EPSS Colloquium - winter-2016
Dynamic Mars: First Results from MAVEN
Jan. 7, 2016
4 p.m. - 5 p.m.
Geology 3656
Presented By:
- Jasper Halekas - Uiowa
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Dynamic Mars: First Results from MAVEN
The Mars Atmosphere and Volatile Evolution (MAVEN) mission achieved orbit around Mars a little over one Earth year ago. In the short half Mars year since then, MAVEN has begun to build a comprehensive picture of the structure and dynamics of the Martian atmosphere, ionosphere, and magnetosphere, the coupling between them, and the escape of atmospheric gases from them. Many processes that we observe at Mars have analogues at Earth, Venus, and even comets, and comparative planetology is critical in building our understanding of the Martian system. However, in the final analysis Mars is a completely unique planet (aren't they all?). Ultimately, we seek to understand not just how Mars works in the present epoch, but how Mars became the way it is today. I'll present to you some of the first building blocks toward that goal, focusing primarily on the structure and dynamics of the Martian ionosphere and magnetosphere, the ion escape channels from Mars, and the response of the system to extreme events.
From Hell to the Himalaya
Jan. 14, 2016
4 p.m. - 5 p.m.
Geology 3656
Presented By:
- T.M. Harrisson - UCLA
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From Hell to the Himalaya
Detrital zircons as old as nearly 4.4 Ga offer insights into the earliest moments of Earth history. Results of geochemical investigations of these grains have been interpreted to indicate their formation in near-H2O saturated meta- and peraluminous magmas under a relatively low (15-30°C/km) geotherm. A key feature in pursuing a petrotectonic model that explains the full spectrum of these observations is their seeming contrast to most Phanerozoic magmatic zircons. The ~22 Ma Arunachal leucogranites of the eastern Himalaya appear, however, to be a rare exception to this generality. They show clear evidence of wet basement melting and are dominated by the same inclusion population and P-T conditions. We suggest that the Arunachal leucogranites originated in the hangingwall of a megathrust that carried H2O-rich foreland sediments to depths of >20 km whereupon de-watering reactions released fluids that fluxed hangingwall anatexis. Modeling suggests the thermal structure of this continental collision environment could have been broadly similar to a Hadean ocean-continent subduction zone. The similarity of these two environments, separated by over 4 Ga may explain the remarkably similar Hadean and Arunachal leucogranite zircons.
Oligarchs, Orphans and Planetary Diversity
Jan. 21, 2016
4 p.m. - 5 p.m.
Geology 3656
Presented By:
- Erik Asphaug - ASU
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Oligarchs, Orphans and Planetary Diversity
Terrestrial planets grew in a series of similar-sized collisions that swept up most of the next-largest bodies. Theia was accreted by the Earth to form the Moon according to this theory. The stochastic nature of this process can explain why Mercury and Mars are so completely different (Asphaug and Reufer 2013, 2014). Planetesimals likewise might have finished their accretion in a sequence of ‘junior giant impacts’, scaled down in size and velocity, with important differences. I will review the inefficiency and complexity of pairwise accretion, and show how it influences the origin of planetesimals and the diversity of meteorites and primary asteroids. I will argue that Vesta and Ceres are two of the largest planetesimals that accreted in the region, the last of ~100 comparable oligarchs that were scattered by giant planet migration. The scenario offers an explanation for the remarkable diversity of ~100-300 km asteroids and associated meteorites, and furthermore predicts that most asteroids are 'orphans' of vanished planetesimals. The Psyche mission, currently in Phase A study, propose to visit one of the largest of the mantle-stripped remnants.
Recovery Following the End-Triassic Mass Extinction
Jan. 28, 2016
4 p.m. - 5 p.m.
Geology 3656
Presented By:
- Frank Corsetti - USC
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Recovery Following the End-Triassic Mass Extinction: Insights from Mercury Anomalies and Their Relationship to the Central Atlantic Magmatic Province
The end-Triassic mass extinction overlapped with the eruption of the Central Atlantic Magmatic Province (CAMP), and release of CO2 and other volatiles has been implicated in the extinction. Thus, the Triassic-Jurassic transition offers an opportunity to study the Earth system response to rapid CO2 release. However, the timing of marine biotic recovery versus CAMP eruptions remains uncertain because the primary record of volcanism is on land and the main archive of faunal data is marine: high resolution correlation between terrestrial and marine remains an issue. Here, we use Hg concentrations, Hg/TOC, and Hg isotopes as indicators of CAMP volcanism in continental shelf sediments, the primary archive of faunal data. In Triassic-Jurassic strata, Muller Canyon, Nevada, Hg and Hg/TOC levels are low prior to the extinction, rise sharply in the extinction interval, peak just prior to the appearance of the first Jurassic ammonite, and remain above background in association with a depauperate (low diversity) earliest Jurassic fauna. The return of Hg to pre-extinction levels is associated with a significant pelagic and benthic faunal recovery. Hg isotopes display no significant mass independent fractionation (MIF) within the extinction and depauperate intervals, consistent with a volcanic origin for the Hg. The Hg and paleontological evidence from the same archive indicate that significant biotic recovery did not begin until CAMP eruptions ceased. Notably, carbonate dominated ecosystems did not recover for ~1 million years following the last eruption of CAMP, longer than the typical duration implied for ocean acidification events implying other factors may have played a role.
History of the geomagnetic field: what do we know and how do we know it?
Feb. 4, 2016
4 p.m. - 5 p.m.
Geology 3656
Presented By:
- Lisa Tauxe - UCSD
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History of the geomagnetic field: what do we know and how do we know it?
The Earth’s magnetic field is generated in the outer core through motions of the conducting liquid metal. Most models of this so-called ‘geodynamo’ require the existence of a solidifying inner core to drive convection. Constraints on when the inner core began to form depend on estimates of thermal conductivity of core, but recent computational and experimental studies predict very different ages ranging from less the half a billion to nearly two billion years ago. Because of the assumed connection of the inner core to the generation of the geomagnetic field, records of the geomagnetic field, in particular the strength of the ancient field, through time could, in principle, allow us to date the timing of the formation of the inner core. I will discuss the experimental requirements of studying past field strength and what if anything can be learned from the large and growing database of paleomagnetic data through time.
A world in a grain of...zircon? What crystal records reveal about magma reservoirs
Feb. 11, 2016
4 p.m. - 5 p.m.
Geology 3656
Presented By:
- Kari Cooper - UC Davis
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A world in a grain of...zircon? What crystal records reveal about magma reservoirs
Upper-crustal magma reservoirs are important sites of magma mixing, crustal refining, and magma storage, and control many aspects of magmatic activity including whether magmas erupt or freeze as plutons in the crust, the chemical composition of erupted magmas or plutons, and the hazard potential for volcanoes. Crystals residing in these reservoirs represent valuable archives of the chemical and physical evolution of reservoirs and the time scales of this evolution. This presentation addresses the question of “What do crystals “see” and record about processes within the upper crust? Two general observations emerge from study of the ages of crystals, combined with crystal-scale geochemical data: 1) Patterns of isotopic and trace-element data over time in zircon crystals from a given magmatic show systematic changes consistent with extraction of melts from a long-lived (up to 100s of kyr), heterogeneous crystal mush. 2) Thermal histories of magma storage derived from crystal records also show that the vast majority of time recorded by major phases was spent in storage as a crystal mush, perhaps at near-solidus conditions. These observations are consistent with a general lack of geophysical observations of large, melt-rich bodies beneath volcanoes and suggests rapid assembly of magma bodies prior to eruption.
Pluto -- The Pugnacious Planet
Feb. 18, 2016
4 p.m. - 5 p.m.
5834 SLICHTER HALL
Presented By:
- Fran Bagenal - University of Colorado
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Pluto -- The Pugnacious Planet
Even in our wildest dreams none of us on the New Horizons team really expected Pluto to produce such riches: water ice mountains as big as the Rocky Mountains, glaciers of nitrogen ice, black hydrocarbons covering aging craters, fresh methane frost dusting tops of mountains, pitted landscapes shaped by sublimation, an ice volcano as big as Mauna Kea, and, most bizarre of all, a landscape that resembles the skin of a snake. My favorite image is a glance back, outbound from the flyby, looking at an icy landscape back-lit by layers of atmospheric hazes. In this talk I describe how New Horizons came to be, how the spacecraft got to Pluto, and how the findings are challenging our understanding of ice worlds in the outer solar system. A surprisingly low rate of atmospheric escape explains why Pluto is more like Mars than a comet. And I will explain why New Horizons does not carry a magnetometer.
Linking mantle flow, surface processes, climate and density variations in the Earth’s crust
Feb. 25, 2016
4 p.m. - 5 p.m.
Geology 3656
Presented By:
- Jean Braun Grenoble - Institut des Sciences de la Terre, Université Joseph Fourier de Grenoble, France
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Linking mantle flow, surface processes, climate and density variations in the Earth’s crust
Dynamic topography is generated by the viscous stress exerted at the base of the lithosphere by the convecting mantle. Constraining the potential contribution of past and present dynamic topography to vertical surface uplift has become essential to comprehend parts of the geological record, but also to validate mantle flow models. For example, episodes of rapid, yet extensive erosion of continental interiors, such as the Late Cretaceous erosional event that affected the southern African craton, can only be explained by large-scale vertical uplift/subsidence generated in the mantle. But how can low amplitude, long wavelength dynamic topography be rapidly eroded is poorly understood. Using novel numerical methods to solve the basic laws governing the evolution of landforms on geological time scales, I will provide a simple explanation for this paradox and apply it to understand the large erosional events that accompanied uplift of the Colorado Plateau and the South African Plateau, respectively. In the second part of my presentation, I will also discuss how lateral variations in surface rock density can strongly affect the response of the crust/lithosphere system to surface erosion and propose how it can explain why, despite its relatively high density, the metamorphic core of many orogenic belts, such as the Tauern Window in the Eastern Alps, is found at the highest topographic levels.
Geophysical and geochemical constraints on mantle temperature and composition beneath the oceans
March 4, 2016
4 p.m. - 5 p.m.
Geology 3656
Presented By:
- Colleen Dalton -
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Geophysical and geochemical constraints on mantle temperature and composition beneath the oceans
Plate tectonics is expressed most simply in oceanic plates. Various types of observations, including seafloor bathymetry and heat flow, provide general support for a simple model of the evolution of the ocean basins. In this model passively upwelling mantle melts beneath the mid-ocean ridge, the melt ultimately forms the oceanic crust, and a thermal boundary layer grows thicker with distance from the ridge and therefore with age of the seafloor. In this talk I will present two examples, using seismic data, that this simple model requires some refinement. First, I will describe a global comparison of seismic velocity, basalt chemistry, and axial depth along the mid-ocean ridge system that allows us to quantify mantle temperature variations beneath the ridge. Second, I will describe our seismic study of the upper mantle beneath the Atlantic Ocean. Notably, the dependence of seismic velocity on seafloor age is different from the age dependence in the Pacific upper mantle, which suggests different cooling histories for the two basins.
Dawn@Ceres, Rendezvous with an Astrobiological Target
March 11, 2016
4 p.m. - 5 p.m.
Geology 3656
Presented By:
- Julie Castillo-Rogez - JPL
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Dawn@Ceres, Rendezvous with an Astrobiological Target
With the Dawn spacecraft in orbit since March 2015, Ceres is de facto the best observed icy-rich body explored to date. Dawn has revealed an intriguing world full of contrasts, where old craters neighbor recent cryovolcanic activity and the darkest materials sit right next to some of the brightest features in the inner Solar system. This seminar will introduce the Dawn mission and the new picture of Ceres' evolution and current state that is emerging from the combination of geology, mineralogy, elemental, and gravity observations returned so far. The seminar will also draw parallels between Ceres and other large volatile-rich bodies and show how Dawn's discoveries are addressing longtime gaps in our understanding of ocean worlds.