CSU Igneous Geochemistry & Petrology
Northwest Hawaiian Ridge Expedition, R/V Falkor, Pacific Ocean
Research Projects
My research interests are very broad and include geochemistry, geology, petrology, geochronology, hydrothermal systems, climate change, past glaciations, and volcanic hazards.
Bathymetry from Tozer et al., 2019
Northwest Hawaiian Ridge Geochemistry
Mantle plumes transport deep mantle material to the surface, where it melts to create volcanoes such as Hawai'i. Unique globally, the Hawaiian mantle plume is one of the strongest, hottest plumes with the highest magmatic flux that, contrary to traditional plume models, has been gaining strength with time. This study investigates the chemical and isotopic composition of the Northwest Hawaiian Ridge (48-6 million years) to investigate changes in composition with time during this increase in magmatic flux. We have found evidence that the deep mantle is composed of different compositional reservoirs that are sampled by the Hawaiian plume as it evolves through time.
Yellowstone Hydrothermal Travertine records Late Pleistocene to Present Climate Changes
Chemical changes in hot springs, as recorded by thermal waters and their mineral deposits, provide a window into the evolution of Yellowstone’s postglacial hydrothermal system. In this study, hydrothermal travertine composition and age (U-Th geochronology) is used to investigate when and why rare travertine within Yellowstone caldera formed, where today only silicious sinter hydrothermal deposits form. Results indicate that climatic changes since ~14 ka changed the chemistry of the Yellowstone hydrothermal system for thousands of years several times during the Holocene.
Mammoth Hot Springs (below), fluorescent travertine (right), Yellowstone National Park
Research conducted under NPS Permit YELL-SCI-8192
View looking towards Twin Buttes, Lower Geyser Basin, Yellowstone National Park. Research conducted under NPS permit YELL-SCI-8158; photo credit S. Hurwitz.
Large Hydrothermal Explosions in Yellowstone: Timing and Triggers
The Yellowstone Plateau Volcanic Field has many hazards, but one of the greatest is from hydrothermal explosions—forceful eruptions of the vigorously active Yellowstone hydrothermal system that throw rock, mud, steam, and boiling water up to four kilometers from the explosion site and produce craters up to two kilometers in diameter—the largest ever documented globally. Much is unknown about what triggers these events, how frequently they happen, what primes the largest explosions, and what precursory activity may indicate elevated risk. This project uses petrology, geology, ballistic mapping, and new geochronological techniques (radiocarbon, optically stimulated luminescence, U-series, and cosmogenic isotope) to understand the timing of past large explosions and the conditions that primed them.
Global Mantle Plume Geochemistry
Mantle plumes can originate at depths near the core−mantle boundary, ~2,800 km, providing invaluable information about the composition of the deep mantle and insight into convection, crust formation, crustal recycling, global heat and volatile budgets. This project is a collaborative review of the effectiveness and challenges of using isotopic analyses of plume-generated rocks (i.e., Hawai'i, Galápagos, Réunion, Kerguelen) to infer mantle composition and constrain geodynamics models, both today and throughout geologic time.
Recently published here!
Figure from Weis et al., 2023
Xenocrystic plagioclase, Crater Mountain (above); sampling a lava flow at the Goosenest, a shield volcano near Mt. Shasta (right; photo credit A. Calvert).
Back-arc Monogenetic Volcanic Plumbing Systems
Crater Mountain is a ~11 cubic km volcano erupted ~370 ka located ~40 km east of Lassen Peak in the southern Cascades Volcanic Arc. Recent paleomagnetic work has shown that the entire edifice erupted in 50-100 years! This study investigates the plumbing system that supported such a rapid eruption rate though mineral compositions (olivine, pyroxene, plagioclase, spinel), thermobarometry, and diffusion chronometry in pyroxene.
The Hawaiian Enriched Geochemical End-members: what it is and how long does it last in the plume?
Hawaiian volcanoes erupt lavas that vary geochemically temporally and spatially. The causes of this heterogeneity, and the origin of different geochemical end-members is still hotly debated. This project investigates the Hawaiian "enriched" compositional end member using isotope and elemental geochemistry, petrology, and geochronology to further investigate the size, longevity, and origin of these enigmatic lavas.
Field work in Waimea Canyon, Kaua'i, Hawai'i (right); Makapu'u point, O'ahu, Hawaii, a type section of the enriched Loa geochemical end-member. Photo credits D. Weis.
Mt Shasta Holocene Volcanism - pulsed growth of the Hotlum cone?
The Hotlum cone is the most recent cone-building episode (and is the current summit) of Mt. Shasta that commenced at ~10 ka. Holocene eruptions are young, hazardous, and it is unknown whether eruptive episodes are pulsed in time or arrive in large batches (like Shastina or Black Butte). This project uses cosmogenic isotopes to constrain eruptive tempo and therefore the potential hazard of future eruptions.
Sampling Hotlum flows, Mt. Shasta (above; photo credit A. Calvert); Shasta and Shastina (above left)