Geology topics

D. Matthew Sublett

Publications and source records attributed to D. Matthew Sublett.

2 recordsLinked to original sources

USGS2024

Insights into magma storage depths and eruption controls at Kīlauea Volcano during explosive and effusive periods of the past 500 years based on melt and fluid inclusions

Kīlauea Volcano experiences centuries-long cycles of explosive and effusive eruptive behavior, but the relation, if any, between these eruptive styles and changing conditions in the magma plumbing system remains poorly known. We analyze olivine-hosted melt and fluid inclusions to determine magma storage depths during the explosive-era Keanakākoʻi Tephra eruptions (∼1500–1840 CE) and compare these results to modern effusive-era Kīlauea eruptions (1959 Kīlauea Iki, 1960 Kapoho, 2018 lower East Rift Zone). We find that shallow (1–3 km) magma storage has persisted for centuries at Kīlauea, spanning both explosive and effusive periods. In contrast, mid-crustal zones of magma storage shallowed over time, from 5 to 8 km during the Keanakākoʻi sequence to 3–5 km during the modern effusive period. Melt and fluid inclusions in high-forsterite olivine (Fo 86–89 ) trapped at shallow depths indicate that high-temperature magmas (1200 to ∼1300 °C) commonly reach depths of ≤3 km. CO 2 -rich fluid inclusions are present in olivine from all investigated Kīlauea eruptions but are larger and much more abundant in Keanakākoʻi units, which we interpret as indicating that a greater volume fraction of exsolved CO 2 -rich fluid was present in pre-eruptive Keanakākoʻi melts. Increased amounts of CO 2 -rich fluids in the Keanakākoʻi-era magmas would have increased magma buoyancy and driven rapid magma ascent, thereby increasing eruption energy and enhancing near-surface magma-water interactions compared to the current effusive period.

Hawaii↗

USGS2019

Shift in the Raman symmetric stretching band of N2, CO2, and CH4 as a function of temperature, pressure, and density

The Raman spectra of pure N 2 , CO 2 , and CH 4 were analyzed over the range 10 to 500 bars and from −160°C to 200°C (N 2 ), 22°C to 350°C (CO 2 ), and −100°C to 450°C (CH 4 ). At constant temperature, Raman peak position, including the more intense CO 2 peak ( ν +), decreases (shifts to lower wave number) with increasing pressure for all three gases over the entire pressure and temperature ( PT ) range studied. At constant pressure, the peak position for CO 2 and CH 4 increases (shifts to higher wave number) with increasing temperature over the entire PT range studied. In contrast, N 2 first shows an increase in peak position with increasing temperature at constant pressure, followed by a decrease in peak position with increasing temperature. The inflection temperature at which the trend reverses for N 2 is located between 0°C and 50°C at pressures above ~50 bars and is pressure dependent. Below ~50 bars, the inflection temperature was observed as low as −120°C. The shifts in Raman peak positions with PT are related to relative density changes, which reflect changes in intermolecular attraction and repulsion. A conceptual model relating the Raman spectral properties of N 2 , CO 2 , and CH 4 to relative density (volume) changes and attractive and repulsive forces is presented here. Additionally, reduced temperature-dependent densimeters and barometers are presented for each pure component over the respective PT ranges. The Raman spectral behavior of the pure gases as a function of temperature and pressure is assessed to provide a framework for understanding the behavior of each component in multicomponent N 2 -CO 2 -CH 4 gas systems in a future study.

Journal of Raman Spectroscopy↗