Abstracts and Schedule: DTM Science at 2017 AGU Fall Meeting

Sunday, December 10, 2017

 

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S11C-0614: ­The Carnegie Quick Deploy Box (QDB) for use with broadband and intermediate period sensors

Lara Wagner | Monday, December 11, 2017 | 08:00 - 12:20 | New Orleans Ernest N. Morial Convention Center - Poster Hall D-F

Abstract: Recent data processing advances have increased the call for dense recordings of teleseismic data. However, traditional broadband field installations typically comprise 1) a sensor vault 2) a field box to hold the recording and power systems, and 3) a solar panel mount. The construction of these installations is time consuming and requires bulky construction materials, limiting the number of stations that can be installed from a single vehicle without repeated trips to a storage facility. Depending on the deployment location, watertight containers for both vault and field box can be difficult to find, resulting in a loss of data due to flooding. Recent technological improvements have made possible the direct burial of sensors (no vault required) and a reduction in the size of the solar panels needed to run a station. With support from the Brinson Foundation, we take advantage of these advances to create a field box/shipping container that will greatly simplify these types of seismic deployments.

The goal of the Carnegie Quick Deploy Box (QDB) is to have everything needed for an intermediate period station install (except battery and shovel) contained in a single box for shipment, and to be able to leave everything (except the shovel) in that box when the station is deployed. The box is small enough (~13"x13"x21") and lightweight enough (< 35 lbs) to be checked as airline luggage. The solar panel mount can be attached securely to the top of the box, but it can also be pole mounted with U-bolts or hose clamps. The sensor can be direct-buried. The sensor cable and solar panel cable plug into watertight bulkhead-fitted plugs on the outside of the box that are in turn plugged into the digitizer and power regulator inside the box. Our prototype boxes (Pelican Cases) have proved watertight when submerged for days. This equipment has been tested in Alaska in winter and Nicaragua in summer without failure due to flooding or power. The cost for parts for a single box (not including sensor cable, sensor, or digitizer) is ~$500. The setup is simple, and can be completed in a matter of minutes once the sensor is installed. QDBs such as ours will make possible a dramatic increase in the number of stations that can be installed, while also significantly decreasing the cost of deployment per station by reducing vehicle time, fuel, personnel time, and shipping costs.

Authors: Diana Roman, Lara S. Wagner, Tyler Bartholomew, Steven Golden, Brian Schleigh


V12A-04: Primordial domains in the depleted upper mantle identified by noble gases in MORBs

Jonathan Tucker | Monday, December 11, 2017 | 11:20 - 11:35 | New Orleans Ernest N. Morial Convention Center - 210

Abstract: The distribution of noble gas isotopic compositions in the mantle provides important constraints on the large-scale mantle evolution, as noble gases can trace the interaction between degassed, or processed, mantle domains and undegassed, or primitive, mantle domains. Data from the radiogenic He, Ne, Ar and Xe isotopic systems have shown that plume-related lavas sample relatively undegassed mantle domains, and the recent identification of isotopic anomalies in the short-lived I-Xe and Hf-W isotopic systems in plume-related lavas further suggests that these domains may be ancient, dating back to Earth's accretion. However, little is known about the potential variability of the heavy noble gas systems and the distribution of undegassed domains in the ambient upper mantle not influenced by plumes.

Here, we present new high-precision He, Ne, Ar, and Xe isotopic data for a series of MORBs from a depleted section of the subtropical north Mid-Atlantic Ridge, distant from any known plume influence. Some samples have extremely low (unradiogenic) 4He/3He, 21Ne/22Ne, 40Ar/36Ar, and 129Xe/130Xe ratios, including some of the lowest values ever determined for MORBs. Such unradiogenic compositions are reminiscent of OIBs and plume-influenced E-MORBs, suggesting the presence of a relatively undegassed or primitive reservoir in the source of these depleted MORBs. The He, Ne, and Ar isotopic systems are sensitive to the long-term degassing history, suggesting that this domain in the MORB source is ancient. The 129Xe/130Xe ratio is sensitive to degassing only during the first ~100 Ma of Earth history, suggesting that some of the isotopic character of these samples has been preserved since Earth's accretion.

Together, these observations suggest that primordial or undegassed material is not only sampled in plumes-related lavas, but also normal, depleted MORBs. Along with data from E-MORBs in the southern EPR (Kurz et al., 2005), southern MAR (Sarda et al., 2000), and equatorial MAR (Tucker et al., 2012), our new data suggest that primordial material may be present throughout the MORB source. Such material could either have been stored for a long term in the upper mantle, or recently mixed into the upper mantle from a deeper reservoir.

Authors: Jonathan Tucker, Sujoy Mukhopadhyay, Charles H. Langmuir, Cedric Hamelin, Jocelyn Fuentes


V12A-06: Hadean silicate differentiation revealed by anomalous 142Nd in the Réunion hotspot source

Bradley Peters | Monday, December 11, 2017 | 11:50 - 12:05 | New Orleans Ernest N. Morial Convention Center - 210

Abstract: Geochemical and geophysical data show that volcanic hotspots can tap ancient domains sequestered in Earth's deep mantle. Evidence from stable and long-lived radiogenic isotope systems has demonstrated that many of these domains result from tectonic and differentiation processes that occurred more than two billion years ago. Recent advances in the analysis of short-lived radiogenic isotopes have further shown that some hotspot sources preserve evidence for metal-silicate differentiation occurring within the first one percent of Earth's history. Despite these discoveries, efforts to detect variability in the lithophile 146Sm-142Nd (t1/2 = 103 Ma) system in Phanerozoic hotspot lavas have not yet detected significant global variation. We report 142Nd/144Nd ratios in Réunion Island basalts that are statistically distinct from the terrestrial Nd standard ranging to both higher and lower 142Nd/144Nd. Variations in 142Nd/144Nd, which total nearly 15 ppm on Réunion, are correlated with 3He/4He among both anomalous and non-anomalous samples. Such behavior implies that there were analogous changes in Sm/Nd and (U+Th)/3He that occurred during a Hadean silicate differentiation event and were not completely overprinted by the depleted mantle. Variations in the 142Nd-143Nd compositions of Réunion basalts can be explained by a single Hadean melting event producing enriched and depleted domains that partially re-mixed after 146Sm was no longer extant. Assuming differentiation occurred at pressures where perovskite is stable, anomalies of the magnitude observed in Réunion basalts require melting of at least 50% across a wide depth range, and up to 90% for melting at pressures near those of the deepest mantle. Models with best fits to Nd isotope data suggest this differentiation occurred around 4.40 Ga and mixing occurred after 4 Ga. This two-stage differentiation process nearly erased the ancient, anomalous 142Nd composition of the Réunion source and produced the relatively invariant 143Nd signature that is a hallmark of Réunion hotspot lavas. Given growing evidence that the Réunion hotspot source represents an unusually ancient, primitive mantle domain, these new data argue that Réunion is a critical source of information regarding the formation and preservation of ancient heterogeneities in Earth's deep interior.

Authors: Bradley Peters, Richard Carlson, James M. Day, Mary Horan


T14A-01: Inheritance vs ongoing evolution of the passive margin lithosphere in the southeastern United States: A comparison of <50Ma tectonism with tomographically imaged lithospheric structures.

Lara Wagner | Monday, December 11,  2017 | 16:00 - 16:15 | New Orleans Ernest N. Morial Convention Center - 215-216

Abstract: The southeastern United States is an archetypical passive margin, and yet significant evidence exists that this region, separated from the nearest plate boundary by thousands of kilometers and over 170 Ma, has experienced significant tectonism since the Eocene. This tectonism includes volcanism, uplift/deformation, and ongoing seismicity such as the 2011 Mw = 5.8 Mineral, VA earthquake and the 1886 M=7 Charleston, SC event. For each of these examples, numerous theories exist on their respective causes. However, there are two common themes that span all of these types of events: first, their proximity to regional terrane boundaries whose inherited structures could play a role; second, the nature of the mantle lithosphere underlying them.

We present a recently completed inversion of seismic Rayleigh waves for the shear wave velocity structure of the uppermost 150 – 200 km beneath the southeastern United States. This inversion includes not only EarthScope Transportable Array data, but also the data from the 85 broadband stations installed as part of the Flex Array SouthEastern Suture of the Appalachian Mountains Experiment (SESAME). We find some evidence for structures inherited from previous episodes of rifting, accretion, and orogenesis. However, we also find several examples of mantle lithospheric structures that spatially correlate strongly with Eocene to recent tectonic activity, but do not correlate to any known inherited geometries. These examples include a small but pronounced sub-crustal low velocity anomaly beneath the Eocene volcanoes in western Virginia and eastern West Virginia, as well as evidence for mantle delamination beneath the Cape Fear Arch and uplifted portions of the Orangeburg Escarpment. We will discuss these, along with instances of recent tectonism in our study area that do not bear any obvious relationship to lithospheric structures, in order to shed light on the causes of ongoing tectonic activity in this supposedly "passive" margin setting.

Authors: Lara Wagner, Karen M. Fisher, Robert B. Hawman, Emily Hopper, Dorran Howell


V33B-0530: On the origin of cratonic 'high-mu' isotopic signatures

Jesse Reimink | Wednesday, December 13,  2017 | 13:40 - 18:15 | New Orleans Ernest N. Morial Convention Center - Poster Hall D-F

Abstract: Some Archean cratons (i.e. Slave, Wyoming) contain Neoarchean granitoids with initial Pb isotopic compositions indicative of derivation from sources characterized by high time-integrated U/Pb ratios (high-mu [1]). Single-stage high-m precursor source reservoir separation from the depleted mantle occurred no later than ~3.9 Ga [2]. However, multi-stage separation could have occurred in the Hadean, suggesting that recycling or reworking of Eoarchean/Hadean crust played a significant role in the generation of Neoarchean granitic crust in many cratons. The Sm-Nd system is similar to the U-Pb system in that it has a short-lived parent-daughter pair (146Sm-142Nd) that is sensitive to very early differentiation events, as well as a long-lived parent-daughter pair (147Sm-143Nd) that is sensitive to differentiation throughout all of Earth history. The 103 Ma half-life of 146Sm makes it sensitive only to Sm/Nd fractionation that occurred in the Hadean, providing a useful tracker for very early differentiation events. Indeed, evidence for Neoarchean remelting of ancient crust in another craton has come from analyses of the paired Sm-Nd isotope systems from the Hudson Bay terrane of the northeastern Superior Province. These results indicate that the source of 2.7 Ga Hudson Bay terrane granitoids was Hadean mafic crust, and not Eoarchean felsic crust [3].

Here, we present new data from Neoarchean granites located in the Slave and Wyoming cratons, along with modeling of the dual paired-isotope systems of U-Pb and Sm-Nd to achieve a tighter constraint on the composition of the precursors and the timing of their melting. Combining our newly collected 142Nd data with the high-m signature of these Neoarchean rocks, we evaluate precursor source separation ages along with the source Sm/Nd and U/Pb compositions. In the simplest end-member scenarios, use of the 142Nd system allows us to test whether the cratonic high-mu signature was created by melting of Hadean mafic crust or Eoarchean felsic crust. Differences between these models have major implications for the longevity of mafic crust on the ancient Earth as well as the growth rate and recycling history of the continents.

[1] Oversby, 1978, EPSL; [2] Kamber et al., 2003, CMP; [3] O'Neil and Carlson, 2017; Science

Authors: Jesse Reimink, Richard Carlson, Steven B. Shirey, D. Graham Pearson, Balz Samuel Kamber


V33F-0577: Interaction of ultra-depleted MORBs with plagioclase: implications for CO2/Ba ratios

Kei Shimizu | Wednesday, December 13,  2017 | 13:40 - 18:00 | New Orleans Ernest N. Morial Convention Center - Poster Hall D-F

AbstractCarbon in Earth's upper mantle can significantly reduce its solidus temperature, which in turn can affect other physical properties through generation of partial melt. Carbon content in the depleted upper mantle can be estimated using ultra-depleted mid-ocean ridge basalt (UD-MORB) glasses and melt inclusions that are undersaturated in CO2. CO2 has been shown to behave as a highly incompatible element during mantle melting both through natural samples and experiments. Given its highly incompatible behavior, CO2/Ba and CO2/Nb ratios in CO2 undersaturated UD-MORBs have been used to estimate the CO2/Ba and CO2/Nb ratios and carbon content in Earth's upper mantle.

A potential issue with part of this approach is the effect of melt-plagioclase chemical interaction on the CO2/Ba ratios in UD-MORBs. Plagioclase is ubiquitous in the oceanic crust and is enriched in Ba relative to other phases. Chemical interactions (assimilation and/or diffusion) between MORB melts and plagioclase bearing rocks have been shown to affect the Ba (and Sr and Eu) concentrations in MORBs, implying that such processes may also affect their CO2/Ba ratio. Hence, understanding the effect of chemical interaction between plagioclase and UD-MORBs is important for having better constraints on CO2/Ba ratio and carbon content in Earth's upper mantle.

In this study, we report on the compositions of olivine-hosted melt inclusions and glasses from the Siqueiros and Garrett transform faults. A subset of melt inclusions in lavas from both transform faults show potential signatures of chemical interaction with plagioclase such as low CO2/Ba, Nb/Ba, and Nd/Sr. CO2 degassing cannot explain the low CO2/Ba ratio in the samples as they are undersaturated in CO2. To better understand the effect of chemical interaction with plagioclase on the composition of UD-MORBs, we model end-member scenarios, which are (1) assimilation of plagioclase and (2) diffusion of elements from plagioclase into the UD-MORBs. In general, the trends produced by these end-member scenarios bracket those observed in the samples (trends between CO2/Ba, Nb/Ba, and Nd/Sr as well as between Al2O3, FeO, and MgO). Hence, chemical interaction with plagioclase may affect the CO2/Ba ratio in UD-MORBs, and care should be taken to evaluate this effect using Nd/Sr and Nb/Ba ratios.

Authors: Kei Shimizu, Erik Hauri, Alberto E. Saal, Michael R. Perfit, Roger Hekinian


DI33B-0410: Sensitivity of geomagnetic reversal rate on core evolution from numerical dynamos

Peter Driscoll | Wednesday, December 13,  2017 | 13:40 - 18:00 | New Orleans Ernest N. Morial Convention Center - Poster Hall D-F

AbstractThe paleomagnetic record indicates the geodynamo has evolved from frequently reversing to non-reversing (superchron) magnetic states several times over the Phanerozoic. Previous theoretical studies demonstrated a positive correlation between magnetic reversal rate and core-mantle boundary heat flux. However, attempts to identify such a correlation between reversal rates and proxies for internal cooling rate, such as plume events, superchron cycles, and subduction rates, have been inconclusive. Here we revisit the magnetic reversal occurrence rate in numerical dynamos at low Ekman numbers (faster rotation) and high magnetic Prandtl numbers (ratio of viscous and magnetic diffusivities). We focus on how the correlation between reversal rate and convective power depends on the core evolution rate and on other factors, such as Ek, Pm, and thermal boundary conditions. We apply our results to the seafloor reversal record in an attempt to infer the energetic evolution of the lower mantle and core over that period.

Authors: Peter Driscoll, Christopher J. Davies


V43G-01: Volatiles in off-axial mid-ocean ridge basalts and the role of the metasomatized oceanic mantle lithosphere (Invited)

Kei Shimizu | Thursday, December 14,  2017 | 13:40 - 13:55 | New Orleans Ernest N. Morial Convention Center - 208-209

Abstract: Volatiles (CO2, H2O, F, Cl, S) significantly affect the physical properties of the upper mantle (e.g. solidus, viscosity, electrical conductivity, and seismic velocity). Hence, it is important to estimate their concentrations in the upper mantle as well as its distribution. In this regard, mid-ocean ridge basalts (MORBs) that erupt off-axis (seamounts and transform faults) are useful as they preserve greater compositional heterogeneity compared to those those erupted on-axis. In this study, however, we show that certain chemical signatures of off-axis MORBs may record asthenosphere derived melt percolating and partially melting a metasomatised lithospheric mantle.

In our previous study [1], we reported major and trace elements, and volatile contents and Sr, Nd, and Pb isotopes [1-3] of off-axis MORB glasses (Northern East Pacific Rise off-axis seamounts, Quebrada-Discovery-Gofar transform fault system, and Macquarie Island). After filtering the volatile element data for shallow level processes (degassing, sulfide saturation, assimilation of seawater-derived component, and fractional crystallization), we use the volatile to refractory element ratios of our samples and a two-component mantle melting-mixing model to estimate the volatile contents of the depleted and enriched upper mantle. Our two-component mantle melting-mixing model suggest that a fraction of the low degree enriched MORB melts (~1.3% melt) may escape melt aggregation by freezing at the base of the oceanic lithosphere, significantly enriching it in volatiles and incompatible trace element contents.

In this study, we evaluate the effect of metasomatized oceanic mantle lithosphere on the composition of the off-axis EPR MORBs. We identify a common compositional component in the off-axis MORBs characterized (but not only) by high K/Nb and H2O/Ce and low Ce/Pb. Our geochemical and geological observations and modeling [4] are consistent with a hypothesis that melting of a hydrous mineral bearing metasomatized oceanic mantle lithosphere generates this component. Neglecting the effect of this shallow component on erupted basalts could lead to erroneous estimates of Earth's upper mantle composition.

References: [1] Shimizu et al., 2016 GCA. [2] Niu et al., 2002 EPSL. [3] Kamenetsky et al., 2002 J Petrol. [4] Pilet et al., 2011 J Petrol.

Authors: Kei Shimizu, Alberto E. Saal


P51B-2594: CubeX: The CubeSAT X-ray Telescope for Elemental Abundance Mapping of Airless Bodies and X-ray Pulsar Navigation

Larry Nittler | Friday, December 15,  2017 | 08:00 - 12:20 | New Orleans Ernest N. Morial Convention Center - Poster Hall D-F

Abstract: The surface elemental composition of a planetary body provides crucial information about its origin, geological evolution, and surface processing, all of which can in turn provide information about solar system evolution as a whole. Remote sensing X-ray fluorescence (XRF) spectroscopy has been used successfully to probe the major-element compositions of airless bodies in the inner solar system, including the Moon, near-Earth asteroids, and Mercury. The CubeSAT X-ray Telescope (CubeX) is a concept for a 6U planetary X-ray telescope (36U with S/C), which utilizes Miniature Wolter-I X-ray optics (MiXO), monolithic CMOS and SDD X-ray sensors for the focal plane, and a Solar X-ray Monitor (heritage from the REXIS XRF instrument on NASA's OSIRIS-REx mission). CubeX will map the surface elemental composition of diverse airless bodies by spectral measurement of XRF excited by solar X-rays. The lightweight (~1 kg) MiXO optics provide sub-arcminute resolution with low background, while the inherently rad-hard CMOS detectors provide improved spectral resolution (~150 eV) at 0 °C. CubeX will also demonstrate X-ray pulsar timing based deep space navigation (XNAV). Successful XNAV will enable autonomous deep navigation with little to no support from the Deep Space Network, hence lowering the operation cost for many more planetary missions. Recently selected by NASA Planetary Science Deep Space SmallSat Studies, the first CubeX concept, designed to rideshare to the Moon as a secondary spacecraft on a primary mission, is under study in collaboration with the Mission Design Center at NASA Ames Research Center. From high altitude (~6,000 km) frozen polar circular orbits, CubeX will study > 8 regions (~110 km) of geological interest on the Moon over one year to produce a high resolution (~2–3 km) elemental abundance map of each region. The novel focal plane design of CubeX also allows us to evaluate the performance of absolute navigation by sequential observations of several millisecond pulsars without moving parts.

Authors: Larry Nittler, Jaesub Hong, Almus Kenter, Suzanne Romaine, Branden Allen, Ralph Kraft, Rebecca Masterson, Martin Elvis, Keith Gendreau, Ian Crawford, Richard Binzel, William V. Boynton, Josh Grindlay, Brian Ramsey


T51E-0540: Amphibious Shear Velocity Structure of the Cascadia Subduction Zone

Helen Janiszewski | Friday, December 15,  2017 | 08:00 - 12:20 | New Orleans Ernest N. Morial Convention Center - Poster Hall D-F

AbstractThe amphibious Cascadia Initiative crosses the coastline of the Cascadia subduction zone (CSZ) deploying seismometers from the Juan de Fuca ridge offshore to beyond the volcanic arc onshore. This allows unprecedented seismic imaging of the CSZ, enabling examination of both the evolution of the Juan de Fuca plate prior to and during subduction as well as the along strike variability of the subduction system. Here we present new results from an amphibious shear velocity model for the crust and upper mantle across the Cascadia subduction zone. The primary data used in this inversion are surface-wave phase velocities derived from ambient-noise Rayleigh-wave data in the 10 – 20 s period band, and teleseismic earthquake Rayleigh wave phase velocities in the 20 – 160 s period band. Phase velocity maps from these data reflect major tectonic structures including the transition from oceanic to continental lithosphere, Juan de Fuca lithosphere that is faster than observations in the Pacific for oceanic crust of its age, slow velocities associated with the accretionary prism, the front of the fast subducting slab, and the Cascades volcanic arc which is associated with slower velocities in the south than in the north. Crustal structures are constrained by receiver functions in the offshore forearc and onshore regions, and by active source constraints on the Juan de Fuca plate prior to subduction. The shear-wave velocities are interpreted in their relationships to temperature, presence of melt or hydrous alteration, and compositional variation of the CSZ.

Authors: Helen Janiszewski, James B. Gaherty, Geoffrey A. Abers, Haiying Gao


P54B-05: Origin of the Martian Moons and Their Volatile Abundances

Miki Nakajima | Friday, December 15,  2017 | 16:48 - 17:00 | New Orleans Ernest N. Morial Convention Center - R08

AbstractThe origin of the Martian moons, Phobos and Deimos, has been actively debated. These moons were initially thought to have been gravitationally captured asteroids given that their spectra appeared to be similar to those of D-type asteroids. However, intact capture is difficult to reconcile with their nearly circular, co-planar orbits. Their orbits may be better explained by recent dynamical studies that suggest that the moons may have instead formed from a disk generated by a large impact, as was likely the case for Earth's Moon. Phobos and Deimos' bulk volatile contents, which are currently very uncertain, would also provide key constraints on their origin. If the moons were captured, their bulk compositions may be similar to those of asteroids, and their sub-surfaces could be volatile-rich. We are here exploring the implications of the alternative impact origin on the moon volatile abundances. We perform numerical simulations to estimate the extent of volatile loss from the moon-forming ejecta produced by a large impact with Mars. We find that hydrogen and water vapor escape hydrodynamically from the disk, leading to moons with dry, hydrogen-depleted bulk compositions. It is thus possible that the moons' mode of origin may be determined by knowledge of their volatile contents, because detection of a substantial (non-exogenically delivered) water content would argue strongly against formation by impact. JAXA's Martian Moons eXploration Mission (MMX) will conduct detailed remote sensing of the moons, including a gamma ray and neutron spectrometer that will for the first time probe their sub-surface elemental compositions, and will return samples from Phobos for laboratory analysis. This should allow for characterization of the moon volatile abundances. We also discuss that the inferred high porosities of these moons could be explained if they are rubble piles formed during accretion from impact-produced ejecta.

Authors: Miki Nakajima, Robin M. Canup