Mafic magmatism and associated tectonism of the central high Cascade Range, Oregon

Journal Article · Sat Nov 10 00:00:00 EST 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB12p19623· OSTI ID:5195666

Hughes, S S ^[1]

---

1. Oregon State Univ., Corvallis (USA)

Volcanism in the central High Cascade Range has been dominated since late Miocene time by the construction of a malif platform of coalescent shield volcanoes within an intra-arc graben that developed in response to extensional plate tectonics. Lithospheric extension along the central Cascade arc is attributed to a decrease in the convergence rate of the Farallon-North American plate system since early Tertiary time. Geochemical variations, compiled from new and existing and basaltic andesites (SiO{sub 2} = 53-60 wt %): (1) early High Cascade high-alumina olivine tholeiitic (HAOT) basalts, (2) normal High Cascade HAOT basalts, (3) Mount Washington (MW) type basaltic andesites, and (4) North Sister (NS) type basaltic andesites. The implication of oceanic mantle beneath the central Cascades is consistent with the existence of the Columbia embayment into which a segment of oceanic lithosphere was compressed and thickened. Relatively high mobile large ion lithophile element and somewhat depleted high field strength elements in the basaltic andesites, considered to be secondary effects to OIB/MORB mantle evolution, are believed to believed to result from interaction of aqueous subduction-derived fluids with evolving magmas or their sources in lower crustal or upper mantle regions. The preponderance of HAOT basalts that exhibit within-plate chemical signatures argues for less input, relative to typical calc-alkaline magmatic arcs, of aqueous fluids due to subduction processes. The petrologic significance of a subduction zone beneath the Cascade arc may be restricted to the tectonic overprinting of an extensional system, caused by a reduction in convergence rate, on a waning of calc-alkaline magmatism. Physical models of the High Cascade subduction system are presented to explain the apparent chemical decoupling between calc-alkaline and tholeiitic magmatism.

• OSTI ID: 5195666
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B12; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
OREGON
VOLCANIC REGIONS
GEOCHEMISTRY
MAGMATISM
TECTONICS
ANDESITES
BARIUM
BASALT
CASCADE MOUNTAINS
CESIUM
CLASSIFICATION
CORRELATIONS
DEFORMATION
EARTH MANTLE
GEOLOGIC HISTORY
GEOLOGIC MODELS
HAFNIUM
LANTHANUM
MAGMA
MIOCENE EPOCH
NIOBIUM
PETROLOGY
PLATE TECTONICS
PLIOCENE EPOCH
POTASSIUM
QUATERNARY PERIOD
RARE EARTHS
RESERVOIR FLUIDS
RUBIDIUM
SCANDIUM
STRONTIUM
SUBDUCTION ZONES
TANTALUM
TERTIARY PERIOD
THORIUM
VOLCANISM
VOLCANOES
YTTERBIUM
ZIRCONIUM
ACTINIDES
ALKALI METALS
ALKALINE EARTH METALS
CENOZOIC ERA
CHEMISTRY
DEVELOPED COUNTRIES
ELEMENTS
FEDERAL REGION X
FLUIDS
GEOLOGIC AGES
GEOLOGY
IGNEOUS ROCKS
METALS
MOUNTAINS
NORTH AMERICA
ROCKS
TRANSITION ELEMENTS
USA
VOLCANIC ROCKS
580000* - Geosciences