Category: Seminars

Speaker
Christy Till
USGS

Abstract
Evidence preserved in the petrology and chemical composition of erupted arc lavas provides the basis for understanding the processes that give rise to arc magmas. Work over the past 30 years has resulted in a preponderance of evidence to suggest arc parental magmas commonly contain up to 4–6 wt% H2O and some arc andesites contain up to 8–10 wt% H2O. However, considerable uncertainty remains about the physically and compositionally complex processes that lead to the generation of hydrous arc magmas with these observed water contents. In this talk, I will present new experimental evidence regarding the systematics of melting H2O-oversaturated and chlorite-bearing undepleted peridotite from 3 to 6 GPa. These experiments are then used to understand the temperatures and chemical reactions of mantle wedge melting that constitute the primary controls on (1) the location of arc volcanoes and (2) the width of the volcanic arc.

Speaker:
Susannah Porter

Speaker:
Christian Fischer
UCLA

Abstract:
Stone sculptures represent an important corpus of artifacts that have often survived the effects of time and their technical study provides the means for a better understanding of the social organization, religious beliefs and level of craftsmanship of ancient cultures. Beside style and iconography, the scientific analysis of the constitutive materials and their alterations is essential for the sourcing of raw materials and the conservation of the sculptures. Because of the very nature of the materials, their complexity and origin, as well as the methodology and analytical techniques used for their characterization, the scientific study of ancient stone sculptures illustrates perfectly the close and fascinating connections between archaeometry and the geosciences. By combining new portable technology and more traditional approaches, these relationships and the challenges posed by the analysis of archaeological stone materials will be discussed with examples from Cambodia and the Easter Island.

Speaker:
John Grotzinger

Abstract:
Scheduled to land in August of 2012, the Mars Science Laboratory (MSL) Mission was initiated to explore the habitability of Mars. This includes both modern environments as well as ancient environments recorded by the stratigraphic rock record preserved at the Gale crater landing site. The Curiosity rover has a designed lifetime of at least one Mars year (~23 months), and drive capability of at least 20 km. Curiosity’s science payload was specifically assembled to assess habitability and includes a gas chromatograph-mass spectrometer and gas analyzer that will search for organic carbon in rocks, regolith fines, and the atmosphere (SAM instrument); an x-ray diffractometer that will determine mineralogical diversity (CheMin instrument); focusable cameras that can image landscapes and rock/regolith textures in natural color (MAHLI, MARDI, and Mastcam instruments); an alpha-particle x-ray spectrometer for in situ determination of rock and soil chemistry (APXS instrument); a laser-induced breakdown spectrometer to remotely sense the chemical composition of rocks and minerals (ChemCam instrument); an active neutron spectrometer designed to search for water in rocks/regolith (DAN instrument); a weather station to measure modern-day environmental variables (REMS instrument); and a sensor designed for continuous monitoring of background solar and cosmic radiation (RAD instrument). The various payload elements will work together to detect and study potential sampling targets with remote and in situ measurements; to acquire samples of rock, soil, and atmosphere and analyze them in onboard analytical instruments; and to observe the environment around the rover. The 155-km diameter Gale Crater was chosen as Curiosity’s field site based on several attributes: an interior mound of ancient flat-lying strata extending almost 5 km above the elevation of the landing site; the lower few hundred meters of the mound show a progression with relative age from clay-bearing to sulfate-bearing strata, separated by an unconformity from overlying likely anhydrous strata; the landing ellipse is characterized by a mixture of alluvial fan and high thermal inertia/high albedo stratified deposits; and a number of stratigraphically/geomorphically distinct fluvial features. Samples of the crater wall and rim rock, and more recent to currently active surface materials also may be studied. Gale’s regional context and strong evidence for a progression through multiple potentially habitable environments, represented by a stratigraphic record of extraordinary extent, insure preservation of a rich record of the environmental history of early Mars.

Speaker:
Paul Weiss
CNSI/UCLA

Abstract:
Precise clusters offer a new set of building blocks with unique properties that can be leveraged both individually and in materials in which their coupling can be controlled by choice of linker, dimensionality, and structure. Initial measurements in both of these worlds have been made. Isolated adsorbed or tethered clusters are probed with low-temperature scanning tunneling microscopy and spectroscopy. Even closely related elements behave differently on identical substrates. Surprising spectral variations are found for repeated measurements of single isolated, tethered clusters. In periodic solids, precise clusters joined by linkers can be measured experimentally and treated theoretically with excellent agreement, in part due to the relatively weak coupling of the clusters. This coupling can be controlled and exploited to produce materials with tailored properties. Some of the rules of thumb for predicting these properties are being developed through these initial studies and the limit to which they can be applied is being explored.

Speaker:
Hilke Schlichting

Abstract:
I will discuss recent insights that we have gained into planet formation and debris disks. In the first half of my talk, I will focus on the Kuiper belt, located at the outskirts of our planetary system, and the formation of debris disks. I will show how studying small km-sized Kuiper belt objects enables us to put our Kuiper belt into context of debris disks around other stars and I will explain how we can use the size distribution of small Kuiper belt objects and debris disks to gain insights into collisional cascades and the material properties of the objects themselves. In the second half, I will review dynamical models and geochemical constraints from the Earth, Moon and Mars and discuss their implications for the last stage of terrestrial planet formation.

Speaker:
Thure Edward Cerling

Speaker:
Bethany Ehlmann
Caltech

Abstract:
The emerging picture of Mars’ first billion years includes diverse environments involving liquid water and chemical alteration. Clay, carbonate, chloride, and sulfate minerals have all been detected and mapped from orbit in coherent geologic units. When near-infrared spectroscopic detections of minerals from the orbiting CRISM imaging spectrometer are coupled with high-resolution images of morphology provided by orbiting cameras, distinctive aqueous, potentially habitable, environments can be identified, preserved in the geologic record. I will give a global overview of the most recent findings, delve into the details of transitions recorded in a few key stratigraphic sections, and discuss the hypothesis that the most widespread and long-lived aqueous environments on early Mars were in the subsurface.

Speaker:
An Yin
UCLA

Speaker:
Raj Dasgupta
Rice University

Abstract:
The Earth is unique among the terrestrial planets in our solar system in having a fluid envelope that fosters life. The key behind Earth’s habitable climate is well-tuned cycles of carbon (C) and other volatiles. While on ten to thousands of year time-scales the chemistry of fluids in the atmosphere, hydrosphere, and biosphere is dictated by fluxes of carbon between the near surface reservoirs, over million to billion years this is maintained by chemical interactions of carbon between the Earth’s interior, more specifically the Earth’s mantle, and the exosphere. This is because of the fact that the estimated total mass of C in the mantle is greater than that observed in the exosphere and the average residence time of carbon in the mantle is on the ≥1 Ga. But how did the Earth’s mantle attain and maintain the inventory of mantle carbon over geologic time and is the residence time of carbon in the mantle as constrained by the present-day fluxes a true reflection of the carbon ingassing and outgassing rates throughout the history? Also, when in the history of the planet carbon inventory of the mantle got established and how did it change through geologic time? The answers to these questions are important because understanding the origin and chemistry of carbon and how they regulate feedbacks between the planet’s interior and the atmosphere is of fundamental importance owing to far-reaching implications for a number of fields of natural sciences, such as the thermal history of the Earth, internal differentiation, long-term evolution of climate, and origin and evolution of life. Because the abundance and mode of storage of mantle carbon are central to carbon’s role in global geodynamics, it is critical to constrain the processes that modulated the carbon inventory of the Earth’s mantle through time. In this talk, I will try to review ingassing, outgassing, and storage mechanisms of terrestrial carbon, from the time period of early planetary differentiation and magma ocean in the Hadean to the plate tectonic cycles of the modern Earth through Phanerozoic.