Kuskokwim Mountains sedimentary, volcanic, and plutonic belt 

(Late Cretaceous and early Tertiary) 

(Southwestern Alaska, units TKv, TKp)

Consists chiefly of volcanic rocks and minor interlayered tuffaceous sedimentary rocks. Also includes 
minor sedimentary rocks, mainly conglomerate to coarse-grained sandstone turbidite deposits deposited in 
deep-marine conditions, and lesser sandstone and conglomerate deposited in shallow-marine to nonmarine 
conditions along the flanks of the unit. Volcanic rocks consist chiefly of rhyolite and dacite domes, flows, 
and tuff, and dacite, andesite, and basalt flows of 58 to 77 Ma that display moderate-K calc-alkalic to 
shoshonitic compositional trends. Belt contains numerous related volcano-plutonic complexes, dikes, and 
plutons that exhibit a wide compositional range, including gabbro, quartz diorite, granodiorite, monzonite, 
and syenite. Belt is coeval with part of Alaska Range-Talkeetna Mountains belt to south, and partly coeval 
with Yukon-Kanuti belt to north. The belt is locally intensely folded and faulted, and extends for over 800 
km in southwestern to east-central Alaska. For paleomagnetic determinations, volcanic and volcanogenic 
sedimentary rocks of Late Cretaceous age (79 Ma) from St. Matthew Island yield displacements between 0 
and 12o depending on the way in which ancient horizontal is estimated. The preferred interpretation shows 
a southerly displacement of 12o+5o with respect to North America. The belt overlies the Kahiltna 
sedimentary and volcanic assemblage to the south, and overlies the Ruby, Angayucham, Nixon Fork, 
Minchumina, Dillinger, Koyukuk, Nyac, Kilbuck, Togiak, and Goodnews terranes to the north.

In northern part of southwestern Alaska and northern part of west-central Alaska, the Kuskokwim 
Mountains belt includes Yukon-Kanuti volcanic-plutonic belt of early Tertiary age. Yukon-Kanuti belt 
chiefly dacite, andesite, rhyodacite, and rhyolite flows, domes, and tuffs of 47 to 66 Ma. Sparse, local 
basalt flows. Yukon-Kanuti belt exhibits moderate- to high-K calc-alkalic compositional trend. Moderate 
number of related granodiorite dikes and plutons. Yukon-Kanuti belt extends for over 300 km in west-
central Alaska, and overlies the Koyukuk, Ruby, and Angayucham terranes. REFERENCES: Bundtzen 
and Gilbert, 1983; Wittbrodt and others, 1989; Moll-Stalcup, 1990, 1994; Miller and Bundtzen, 1993; 
Moll-Stalcup and others, 1994.