Geophysics and Tectonics Seminar - spring-2024
Chasing Darwin’s Shadow: Geophysics and Evolution in the Galapagos
April 3, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Mark Richards - University of Washington
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In the autumn of 1835, young geologist Charles Darwin spent a month exploring the Galapagos Islands, coming to the realization that these new and ephemeral volcanic habitats had given rise to new species of otherwise familiar creatures, and leading him to conclude that biological evolution was a fact, with natural selection as the primary mechanism. The active Galapagos mantle plume (“hotspot”) and mid-ocean ridge system is a spectacular showplace for plume-ridge interaction, with geophysical and geochemical signatures that elucidate upper mantle dynamics and evolution, and a geological history of continuously emerging and subsiding island habitats that have provided stepping stones for at least 20 million years of evolutionary divergence for mainland-derived species such as iguanas, tortoises, and finches. This talk will discuss how several different lines of geophysical investigations are revealing new secrets about the geological evolution of the Galapagos plume-ridge system, how these discoveries are helping us understand volatile (H2O) fluxes from the deep mantle, and new horizons for how to formally combine increasingly rich genetic constraints on evolutionary biology with the geological history of ancient island habitats to obtain a more integrated understanding of geo-biological evolution in ocean island systems.
How High Was Sea Level in the Holocene?
April 4, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Roger Creel - Woods Hole Oceanographic Institution
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I will present work that aims to constrain sea-level change over the last glacial cycle by merging relative sea-level observations and glacial isostatic adjustment models via Bayesian statistical frameworks. I will first reconstruct Norwegian sea level over the last 16,000 years. I will then infer global mean sea level during the Holocene (11.7 - 0 thousand years ago), which is the last time global temperatures may have exceeded early Industrial (1850 CE) values. I will show that the available evidence is consistent with global mean sea level that exceeded early industrial levels in the mid-Holocene. I will also present the first quantitative estimates of Holocene mountain glacier volume and sea level change due to ocean thermal expansion.
Spatiotemporal Imaging of the Earth’s Near Surface with Fiber-Optic Sensors
April 10, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Yan Yang - Caltech
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Understanding the Earth's subsurface is essential for mitigating natural hazards and ensuring environmental sustainability. Seismological methods, which measure seismic velocity (v) and its relative temporal changes (dv/v), provide a 4D (space-time) view of the subsurface. However, high-resolution imaging and monitoring of the near surface—the top tens of meters subject to rapid spatiotemporal changes—remains challenging. This is primarily due to the prohibitive costs of dense seismic arrays necessary for capturing high-frequency signals that can probe shallow depths. Distributed Acoustic Sensing (DAS) offers an affordable solution by converting telecommunication fiber-optic cables into ultra-dense seismic arrays, enhancing our ability to study environmental phenomena with details as fine as tens of meters. When combined with seismic ambient noise interferometry, DAS enables time-lapse imaging of the near surface. In the talk, I will present an exemplary work in Ridgecrest, California, demonstrating a comprehensive spatiotemporal imaging approach for the near surface. The results provide new insights into high-resolution urban seismic hazard mapping and vadose zone soil moisture monitoring during California's drought periods.
Bridging Seismology and Oceanography with Seafloor Fiber-Optic Sensing
April 11, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Ethan Williams - University of Washington
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Observational geophysics conventionally relies on point sensors, from locating earthquakes and imaging subsurface structure with seismometers to forecasting coastal wave heights and detecting tsunamis with buoys. The emerging field of fiber-optic sensing offers a fundamentally different paradigm: distributed instead of point sensing, leveraging pre-existing telecommunications infrastructure to construct inherently multi-scale images of Earth’s dynamic processes over distances >100 km using a single instrument. In two topical vignettes, I will summarize some of my recent and ongoing research utilizing distributed acoustic sensing (DAS) on seafloor cables at the intersection of seismology and oceanography. (1) Offshore site characterization and ground motion. From quantitative estimation of tsunamigenic landslide hazard to interpretation of the turbidite record as a paleo-seismometer, accurate models of shallow sediment shear-wave velocity structure are required to anticipate the distribution of offshore ground motion in great earthquakes. Yet, because the water column is opaque to shear waves, this structure often remains poorly constrained, especially in the top 100s of meters. Interferometry of ambient seismic Scholte waves recorded with DAS reveals a typical power-law shear wave velocity profile immediately below the seafloor, with Vs30 as low as 150 m/s at locations ranging from the North Sea to the Oregon margin. This value is nearly an order of magnitude lower than used in Cascadia M9 simulations and in previous studies of turbidite triggering, suggesting that offshore site amplification has been systematically underestimated. With physics-based modeling of ambient seismic noise amplitude, I will show site amplification varies by nearly an order of magnitude over sub-kilometer distances and is strongly correlated with topography. Finally, I will summarize an ongoing experiment offshore southern Alaska combining seafloor compliance under ocean surface gravity wave loading with recordings of over 3000 local earthquakes to infer the nonlinear response of shallow sediment to strong ground motion. (2) Long-period DAS: from ocean mixing to seafloor geodesy. Where fiber-optic cables are unburied and exposed at the seafloor, DAS is also sensitive to temperature fluctuations from internal wave and tide dynamics in the bottom boundary layer, a region of enhanced ocean mixing but scarce observations. I will highlight two novel DAS datasets and discuss ongoing work to quantify rates of turbulent kinetic energy dissipation. DAS data recorded on a power cable across the Strait of Gibraltar show temperature transients up to 4 K associated with passing large-amplitude internal waves propagating on the near-surface thermocline. On the slope of Gran Canaria, an island off the coast of west Africa, temperature variability of about 2 K at 1-km depth decreasing to 0.2 K at 2.5-km depth reveals the bore-like propagation of the nonlinear internal tide at locations where the slope is near critical. The latter dataset also includes a long-wavelength signal proportional to the barotropic tidal pressure, including the lunar fortnightly variation, likely due to elastic strain from ocean-tidal loading. The demonstrated sensitivity of order 1 microstrain at 14-day period suggests that contemporary DAS already possesses sufficient long-period stability for (some) seafloor geodetic applications.
Geophysics of the Changing Hydro-cryosphere: From California’s Aquifers to Greenland’s Supraglacial Lakes
April 17, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Stacy Larochelle - Columbia University
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Human activity and climate change are rapidly transforming Earth's hydrological and glaciological systems, posing critical challenges for global water security, coastal communities, and ecosystem resilience. In recent years, geophysics has become pivotal in both tracking hydro-cryospheric changes and unveiling the physics behind them. In this talk, I will discuss insight gained from applying a comprehensive geophysical approach to two critical and rapidly evolving systems: The Sacramento Valley aquifer system in California and supraglacial lakes on the Greenland Ice Sheet. Combining GNSS, InSAR, and GRACE/-FO satellite observations with in situ groundwater level measurements and lithologic logs in the Sacramento Valley reveals that the aquifer system has transitioned from a primarily reversible to irreversible deformation regime over the 2021-22 drought, indicating severe permanent compaction and loss of aquifer storage capacity that pose a serious threat to California’s water resources and infrastructure. In Greenland, we harness observations from on-ice GNSS stations, satellite imagery, ice-penetrating radar, seismometers, and water pressure instruments to decipher how meltwater lakes that form at the surface of the ice sheet interact through englacial stress to rapidly funnel surface meltwater to the ice-sheet bed and modulate ice basal sliding. Together, these case studies highlight the importance of multi-technique geophysical surveys in understanding the Earth’s changing hydro-cryosphere and enabling space-based monitoring at the global scale.
New Earth and Planetary Science Discoveries Enabled by the Optical Fiber Sensing Revolution
April 17, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Bradley Lipovsky - University of Washington
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Optical fiber sensors constitute the biggest revolution in geophysical and environmental sensor technology since digitization. Although traditional sensors have been refined through decades of incremental progress, optical fiber sensors provide an entirely new lens with which to study fundamental processes. These sensors are particularly advantageous for systems that require high spatial and temporal resolution (i.e., on the order of 1-10m spatial scale and 100 s to 100 kHz sampling rate). As director of the UW Fiber Lab, Dr. Bradley Paul Lipovsky has deployed these technologies in Antarctica, Greenland, Alaska, New Zealand, and at a dozen sites in Europe and the lower United States. The main focus of this research has been on studying Earth's cryosphere, submarine, urban, and otherwise difficult-to-instrument environments. This talk will focus specifically on use cases where basic knowledge has been gained regarding the calving front of large, ocean-terminating glaciers in Greenland, paleoclimatic history of the Antarctic ice sheet, monitoring of clean energy systems, and earthquake detection and ground motion hazard characterization. The presentation will conclude with a forward looking discussion regarding the rapid pace of development of basic optical physics and engineering, and the prospects for future growth at the intersection of optical fiber sensors and the Earth, Planetary, and Space Sciences
Closing Gaps in Polar Geophysics: How Combining Models and Observations Rewrites the Story of Mass Loss Across Antarctica
April 24, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Eliza Dawson - Stanford University
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Sea-level rise estimates rely on accurate model projections of ice sheet mass loss. However, ice sheet models lack sufficient observational constraints in critical parts of the ice sheet, including the difficult-to-observe ice-bed and ice-ocean interfaces. An important, but poorly constrained field is the temperature of ice sheets. The temperature at the ice sheet base affects the onset of sliding and ice thermo-frictional feedback mechanisms. In this presentation, I will explore fundamental processes related to the thermal state that are capable of driving mass loss in Antarctica but have been largely overlooked. I will show how joint ice sheet model and radar sounding data analysis is able to identify regions that could be vulnerable to basal thawing. This work redefines our understanding of Antarctica, opening the possibility that the East Antarctic Ice Sheet will become a new locus of mass loss.
Origins, Evolution, & Response to Our Rapidly Changing World
April 25, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Austin Chadwick - Columbia University
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River systems form the arteries of Earth’s water and rock cycles, and directly sustain more than half the global population with food, water, and energy. As a geophysicist, I tackle fundamental questions about the origins and evolution of river systems on Earth and other planets, as well as practical concerns about environmental hazards and sustainability. In this talk, I highlight my research to date on three topics: river deltas, channel patterns, and the connection between rivers and the shallow subsurface. (1) First, I concentrate on river deltas. Using field data, morphodynamic modeling, and laboratory experiments, I quantify the natural river-diversion processes that give deltas their fundamental size and shape. By coupling this river-diversion model with next-century projections for sea-level rise, I show that mitigating flood hazards will require more sediment resources than previously thought. (2) Second, I investigate the origin of fundamental river channel patterns (e.g., meandering, braided). I present a state-of-the-art remote-sensing tool for quantifying riverbank migration—the first of its kind that is equally applicable to all river patterns—and apply it to 36 years of global Landsat imagery. My results demonstrate that river patterns originate from channel width (in)stability. Where riverbank erosion and accretion are in balance, rivers maintain stable meandering patterns. In contrast, where erosion outpaces accretion, rivers repeatedly widen and split to form braided patterns. (3) Third, I present ongoing work on how rivers interact with Earth’s shallow subsurface. Using a suite of geophysical methods (e.g., GPS/GNSS, rod-surface-elevation tables, sediment cores), I am characterizing how rivers build, deform, and at times contaminate subsurface aquifers in lowland Bangladesh. Preliminary results highlight saltwater-contamination risks in coastal farmlands, where man-made embankments disrupt natural connectivity between rivers and the subsurface. In partnership with the leading Bangladesh-based nonprofit organization (BRAC), this ongoing work supports the development of climate-change-adaptation plans to secure drinking water and sustainable agriculture for the 35+ million people living in lowland Bangladesh.
Observations and Simulations of Small-scale Convection Beneath the Oceanic Plates
May 1, 2024
2 p.m. - 2:30 p.m.
3853 Slichter Hall
Presented By:
- Zach Eilon - UC Santa Barbara
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Several aspects of the oceanic lithosphere confound simple models of plate growth through conductive cooling. These include off-ridge non-plume volcanism, systematic departures from expected depth-age relationships, and intraplate gravity lineations. Small-scale convection (SSC), driven by density instability at the base of a cool, dense plate, might explain these phenomena. However, it has not previously been observed tomographically, and computational models of this process are highly contingent on poorly-constrained rheological parameters. To address this, we conducted an ocean-bottom seismic experiment, deploying instruments in the central Pacific in two regions notable for elongated gravity anomalies. Our goal was to image 3-D seismic wavespeeds beneath the plates. At ~40My plate age, we discovered alternating velocity anomalies in the upper mantle in elongated bands parallel to gravity lineations and local plate motion. These features require large (300-500 K) lateral temperature contrasts and/or partial melt. Together with new gravity and bathymetry analysis, this is the first direct evidence for small-scale convective rolls beneath the oceanic plates. At ~90My plage age, we find several upper mantle structures that confound classic plate evolution models, but putative convection cells are less clearly organized. We use these seismic observations as a reference for a new suite of high-resolution dynamical models of maturing oceanic plates that include complex rheology and dynamically evolving grain size. By attempting to match the observed wavelength, depth, and amplitude of SSC, we determine the range of parameters that reproduce this behavior. These models shed new light on the fundamental dynamics which govern 70% of our planet’s (sub)surface.
Improving Environmental Security in the Era of Climate Change
May 2, 2024
noon - 1 p.m.
Slichter Hall 3853
Presented By:
- Leonard Ohenhen - National Security Institute Department of Geosciences Virginia Tech
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Climate change is intensifying environmental hazards globally and imposing widespread consequences on human communities and ecosystems. During this century, climate change will cause an increase in the frequency and intensity of heat waves, hurricanes, and wildfires, and severely impact the world's freshwater resources through frequent droughts, alterations in precipitation and evapotranspiration patterns, and sea-level rise (SLR). Among these impacts, SLR is poised to have one of the most profound socioeconomic impacts due to the dense populations, critical infrastructure, and ecosystems situated along coastlines. Global mean sea level has risen by about 17 cm over the past 100 years, however, SLR on local and regional scales are the most relevant for coastal communities. Regional and local SLR are not uniform in space and time and are dependent on vertical land motion (VLM) - the raising or lowering of land. In most coastal communities the risks posed by rising sea levels are recognized, what is often underappreciated is the role of land subsidence (or lowering of land) to exacerbate these hazards. Without incorporating land subsidence into coastal vulnerability assessment, coastal communities may underestimate the environmental threat of rising sea levels, leading to policies that fall short of the required response. This presentation focuses on the use of sophisticated radar satellite data to create high-resolution maps of VLM at mm-level accuracy for the coasts of the United States mainland. I will discuss the impacts of land subsidence as a recognized and an emerging environmental security threat. I will present result of combining land subsidence data with climate change SLR projections to predict areas, people, and properties that will be affected by future flooding hazards in several U.S. coastal cities. The understanding of multi-hazard faced by communities is important to forge a path toward a sustainable future, where communities are shielded from the most severe consequences of environmental hazards in the era of climate change.
The Effect of Bathymetry on the Long-term Carbon Cycle and CCD
May 8, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Matthew Bogumil - EPSS, UCLA
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The shape of the ocean floor (bathymetry) and the overlying sediments provide the largest carbon sink throughout Earth’s history, supporting approximately one to two orders of magnitude more carbon storage than the oceans and atmosphere combined. While accumulation and erosion of these sediments are bathymetry dependent (e.g., due to pressure, temperature, salinity, ion concentration, and available productivity), no systematic study has quantified how global and basin scale bathymetry, controlled by the evolution of tectonics and mantle convection, affects the long-term carbon cycle. I reconstruct bathymetry spanning the last 80 Myr to describe steady-state changes in ocean chemistry within the Earth system model LOSCAR. Our study illustrates that seafloor bathymetry – both mean depth as well as bathymetry distribution - has a significant influence on the global carbon cycle by controlling the location of seafloor carbonate sedimentation. Considering the plausible range of bathymetric configurations over the last 80 Myr of Earth’s history, bathymetry cannot be ignored when studying the carbon cycle and inferring changes in ocean chemistry and productivity.
Studying the Solar Convection Zone Using Laboratory and Numerical Simulations
May 22, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Brandon Lazard - EPSS, UCLA
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The solar convection zone is the site of many complex dynamics including the generation of the sun's magnetic field. In this talk, I will detail novel laboratory experiments that will tackle the effects of the top boundary layer of the solar convection zone known as the near-surface shear layer. In particular, how does the near-surface shear layer affect the heat transport to the solar surface and what role does it play in the dynamics in the bulk of the convection zone?
Exploring the Rupture Fault of the 2024 Mw7.4 Hualien Earthquake and Its Preceding Seismic Sequences
May 22, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Liuwei Xu - UCLA, EPSS
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On April 2, 2024, a Mw 7.4 earthquake happened on the eastern coast of Taiwan, near Hualien City. We collect the local and teleseismic recordings and near-field geodetic data to analyze its rupture process. We apply Slowness-Enhanced Back-Projection and joint Finite Fault Inversion to multiple seismic and geodetic datasets. The ground deformation suggests that the rupture unzips the east-dipping Longitudinal Valley Fault (LVF), where the relocated hypocenter is. The LVF shows distinct earthquake patterns with the nearby Central Range Fault (CRF): most small and moderate earthquakes since 2000 happened on the west-dipping CRF, while magnitude 7 events mainly happen on the LVF, with a recurrence interval of 30-40 years.
The Influence of Active Fault-Rock Damage on River Networks at Different Scales
May 22, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Boontigan Kuhasubpasin - EPSS, UCLA
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Active faults shape landscapes through movements like uplift, subsidence, and translation, also causing rock damage and erosion. While studies have explored surface movements along faults, fewer have focused on rock damage. This study examines if rock damage near active faults affects river networks, using two methods. First, we analyze the relationship between bedrock erodibility and distance to faults, and second, the angular differences between fault traces and river flow directions. We conduct this analysis globally and locally, focusing on Southern California, Eastern Tibet, Taiwan, and Japan. Locally, rivers closer to faults show higher erodibility, similar to areas where parallel F-R trends relate to longer fault lengths, such as Southern California and Eastern Tibet. In Taiwan and Central Japan, where this trend is less evident, other factors may dominate erodibility, like rock properties. Globally, larger rivers are more aligned with fault tracts, similar to longer fault lengths. This study highlights active faults' role in landscape evolution, impacting rock damage and uplift across scales.
Paraboloidal Free-Surface Experimental Models of Geophysical and Astrophysical Jets
May 29, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Cy David - EPSS, UCLA
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Zonal (east-west) jets, such as those visible on Jupiter, are ubiquitous in gas planets as well as subsurface oceans and planetary cores. Yet, fundamental questions regarding jet migration and magnitude remain open. Advances in these areas will benefit from detailed laboratory data obtainable with UCLA's Coreaboloid device. The Coreaboloid is a world-unique rotating laboratory platform that uses an imposed thermal gradient and a paraboloidal free surface to produce the key ingredients of geophysical and astrophysical jets: rotational forces, convective turbulence, and boundary curvature effects. Initial data from ultrasonic Doppler velocimetry (UDV) and thermographic imaging reveal thermal Rossby waves and multiple zonal jets, which extend in cylindrical radius in proportion to the so-called Rhines scale and migrate outwards in accordance with empirical scaling estimates. These jovian-style "zonostrophic" jets are the first to ever be generated using a realistic convective driving mechanism in any laboratory setting. With our newly-constructed thermovelocimetric data acquisition system, I will obtain high spatio-temporal-resolution measurements of these flow features over thousands of rotation periods, allowing us to investigate the fundamental mechanisms of jet formation and evolution.
The 2024 Noto Earthquake and Tsunami: A Triggered Landslide Imaged by the Adjoint-state Inversion Method
May 29, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Saeed Mohanna - EPSS, UCLA
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We investigated the coseismic slip and deformation caused by the 2024 Mw 7.5 earthquake on the Noto Peninsula and the subsequent tsunami through both adjoint and static inversion modeling techniques. We capitalized on the extensive network of tsunami stations available across the Sea of Japan, combined with detailed near-field geodetic data from GNSS stations, to perform these inversions. Our analyses consistently identified a region of significant slip located northeast of the epicenter, corresponding to a deeper fault plane that dips at 25º toward the southeast. Notably, the results from our adjoint inversion method successfully pinpointed a landslide source in Toyama Bay, directly inferred from tsunami waveform data. This landmark achievement marks the first instance of resolving a landslide source from water elevation data, underscoring the exceptional capability of the adjoint method in detecting non-seismic tsunami sources. The use of both modeling techniques not only enhanced our understanding of seismic events in this geologically complex region but also demonstrated the critical role of integrated geodetic and water elevation data in improving tsunami prediction and hazard assessment.
Coevolution of Organic Matter Burial in Sediments and Granite Geochemistry
June 5, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Claire Bucholz - California Institute of Technology
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Phosphorus plays a critical role in both surface biological cycles as an essential nutrient and in magmatic systems as the backbone for trace element-rich phosphate minerals. Further, phosphorus cycling between sedimentary and igneous systems throughout Earth history has had potentially profound effects on biogeochemical cycles. I will discuss my recent work on phosphorus concentrations in strongly peraluminous granites (SPGs) from the past 3.5 billion years. SPGs are generated by the partial melting of sedimentary rocks and can thus provide a novel archive to reveal secular trends in Earth’s environmental history that integrate large volumes of siliciclastic sediments. I find that phosphorus contents of SPGs systematically increase across the Precambrian-Phanerozoic boundary, mirroring a previously documented increase in the phosphorus contents of marine siliciclastic sediments. After consideration of the effects of metamorphic, partial melting, and igneous differentiation processes on SPG phosphorus contents, I conclude that low phosphorus contents in Precambrian SPGs are most parsimoniously explained as resulting from low phosphorus contents in their source rocks. This increase is also mirrored in nitrogen (N) contents of SPGs across the same time interval. Collectively, this data is most parsimoniously explained by an absolute increase in biomass burial in the late Proterozoic or early Phanerozoic. I will also discuss the implications of this work for the use of trace elements in detrital zircon as a tool to fingerprint for the nature of their source rocks. Relevant references: Bucholz, C.E., 2022. Coevolution of sedimentary and strongly peraluminous granite phosphorus records. Earth and Planetary Science Letters, 596, p.117795. Bucholz, C.E., Liebmann, J. and Spencer, C.J., 2022. Secular variability in zircon phosphorus concentrations prevents simple petrogenetic classification. Geochemical Perspectives Letters, 24, pp.12-16. Mikhail, S., Stüeken, E.E., Boocock, T.J., Athey, M., Mappin, N., Boyce, A.J., Liebmann, J., Spencer, C.J. and Bucholz, C.E., 2024. Strongly peraluminous granites provide independent evidence for an increase in biomass burial across the Precambrian–Phanerozoic boundary. Geology, 52(1), pp.87-91.