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 Smith, T.E., Albanese, M.D., and Kline, G.L., 1988, Geologic map of the Healy A-2 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 95, 1 sheet, scale 1:63,360.
Symbol Trab
Unit name Basaltic metavolcanic rocks
Description Gray-olive to gray-green metabasalt and basaltic andesite. Aphanitic to porphyro-aphanitic with plagioclase clusters as large as several millimeters. Volcanic rocks consist mainly of plagioclase, clinopyroxene, and iron-titanium oxides with subophitic or intergranular texture. Propylitic alteration common, especially along shear zones or fractures. Flows vary in thickness from several inches to 100 ft. Columnar jointing present.
Lithology Igneous

Correlated geologic units

Label Trn
Description Nikolai Greenstone, Late and/or Middle Triassic
Geologic age Anisian to Norian
Geologic setting Extrusive
Lithology Form Importance
Basalt < Mafic-volcanic < Volcanic < Igneous Flow, pillows Major
Basalt < Mafic-volcanic < Volcanic < Igneous Pyroclastic, tuff Indeterminate, major
Basalt < Mafic-volcanic < Volcanic < Igneous Volcaniclastic, volcanic breccia Indeterminate, major
Limestone < Carbonate < Sedimentary Bed Incidental
Conglomerate < Clastic < Sedimentary Bed Incidental
Sandstone < Clastic < Sedimentary Bed Incidental
Siltstone < Clastic < Sedimentary Bed Incidental