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THE TECTONOMAGMATIC EVOLUTION OF THE LATE CENOZOIC OWYHEE PLATEAU, NORTHWESTERN UNITED STATES

Shoemaker, Kurt A.
http://rave.ohiolink.edu/etdc/view?acc_num=miami1082580947

Abstract Details

2004, Doctor of Philosophy, Miami University, Geology and Environmental Earth Science.
The Owyhee Plateau (OWP) is an intermontane basalt plateau located at the nexus of the Snake River Plain (SRP) and Oregon Plateau/High Lava Plains (OP/HLP) volcanic provinces, which has been the locus of nearly continuous basaltic magmatism since 17 Ma. Between 17-11 Ma, generally evolved basaltic lavas related to the Steens flood basalt event and Oregon-Idaho Graben (OIG) volcanism were erupted around the extending margins of the OWP. Beginning 11 Ma, less differentiated olivine tholeiites were erupted throughout the OWP proper, from low shield vents with alignments consistent with regional stress fields. After 5 Ma, volcanism retreated to the margins of the OWP, ultimately becoming limited to the northern transition region between the OWP and the OIG. The youngest basalts in the OWP region are <0.25 Ma mildly alkaline basalts erupted in this transition region. The OWP is the only location in the northwestern US where basalt types characteristic of the OP/HLP (high-alumina olivine tholeiite, HAOT) and the SRP (SRP-type olivine tholeiite, SROT) occur together in significant quantity, in close spatial and temporal association, and with a full spectrum of compositions intermediate between the two. Sr, Nd, and Pb isotopic characteristics are decoupled from bulk chemistry, and reflect time-dependent variations in contributions from different lithospheric and sublithospheric mantle reservoirs. I propose that the OWP is a discrete tectonomagmatic entity within the North American Cordillera resulting from Sevier-style thrusting of accreted lithosphere over a westward-projecting shelf of Precambrian cratonic lithospheric mantle. Low-angle subduction during Laramide time trapped a layer of asthenospheric mantle below the OWP region, which was subsequently modified by fluids and melts from the subducting Farallon slab. Foundering of the Farallon slab caused upwelling of hot, fertile asthenosphere that mixed with this volatile-enriched layer, triggering Steens volcanism. Subsequent melt production from fluid- and melt-metasomatized cratonic and accreted mantle reservoirs beneath the OWP produced the post-11 Ma HAOT-SROT association. The retreat of volcanism to the margins of the OWP, the isotopic character of these lavas, and the absence of endmember SROT on the OWP after 5 Ma reflect the exhaustion of fusible components from the Precambrian lithospheric mantle shelf.
William Hart (Advisor)
288 p.
Geochemistry; Geology
basalt; Owyhee Plateau; high alumina olivine tholeiite; Oregon Plateau; Snake River Plain; magma genesis; mantle; mantle metasomatism; subcontinental lithospheric mantle; tectonic; tectonomagmatic evolution

Recommended Citations

Citations

  • Shoemaker, K. A. (2004). THE TECTONOMAGMATIC EVOLUTION OF THE LATE CENOZOIC OWYHEE PLATEAU, NORTHWESTERN UNITED STATES [Doctoral dissertation, Miami University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=miami1082580947

    APA Style (7th edition)

  • Shoemaker, Kurt. THE TECTONOMAGMATIC EVOLUTION OF THE LATE CENOZOIC OWYHEE PLATEAU, NORTHWESTERN UNITED STATES. 2004. Miami University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=miami1082580947.

    MLA Style (8th edition)

  • Shoemaker, Kurt. "THE TECTONOMAGMATIC EVOLUTION OF THE LATE CENOZOIC OWYHEE PLATEAU, NORTHWESTERN UNITED STATES." Doctoral dissertation, Miami University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=miami1082580947

    Chicago Manual of Style (17th edition)

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This open access ETD is published by Miami University and OhioLINK.