Award Date

December 2023

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Kevin Konrad

Second Committee Member

Andrew Martin

Third Committee Member

Arya Udry

Fourth Committee Member

Jason Steffen

Number of Pages

105

Abstract

Investigation into seamounts that stem from intraplate volcanism—that is volcanism occurring far from plate boundaries—presents an opportunity to deconvolve processes associated with mantle compositional heterogeneities and melting dynamics. Upwelling and decompression of thermochemically anomalous mantle plumes is the primary mechanism for significant intraplate volcanism; however, many seamounts dotted across the Pacific Plate do not correlate spatially, temporally, or geochemically with mantle plume volcanism. One region of enigmatic volcanism in the ocean basins that is not clearly attributable to plume-derived magmatism are the Geologist Seamounts and the wider South Hawaiian Seamount Province (∼19°N, 157°W). Here we present merged multibeam (<100 m) and satellite altimetry bathymetric maps of the Geologist Seamounts region, new 40Ar/39Ar age determinations, and major and trace element geochemistry for six remote-operated vehicle recovered igneous rock samples (NOAA-OER EX1504L3) and two dredged samples (KK840824-02) from the Geologist Seamounts. The new ages indicate volcanism was active from 89–86 Ma and 73–72 Ma, inferring that, in conjunction with previous ages of ~83 Ma, seamount emplacement initiated near the paleo Pacific-Farallon spreading ridge and volcanism continued for at least a ~17 Ma period. Geochemical analyses indicate that Geologist Seamounts lava flows are highly alkalic and represent low-degree partial mantle melts primarily formed from a mixture of melting within the garnet and spinel stability field prior to eruption. Using the new age and chemical constraints three separate formation models for the Geologist Seamounts are tested: (1) a mantle-plume derived origin, (2) a shear-driven upwelling origin, and (3) a lithospheric extension origin. The ages and morphological characteristics infer the seamounts were likely not related to the Euterpe Plume (Musician Seamounts) or a different extinct plume. Shear driven upwelling cannot account for ~17 Ma of volcanism in a limited geographic region, nor for the oblique orientation of Geologist Seamounts relative to paleo spreading direction as shear driven upwelling forms seamount chains mirroring the direction of crustal spreading. Lastly, we build upon previous models that local microblock formation and rotation corresponded with regional lithospheric extension and the formation of the Geologist Seamounts. Using available multibeam bathymetry and magnetic reversal data, we propose the microblock was bounded by the Molokai and short-lived Kana Keoki Fracture Zones. Regional deformation and corresponding volcanism among the Geologist Seamounts associated with the microblock potentially occurred in pulses contemporaneous to independently constrained changes in Pacific Plate motion vectors at ca. 85 and 75 Ma—indicating that major changes in plate vectors can generate intraplate volcanism.

Keywords

Argon Geochronology; Extension; Mantle Plumes; microblock; Pacific; Plate motion

Disciplines

Geochemistry | Geology | Oceanography and Atmospheric Sciences and Meteorology

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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