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 Kvvs
Unit name Valdez Group: Interbedded metavolcanic and metasedimentary rocks
Description Equal proportions of interbedded metavolcanic and metasedimentary rocks. Metavolcanic--semischistose metatuff and breccia and minor pillow basalt. Metasedimentary--slate, phyllite, with metasiltstone and metasandstone interbedding. Variable metamorphic grades.
Lithology Metamorphic

Correlated geologic units

Label Kvvs
Description Valdez Group, Interbedded volcanic and sedimentary rocks
Geologic age Late-Cretaceous
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Metabasalt < Metavolcanic < Metaigneous < Metamorphic Greenschist Indeterminate, major
Metasandstone < Metaclastic < Metasedimentary < Metamorphic Greenschist Indeterminate, major
Metasiltstone < Metaclastic < Metasedimentary < Metamorphic Greenschist Indeterminate, major
Slate < Metaclastic < Metasedimentary < Metamorphic Greenschist Indeterminate, major
Mixed-clastic < Clastic < Sedimentary Bed Indeterminate, major