Geologic Map of Alaska: Mafic volcanic rocks of Chilkat Peninsula

Mafic volcanic rocks of Chilkat Peninsula

Unit symbol:	Trb
Age range	Late Triassic (235 to 201.3 Ma)
Lithology:	Igneous - Volcanic
Group name:	Massive basalt and greenstone

Dark green, massive to pillowed and amygdaloidal mafic volcanic flows and minor tuff. Amygdules are undeformed and contain calcite and epidote. Massive, flow-banded, and locally pillowed or amygdaloidal metabasalt (Plafker and Hudson, 1980). Up to 3.4 km thick, unit also contains magnetite, traces of malachite, pods and veins of epidote and has associated tuffaceous metasediment. Metamorphosed to low greenschist facies and intruded by the Mount Kashagnak pluton of inferred mid-Cretaceous age (included in unit Kmqm, here) (Redman and others, 1984)

Source map information

Source map	Gilbert, W.G., Burns, L.E., Redman, E.C., and Forbes, R.B.,1987, Preliminary bedrock geology and geochemistry of the Skagway B-3 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 87-2, 2 sheets, scale 1:36,200.
Symbol	Trmb
Unit name	Metabasalt
Description	Dark green and black metabasalt and metaandesite. Flow units and intercalated metasedimentary rocks strike NW and dip steeply east. Local pillow structures; local malachite staining. Foliated and greenschist facies.
Lithology	Metamorphic

Correlated geologic units

Label	Trn?
Description	Greenstone of Chilkat Peninsula
Geologic age	Late-Triassic
Geologic setting	Extrusive

Lithology	Form	Importance
Metavolcanic < Metaigneous < Metamorphic	Amphibolite	Major
Metavolcanic < Metaigneous < Metamorphic	Greenschist	Major