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Geophysics and Tectonics Seminar - fall-2023

New measurements of seismic attenuation across the East African Rift support role of rift-related melting

Oct. 11, 2023
noon - 1 p.m.
Geology 1707

Presented By:

  • Prof. Heather Ford - UC Riverside
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The remarkably low seismic velocities in the mantle beneath the East African Rift are plausibly explained by elevated mantle potential temperatures and/or the presence of partial melt. Previous work proposed that a plume-like conduit of elevated temperatures extending from the mantle transition zone can explain observations of seismic attenuation beneath the southern portion of the rift, but this disagrees with geochemical constraints on the temperatures during melt generation of East African Rift lavas. We measure the attenuation of a large dataset of teleseismic P phases stretching from the Arabian Platform to the Kaapvaal Craton to constrain the nature of seismic anomalies beneath this plate boundary. We show that the anomaly in attenuation at the Afar Depression and Main Ethiopian Rift is best explained by a relatively thin layer of high attenuation, akin to other regions of rifting, which we interpret to be due to the presence of melt.

Using Turbulent Magnetic Diffusion in Earth’s Core to Constrain Average Bulk Core Velocity

Oct. 18, 2023
noon - 1 p.m.
Geology 1707

Presented By:

  • Dr. Daria Holdenreid-Chernoff - UC Berkeley
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Studying the long timescale evolution of the geodynamo is challenging, in part due to the sparsity of long timescale data. However, when considered statistically, paleomagnetic data can provide valuable insight into the dynamics underlying turbulent magnetic field generation. Using a field theory formalism, we construct a framework that allows us to study average properties of the magnetic field over long timescales. Paleomagnetic field fluctuations suggest a shorter dipole decay time than expected from current estimates of the molecular magnetic diffusivity in the outer core. This short decay time can be interpreted as a signature of turbulent diffusion, which depends on the amplitude of the flow that interacts with the magnetic field. By combining an expression for the turbulent diffusivity derived from our model with the paleomagnetic observations, we compute an estimate of the bulk root-mean-square velocity in the core, which must be smaller than 0.8–1.2 mm s-1. This is slightly larger than estimates of the velocity at the top of the core from observations of secular variation (~0.3-0.6 mm s−1). These results show that velocities in the interior of the core can be constrained by paleomagnetic observations, and that this flow’s amplitude cannot substantially exceed core surface estimates.

Equation of State of Iron and Origin of Saturn’s Rings

Oct. 25, 2023
noon - 1 p.m.
Geology 1707

Presented By:

  • Prof. Burkhard Militzer - UC Berkeley
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This talk will discuss ab initio free energy calculations to determine the equation of state of iron a megabar pressures [1]. We compute isentropes and the melting line and show that the crystallization of iron in the cores of Super-Earths begins from the center like on Earth. Then the gravity measurements of Saturn and Jupiter by the Cassini and Juno spacecrafts will be reviewed. The Juno mission determined unexpectedly low magnitudes of the gravity coefficients J4 and J6. We illustrate why this implies that Jupiter has a dilute core at its center instead having of a traditional compact core that is composed to 100% of heavy elements [2,3]. Saturn stands out among the planets in our solar system for two reasons: It has a prominent set of rings and its spin axis is tilted by 27o. Both facts are difficult to reconcile with the well-established picture of planet formation, which assumes the planets emerged from a protoplanetary disk. Furthermore recent gravity measurements by the Cassini spacecraft implied an unexpected young age for Saturn’s rings of only ~100 million years, which rules out that the rings are primordial. Here we reconcile all these observations by constructing models for Saturn’s interior structure and by performing dynamical simulations of all relevant solar system objects [4]. We present a dynamical scenario that explains how Saturn’s rings formed and how its spin axis was tilted.

The elastic, electronic, and vibrational properties of szomolnokite (FeSO4 H2O): Characterizing hydrated sulfates in the solar system

Nov. 1, 2023
noon - 1 p.m.
Geology 1707

Presented By:

  • Dr. Olivia Pardo - Lawrence Livermore National Laboratory
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Hydrated sulfates are observed throughout the solar system on a variety of planetary bodies, including Earth, Mars, and the icy satellites, prompting theoretical and experimental work constructing sulfur-rich planetary interior models. Planetary surface observations have demonstrated the tendency for complex solid solutions of hydrated sulfates to form, such as the szomolnokite-kieserite solid solution (FeSO4·H2O–MgSO4·H2O). To better understand the high pressure and low temperature environments hydrated sulfates are found in, we have performed a suite of diamond anvil cell experiments on the iron-endmember monohydrated sulfate, szomolnokite (FeSO4·H2O), characterizing its elastic, electronic, and structural properties under planetary surface and interior conditions. We identify structural phase transitions and the related effects on both the bulk elastic properties and specific atomic environments in szomolnokite through synchrotron infrared spectroscopy, synchrotron Mössbauer spectroscopy, nuclear resonant inelastic X-ray scattering, and X-ray diffraction. Using this comprehensive dataset we evaluate szomolnokite’s contribution to planetary interior properties, including seismic wave velocities, water storage, and implications for tidal observations.

Coronae provide unique insights into Venus’ mantle dynamics and tectonic activity: mission data analysis and geodynamic modeling

Nov. 8, 2023
noon - 1 p.m.
Geology 1707

Presented By:

  • Dr. Anna Gulcher - Caltech
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Understanding Venus’ geological history helps to answer why Earth and Venus have undergone such staggeringly divergent evolutionary paths. At present, Venus does not exhibit evidence of plate tectonics that dominates geological processes on Earth, although the planet’s surface is covered with tectonic and volcanic structures. Perhaps the most puzzling surface features on Venus are the so-called “coronae”, ~circular crown-like structures often linked to mantle plume upwellings and/or magmatism. Unravelling their origin may hold clues for Venus’ global tectonic regime as well as current tectonic/volcanic activity, making coronae features of particular interest for the several Venus space missions currently in preparation (e.g., NASA’s VERITAS and ESA’s EnVision). In this seminar, I will present joint studies of mission data analysis and geodynamic modeling of the the unique corona features. I will provide a framework that summarizes several tectonic end-member styles responsible for coronae development at different settings on the planet. We find that the topographic signature of at least 37 large coronae on Venus show features that indicate ongoing plume-lithosphere interactions, and we propose widespread and active magmatic activity on Venus on geological timescales. We further find that a lateral gradient in lithospheric strength enhances lithospheric resurfacing and prolongs the corona’s lifetime. Finally, the density increase associated with the basalt-to-eclogite phase change provides the extra negative gravitational force required for downgoing crust to be recycled into the mantle under Venusian conditions. Relevant to several Venus space missions that are currently under development, I will outline key hypotheses on Venus’ tectonics and volcanism to be tested with the future mission data. Finally, I will touch upon the synergies of Venus sciences with Earth and (exo)planetary sciences, which highlights the importance of studying our mysterious twin planet for the wider (scientific) community.

The physics of magma oceans in Io and early Earth

Nov. 15, 2023
noon - 1 p.m.
Geology 1707

Presented By:

  • Dr. Yoshi Miyazaki - Caltech
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Two upcoming flybys of Io by the Juno spacecraft hold the potential to confirm the presence of a magma ocean on the Jupiter’s moon. As we await this pivotal event, my talk will delve into the physics of magma oceans formed under various settings. Magma oceans (large-scale silicate melting) appear multiple times during the formation and evolution of rocky celestial bodies, and their evolution significantly influences both planetary surfaces and interiors. The trajectory of magma ocean evolution depends on surface boundary conditions, heating sources, and planetary size, resulting in a diverse array of magma ocean outcomes. For instance, magma oceans in Io and early Earth are characterized by distinct physical phenomena (heat pipes v.s. gradational instability), and understanding the primary process governing the magma ocean evolution is crucial for unraveling its impact on volatile degassing and compositional evolution. I will touch upon how the mode of solidification plays a crucial role in determining the surface volatile budget, along with elemental partitioning between core and mantle during planetary formation, aiming to review the interplay of various factors shaping the evolution of rocky bodies with magma oceans.

Probing Martian Aeolian Activity Through Rover Track Degradation

Nov. 29, 2023
noon - 12:30 p.m.
1707 Geology

Presented By:

  • Jake Widmer - UCLA
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Present-day activity on Mars is dominated by wind, but a shortage of detailed surface observations characterizing wind across the planet make it difficult to answer basic questions about how aeolian activity drives surface changes. Over the past 18 years, five rovers have explored the martian surface, leaving tracks (i.e., surface depressions) in their wake. In this study, we combine orbital images from the HiRISE camera with surface images from each rover to determine the duration of rover tracks left on the surface and classify the types of terrains capable of recording tracks. Our results aim to create a qualitative record of aeolian activity in place of detailed surface observations and quantify rates of terrain restoration across multiple terrain types.