Petrochemical evolution of high cascade volcanic rocks in the Three Sisters region, Oregon
Multi-element abundances and petrographic data are compiled for a suite of 50 volcanic rocks and selected mineral separates located within the Three Sisters area. Major element oxides, obtained by x-ray fluorescence and atomic absorption spectrophotometry, and trace element concentrations, obtained by sequential instrumental neutron activation analyses, enable classifications of normal basalts, divergent basalts, Mount Washington (MW) and North Sister (NS) type basaltic andesites, dacites and rhyodacites. Petrochemical types and geochemical models are evaluated in light of field studies, regional geologic environment and comparisons with similar systems. High-alumina olivine tholeiites exhibit low Fe' values and fractionated abundances of K, Ba, Sr, REE and Sc which produce nonchondritic monotonic patterns relative to ionic radii. Primary basalts are modeled as 14% melts, with minor olivine crystallization, from a LIL element-enriched spinel Iherzolite source. A comprehensive model of High Cascades volcanic evolution is presented which incorporates a series of events in a subduction zone-mantle-crust system: Hydrous fluids, expelled from a dehydrating subducted slab, become enriched in incompatible elements through processes of liquid extraction and small amounts of partial melting. These fluids ascend through the overlying mantle wedge contaminating and catalyzing mafic melts which accumulate and fractionate in upper mantle and lower crust regions. Mafic magmas erupt as near-primary liquids or are intruded into upper crust regions where extensive fractionation produces siliceous dacites and rhyodacites.
- OSTI ID:
- 5693790
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
Similar Records
Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: Role of crystal fractionation and mantle heterogeneity
Petrogenesis of Late Cenozoic volcanic rocks from the Raton-Clayton volcanic field, northeastern New Mexico and southeastern Colorado
Related Subjects
OREGON
VOLCANIC ROCKS
PETROCHEMISTRY
ABUNDANCE
ACTIVATION ANALYSIS
BASALT
NEUTRON REACTIONS
X-RAY FLUORESCENCE ANALYSIS
BARYON REACTIONS
CHEMICAL ANALYSIS
FEDERAL REGION X
HADRON REACTIONS
IGNEOUS ROCKS
NONDESTRUCTIVE ANALYSIS
NORTH AMERICA
NUCLEAR REACTIONS
NUCLEON REACTIONS
ROCKS
USA
X-RAY EMISSION ANALYSIS
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)