Earth and Planetary Sciences Event Calendar

Unless noted, all listed events are open to the general public.

Wednesday Seminar in Geology: GEL 190/290
Seminars are scheduled for Wednesday afternoon at 4:00 PM. Additional optional seminars that may be included as part of the Geology 190 series may be scheduled at other times.

Friday Lunch Seminar: "A Geology tradition since the Phanerozoic!"
Fridays at noon. Students and faculty give informal lectures on research, travel, or other interests.

Campus map: Earth & Physical Sciences Building | Roessler Hall

submit an event to the department calendar (restricted access)

Wednesday, October 23rd, 2019, Wednesday Seminar
4:10 PM, 55 Roessler
Tea and cookies at 3:45 in the aviary - (2110 EPS)
Geological Expression of the Seismic-Aseismic Transition along the Subduction Zone Interface  -- by Dr. John Paul Platt, University of Southern California

Major earthquakes are largely limited to the shallowest 40 km of subduction zones, below which there is a transition into aseismic creep.  The transition zone in several subduction zones is the source of a range of phenomena in which elastic energy is released at rates 1-6 orders of magnitude more slowly than in normal earthquakes. These include low frequency earthquakes (LFEs), which are very small events with durations of a few seconds; tremor bursts, which appear to be concatenated sequences of LFEs with durations up to ~104 seconds; and slow slip events, which may or may not be accompanied by tremor, have geodetically measurable displacements of 10s of cm, and durations up to ~106 seconds.  Rocks exhumed from subduction zones show deformational structures that may reflect this range of phenomena.  

The seismic zone is characterized by shear zones 100-350 m thick, comprising several anastomosing fault strands 5-35 m thick, made up of foliated and unfoliated cataclasite, as described from the Kodiak Island accretionary complex in Alaska by Rowe et al (Geology, 2013).  These fault strands host slip zones 1-20 cm thick formed during seismic events, occupied by pseudotachylite and ultracataclasite. 

The transition zone is characterized by abundant quartz veins, and trains of mm-scale kinks or microfolds developed in strongly foliated metasedimentary material.  The kink-bands are occupied by dilational arcs formed by hydraulic fracture, and filled with precipitated quartz.  They are likely to propagate at rapid but subseismic rates, limited by dilational hardening.  Propagating dilational kink-bands are likely to have effective seismic moments comparable to LFEs.  Repeated hydraulic fracture events are required to allow the transport of sufficient SiO2 to fill the arcs, so kink-band propagation may explain repeating LFEs. They are associated with the overturned limbs of asymmetric folds, which may produce tremor bursts as they amplify. The amplification of larger folds with scales up to 1 km may be associated with slow slip events. At each scale, displacement will be limited by dilational hardening in the propagating kink-bands.  At 350°C, this type of deformation can accommodate ~ 30% of the total displacement rate in a 3.5 km thick subduction channel, as seen in the South Fork Mountain Schist of northern California (Platt et al. Progress in Earth and Planetary Science, 2018). The remaining displacement is taken up on discrete slip surfaces.   

The creep zone is characterized by intense ductile deformation, without evidence for discrete slip zones. At 500°C, metagreywacke deforms predominantly by pressure-solution creep, but intercalated metachert deforms by dislocation creep at shear stresses ~ 10 MPa. At these stresses, pressure solution can produce a strain rate of 10-12 s-1, which is sufficient to accommodate a subduction rate of 100 mm/yr in a 10 km thick subduction channel, as seen in the Pelona Schist of southern California (Xia & Platt, Solid Earth, 2017).

Friday, October 25th, 2019, Friday Lunch Seminar
12:10 PM, 1348 Earth and Physical Sciences
Two 20 minute talks on recent research highlights, ideas or challenges
Linking surface geochemistry to the thermo-chemical structure of Earth’s mantle  -- by Curtis Willams, UC Davis
Aurora, a puzzle piece in the evolution of oxygenic photosynthesis and the rise of oxygen on Earth  -- by Christy Grettenberger, UC Davis

Curtis Williams: A major goal in Earth Science has been to understand how geochemical characteristics of lavas at the Earth's surface relate to the location and formation history of specific regions in the Earth'€™s interior. In this presentation, I will show how models of mantle flow directly link hotspots with more primitive geochemical signatures (as indicated by the isotopes of helium) to the two seismically imaged large low shear €velocity provinces in the lowermost mantle. 

Wednesday, October 30th, 2019, Wednesday Seminar
4:10 PM, 55 Roessler
Insights into global carbon cycling from a 35 Ma record of Sr isotopes in seawater  -- by Dr. Adina Paytan, UC Santa Cruz

The radiogenic Sr-isotopic signature (87Sr/86Sr) of seawater fluctuates primarily in response to changes in the inputs of Sr from weathering and hydrothermal activity, which have distinct 87Sr/86Sr values. Changes in the isotopic ratio of the weathered terrain also contribute to observed changes in seawater 87Sr/86Sr. The stable Sr-isotope ratios in seawater (mass dependent isotopic fractionation; d88/86Sr) fluctuate primarily in response to the rate of calcium carbonate (CaCO3) accumulation at the seafloor. Together radiogenic and stable Sr can constrain the coupling between weathering and sedimentation and shed light on the relation between weathering, CaCO3 deposition, the global carbon (C) cycle and climate. Reconstruction of the coupled stable and radiogenic Sr seawater curves over the past 35 Ma of Earth history suggests that the Sr flux in and out of the ocean, and thus the seawater dissolved Sr concentration have fluctuated considerably over this time interval. The location and rates of CaCO3 burial in the ocean have also fluctuated. Between 35 to 18 Ma an increase in the net Sr input results from a reduction in neritic CaCO3 burial and increased burial in pelagic settings. The trend is reversed between 18 and 5 Ma and finally over the last ~5 million years a rapid increase in the net Sr input to the ocean and change from neritic to pelagic burial is seen. The lack of a continuous increase in pelagic CaCO3 burial, inferred from the stable Sr data, indicates that silicate weathering rates have not increased monotonically over the past 35 Ma and hence associated atmospheric carbon-dioxide consumption rates were also not unidirectional. Modeling of the combined 87Sr/86Sr and d88/86Sr data suggest a relatively modest increase of about 20% in continental weathering since 35 Ma.

Friday, November 1st, 2019, Friday Lunch Seminar
12:10 PM, 1348 Earth and Physical Sciences
Two 20 minute talks on recent research highlights, ideas or challenges
Pre-eruptive architecture of the Oruanui magma reservoir (New Zealand) revealed by zircon U-Th ages and trace element systematics -- by Tyler Schiedler, UC Davis
TBD -- by Veronica Prush, UC Davis

Tyler: I will be presenting new U-Th age and trace element data for zircons extracted from the 25.4 ka Oruanui super-eruption (the world's youngest super-eruption). I will be discussing how these new age and TE data can provide information about the pre-eruptive architecture and assembly timescales of a large silicic magma reservoir. 

Veronica: TBD

Wednesday, November 6th, 2019, Wednesday Seminar
4:10 PM, 55 Roessler
Unsuspected Collapse of Southern California Marine Communities in Historic Times: Novel Insights from Very Young Fossils -- Dr. Susan Kidwell, University of Chicago

One of the big challenges in environmental management and conservation biology is discovering ‘what was natural’ before human impacts. This problem is especially pressing in marine systems, where direct monitoring of conditions is usually short relative to the span of cultural stressors or is lacking for key variables. Susan Kidwell has been tackling this problem in Southern California marine ecosystems by using the dead shells acquired from the top 10-15cm of the seabed during biological surveys as a young fossil record. This reconstructed history of the last few thousand years reveals a dramatic and unsuspected transformation of the open shelf in response to the last two centuries of shifting land use, providing a tool that can help set priorities for protection and baselines for gauging recovery. The extensive age-dating of shells from time-averaged assemblages within these intensely bioturbated seabeds is also providing insights into the formation and resolving power of much older fossil records, as penetrated by cores and sampled in outcrops.

Friday, November 8th, 2019, Friday Lunch Seminar
12:10 PM, 1348 Earth and Physical Sciences
Two 20 minute talks on recent research highlights, ideas, challenges, or experiences
Lack of Life Long Ago -- by Dawn Sumner
Extra-ordinary Earthquakes -- by Magali Billen

Dawn: Stromatolites (not) in 3.7-3.8 Ga Metamorphic Rocks, Isua, Greenland
NASA Astrobiology sponsored a field workshop in the Isua Belt, Greenland, to evaluate the origin of structure controversially interpreted as stromatolites (See https://www.sciencedirect.com/science/article/pii/S030192681930107X (sorry it's Elsevier - let me [Dawn] know if you want a copy) and https://www.nature.com/articles/s41586-018-0610-4). Workshop participants, with the exception of Nutman and Friend, concluded that the structures are not demonstrably stromatolites. I will present the controversy, context for the structures, and why we do not think there is evidence that they were biologically influenced.

Magali: The extra-ordinary seismicity of the Tonga Slab: My secondary plume hypothesis 

Wednesday, November 13th, 2019, Wednesday Seminar
4:10 PM, 55 Roessler
Exploring the Earth with global adjoint tomography -- Dr. Ebru Bozdag, Colorado School of Mines

Accurate and high-resolution images of Earth’s interior are crucial to improve our understanding of the inner dynamics of our planet. Global adjoint tomography is one of the extreme projects in seismology due to the intense computational requirements and vast amount of data that can potentially be assimilated in inversions. GLAD-M15 is the first-generation global adjoint tomography model which has transverse isotropy confined to the upper mantle where crust and mantle were inverted simultaneously. After GLAD-M25, which is the successor of GLAD-M15, we now explore more complete parameterizations including surface-wave azimuthal anisotropy, anelasticity, etc. while increasing the database in complementary inversions. Meanwhile we define and adapt new measurement techniques, such as exponentiated-phase and double-difference measurements, to improve the resolution and speed up convergence in global full-waveform inversions. The ultimate aim is to go down to 1 Hz in global simulations to perform whole-Earth inversions including the core and assimilate all available seismic data in seismic tomography.

Friday, November 15th, 2019, Friday Lunch Seminar
12:10 PM, 1348 Earth and Physical Sciences
Making Earths Layered Outer Core with Immiscible Iron Alloys  -- by Dr. Sarah Arveson, UC Berkeley

Earth's outer core is composed of a liquid iron alloy with up to 10% of unknown light elements, likely silicon, oxygen, sulfur, carbon, or hydrogen. The release of these light elements upon freezing of the solid iron inner core plays an important role in sustaining Earth'™s magnetic field, but the exact chemical makeup of the core is widely debated. We performed high-pressure, high-temperature melting experiments in the laser-heated diamond-anvil cell and first-principles simulations on iron alloys containing silicon and oxygen and found that two distinct liquids form at high pressures. High-pressure immiscibility in the Fe-Si-O system may explain a seismically observed stratified layer atop the outer core, complicate differentiation and evolution of the deep Earth, and affect the structure and intensity of Earth's magnetic field. Our results support silicon and oxygen as coexisting light elements in the core and suggest that SiO2 does not crystallize out of molten Fe-Si-O at the core-mantle boundary contrary to the inference of a recent study.

Wednesday, November 20th, 2019, Wednesday Seminar
4:10 PM, 55 Roessler
Consequences of the Cambrian (or Why Humans Don’t Regenerate Their Heads -- Dr. David Gold, UC Davis

The Cambrian “explosion” (~541 million years ago) is the first major event in the animal fossil record, with many animal groups appearing within a relatively brief geological window. In this talk, I will briefly review how scientists have sought to understand this phenomenon. New insights from genetic data and the fossil record suggest that the “explosion” is not as explosive as originally thought, and can likely be explained through standard Darwinian processes combined with changes in environment and geochemistry. I will then turn this question around; instead of focusing on the cause of the explosion I ask why we can recognize living animal groups in half-billion-year-old fossils. I argue that the answer lies in the power that biological constraint plays on the evolution of animal life. This hypothesis can help explain differences between animal groups in basic biological processes, including aging and regeneration. In this regard, the consequences of the Cambrian “explosion” may prove more intriguing than its cause.

Friday, November 22nd, 2019, Friday Lunch Seminar
12:10 PM, 1348 Earth and Physical Sciences
Earth is the Globe: Adventures in Scientific Research and Engagement -- by EPS Graduate Students, UC Davis

As Earth scientists, we follow important research questions around the globe through fieldwork and collaborations. Come hear 15 minute highlights of internationally engaged research from students, postdocs, and researchers from the Department of Earth and Planetary Sciences. We promise stimulating ideas, beautiful images, and engaging stories from Africa, the Americas, Antarctica, Asia, Greenland, and New Zealand.

Wednesday, December 4th, 2019, Wednesday Seminar
4:10 PM, 55 Roessler
Slow slip events on the Southern San Andreas Fault -- Dr. Yuri Fialko, UC San Diego

Friday, December 6th, 2019, Friday Lunch Seminar
12:10 PM, 1348 Earth and Physical Sciences
AGU Practice Talks - Special 2-hour Seminar  -- by EPS Scientists, UC Davis

Anyone from the EPS Department who is giving a talk at AGU and would like a chance to practice and get some feedback before the meeting can sign-up to give a talk. We will follow strict time rules and ask the audience to give feedback on a written paper (or separately). This special Lunch Seminar will be followed by a poster session, for those presenting posters instead of talks, and the department end-of-fall gathering.