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 Johnson, B.R., and Karl, S.M., 1985, Geologic map of western Chichagof and Yakobi Islands, southeastern Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-1506, pamphlet, 15 p., 1 sheet, scale 1:125,000.
Symbol Kd
Unit name Diorite
Description An extensively altered and sheared, green to gray green (C.I. 15-25), medium grained, hornblende + or - biotite diorite with minor quartz diorite forms extensive sills and dikes within the Whitestripe Marble and along the contacts of the Whitestripe Marble and Goon Dip Greenstone with the Kelp Bay Group. Mafic mineral are generally altered to chlorite + epidote = or - clinozoisite. Generally foliated with locally extensive shearing and cataclasis. Similar sheared dioritic rock intrudes marble and greenstone and also occurs as large blocks in the melange facies of the Yakutat Group, which is thought to be correlative with the Kelp Bay Group. The diorite which intrudes the Whitestripe Marble and Goon Dip Greenstone along the Border Ranges fault may also be correlative.
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