Nikolai and Goon Dip Greenstones and equivalent rocks

Unit symbol: Trn
Age range Late and Middle Triassic (247.2 to 201.3 Ma)
Lithology: Igneous - Volcanic
Group name: Massive basalt and greenstone
Massive, dark-gray-green, dark-gray-brown, and maroon-gray, subaerial and submarine basalt flows and minor interbedded volcaniclastic sedimentary rocks, aquagene and epiclastic tuff, breccia, argillite, and radiolarian chert (Nokleberg and others, 1992a), commonly metamorphosed to lower greenschist facies. Widely distributed and several thousands of meters thick. Includes unnamed Triassic greenstone units in Talkeetna Mountains quadrangle (Csejtey and others, 1978). Commonly associated with Late Triassic carbonate and cherty carbonate rocks. Together with Chitistone and Nizina Limestones, this is one of the diagnostic units of the Wrangellia terrane (Jones and others, 1977). Plafker and others (1976) and Jones and others (1977) correlated the Goon Dip Greenstone of southeast Alaska with the Nikolai Greenstone based on similar lithology and stratigraphic position relative to the overlying Whitestripe Marble, which they correlated with the Upper Triassic Chitistone Limestone. Goon Dip Greenstone is dominantly massive greenstone and minor greenschist and marble. The greenstone also commonly contains sparsely distributed copper-bearing sulfides; the Nikolai was the host rock for the Kennecott group of mines. Similar and possibly correlative units, the Cottonwood Bay and Chilikradrotna Greenstones of the Alaska Peninsula, are described below as unit Trcb

Source map information

Source map Karl, S.M., Haeussler, P.J., Himmelberg, G.R., Zumsteg, C.L., Layer, P.W., Friedman, R.M., Roeske, S.M.,and Snee, L.W., 2015, Geologic map of Baranof Island: U.S. Geological Survey Scientific Investigations Map SIM-3335, pamphlet 82 p., 1 sheet, scale 1:250,000.
Symbol Trg
Unit name Goon Dip Greenstone
Description Massive mafic metavolcanic rocks locally contains vesicles and calcite-filled amygdules. Unit consists mostly of massive greenstone; and includes pillow breccia, rare lenses of lapilli tuff, and feeder dikes. Greenstone is several 100 meters thick east of Patterson Bay. No marble was observed associated with the greenstone east of Patterson Bay. Based on lithologic association and trace element chemistry similar to that of basalts assigned to Wrangellia (figs. 3a-3e), these mafic volcanic rocks are inferred to represent faulted slivers of upper plate basalt of the Wrangellia terrane
Lithology Igneous

Correlated geologic units

Label Trgn
Description Goon Dip Greenstone and related rocks, southeast Alaska
Geologic age Triassic
Geologic setting Extrusive, mafic
Lithology Form Importance
Basalt < Mafic-volcanic < Volcanic < Igneous Flow, pillows Major
Marble < Metacarbonate < Metasedimentary < Metamorphic Minor
Schist < Metamorphic Minor
Limestone < Carbonate < Sedimentary Calcareous Incidental