Nathan David Brown

Southern Italy preserves a well-studied record of deformation and uplift related to migrating oblique collision, trench retreat, and tearing of subducted ocean slabs. However, the surface expression of these processes is incompletely understood due to a lack of reliable ages for marine terraces >200 m above sea level (masl). Here we use luminescence methods to date shallow marine sands from terraces ~ 100 to 1,000 masl in southern Calabria and interpolate the results with regional surface mapping. Burial ages overlap across the full range of sampled elevations with a weighted mean of 118.8 ± 8.7 thousand years before present (ka). Calculated uplift rates vary from 12 mm yr-1 and throw rates on active normal faults are 0.8–4.2 mm yr-1. We infer that rapid post-120 ka uplift is an ongoing isostatic response to an active tear in the Ionian slab, consistent with recent geophysical observations and predictions of geodynamic models. These results have important implications for assessment of geohazards in southern Calabria and northeast Sicily, one of the highest seismic risk areas in the Mediterranean region.

Southern Italy preserves a well-studied record of deformation and uplift related to migrating oblique collision, trench retreat, and tearing of subducted ocean slabs. However, the surface expression of these processes is incompletely understood due to a lack of reliable ages for marine terraces >200 m above sea level (masl). Here we use luminescence methods to date shallow marine sands from terraces ~ 100 to 1,000 masl in southern Calabria and interpolate the results with regional surface mapping. Burial ages overlap across the full range of sampled elevations with a weighted mean of 118.8 ± 8.7 thousand years before present (ka). These ages, combined with map data and fault-zone morphology, indicate that the terraces are erosional remnants of a single, once-continuous deformed surface. Calculated uplift rates vary from 12 mm yr-1 and throw rates on active normal faults are 0.8–4.2 mm yr-1. We infer that rapid post-120 ka uplift is an ongoing isostatic response to an active tear in the Ionian slab, consistent with recent geophysical observations and predictions of geodynamic models. These results have important implications for assessment of geohazards in southern Calabria and northeast Sicily, one of the highest seismic risk areas in the Mediterranean region.

Why do some earthquakes repeatedly rupture discrete fault segments, while others rupture entirefaults? Answering this remains fundamental to improving seismic hazard analysis and, in turn, tohazard preparedness and mitigation efforts. Over the past two decades, several mechanisms forrupture termination and propagation have been proposed, including variation in geometric,structural, and geologic characteristics of faults (Aki, 1979; King and Nabelek, 1985). In this studywe investigated the Eastern Precordillera (EPC) of the Andes Mountain in Argentina which isclassified into three segments: Villicum, Las Tapias, and Zonda–Pedernal (Siame et al., 2002) todetermine whether the historical surface ruptures associated with major earthquakes crossed thesegment boundaries, or whether rupture propagation was arrested by structural asperitiesindicating an asperity-controlled behavior. To address this, we conducted a new paleoseismicinvestigation at this site to complement and integrated with the preexisting dataset to evaluate theextent of past surface ruptures in relation to fault geometry and structural segmentation. We havecomplied earthquake timing of six earthquakes. Preliminary results suggest that, of the sixidentified events, only one earthquake appears to have ruptured across an ~18 km-long segmentgap, including a ~4 km stepover and notable lithologic variation evidence consistent with a multi-segment rupture event.

The Mission Creek fault strand (MCF) of the San Andreas Fault is proposed to be the primary strand accommodating slip between the Pacific and North American plates in Southern California, but its Holocene activity northwest of Indio is debated. This study presents new depositional ages for alluvial deposits near the mouth of the Mission Creek drainage to investigate potential Holocene activity of the MCF. We estimate a mean depositional age of 0.7 ± 0.2 ka for the alluvium deposited in the drainage valley, contradicting previously inferred ages of >3–18 ka. The young ages for alluvium, often indistinguishable from the age of modern alluvium, suggest that grains are transported during high-energy flash flood–like events. A comparison of luminescence and cosmogenic ¹⁰ Be ages from alluvial surfaces adjacent to the Mission Creek suggests a possible reworking event at ∼30 ka. Young alluvium ages, together with evidence for frequent flash floods, suggest that this site is rapidly resurfacing and therefore unlikely to preserve surficial rupture signatures older than a few hundred years. Therefore, the lack of observable offsets in deposits overlying the MCF does not imply Holocene inactivity.

Hydrothermal explosions are a significant geological hazard in some active volcanic systems; however, the timing and triggering mechanisms of these explosions are poorly constrained. This study applies luminescence dating techniques to hydrothermal explosion deposits in the Yellowstone Plateau volcanic field to constrain explosion chronologies and evaluate potential triggering mechanisms. We tested four luminescence dating techniques: K-feldspar post-infrared infrared stimulated luminescence (pIRIR ₂₂₅ ), quartz blue light optically stimulated luminescence (BLOSL), quartz blue thermoluminescence (BTL), and quartz red thermoluminescence (RTL). The pIRIR ₂₂₅ and RTL protocols produce consistent age estimates that agree with independent radiocarbon ages and with the timing of the Pinedale deglaciation. This study focuses on two craters, Mary Bay, along the northern shore of Yellowstone Lake, and Pocket Basin in Lower Geyser Basin. The mean pIRIR ₂₂₅ ages from Mary Bay deposits (11.99 ± 0.68 ka) agree with previous radiocarbon constraints. The mean pIRIR ₂₂₅ results from Pocket Basin deposits (13.44 ± 1.06 ka) suggest a history of explosion following Pinedale deglaciation, followed by recent hydrothermal alteration. Luminescence dating techniques are a promising tool for reconstructing the timing of hydrothermal explosions in the Late Pleistocene and Holocene, helping to constrain recurrence intervals of the largest hydrothermal systems, informing risk, and improving hazard assessments.

Luminescence dating researchers benefit from many community-led software packages. These packages assist with data reduction, statistical modeling, calculation of dosimetric values, and plot production. Yet few resources are simultaneously intuitive, meant for simulating the reduction and growth of luminescence signals, and accessible to non-specialists. The Luminescence Sample Simulator (LuSS) is an application with a graphical user interface that simulates how apparent age and fractional saturation respond to three key scenarios in luminescence dating: sunlight exposure, heat exposure, and burial. Users can simulate these scenarios for an individual cobble or sand grain, or for a population of 100 sand grains. The underlying kinetic parameters can be adjusted manually or taken from a built-in library of published values. Plots of apparent age histograms, luminescence depth profiles, or fractional saturation and apparent age histories are visualized and can be exported. LuSS is written in MATLAB and can operate as a free-to-use, standalone application, or as an app within an existing MATLAB installation. A typical user workflow and three worked examples show how LuSS can model luminescence signal evolution in response to geologic scenarios. Limitations of LuSS include its inability to capture athermal fading or between-grain variability in geologic dose rate or sensitivity.

Over the past fifteen years, trapped-charge (T-C) thermochronometry has been established as an ultra-low temperature (<80 °C) thermochronometric system. Its novelty is its ability to resolve rock cooling within the final few km of Earth's surface, as well as rock-surface temperature changes since the Last Glacial Maximum to the present day. Deriving temperature histories from the luminescence signals of feldspar minerals, or the electron spin resonance signals of quartz minerals, requires the modelling of both signal accumulation and signal loss in response to mineral exposure to ionizing radiation and temperature, as well as athermal signal losses for feldspar minerals. Two open-source libraries have been developed in MATLAB that allow different numerical models to be used for this purpose; the first is applicable to the infra-red stimulated luminescence (IRSL) of feldspar minerals (OSLThermo) and the second to the electron spin resonance (ESR) signal of quartz minerals (ESRThermo). These libraries have been made available in GITHUB and this contribution describes their broad structure, the T-C models that have been implemented and their practical use. Codes are available for download on GitHub: https://github.com/GeorginaKing/OSLThermo for luminescence thermochronometry & https://github.com/GeorginaKing/ESRThermo for ESR thermochronometry.

Rapid warming and permafrost thaw across Arctic landscapes are projected to drastically accelerate local erosion rates and sediment fluxes to downstream systems and the communities that rely on them. However, interpreting this signal of change first requires disentangling the relative contributions of postglacial landscape responses, periglacial processes, and modern warming to observed changes in erosion. To explore this problem, we combine a suite of geochronometers to examine erosion and deposition rates over 102–107 timescales across a periglacial alluvial fan and catchment system on the former margin of the Laurentide Ice Sheet in the Aklavik Range of Northwest Territories, Canada. We use low-temperature thermochronology (apatite fission-track and apatite/zircon (U-Th)/He) to constrain the long-term (~10 Ma) erosion rate of the Aklavik Range at ~0.09 mm/yr. Cosmogenic nuclide (10Be) dating of erratic boulders near the Laurentide glacial limit in the Aklavik Range suggest that the region was last glaciated prior to ~19.6 ka, about 1.1 ka earlier than previously thought. Postglacial fan- and catchment-derived erosion rates (~1-7 mm/year), calculated using mass balance, detrital 10Be concentrations, radiocarbon (14C) geochronology, and optically stimulated luminescence (OSL) dating, exceed background rates by an order of magnitude or more. These results underscore that contributions to observed erosion rates from modern warming must account for persistent postglacial landscape disequilibrium in Arctic ice-marginal settings.