Petrology and Sr and Nd isotopic characteristics of five late Cretaceous-early Tertiary volcanic fields in western Alaska
Chemical and Sr and Nd isotopic characteristics were studied in an attempt to determine if old continental crust having high /sup 87/Sr//sup 86/Sr (SIR) and low /sup 143/Nd//sup 144/Nd (NIR) underlies the Yukon-Koyukuk province. The Blackburn Hills, Yukon River, and Kanuti fields lie within the Yukon-Koyukuk province and the Sischu and Nowitna fields overlie Paleozoic and Precambrian metamorphic terranes to the southeast. The Nowitna field is chiefly andesite having SIR = 0.7044-0.7051 and NIR = 0.51256-0.51257. The Sischu field is chiefly rhyolite and dacite having high SIR (0.7079-0.7140) and low NIR (0.51246-0.51252), which suggests that old continental crust was involved in their genesis, either by direct partial melting or by large degrees of assimilation. The Blackburn Hills field consists of medium-K basalt, andesite, and rhyolite intruded by a small granodiorite pluton and has SIR = 0.7033-0.7052 and NIR = 0.51253-51290. The Yukon River field is basalt, andesite, dacite, and rhyolite having SIR = 0.70374-0.70511 and NIR = 0.51270-0.51284, and much of its isotopic variation can be modeled by assimilation of seawater-altered oceanic crust during fractionation of basalt. Isotopic compositions of most felsic rocks from the Blackburn Hills field (SIR = 0.7038-0.7041) and dacites from the Kanuti volcanic field (SIR = 0.7043-0.7048) require little or no old continental crust in their genesis, suggesting that ancient crust does not extend beneath this part of the Yukon-Koyukuk province. However, the ultimate source of the shoshonitic lower crust of the Koyukuk terrane (SIR = 0.705, NIR = 0.5125) may be continental mantle, which may have been thrust under this part of the Yukon-Koyukuk province during arc-continent collision in the early Cretaceous.
- Research Organization:
- Stanford Univ., CA (USA)
- OSTI ID:
- 7188906
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580100* -- Geology & Hydrology-- (-1989)
580300 -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
ALASKA
ALKALINE EARTH ISOTOPES
ALPHA DECAY RADIOISOTOPES
ANDESITES
BASALT
BETA DECAY RADIOISOTOPES
CENOZOIC ERA
CONTINENTAL CRUST
CRETACEOUS PERIOD
EARTH CRUST
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGY
HOURS LIVING RADIOISOTOPES
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPE RATIO
ISOTOPES
MESOZOIC ERA
NEODYMIUM 143
NEODYMIUM 144
NEODYMIUM ISOTOPES
NORTH AMERICA
NUCLEI
OCEANIC CRUST
OXYGEN COMPOUNDS
PETROLOGY
RADIOISOTOPES
RARE EARTH NUCLEI
RHYOLITES
ROCKS
SEAWATER
STABLE ISOTOPES
STRONTIUM 87
STRONTIUM ISOTOPES
TERTIARY PERIOD
USA
VOLCANIC REGIONS
VOLCANIC ROCKS
WATER
YEARS LIVING RADIOISOTOPES