Pervasive upper mantle melting beneath the western US

We report from converted seismic waves, a pervasive seismically anomalous layer above the transition zone beneath the western US. The layer, characterized by an average shear wave speed reduction of 1.6%, spans over an area of similar to 1.8 x10(6) km(2) with thicknesses varying between 25 and 70 km. The location of the layer correlates with the present location of a segment of the Farallon plate. This spatial correlation and the sharp seismic signal atop of the layer indicate that the layer is caused by compositional heterogeneity. Analysis of the seismic signature reveals that the compositional heterogeneity can be ascribed to a small volume of partial melt (0.5 +/- 0.2 vol% on average). This article presents the first high resolution map of the melt present within the layer. Despite spatial variations in temperature, the calculated melt volume fraction correlates strongly with the amplitude of P-S conversion throughout the region. Comparing the values of temperature calculated from the seismic signal with available petrological constraints, we infer that melting in the layer is caused by release of volatiles from the subducted Farallon slab. This partially molten zone beneath the western US can sequester at least 1.2 x 10(17) kg of volatiles, and can act as a large regional reservoir of volatile species such as H or C. (C) 2017 Elsevier B.V. All rights reserved

An inversion approach for analysing the physical properties of a seismic low-velocity layer in the upper mantle

International audienceIn this article, we propose a new inversion scheme to calculate the melt volume 17 fractions from observed seismic anomalies in a low-velocity layer (LVL) located atop 18 the mantle transition zone. Our method identifies the trade-offs in the seismic 19 signature caused by temperature, solid composition, melt volume fraction, and 20 dihedral angle at the solid-melt interface. Using the information derived from the 2

Pervasive seismic low-velocity zones within stagnant plates in the mantle transition zone: Thermal or compositional origin?

We exploit conversions between P and S waves for large-scale, high-resolution imaging of the mantle transition zone beneath Northwest Pacific and the margin of Eastern Asia. We find pervasive reflectivity concentrated in two bands with apparent wave-speed reduction of −2% to −4% about 50km thick at the top of the transition zone and 100km thick at the bottom. This negative reflectivity associated with the scattered-waves at depth is interpreted jointly with larger-scale mantle tomographic images, and is shown to delineate the stagnant portions of the subducted Pacific plate in the transition zone, with largely positive shear-wave velocity contrasts. The upper reflectivity zone connects to broad low-velocity regions below major intra-plate volcanoes, whereas the lower zone coincides locally with the occurrence of deep-focus earthquakes along the East Asia margin. Similar reflectivity is found in Pacific Northwest of the USA. We demonstrate that the thermal signature of plates alone is not sufficient to explain such features. Alternative explanations for these reflective zones include kinetic effects on olivine phase transitions (meta-stability), compositional heterogeneities within and above stagnant plates, complex wave-propagation effects in the heterogeneous slab structure, or a combination of such factors. We speculate that part of the negative reflectivity is the signature of compositional heterogeneities, as revealed by numerous other studies of seismic scattering throughout the mantle, and that such features could be widespread across the globe.B.T. was funded with a Délégation CNRS and Congé pour Recherches et Conversion Thématique from the Université de Lyon at the Research School of Earth Sciences (RSES), Australian National University (ANU)

Multiple Phase Changes in the Mantle Transition Zone Beneath Northeast Asia: Constraints From Teleseismic Reflected and Converted Body Waves

We reassess the mantle transition zone structure below the northeast Asia margin in the context of subduction of the Pacific plate below the Eurasian continent. We use two independent approaches of teleseismic imaging, namely, compressional-to-shear converted waves (receiver functions) and shear wave underside reflections (SS precursors), and compare them within their statistical uncertainties. We find localized complexity in the interfaces marking solid phase changes in mantle minerals, in terms of both apparent topography and reflectivity. The 660-km discontinuity is doubled, with ∼80-km maximum vertical distance between the interfaces, over an 890 × 350 km2 region between 36–44°N and 130–133°E at the tip of the subducted Pacific plate. A similar complexity exists on the 410-km discontinuity, coinciding with the presence of a deep cluster of seismicity below the Japan Sea. Both methods suggest the presence of low-velocity zones atop the 410, within the mantle transition zone, and below the 660. This complex seismic signature is related to the Pacific plate and interpreted in light of the subduction thermal regime and phase equilibria for a pyrolitic mantle composition. Phase changes manifest themselves as broad zones of velocity gradients with localized doubled or multiple first-order discontinuities, associated with transitions in the olivine, pyroxene, and garnet systems. An average pyrolitic composition and local temperatures of 1000–1300 K can explain the observed velocity gradients and multiple discontinuities. We show that the dissolution of stishovite, a high-pressure polymorph of SiO2, into the higher-pressure perovskite mineral, is a possible explanation for the low-velocity zones at the top of the lower mantle.S. K. was funded by the Korea Meteorological Administration under grant KMI2017-01010. The work of J. C. A. was supported by an ARC DP project (DP160103502) and Macquarie University grant

Evidence of Volatile-Induced Melting in the Northeast Asian Upper Mantle

International audienc

Proteomic characterisation of endoplasmic reticulum-derived protein bodies in tobacco leaves

<p>Abstract</p> <p>Background</p> <p>The N-terminal proline-rich domain (Zera) of the maize storage protein γ-zein, is able to induce the formation of endoplasmic reticulum (ER)-derived protein bodies (PBs) when fused to proteins of interest. This encapsulation enables a recombinant fused protein to escape from degradation and facilitates its recovery from plant biomass by gradient purification. The aim of the present work was to evaluate if induced PBs encapsulate additional proteins jointly with the recombinant protein. The exhaustive analysis of protein composition of PBs is expected to facilitate a better understanding of PB formation and the optimization of recombinant protein purification approaches from these organelles.</p> <p>Results</p> <p>We analysed the proteome of PBs induced in <it>Nicotiana benthamiana </it>leaves by transient transformation with Zera fused to a fluorescent marker protein (DsRed). Intact PBs with their surrounding ER-membrane were isolated on iodixanol based density gradients and their integrity verified by confocal and electron microscopy. SDS-PAGE analysis of isolated PBs showed that Zera-DsRed accounted for around 85% of PB proteins in term of abundance. Differential extraction of PBs was performed for in-depth analysis of their proteome and structure. Besides Zera-DsRed, 195 additional proteins were identified including a broad range of proteins resident or trafficking through the ER and recruited within the Zera-DsRed polymer.</p> <p>Conclusions</p> <p>This study indicates that Zera-protein fusion is still the major protein component of the new formed organelle in tobacco leaves. The analysis also reveals the presence of an unexpected diversity of proteins in PBs derived from both the insoluble Zera-DsRed polymer formation, including ER-resident and secretory proteins, and a secretory stress response induced most likely by the recombinant protein overloading. Knowledge of PBs protein composition is likely to be useful to optimize downstream purification of recombinant proteins in molecular farming applications.</p

Seismoacoustic coupling induced by the breakup of the 15 February 2013 Chelyabinsk meteor

International audienceOn 15 February 2013 around 03:20:00 UTC, the largest meteor reported since the 1908 Tunguska event was observed as a fireball traveling through the Earth's atmosphere, exploding in an air burst near the city of Chelyabinsk, Russia. The rarity of such an event provides a unique window on the physics of meteoroid collision. We report the fine seismic detection of Rayleigh waves produced by the coupling of ground motion with the incident shock wave at distances up to 4000 km from the event. Combining information from seismic beam-forming analysis, recon- structed trajectory from casual video records, and remote sensing, we identify the Rayleigh waves as being initiated by the shock wave produced by the main blast that occasioned damages and injuries in Chelyabinsk. From the Rayleigh wave observations, we report a magnitude Ms ~ 3.7 seismic source

The mantle transition zone as seen by global Pds phases: No clear evidence for a thin transition zone beneath hotspots

International audienceWe present a new global study of the transition zone from Pds converted waves at the 410- and 660-km discontinuities. Our observations extend previous global Pds studies with a larger data set, especially in oceanic regions where we have been able to measure Pds travel times, sampling the mantle transition zone (MTZ) beneath 26 hotspot locations. We find significant lateral variations of the MTZ thickness. Both the maximum variations (+/- 35 - 40 km) and the long-wavelength pattern are in overall agreement with previous SS precursors studies. The MTZ is generally thick beneath subduction zones, where the observed MTZ variations are consistent with thermal anomalies ranging between -100 degrees K and -300 degrees K. In Central and North America, we observe an NW - SE pattern of thick MTZ, which can be associated with the fossil Farallon subduction. We do not find clear evidence for a thin MTZ beneath hotspots. However, the 410- km discontinuity remains generally deepened after correcting our Pds travel times for the 3D heterogeneities located above the MTZ, and its topography variations can be explained by thermal anomalies between + 100 degrees K and +300 degrees K. The depth of the 660-km discontinuity may be less temperature sensitive in hot regions of the mantle, which is consistent with the effect of a phase transition from majorite garnet to perovskite at a depth of 660 km

Autocorrelation of the Ground Vibrations Recorded by the SEIS-InSight Seismometer on Mars

Since early February 2019, the SEIS (Seismic Experiment for Interior Structure) seismometer deployed at the surface of Mars in the framework of the InSight mission has been continuously recording the ground motion at Elysium Planitia. In this study, we take advantage of this exceptional data set to put constraints on the crustal properties of Mars using seismic interferometry (SI). To carry out this task, we first examine the continuous records from the very broadband seismometer. Several deterministic sources of environmental noise are identified and specific preprocessing strategies are presented to mitigate their influence. Applying the principles of SI to the single-station configuration of InSight, we compute, for each Sol and each hour of the martian day, the diagonal elements of the time-domain correlation tensor of random ambient vibrations recorded by SEIS. A similar computation is performed on the diffuse waveforms generated by more than a hundred Marsquakes. A careful signal-to-noise ratio analysis and an inter-comparison between the two datasets suggest that the results from SI are most reliable in a narrow frequency band around 2.4 Hz, where an amplification of both ambient vibrations and seismic events is observed. The average autocorrelation functions (ACFs) contain well identifiable seismic arrivals, that are very consistent between the two datasets. Interpreting the vertical and horizontal ACFs as, respectively, the P- and S- seismic reflectivity below InSight, we propose a simple stratified velocity model of the crust, which is mostly compatible with previous results from receiver function analysis. Our results are discussed and compared to recent works from the literature.This study is InSight contribution number 164. The authors acknowledge both “Université Fédérale de Toulouse Midi Pyrénées” and the “Région Occitanie” for funding the PhD grant of Nicolas Compaire. The French authors acknowledge the French Space Agency CNES and ANR (ANR-14-CE36-0012-02 and ANR-19-CE31-0008-08) for funding the InSight Science analysis

Hydrous upwelling across the mantle transition zone beneath the Afar Triple Junction

The mechanisms that drive the upwelling of chemical heterogeneity from the lower to upper mantle (e.g., thermal versus compositional buoyancy) are key to our understanding of whole mantle con- vective processes. We address these issues through a receiver function study on new seismic data from recent deployments located on the Afar Triple Junction, a location associated with deep mantle upwelling. The detailed images of upper mantle and mantle transition zone structure illuminate features that give insights into the nature of upwelling from the deep Earth. A seismic low-velocity layer directly above the mantle transition zone, interpreted as a stable melt layer, along with a prominent 520 km discontinuity sug- gest the presence of a hydrous upwelling. A relatively uniform transition zone thickness across the region suggests a weak thermal anomaly (<100 K) may be present and that upwelling must be at least partly driven by compositional buoyancy. The results suggest that the lower mantle is a source of volatile rich, chemically distinct upwellings that influence the structure of the upper mantle, and potentially the chemis- try of surface lavas