Migmatite and metaplutonic rocks

Unit symbol: Kmig
Age range Cretaceous (145 to 66 Ma)
Lithology: Metamorphic
Group name: Migmatite and metaplutonic rocks
These migmatitic rocks are exposed in three areas of the state: southeast Alaska, the southern Brooks Range, and on the Seward Peninsula. In southeast Alaska, migmatite is widespread and associated with Cretaceous plutons and tends to be of granodioritic to quartz dioritic composition (Brew and others, 1984; Brew and Ford, 1985; Brew, 1996; Karl, 1999; Karl and others, 1999; D.A. Brew, written commun., 1997). It ranges from agmatite (brecciated migmatite) to gneiss. Locally, schist, gneiss, and marble inclusions are present. In the southern Brooks Range and Seward Peninsula areas, these migmatitic rocks are associated with the mid-Cretaceous quartz monzonite bodies of map unit Kmqm (Brosgé and others, 1973; Till and others, 2008, 2010). In the Chandalar quadrangle, the migmatite forms an annular ring around rocks interpreted as one of the metamorphosed Devonian plutons of the Brooks Range (unit Dogn) (Brosgé and Reiser, 1964). The migmatite also forms a roof pendant on a nearby mid-Cretaceous quartz monzonite. On the Seward Peninsula, the unit is a gneissic monzonite exposed between rocks of the Casadepaga Schist (unit Ocs) and the mid-Cretaceous Kachauik pluton (units Kmgd and Kmgm) (Till and others, 2010)

Source map information

Source map Karl, S.M., Haeussler, P.J., and McCafferty, Anne, 1999, Reconnaissance geologic map of the Duncan Canal-Zarembo Island area, southeast Alaska: U.S. Geological Survey Open File Report 99-168, 1 sheet, scale 1:125,000.
Symbol Kmgf
Unit name Granodioritic migmatite
Description Agmatite (migmatite?) and irregular banded gneiss of granodioritic to quartz dioritic composition. Associated with Ktef, Kqo, and Ktob.
Lithology Igneous

Correlated geologic units

Label Mzsa
Description Migmatite and migmatitic schist
Geologic age Late-Cretaceous to Cretaceous
Geologic setting Metamorphic, undivided
Lithology Form Importance
Migmatite < Metamorphic Amphibolite Indeterminate, major
Schist < Metamorphic Amphibolite Indeterminate, major