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 Brew, D.A., 1997, Reconnaissance bedrock geologic map of Glacier Bay National Park, Alaska. in Geiselman, Joy, Dunlap, J., Hodge, P. and Albert, D., eds., Glacier Bay Ecosystem GIS Volume 1: U.S. Geological Survey, Biological Resources Division. (Digital map)
Symbol Kmm
Unit name Migmatite associated with Cretaceous plutons
Description Migmatite - found in Geikie and Muir provinces, and associated with granitic units Kggd and Kgto (Brew, pers. comm., 1999).
Lithology Metamorphic

Correlated geologic units

Label Kmg
Description Migmatite associated with western plutonic belt of southeast Alaska (Wales-Chichagof arc)
Geologic age Cretaceous
Geologic setting Intrusive
Lithology Form Importance
Migmatite < Metamorphic Amphibolite Major