Isotopic evidence for Early Proterozoic age of the Idono Complex, west-central Alaska

Journal Article · Fri Mar 01 00:00:00 EST 1991 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629485· OSTI ID:5541911

Miller, M L; Bradshaw, J Y ^[1]; Kimbrough, D L ^[2]; Stern, T W ^[3]; Bundtzen, T K ^[4]

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1. Geological Survey, Anchorage, AK (USA)
2. San Diego State Univ., CA (USA)
3. Geological Survey, Reston, VA (USA)
4. 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), Vol. 99:2; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ALASKA
GEOLOGIC FORMATIONS
AGE ESTIMATION
AMPHIBOLITES
ARGON ISOTOPES
BIOTITE
CONTINENTAL CRUST
CRETACEOUS PERIOD
CRYSTALLIZATION
ELEMENTS
GEOLOGIC FAULTS
GEOLOGIC MODELS
GEOLOGY
GNEISSES
GRANITES
HORNBLENDE
LEAD ISOTOPES
MAGMA
MESOZOIC ERA
MICA
NEODYMIUM ISOTOPES
PLATE TECTONICS
POTASSIUM ISOTOPES
PRECAMBRIAN ERA
SAMARIUM ISOTOPES
SEDIMENTARY ROCKS
TRACE AMOUNTS
URANIUM ISOTOPES
VOLCANIC ROCKS
ZIRCON
ACTINIDE ISOTOPES
ALKALI METAL ISOTOPES
AMPHIBOLE
DEVELOPED COUNTRIES
EARTH CRUST
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
IGNEOUS ROCKS
ISOTOPES
METAMORPHIC ROCKS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
RARE EARTH ISOTOPES
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TECTONICS
TRANSITION ELEMENT COMPOUNDS
USA
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES
580000* - Geosciences