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., Ovenshine, A.T., Karl, S.M., and Hunt, S.J., 1984, Preliminary reconnaissance geologic map of the Petersburg and parts of the Port Alexander and Sumdum 1:250,000 quadrangles, southeastern Alaska: U.S. Geological Survey Open File Report 84-405, 43 p., scale 1:250,000.
Symbol Phb
Unit name Halleck Formation volcanic rocks
Description Halleck Formation volcanic rocks - olivine-rich basalt, pillow flows, pillow breccias, and angular breccias; intercalated with sedimentary rocks of above unit in Saginaw Bay.
Lithology Igneous

Correlated geologic units

Label Phb
Description Volcanic rocks of the Halleck Formation and related units of southeast Alaska
Geologic age Asselian to Kungurian
Geologic setting Extrusive, mafic
Lithology Form Importance
Basalt < Mafic-volcanic < Volcanic < Igneous Flow, pillows Major
Greenstone < Metaigneous < Metamorphic Indeterminate, major
Phyllite < Metaclastic < Metasedimentary < Metamorphic Incidental
Chlorite-schist < Schist < Metamorphic Incidental