Colloquium Schedule
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January 30, 2015
3:00pm in PLS 1140
Lara Wagner from CIW - Department of Terrestrial Magnetism
Can Flat Slabs Really Do That? New Constraints from New Data
February 6, 2015
3:00pm in PLS 1140
Rita Parai from Carnegie - DTM
Deep Earth volatile inventories and the formation of the Moon

Abstract: Noble gases in mantle-derived rocks provide unique insights into the evolution of planetary volatile budgets. We measured noble gas isotopic compositions in a suite of mid-ocean ridge basalts with sufficient precision to demonstrate that atmospheric heavy noble gases are recycled to the deep mantle. We find that although significant Xe recycling occurs, the Xe isotopic compositions of mantle sources have not been entirely overprinted, but rather preserve a record of very early differentiation of the upper mantle from the mantle plume source. Based on Xe isotopes produced by short-lived radioactive species, differences in the delivery and retention of volatiles in the plume source and upper mantle must have been established within the first 100 million years of Earth history. Accordingly, the two mantle reservoirs cannot have been completely homogenized by 4.45 Gyr of mantle convection. The fission isotopes of Xe indicate that the plume source has experienced less degassing than the upper mantle and has therefore experienced less processing by partial melting. Lastly, based on the proportions of Xe produced by different short-lived radionuclides in the first ~500 million years of Earth history, we compute an upper mantle Xe closure age of ~44-70 million years after the start of the Solar System, signifying that catastrophic loss of gas from the upper mantle associated with lunar formation occurred before that time.

Additional Information: Postdoctoral Fellow

February 20, 2015
3:00pm in PLS 1140
Colin Jackson from CIW - Department of Terrestrial Magnetism
An oxygen isotope perspective on Earth's oldest silicate reservoir

Abstract: We test the hypothesis that plume mantle with high-3He/4He signatures contains cosmochemically distinct O compared to the bulk Earth. This test is motivated by the recent observations of short-lived isotopic heterogeneity associated with high-3He/4He plume rocks and by the concept that large, stochastic additions of materials occurred during the final stages of accretion. Our measurements of olivines with high-3He/4He values indicate that high-3He/4He mantle has a uniform δ18O and Δ17O composition. δ18O measurements on high 3He/4He olivine are displaced to lower values than mean mantle olivine and are shown to correlate with radiogenic isotopes (He, Nd, Sr, and Nd). These observations provide evidence that O remains coupled to the more incompatible elements during melt production and migration processes, and that O measurements of high-3He/4He olivine have bearing on high-3He/4He mantle. To high precision, ∆17O determinations for high-3He/4He olivine are indistinguishable from bulk mantle (Δ17O San Carlos olivine - Δ17O3He/4He olivine = -0.002 ± 0.004 ‰). This indicates that there is no major element evidence for heterogeneous accretion in the high 3He/4He source. There are two scenarios to account for the similarity of Δ17O between high-3He/4He olivines and bulk mantle olivine: 1) extensive homogenization of the high-3He/4He source and bulk mantle has obscured any Δ17O differences initially present, or 2) the high-3He/4He source was isolated after the last significant shift of Δ17O in the bulk mantle. The first scenario is favored given the observations of short-lived isotopic heterogeneity associated with plumes and the available evidence regarding the timing of the Moon-forming impact.

March 6, 2015
3:00pm in PLS 1140
Marcia McNutt from American Association for the Advancement of Science
Geoscience Problem Solving for Sustainability: Focus on Climate and Energy

Abstract: Geoscientists are and will continue to be at the forefront of finding solutions to many of the world¹s most pressing challenges for how to find solutions to many of problems in maintaining and enhancing the quality of life for the billions of people on Earth in a sustainable manner. At the center of this challenge is the energy-climate change nexus: how to provide abundant energy to power modern society without continuing to contribute to the risk of climate change. Geoscientists are solving these problems by helping to find energy sources with lower CO2 emissions, providing the science for climate change adaptation, and exploring the prospects for climate intervention. Hand-in-hand with these issues, geoscientists need to be cognizant of the continuing need for abundant critical materials and water for alternative energy technologies and energy production.

March 27, 2015
3:00pm in PLS 1140
Mike Brown from University of Maryland, College Park
The unification of Gondwana: From sapphires to diamonds at the dawn of the Phanerozoic---for the times they are a-changin' 

Additional Information: Distinguished Faculty Lecture

April 3, 2015
3:00pm in PLS 1140
Jeroen Ritsema from U. Michigan
Blobs in the bowels of the Earth

Abstract: Large-scale density variations in Earth's mantle cause interior flow, tectonic plate motions and lithosphere dynamics. Images of
Earth's heterogeneous composition and variable temperature come primarily from the analyses of earthquake-generated seismic waves. Seismic CAT scans reveal the stagnation and deep descent of slabs of oceanic lithosphere, passive spreading at mid-ocean ridges, and, with some imagination, hot ascending plumes beneath mid-plate volcanoes. Direct constraints on density can be obtained from whole-Earth free-oscillation frequency measurements. Our analysis of unique Stoneley modes suggest that the largest blobs (i.e., the so-called LLSVPs) in the lowermost mantle are buoyant. They provide a link between intraplate volcanism and dynamic uplift to deep mantle dynamics.

April 10, 2015
3:00pm in PLS 1140
Distinguished Alumnus
April 24, 2015
3:00pm in PLS 1140
Mary Anne Holmes from Univ. Nebraska and NSF
May 1, 2015
3:00pm in PLS 1140
June Wicks from Princeton University

The coordinator for the Colloquium Series is Dr. Vedran Lekic. You can contact him at