Geochemical and petrological observations of the June Lake Basalt, Eastern California

Author

• Daniel Jacob AbelFollow

Graduation Date

Summer 2026

Document Type

Thesis

Program

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

Committee Chair Name

Brandon Browne

Committee Chair Affiliation

Cal Poly Humboldt Faculty or Staff

Second Committee Member Name

Jacky Baughman

Second Committee Member Affiliation

Cal Poly Humboldt Faculty or Staff

Third Committee Member Name

Laura Levy

Third Committee Member Affiliation

Cal Poly Humboldt Faculty or Staff

Keywords

Eastern California, June Lake, Cinder cone, Geology, Basalt, Volcano, Mammoth Mountain, Mono-Inyo Chain, Geochemistry, Petrology, Mineral chemistry, Magma evolution

Subject Categories

Geology

Abstract

The June Lake basalt is a monogenetic cinder cone and 11-km-long lava flow in eastern California located ~10 km NW of the Long Valley caldera. The stratigraphic position of the June Lake basalt between Tahoe and Tioga glacial deposits suggests an eruption age of only ~20-45ka. This age places the June Lake Basalt among the youngest volcanic eruptions in the Long Valley-Mono Basin region, where volcanic activity spans from the late Pliocene to the Holocene. The goal of this study is to use field observations coupled with whole-rock and crystal geochemical analyses to investigate the magma source and pre-eruption magma storage conditions of the June Lake basalt. Geologic mapping and sampling of the cinder cone, lava flow, and rafted cinder cone deposits occurred during the summers of 2024 and 2025. Whole-rock concentrations of 29 major and trace elements in 32 lava and cinder samples were measured by X-ray fluorescence. Back-scattered electron images and in situ concentrations of major and minor elements in plagioclase, clinopyroxene (CPX), and olivine crystals from cinder and lava samples were measured by electron microprobe. Whole-rock geochemical results show that the June Lake eruption produced a compositionally-zoned suite of basaltic trachyandesite lava, where the cinder cone and lavas produced early in the eruption contain higher concentrations of TiO₂, FeO, P₂O₅, Ba, Rb, Y, and Nb and lower concentrations of MgO, Al₂O₃, Ca, Ni, and Sr compared to lavas produced late in the eruption. In situgeochemical results of common crystals in the June Lake cinder and lavas reveal abundant disequilibria textures, a range of olivine and CPX compositions, and multiple populations of plagioclase crystals defined by different Anorthite (An) core and rim compositions that record both open and closed system magma evolution. Observations of field relations combined with whole-rock and crystal geochemical analyses are consistent with a multi-stage and trans-crustal pre-eruption magma storage scenario involving the interaction of basaltic magma from the lower crust, magma mixing, incorporation of gabbroic mush, and multiple storage reservoirs prior to eruption. These results highlight the importance of integrating field observations with mineral and whole-rock geochemistry to reconstruct the evolution of magma systems that feed small monogenetic basaltic eruptions.

Citation Style

APA

Recommended Citation

Abel, Daniel Jacob, "Geochemical and petrological observations of the June Lake Basalt, Eastern California" (2026). Cal Poly Humboldt theses and projects. 2591.
https://digitalcommons.humboldt.edu/etd/2591