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Geologic Unit: Nelchina River
Map showing publication footprint
  • Usage in publication:
    • Nelchina River Gabbronorite*
  • Modifications:
    • Age modified
    • Geochronologic dating
  • Dominant lithology:
    • Gabbro
  • AAPG geologic province:
    • Alaska Southern region
Publication:

Plafker, George, Nokleberg, W.J., and Lull, J.S., 1989, Bedrock geology and tectonic evolution of the Wrangellia, Peninsular, and Chugach terranes along the Trans-Alaska Crustal Transect in the Chugach Mountains and southern Copper River basin, Alaska, IN Page, R.A., ed., Special section on northern Chugach Mountains-southern Copper River basin segment of the Alaskan Transect, Part 1: Journal of Geophysical Research, B, Solid Earth and Planets, v. 94, no. 4, p. 4255-4295.


Summary:

Exceptionally well exposed at headwaters of Nelchina River at western margin of Nelchina Glacier. West of Richardson HWY, southern contact with McHugh Complex is complex fault zone along Border Ranges fault system. Northern contact with Talkeetna Formation is faulted. Age of unit is in part Middle Jurassic based on K-Ar ages on hornblende from 3 samples (180 to 175 Ma) and Ar40/Ar39 analysis of one of these hornblendes. Age on explanation of geologic sketch map is given as Early and (or) Middle Jurassic.

Source: GNU records (USGS DDS-6; Menlo GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Nelchina River Gabbronorite*
  • Modifications:
    • Age modified
    • Geochronologic dating
  • AAPG geologic province:
    • Alaska Southern region
Publication:

Plafker, George, Lull, J.S., Nokleberg, W.J., Pessel, G.H., Wallace, W.K., and Winkler, G.R., 1992, Geologic map of the Valdez A-4, B-3, B-4, C-3, C-4, and D-4 quadrangles, northern Chugach Mountains and southern Copper River basin, Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map, I-2164, 1 sheet, scale 1:125,000


Summary:

Age of unit is Middle Jurassic and older(?) based on radiometric ages (180 to 175 Ma) and stratigraphic relations.

Source: GNU records (USGS DDS-6; Menlo GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Nelchina River Gabbronorite*
  • Modifications:
    • Named
    • Geochronologic dating
  • Dominant lithology:
    • Gabbro
  • AAPG geologic province:
    • Alaska Southern region
Publication:

Burns, L.E., 1996, Geology of part of the Nelchina River Gabbronorite and associated rocks, south-central Alaska: U.S. Geological Survey Bulletin, 2058, 32 p., (incl. geologic maps, scale 1:2,400)


Summary:

Unit named for Nelchina River. Type locality designated as in westernmost parts of secs.29 and 32 T1S R10W and secs.5 and 8 T2S R10W, Anchorage C-1 (1:63,360) quad, southern AK. Consists dominantly of gabbronorite with minor ultramafic rocks, quartz diorite, tonalite, granodiorite, and metasedimentary and metavolcanic rocks. Area of exposure is 170 km by 2 to 10 km. Age is considered to be Early to Middle Jurassic based on K-Ar ages (188 to 165 Ma) for most of the gabbronorites.

Source: GNU records (USGS DDS-6; Menlo GNULEX).


For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates published by U.S. Geological Survey authors.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).

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