Isotopic evidence for Early Proterozoic age of the Idono Complex, west-central Alaska
- Geological Survey, Anchorage, AK (USA)
- San Diego State Univ., CA (USA)
- Geological Survey, Reston, VA (USA)
- Alaska Div. of Geological and Geophysical Surveys, Fairbanks (USA)
The Idono Complex of west-central Alaska is a fault-bounded, {approximately}300 km{sup 2} fragment of Early Proterozoic continental crust surrounded by overlap assemblages and younger terranes accreted in Mesozoic time. Nine zircon fractions from three samples of granitoid orthogneiss define a U-Pb discordia line intersecting concordia at 2,062 {plus minus} 7 Ma and 182 {plus minus} 8 Ma. The upper and lower intercepts are interpreted, respectively, as approximations of the time of granitoid crystallization and major episodic Pb-loss. The lower intercept age is similar to that indicated by some hornblende and biotite K-Ar ages. Other biotite, hornblende, and white mica K-Ar ages record later isotopic disturbance in Early Cretaceous time. Nd isotopic compositions at 2.06 Ga for tonalite orthogneiss ({epsilon}{sub Nd}(t) = +2.8) and amphibolite ({epsilon}{sub Nd}(t) = +1.8 and +2.3) indicate that Early Proterozoic crust formation in the Idono Complex involved significant additions of mantle-derived magma. These rocks yield T{sub Sm-Nd} (depleted mantle) model ages of 2.0 to 2.1 Ga, similar to the U-Pb zircon upper intercept age. Involvement of Archean crust in the formation of at least some rocks of the Idono Complex is indicated by a granitic orthogneiss ({epsilon}{sub Nd}(t) = {minus}4.6), which yields a T{sub sm-Nd} model age of 2.5 Ga. The {approximately}2.06-Ga age of the Idono Complex is similar to that indicated for provenance(s) of widely distributed sedimentary rocks in western North America and may represent a fragment of the North American craton displaced by northward movement of the Pacific plate.
- OSTI ID:
- 5541911
- Journal Information:
- Journal of Geology; (USA), Journal Name: Journal of Geology; (USA) Vol. 99:2; ISSN JGEOA; ISSN 0022-1376
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ACTINIDE ISOTOPES
AGE ESTIMATION
ALASKA
ALKALI METAL ISOTOPES
AMPHIBOLE
AMPHIBOLITES
ARGON ISOTOPES
BIOTITE
CONTINENTAL CRUST
CRETACEOUS PERIOD
CRYSTALLIZATION
DEVELOPED COUNTRIES
EARTH CRUST
ELEMENTS
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
GEOLOGY
GNEISSES
GRANITES
HORNBLENDE
IGNEOUS ROCKS
ISOTOPES
LEAD ISOTOPES
MAGMA
MESOZOIC ERA
METAMORPHIC ROCKS
MICA
MINERALS
NEODYMIUM ISOTOPES
NORTH AMERICA
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PLATE TECTONICS
PLUTONIC ROCKS
POTASSIUM ISOTOPES
PRECAMBRIAN ERA
RARE EARTH ISOTOPES
ROCKS
SAMARIUM ISOTOPES
SEDIMENTARY ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TECTONICS
TRACE AMOUNTS
TRANSITION ELEMENT COMPOUNDS
URANIUM ISOTOPES
USA
VOLCANIC ROCKS
ZIRCON
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES