Volcanic rocks of Chugach accretionary complex

Unit symbol: Kafv
Age range Upper Cretaceous (83.6 to 66 Ma)
Lithology: Sedimentary
Group name: Chugach accretionary complex
Tholeiitic metabasalt; massive greenstone; and basaltic metatuff, including local pillow lava, pillow breccia, and gabbroic dikes and sills (Winkler and Plafker, 1993) typically interbedded with flysch of the Valdez Group (unit Kaf) and Sitka Graywacke (unit Ksg). Metabasalt forms rugged, nearly massive outcrops, whereas semischistose metatuff forms more subdued outcrops (Winkler and Plafker, 1993). Dated by association with the sedimentary part of the Valdez Group. Metamorphic grade ranges from prehnite-pumpellyite to lower greenschist facies (Winkler and Plafker, 1993). Basalt and basaltic tuff north of Cross Sound are deformed and regionally metamorphosed as high as amphibolite facies (Gehrels and Berg, 1992, Dusel-Bacon and others, 1996b). Common rock types include schist, gneiss, and amphibolite (Brew and others, 1978). Correlation with volcanic rocks in Valdez Group to northwest suggests a Cretaceous age (Brew and Morrell, 1979a; Plafker and Campbell, 1979)

Source map information

Source map Winkler, G.R., and Plafker, George, 1993, Geologic map of the Cordova and Middleton Island quadrangles, southern Alaska: U.S. Geological Survey Miscellaneous Investigations Map I-1984, 1 sheet, scale 1:250,000.
Symbol Kvv
Unit name Valdez Group: Metavolcanic rocks, undivided
Description Tholeiitic metabasalt and basaltic metatuff, including local pillow lava, pillow breccia, and gabbroic dikes and sills. Metabasalt forms rugged, nearly massive outcrops, whereas semischistose metatuff forms more subdued outcrops. Variable metamorphic grades.
Lithology Metamorphic

Correlated geologic units

Label Kvv
Description Valdez Group, metavolcanic rocks, undivided
Geologic age Late-Cretaceous
Geologic setting Extrusive
Lithology Form Importance
Amphibolite < Metamorphic Indeterminate, major
Greenstone < Metaigneous < Metamorphic Greenschist Indeterminate, major
Metavolcanic < Metaigneous < Metamorphic Indeterminate, major