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Geocheminar - spring-2013

Wielicki-TBD

April 9, 2013
noon - 1 p.m.
Slicther 3853

Presented By:

  • Matt Wielicki - UCLA
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Seminar Description coming soon.

Geophysical constraints on glacial earthquakes and glacier dynamics in Greenland

April 9, 2013
noon - 1 p.m.
Geology 3656

Presented By:

  • Meredith Nettles - Columbia
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Many of Greenland's largest glaciers produce seismic signals equivalent in amplitude to those from earthquakes of M ~ 5. The earthquakes show a strong seasonal signal, with most events occurring in late summer, as well as a secular variation, with 3-6 times as many earthquakes occurring in each recent year as in the early 1990s. Rapid changes in glacier flow speeds, thinning rates, and terminus positions have also been observed during the past decade, but remain poorly understood. These dynamic glacier processes account for approximately half of the ice-mass loss currently occurring in Greenland. We combine globally recorded seismic signals, space-based remote-sensing data, and local geodetic observations at large Greenland outlet glaciers to obtain insight into the glacial-earthquake source process and the response of outlet glaciers to changing environmental conditions, including ice loss at the glacier terminus and varying surface meltwater input. Systematic analysis of glacial earthquakes across Greenland shows that spatio-temporal trends in earthquake occurrence are closely linked to changes in ice dynamics, and allows us to use the earthquakes as a remote-sensing tool.

Making sense of Vesta using noble gas analysis of HEDs:

April 30, 2013
noon - 1 p.m.
Slichter 3853

Presented By:

  • Julia Cartwright - Caltech
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The HED clan of achondrites are believed to be sourced from the asteroid 4 Vesta. Though the howardites represent polymict breccias that contain eucritic and diogenitic material and likely have a surface origin, their true regolithic nature is not well defined. As trapped solar wind would be expected in samples that have been exposed to the vestan surface, noble gas analysis can be used as a key technique to determine a truly regolithic howardite. In this research, we introduce our three-pronged approach of compositional, petrological and specifically noble gas analysis to identify such regolithic samples, with a view to better understanding the geological evolution of Vesta, and the processes responsible for the formation of its surface.

Empirical estimation of global chemical weathering : big data for the big picture

May 7, 2013
noon - 1 p.m.
Slichter 3853

Presented By:

  • Nils Moosdorf - USC
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Chemical rock weathering controls long term biogeochemical cycling. It is a source of nutrients and a sink of atmospheric CO2. To estimate global chemical weathering rates, we use empirical analyses of existing water quality data from a large number of catchments. Our results indicate that runoff, lithology and land cover are the main controls of chemical weathering fluxes at large scales. Other factors, which were identified in the laboratory or in local scale studies, do not leave significant signatures at large scale. In addition, our results highlight the importance of representing and resolving regional variability even at global scales. A small fraction of the global land area produces large proportions of the total global chemical weathering fluxes. Chemical weathering in these areas, but also other, less obvious, aspects of chemical weathering, like the influence of glaciers on biogeochemical matter fluxes, are ill constrained. They should receive more attention to enable a thorough understanding of the processes steering this major compartment of the earth system.

Subsurface hydrothermal processes at marine shallow-water hydrothermal vents: Implications for assoc

May 14, 2013
noon - 1 p.m.
Slichter 3853

Presented By:

  • Roy Price - USC
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Shallow-sea hydrothermal vents have been documented on the summits of seamounts, on the flanks of volcanic islands, and in other near-shore environments characterized by high heat flow. Their easy accessibility, relative to deep-sea hydrothermal systems, makes them excellent natural laboratories to study a wide range of chemical, physical, and biological processes. This talk will present my recent investigations of geochemistry and microbiology from the shallow-sea hydrothermal vents off Milos Island (Greece), and will focus on attempts at understanding how the fluids got their unusual geochemistry (e.g., the occurrence of both a high- and low-salinity fluid relative to seawater (11 to 66 per mil), with extreme enrichment in arsenic (up to 78 ?M) in both fluid types), using a combination of elemental analyses and stable and radiogenic isotope data (oxygen, deuterium, and strontium). A follow-up investigation at the site indicated that, as a consequence of subsurface hydrothermal processes, associated seafloor microbial communities at the two sites with nearly equivalent temperature and pH were distinctly different. If time allows, I will discuss some of my upcoming research at two alkaline shallow-sea hydrothermal vents: The Strytan Hydrothermal Cones (Eyjafjordur, Iceland) and the Needle of Prony Hydrothermal System (PHS) (New Caledonia). Because of their unusual characteristics, both systems offer information about the possibility of life on other planets.

Simple granites and water

May 21, 2013
noon - 1 p.m.
Geology 1707

Presented By:

  • Adam Makhluf - UCLA
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description: Simple granitic quenched products from hydrothermal piston-cylinder experiments were analyzed by petrographic microscopy and scanning electron microscopy. By textural analysis, the eutectic phase diagram was determined for the simplest model system, albite-water, between 10.0-16.0 kbar and 650-1060o C. The critical end point was found at 16.5±0.8 kbar, 667±37o C and 50.0 weight percent (wt%) water. The same technique has been applied to a relatively more complex model granite (albite, quartz, k-spar). At deep crustal conditions of 10.0 kbar and T=800-900o C where granitic melts are believed to be produced, the water content was found to be underestimated by as much as 30%. The case for dehydration melting becomes increasingly difficult given these new results.