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Title: Kilbuck terrane: Oldest known rocks in Alaska

Abstract

The Kilbuck terrane in southwestern Alaska is a narrow, thin crustal sliver or flake of amphibolite facies orthogneiss. The igneous protolith of this gneiss was a suite of subduction-related plutonic rocks. U-Pb data on zircons from trondhjemitic and granitic samples yield upper-intercept (igneous) ages of 2,070 {plus minus}16 and 2,040 {plus minus}74 Ma, respectively. Nd isotope data from these rocks suggest that a diorite-tonalite-trondhjemite suite ({epsilon}{sub Nd}(T) = +2.1 to +2.7; T is time of crystallization) evolved from partial melts of depleted mantle with no discernible contamination by older crust, whereas a coeval granitic pluton ({epsilon}{sub Nd}(T) = {minus}5.7) contains a significant component derived from Archean crust. Orthogneisses with similar age and Nd isotope characteristics are found in the Idono complex 250 km to the north. Early Proterozoic rocks are unknown elsewhere in Alaska. However, Phanerozoic plutons cutting several continental terranes in Alaska (southern Brooks Range and Ruby, Seward, and Yukon-Tanana terranes) have Nd isotope compositions indicative of Early Proterozoic (or older) crustal components that could be correlative with rocks of the Kilbuck terrane. Rocks with similar igneous ages in cratonal North America are rare, and those few that are known have Nd isotope compositions distinct from those of themore » Kilbuck terrane. Conversely, provinces with Nd model ages of 2.0-2.1 Ga are characterized by extensive 1.8 Ga or younger plutonism, which is unknown in the Kilbuck terrane. At present the case for a North American parentage of the Kilbuck terrane is not compelling. The possibility that the Kilbuck terrane was displaced from provinces of similar age in other cratons (e.g., Australian, Baltic, Guiana, and west African shields), or from the poorly dated Siberian craton, cannot be excluded.« less

Authors:
 [1]; ;  [2];  [3]
  1. (U.S. Geological Survey, Spokane, WA (USA))
  2. (U.S. Geological Survey, Menlo Park, CA (USA))
  3. (U.S. Geological Survey, Anchorage, Alaska (USA))
Publication Date:
OSTI Identifier:
5679914
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geology; (USA); Journal Volume: 18:12
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; ALASKA; GEOLOGIC FORMATIONS; AGE ESTIMATION; GEOCHEMISTRY; CONTINENTAL CRUST; EARTH MANTLE; GEOLOGIC FAULTS; GEOLOGY; ISOTOPE DATING; ISOTOPE RATIO; LEAD ISOTOPES; MAGMA; NEODYMIUM ISOTOPES; PLUTONIC ROCKS; PRECAMBRIAN ERA; SUBDUCTION ZONES; URANIUM ISOTOPES; ZIRCON; ACTINIDE ISOTOPES; CHEMISTRY; EARTH CRUST; FEDERAL REGION X; GEOLOGIC AGES; GEOLOGIC FRACTURES; GEOLOGIC STRUCTURES; IGNEOUS ROCKS; ISOTOPES; MINERALS; NORTH AMERICA; OXYGEN COMPOUNDS; ROCKS; SILICATE MINERALS; SILICATES; SILICON COMPOUNDS; TRANSITION ELEMENT COMPOUNDS; USA; ZIRCONIUM COMPOUNDS; ZIRCONIUM SILICATES; 580000* - Geosciences

Citation Formats

Box, S.E., Moll-Stalcup, E.J., Wooden, J.L., and Bradshaw, J.Y. Kilbuck terrane: Oldest known rocks in Alaska. United States: N. p., 1990. Web. doi:10.1130/0091-7613(1990)018<1219:KTOKRI>2.3.CO;2.
Box, S.E., Moll-Stalcup, E.J., Wooden, J.L., & Bradshaw, J.Y. Kilbuck terrane: Oldest known rocks in Alaska. United States. doi:10.1130/0091-7613(1990)018<1219:KTOKRI>2.3.CO;2.
Box, S.E., Moll-Stalcup, E.J., Wooden, J.L., and Bradshaw, J.Y. Sat . "Kilbuck terrane: Oldest known rocks in Alaska". United States. doi:10.1130/0091-7613(1990)018<1219:KTOKRI>2.3.CO;2.
@article{osti_5679914,
title = {Kilbuck terrane: Oldest known rocks in Alaska},
author = {Box, S.E. and Moll-Stalcup, E.J. and Wooden, J.L. and Bradshaw, J.Y.},
abstractNote = {The Kilbuck terrane in southwestern Alaska is a narrow, thin crustal sliver or flake of amphibolite facies orthogneiss. The igneous protolith of this gneiss was a suite of subduction-related plutonic rocks. U-Pb data on zircons from trondhjemitic and granitic samples yield upper-intercept (igneous) ages of 2,070 {plus minus}16 and 2,040 {plus minus}74 Ma, respectively. Nd isotope data from these rocks suggest that a diorite-tonalite-trondhjemite suite ({epsilon}{sub Nd}(T) = +2.1 to +2.7; T is time of crystallization) evolved from partial melts of depleted mantle with no discernible contamination by older crust, whereas a coeval granitic pluton ({epsilon}{sub Nd}(T) = {minus}5.7) contains a significant component derived from Archean crust. Orthogneisses with similar age and Nd isotope characteristics are found in the Idono complex 250 km to the north. Early Proterozoic rocks are unknown elsewhere in Alaska. However, Phanerozoic plutons cutting several continental terranes in Alaska (southern Brooks Range and Ruby, Seward, and Yukon-Tanana terranes) have Nd isotope compositions indicative of Early Proterozoic (or older) crustal components that could be correlative with rocks of the Kilbuck terrane. Rocks with similar igneous ages in cratonal North America are rare, and those few that are known have Nd isotope compositions distinct from those of the Kilbuck terrane. Conversely, provinces with Nd model ages of 2.0-2.1 Ga are characterized by extensive 1.8 Ga or younger plutonism, which is unknown in the Kilbuck terrane. At present the case for a North American parentage of the Kilbuck terrane is not compelling. The possibility that the Kilbuck terrane was displaced from provinces of similar age in other cratons (e.g., Australian, Baltic, Guiana, and west African shields), or from the poorly dated Siberian craton, cannot be excluded.},
doi = {10.1130/0091-7613(1990)018<1219:KTOKRI>2.3.CO;2},
journal = {Geology; (USA)},
number = ,
volume = 18:12,
place = {United States},
year = {Sat Dec 01 00:00:00 EST 1990},
month = {Sat Dec 01 00:00:00 EST 1990}
}