Dr Rowe’s research is in geochemistry and mineralogy, igneous petrology, and volcanology. Broad interests include the cycling of magmatic volatiles and volatile metals from the mantle to the surface, and into hydrothermal systems, and the processes relating magma generation and evolution to tectonic sett
ings, such as continental rifts and subduction zones. He specialises in x-ray diffraction (XRD) analysis and in situ geochemical techniques (including electron microprobe analysis, laser ablation ICP-MS, and secondary ion mass spectrometry) to measure spatial changes in the chemical compositions of geologic materials. Recent work has focused on the characterization of amorphous and partially crystalline materials in volcanic and hydrothermal settings as potential analogues for other planetary systems associated with the early development of life.
The Columbia River Basalt Group (western United States) is Earth’s youngest and best-studied flood basalt province, but attempts to link it with mid-Miocene global change have proven elusive. Part of the difficulty lies in a lack of comprehensive data for volatile emissions from the most intense main phase of activity. We present measurements of sulfur contents in magmas that erupted to form the Wapshilla Ridge Member and associated units of the Grande Ronde Basalt, the most voluminous portion of the Columbia River Basalt Group, erupted at the time of peak magma flux. We sampled melt inclusions and host glasses preserved in near-vent phreatomagmatic deposits associated with the voluminous lavas. Sulfur contents of melt inclusions range up to 0.19 wt% S, while host glasses are variably degassed with 0.01–0.13 wt% S. Incomplete degassing of glassy lapilli is attributed to phreatomagmatic quenching in the vent. The magmatic S contents in the very voluminous (∼40,000 km3) Wapshilla Ridge Member scale up to 242–305 Gt SO2 release to the atmosphere over a maximum time period of 94 k.y. The time of the eruption is close to that of a global temperature drop near the peak of the Miocene Climatic Optimum, but refinement of eruption tempo is needed before a cause-and-effect relation can be established.
Read MoreLava domes pose a significant hazard to infrastructure, human lives and the environment when they collapse. Their stability is partly dictated by internal mechanical properties. Here, we present a detailed investigation into the lithology and composition of a < 250-year-old lava dome exposed at the summit of Mt. Taranaki in the western North Island of New Zealand. We also examined samples from 400 to 600-year-old block-and-ash flow deposits, formed by the collapse of earlier, short-lived domes extruded at the same vent. Rocks with variable porosity and groundmass crystallinity were compared using measured compressive and tensile strength, derived from deformation experiments performed at room temperature and low (3 MPa) confining pressures. Based on data obtained, porosity exerts the main control on rock strength and mode of failure. High porosity (> 23%) rocks show low rock strength (< 41 MPa) and dominantly ductile failure, whereas lower porosity rocks (5–23%) exhibit higher measured rock strengths (up to 278 MPa) and brittle failure. Groundmass crystallinity, porosity and rock strength are intercorrelated. High groundmass crystal content is inversely related to low porosity, implying crystallisation and degassing of a slowly undercooled magma that experienced rheological stiffening under high pressures deeper within the conduit. This is linked to a slow magma ascent rate and results in a lava dome with higher rock strength. Samples with low groundmass crystallinity are associated with higher porosity and lower rock strength, and represent magma that ascended more rapidly, with faster undercooling, and solidification in the upper conduit at low pressures. Our experimental results show that the inherent strength of rocks within a growing dome may vary considerably depending on ascent/emplacement rates, thus significantly affecting dome stability and collapse hazards.
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