EPSS Colloquium - fall-2017

Oct. 3, 2017
3:30 p.m. - 4:30 p.m.
Geology 3656

Presented By:

• James Day - UCSD

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A paradigm has arisen over the relationship of late accretion and the delivery of water and other volatile compounds and element. Late accretion, which can be defined as the addition of materials after metal-silicate equilibrium, is effectively tracked using the highly siderophile elements (HSE). Thus, there should be a link between the HSE and volatile elements. Alternatively, the distribution of volatile elements and the HSE in the Earth and Moon were set by a range of fundamental processes, including planetary accretion processes and the feedstocks that formed the proto-Earth and Moon, as well as late accretion. The timing of these processes on planetary bodies likely varied in response to mechanisms of accretion, availability and nature of feedstock materials, and cessation of metal-silicate equilibrium. Arguably, the most complex locations to address these issues in the inner Solar System are the Earth and Moon. The likely origin of these bodies, during a late-stage catastrophic ‘Giant Impact’, led to significant volatile loss from the Moon, redistribution of the HSE and volatile elements between the colliding bodies, planetary-scale magma oceans, prolonged late accretion and, in the case of Earth, silicate remixing (aka Plate Tectonics). Given this diverse array of processes, how is it possible to go about deriving likely distributions of the HSE and volatile elements in Proto-Earth or Moon materials? In this talk, I will review evidence from the distribution of volatiles and HSE in chondrites and achondrites – the likeliest examples of possible feedstock materials to the proto-Earth and Moon and possible scenarios of feedstock composition.

Oct. 10, 2017
3:30 p.m. - 4:30 p.m.
Geology 3656

Presented By:

• Jay Melosh - Purdue

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NASA’s GRAIL mission to the Moon was completed in 2012 when both spacecraft were intentionally “de-orbited” (i.e. crashed) into a nearside mountainside. This orbital mission measured tiny variations in the Moon’s gravitational field by continuously monitoring the distance between two co-orbiting spacecraft (dubbed Ebb and Flow) to a precision of less than 0.1 micron. The resulting enormous improvement in the gravity field reveals buried structures otherwise hidden from view, from the underpinnings of large impact scars and the nearside lava flows down to a detection of the Moon’s core and perhaps an inner core. We have finally achieved a clear understanding of the previously mysterious mascons that posed a navigational hazard to the Apollo spacecraft and can now document a complete catalog of all of the ancient and, in many cases, otherwise invisible scars of large impacts that have breached the Moon’s crust. The Moon’s gravity field turns out to be qualitatively different from that of the other terrestrial-type planets in our solar system, but is now yielding insights into the nature of the earliest crusts of planetary bodies.

Oct. 17, 2017
3:30 p.m. - 4:30 p.m.
Geology 3656

Presented By:

• David Valentine - UCSB

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The 2010 Deepwater Horizon blowout in the Gulf of Mexico was an event of national significance that placed geoscientists in the in the media spotlight. During this seminar I will talk about the questions that drove scientists to study this event, the resolution to some of those questions, and the interplay with an information-starved media.

Oct. 31, 2017
3:30 p.m. - 4:30 p.m.
Geology 3656

Presented By:

• Rob van der Hilst - MIT

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A deep thermal plume in the mantle beneath Hawaii?
Constraints from tomography and reflection seismology

The topic of today’s lecture is mantle convection in broad sense and, specifically, the question as to whether or not a hot thermal plume exists in the deep mantle beneath Hawaii. Mantle transition zone (MTZ) discontinuities due to phase transitions in silicate minerals (e.g., olivine, garnet) near 410 and 660 km depth play an important role in modulating mantle flow. Convection is foremost a thermally driven system and most MTZ studies use discontinuity topography to estimate in situ temperature anomalies. Compositional heterogeneity is also expected but direct observational evidence is scarce and often qualitative. We study the base of the MTZ with a joint seismological and mineral physics analysis of the amplitudes of so-called SS precursors (S waves that bounce off MTZ discontinuities). The study area includes Hawaii, where a hot upwelling has long been proposed. The data are not consistent with a simple thermal plume but provide evidence for lateral variation in composition at the base of the MTZ as expected in high temperature, low viscosity environments near lower mantle upwellings. Combined with tomographic models the results suggest that the MTZ acts as a partial barrier for mantle flow.

Nov. 7, 2017
3:30 p.m. - 4:30 p.m.
Geology 3656

Presented By:

• Katherine de Kleer - UC Berkeley

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Tidal heating is a major driver of geological activity within our Solar System, and may play an important role on many exoplanets. On Io, the effects of tidal heating are clearly observable in the form of large-scale volcanism, making it an ideal laboratory for studying this process. I will present an ongoing observing campaign aimed at understanding Io’s volcanic activity, including its connection to Io’s atmosphere and to tidal heat dissipation. Between 2013 and 2017 we have observed Io on over 200 nights with adaptive optics on the Keck and Gemini N telescopes, and have tracked the evolution of thermal emission from dozens of individual active volcanic sites. The temporal progression of individual eruptions yields characteristic timescales and constrains the thermal properties of the magma. The spatial distribution of activity throughout this period reveals significant large-scale asymmetries and deviates from current tidal heating model predictions. Finally, comparisons with simultaneous long-term observing programs at other wavelengths are refining our understanding of how Io’s volcanism impacts variability in the jovian neutral and plasma environment.

Nov. 14, 2017
3:30 p.m. - 4:30 p.m.
Geology 3656

Presented By:

• Inez Fung - UCB

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The concept of the “Asian monsoon” masks the existence of two separate summer rainfall regimes: convective storms over India, Bangladesh and Nepal (the South Asian monsoon) and frontal rainfall over China, Japan and Korea (East Asian monsoon). In addition, the Tibetan Plateau and other mountains impacts the atmospheric circulation and hence precipitation patterns. Here we focus on the East Asian summer monsoon, and present analysis of precipitation variability over the past 50 years and the Last Glacial Maximum. The discussion will highlight the roles of moisture sources and mechanisms for precipitation changes.

Nov. 21, 2017
3:30 p.m. - 4:30 p.m.
Geology 3656

Presented By:

• Marc Hirschmann - University of Minnesota

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Seminar Description coming soon.

Nov. 28, 2017
3:30 p.m. - 4:30 p.m.
Geology 3656

Presented By:

• David Jewitt - UCLA

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I will describe two exciting objects discovered this year. K2 is a comet infalling from the Oort cloud and discovered to be active at unprecedented distances, far beyond the orbit of Uranus. U1 is the first-discovered interstellar interloper and, I believe, the tip of the iceberg. I will describe in an accessible way the big-picture significance of these objects for cometary science and for understanding the formation of the solar system.

Dec. 5, 2017
3:30 p.m. - 4:30 p.m.
Geology 3656

Presented By:

• Naomi Levin - University of Michigan

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¹⁸O/¹⁶O ratios are widely used in paleoclimate studies as proxies for temperature, precipitation amount and hydrologic change, but interpretations of these records are often challenged by the multiple factors that can influence them. Variation in ¹⁷O/¹⁶O ratios of Earth materials have long been assumed to co-vary with ¹⁸O/¹⁶O ratios in predictable and uniform ways such that they were not considered useful in studies of Phanerozoic climate. However, recent advances in the ability to measure small differences in D¹⁷O, the deviation from an expected relationship between ¹⁸O/¹⁶O and ¹⁷O/¹⁶O ratios, both in waters and low-temperature materials (e.g., carbonates, bioapatites, silicates, oxides) present the opportunity to use triple oxygen isotope measurements in hydrological and paleoclimate studies. In particular, the sensitivity of D¹⁷O to kinetic fractionation means that it can be used to constrain the influence of kinetic effects on variations in d¹⁸O. In this talk, I will review the growing number of datasets on the triple oxygen isotope composition of the hydrosphere and present an example of how triple oxygen isotopes in lacustrine carbonates can be used to constrain hydroclimate in the past. A compilation of D¹⁷O data from precipitation, which includes snow from polar regions, tropical storms and weekly precipitation collections from mid-latitudes, shows that the D¹⁷O of precipitation can range from -0.06 to +0.07‰. In the western U.S., there are clear seasonal differences in D¹⁷O of precipitation. A continent-wide survey of tap waters from the U.S. mirrors the variation observed in precipitation. Among leaf waters, D¹⁷O values range from -0.28 to +0.04‰ and can vary by as much as 0.16‰ in a plant within a single day. The mass-dependent effects associated with kinetic fractionation are likely responsible for the majority of the observed variation in waters, either during re-evaporation of rainfall in warm climates, snow formation at very cold temperatures, or evapotranspiration. In lakes, variation in D¹⁷O can be used to discern the role of evaporative water loss in the overall water balance. In summary, the combination of the observed variation of D¹⁷O in continental waters and the emerging techniques for measuring D¹⁷O in a wide range of geologic materials means that it is now possible to use D¹⁷O to monitor the effects of kinetic fractionation on meteoric waters and provide additional constraints on variation of d¹⁸O in sedimentary archives.