Isotopic Evidence for Early Proterozoic Age of the Idono Complex, West-Central Alaska
| Autor: | J. Y. Bradshaw, Marti L. Miller, D. L. Kimbrough, T. W. Stern, T. K. Bundtzen |
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| Rok vydání: | 1991 |
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| Zdroj: | The Journal of Geology. 99:209-223 |
| ISSN: | 1537-5269 0022-1376 |
| Popis: | The Idono Complex of west-central Alaska is a fault-bounded, $$\sim300 km^{2}$$ fragment of Early Proterozoic continental crust surrounded by overlap assemblages and younger terranes accreted in Mesozoic time. It is composed of granitic to dioritic orthogneiss, amphibolite, and metasedimentary rocks. Trace element compositions of the granitoids and amphibolite suggest rock formation in a subduction-related volcanic arc terrain. Nine zircon fractions from three samples of granitoid orthogneiss define a U-Pb discordia line intersecting concordia at $$2062 \pm 7 Ma$$ and $$182 \pm 8 Ma$$. 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 ($$\epsilo... |
| Databáze: | OpenAIRE |
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