Kilbuck terrane: Oldest known rocks in Alaska

Journal Article · Sat Dec 01 00:00:00 EST 1990 · Geology; (USA)

DOI:https://doi.org/10.1130/0091-7613(1990)018<1219:KTOKRI>2.3.CO;2· OSTI ID:5679914

Box, S E ^[1]; Moll-Stalcup, E J; Wooden, J L ^[2]; Bradshaw, J Y ^[3]

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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)

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.

• OSTI ID: 5679914
• Journal Information: Geology; (USA), Vol. 18:12; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

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