Volcanic rocks of the Halleck Formation and related rocks of southeast Alaska

Unit symbol: Phb
Age range early Permian (298.9 to 259.9 Ma)
Lithology: Igneous - Volcanic
Group name: Andesite and basalt of southern Alaska
Olivine-rich basalt, pillow flows, pillow breccia, and angular breccia, intercalated with the clastic sedimentary rocks of the Halleck Formation (Ph), which constrains age (Brew and others, 1984). Unit also includes informally named Permian Sitth-gha-ee Peak formation, which consists of basaltic(?) greenstone, greenschist, phyllite, and slate northeast of Glacier Bay (D.A. Brew, written commun., 1999)

Source map information

Source map Brew, D.A., and Ford, A.B., 1985, Preliminary reconnaissance geologic map of the Juneau, Taku River, Atlin, and part of the Skagway 1:250,000 quadrangles, southeastern Alaska: U.S. Geological Survey Open-File Report 85-395, pamphlet 23 p., 2 sheets, scale 1:250,000.
Symbol Puv
Unit name Amygdaloidal basalt or andesite
Description ALEXANDER BELT: UNNAMED PERMIAN FORMATION(S) IN GLACIER BAY-CHILKAT MOUNTAINS AREA Includes some greenstone, greenschist, and phyllite; exposed north of Casement Glacier and south of Adams Inlet, Glacier Bay.
Lithology Igneous

Correlated geologic units

Label Psfv
Description Greenstone, greenschist, and phyllite of Sitth-gha-ee Peak formation of Brew (1997)
Geologic age Permian to Guadalupian
Geologic setting Mixed volcanic and sedimentary rocks
Lithology Form Importance
Greenstone < Metaigneous < Metamorphic Major
Phyllite < Metaclastic < Metasedimentary < Metamorphic Indeterminate, major
Amphibole-schist < Schist < Metamorphic Indeterminate, major