Mafic igneous rocks of Duke Island

Unit symbol: Trdg
Age range Middle Triassic (242 to 228 Ma)
Lithology: Igneous - Plutonic
Group name: Mafic and ultramafic rocks in southern Alaska
“Much of central and eastern Duke Island is underlain by a large body of pyroxene gabbro that consists of varying proportions of olivine, hypersthene, augite, plagioclase, hornblende, and minor opaque minerals (Irvine, 1974). The gabbro intrudes deformed and metamorphosed Ordovician and Silurian sedimentary and igneous rocks [unit SOgi, here] and in turn is intruded by Cretaceous ultramafic rocks [unit Kum, here] * * *” (Berg and others, 1988). Gehrels and others (1987) report a U/Pb age of 226±3 Ma

Source map information

Source map Butler, R.F., Gehrels, G.E., and Saleeby, J.B., 2001, Paleomagnetism of the Duke Island, Alaska, ultramafic complex revisited: Journal of Geophysical Research, v. 106, p. 19259-19269.
Symbol fine ordered dots
Unit name Olivine gabbro, hypersthene gabbro norite, olivine ferronorite
Description Olivine gabbro, hypersthene gabbro norite, olivine ferronorite
Lithology Igneous

Correlated geologic units

Label Trdg
Description Middle Triassic age rocks of intrusive-gabbro association, Duke Island
Geologic age Ladinian to Carnian
Geologic setting Intrusive, gabbro
Lithology Form Importance
Gabbro < Gabbroic < Plutonic < Igneous Indeterminate, major