Isotopic and chemical constraints on the petrogenesis of Blackburn Hills volcanic field, western Alaska
- Geological Survey, Menlo Park, CA (United States)
The Blackburn Hills volcanic field is one of several Late Cretaceous and early Tertiary (75-50 Ma) volcanic fields in western Alaska that comprise a vast magmatic province extending from the Arctic Circle to Bristol Bay. It consists of andesite flows, rhyolite domes, a central granodiorite to quartz monzonite pluton, and small intrusive rhyolite porphyries, overlain by basalt and alkali-rhyolites. Most of the field consists of andesite flows which can be divided into two groups on the basis of elemental and isotopic composition: a group having lower ({sup 87}Sr/{sup 86}Sr){sub i}, higher ({sup 143}Nd/{sup 144}Nd){sub i}, and moderate LREE and HREE contents (group 1), and a group having higher ({sup 87}Sr/{sup 86}Sr){sub i}, lower ({sup 143}Nd/{sup 144}Nd){sub i}, and lower HREE contents. Basalts are restricted to the top of the stratigraphic section, comprise the most primitive part of group 1 (({sup 87}Sr/{sup 86}Sr){sub i} = 0.7033; ({sup 143}Nd/{sup 144}Nd){sub i} = 0.5129), and have trace-element ratios that are similar to those of oceanic island basalts (OIBs). Although some workers have suggested that the volcanic field is underlain by old continental crust, none of the data require the presence of Paleozoic or Precambrian continental middle or upper crust under this part of the volcanic field. However, the ultimate source of some of the rocks in the Yukon-Koyukuk province that have high {sup 87}Sr/{sup 86}Sr and low {sup 143}Nd/{sup 144}Nd ratios may be old sub-continental mantle and/or lower crust, which was previously subducted beneath the Yukon-Koyukuk province during Early Cretaceous arc-continent collision.
- OSTI ID:
- 7206237
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:12; ISSN GCACA; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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580000* -- Geosciences
ALASKA
ALKALINE EARTH ISOTOPES
ALPHA DECAY RADIOISOTOPES
ANDESITES
BASALT
BETA DECAY RADIOISOTOPES
CENOZOIC ERA
CHEMICAL COMPOSITION
CHEMISTRY
CONTINENTAL CRUST
CRETACEOUS PERIOD
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ELECTRON CAPTURE RADIOISOTOPES
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GEOCHEMISTRY
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ISOTOPE RATIO
ISOTOPES
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METALS
NEODYMIUM 143
NEODYMIUM 144
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NORTH AMERICA
NUCLEI
PETROCHEMISTRY
PETROGENESIS
RADIOISOTOPES
RARE EARTH NUCLEI
RARE EARTHS
RHYOLITES
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STABLE ISOTOPES
STRONTIUM 86
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VOLCANIC REGIONS
VOLCANIC ROCKS
YEARS LIVING RADIOISOTOPES