U/Pb geochronologic and petrologic studies in the Blue Mountains terrane, northwestern Oregon and westernmost central Idaho: implications for pre-Tertiary tectonic evolution
This assemblage includes tectonically juxtaposed, variably deformed and metamorphosed Permo-Triassic volcanic-plutonic complexes and related sedimentary rocks, ultramafic-mafic-silicic igneous suites, polymict melange tracts, and thick sequences of Upper Triassic to Upper Cretaceous volcaniclastic sediments. Numerous undeformed mesozonal gabbroic to granodioritic plutons of Late Jurassic to Early Cretaceous age cross-cut these older rocks indicating juxtaposition of the older components took place prior to emplacement of the plutons. Field, petrologic, and U-Pb geochronologic investigation of igneous and metamorphic components of this region demonstrate the Permo-Triassic Seven Devils Group was constructed, at least in part, within and upon a Late Carboniferous basement whose protolith was plutonic. Geochemical data suggest this basement is of oceanic origin. Regional U-Pb geochronologic data from pre-Jurassic igneous and meta-igneous components throughout this region reveal an age range of plutonic activity of 279 Ma to 215 Ma. This fact considered in concern with field evidence, paleomagnetic evidence, and paleontologic data supports the conclusion that although there are distinct structural/stratigraphic blocks within this region, they are vestiges of a single, ensimatic convergent margin system that was magmatically and tectonically active intermittently from Early Permian to Early Cretaceous time.
- Research Organization:
- California Univ., Santa Barbara (USA)
- OSTI ID:
- 6409382
- Country of Publication:
- United States
- Language:
- English
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580100* -- Geology & Hydrology-- (-1989)
580300 -- Mineralogy
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& Rock Mechanics-- (-1989)
ACTINIDES
AGE ESTIMATION
BASEMENT ROCK
ELEMENTS
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGY
IDAHO
IGNEOUS ROCKS
INTRUSION
LEAD
MESOZOIC ERA
METALS
METAMORPHIC ROCKS
MOUNTAINS
NORTH AMERICA
OREGON
PALEOZOIC ERA
PETROLOGY
PLUTONIC ROCKS
ROCKS
TECTONICS
URANIUM
USA
VOLCANIC ROCKS