Graduation Date

Summer 2018

Document Type

Thesis

Program

Master of Science degree with a major in Environmental Systems, option Geology

Committee Chair Name

Brandon Browne

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Jasper Oshun

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Melanie Michalak

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Mark Hemphill-Haley

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Geology

Abstract

Quaternary mafic volcanism in the western Basin and Range and in the southeastern Sierra Nevada is largely controlled by extensional stresses that promote magma generation through decompression melting of the lithospheric and asthenospheric mantle. Where volcanism occurs in the Sierra Nevada, like at the Golden Trout Volcanic Field GTVF), the eruption rate, number of vents, and eruption volume is an order of magnitude less than at neighboring Basin and Range volcanic fields such as the Big Pine Volcanic Field (BPVF). To determine the factors that cause these differences in adjacent and contemporaneous volcanic fields, I sampled rocks from both fields and analyzed major and trace element compositions of olivine phenocrysts via electron microprobe, stable oxygen isotope compositions of olivine via laser fluorination, and whole-rock radiogenic isotope compositions via HR MC-ICP-MS. Major and trace element compositions between the GTVF and BPVF are overlapping with Fo values ranging from 67.61 to 88.77 and 77.72 to 88.13, respectively. δ18O values are higher at GTVF (5.680 to 6.520 ‰) than at BPVF (5.554 to 5.750 ‰). Whole rock 87Sr/86Sr and 143Nd/144Nd ratios at the GTVF range from 0.705420 to 0.706026 and 0.512492 to 0.512604 and overlap with values from BPVF and other regional volcanic fields. Similar mantle source compositions between the GTVF and BPVF indicate that differences in eruption rate, number of vents, and eruption volume are resultant from greater amounts of crustal contamination at GTVF. The presence of magmas with similar source compositions in and near the southern Sierra Nevada suggests that the regional extension characteristic of the Basin and Range has affected the southeastern Sierra Nevada block. Unfaulted crust in regionally extensional tectonic settings limits magma ascent, but doesn’t seem to inhibit magma genesis at depth.

Citation Style

GSA

Share

Thesis/Project Location

 
COinS