Coast-North Cascade plutonic belt 

(Late Cretaceous-early Tertiary) 

(East-Central Alaska, southeastern Alaska, western Canadian Cordillera, and northern U.S.A. 
Pacific Northwest, units Kpf, TKpf, Tpf)

Consists chiefly of a major granitic plutonic belt that extends the full length of the Canadian Cordillera 
from latitude 49  to 62  N. Also present in the metamorphic core and eastern part of North Cascade 
mountains as far south as latitude 48  N, and in east-central Alaska. Consists chiefly of quartz diorite, 
granodiorite, and locally more mafic or felsic plutons. Crystallization ages generally younger toward the 
east. In the central and southern parts of the belt, age zonation permits division into three subbelts: (1) mid-
and Late Cretaceous plutons (about 96-70 Ma); (2) plutons that straddle the Cretaceous-Tertiary boundary 
(70 to 60 Ma); and (3) early Tertiary plutons (60-40 Ma). Coeval to these three belts are units of 
intermediate to felsic volcanic and minor plutonic rocks that are exposed locally to the east in the 
Intermontane Belt of the Canadian Cordillera (Armstrong, 1988; Wheeler and McFeeley, 1991; van der 
Heyden, 1992; Woodsworth and others, 1991). The northern part of the Coast-North Cascade belt (north of 
latitude 54  N) consists chiefly of latest Cretaceous and earliest Tertiary (83-57 Ma), and early Tertiary 
granitic rocks (51-48 Ma) (Gehrels and others, 1990; Wheeler and McFeely, 1991).

Early Late Cretaceous through early Tertiary intrusions were emplaced concurrently with structures formed 
sequentially during contraction, local(?) dextral transpression and transtension, and accompanied by 
regional metamorphism (Rubin and others, 1990; Journeay and Friedman, 1993). Together, the plutonic 
belt and associated structure and metamorphism define the gemorphologic Coast-North Cascade plutonic 
belt. Intrusion of the early Late Cretaceous granitic rocks of this belt postdates the accretion of the Stikinia, 
Yukon-Tanana, and Quesnellia terranes that were unequivocally linked to the outboard Wrangellia 
superterrane by intrusion of this plutonic belt.

In U.S.A. Pacific Northwest, plutonic belt consists chiefly of abundant deep-seated tonalite to granodiorite 
plutons with minor paragneiss and schist, variously metamorphosed in Late Cretaceous to middle Eocene 
regional metamorphism. Protoliths of the metamorphosed supracrustal rocks are probably correlative to 
parts of the Chelan Mountains terrane and in part to the Bridge River terrane. In U.S.A. Pacific Northwest 
and in southernmost British Columbia, belt includes most of the Skagit Metamorphic Complex (Misch, 
1966; Haugerud, 1991).

In east-central Alaska, belt consists chiefly of extensive granitic plutons, chiefly granodiorite, lesser diorite, 
and granite that intrude rocks of the Yukon-Tanana terrane. REFERENCES: Misch, 1966; Foster and 
others, 1987, 1994; Armstrong, 1988; Rubin and others, 1990; Gehrels and others, 1990; Haugerud, 1991; 
Wheeler and McFeeley, 1991; Woodsworth and others, 1991; van der Heyden, 1992; Journeay and 
Friedman, 1993