[Geodynamics] PhD studentship at UCL: "Numerical modeling of Mantle Dynamics, Evolution and Compositional structure"

Sat Mar 21 22:27:26 AEDT 2020

Dear all,

if anyone of you is aware of a suitable candidate for a PhD studentship in geodynamics at UCL (London), please let me know, or point the candidate in this direction:

https://protect-au.mimecast.com/s/tJDCCVARKgC0Yo6qsGjSf3?domain=earthworks-jobs.com

or this one:

https://protect-au.mimecast.com/s/AueXCWLVXkUzVmKrfxdMAC?domain=jupiter.ethz.ch

As usual, a MSc in a related field, enthusiasm for the Earth and Planetary Sciences, as well as good skills/interest/talent in mathematics/physics and programming are required. More details can be found under the links above, or appended below.

One caveat involves that the full tuition can only be covered for candidates with EU/UK passports. Salary will be at the relevant RCUK rate (i.e., usual salary for London PhD students).

Hope all is well for everybody these days.

Cheers,
    Maxim

.............................................................
Maxim D. Ballmer
原眞マキシム
Asst. Professor @ Univ. College London, Dept. Earth Sciences
office:  KLB 341, Gower Place, WC1E 6BT London
Visiting Scientist @ Inst. Geophysics, ETH Zurich
office:  NO H 9.3, 5, CH-8092 Zurich
https://protect-au.mimecast.com/s/NLRfCXLW2mUBWoREtDTPIU?domain=jupiter.ethz.ch<https://protect-au.mimecast.com/s/NLRfCXLW2mUBWoREtDTPIU?domain=jupiter.ethz.ch>
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Numerical modeling of Earth (and planetary) mantle dynamics, evolution and compositional structure

The Dept. of Earth Sciences at UCL can offer one PhD studentship in the field of geodynamics. The start date is not fixed, but the preferred start date will be in autumn 2020. There is some freedom in the choice of research topics, but the main theme should overlap with the research interests of the main advisor, Dr. Maxim Ballmer (also see his website https://protect-au.mimecast.com/s/NLRfCXLW2mUBWoREtDTPIU?domain=jupiter.ethz.ch). Three example projects are explained in detail below, but Maxim’s research interests also involve, e.g., the long-term evolution of terrestrial planets (e.g. Mars, Moon, Exoplanets), and Earth’s asthenospheric dynamics (and its geophysical signals). Maxim is particularly keen to quantitatively compare geodynamic model predictions with geophysical and geochemical data. In any project, including the three examples below, there will be at least one co-advisor from UCL, and potentially several collaborators UK- and worldwide.

The project is fully funded for UK/EU applicants for three years at the normal RCUK rate (£17,428 in 2020/21). Tuition will be covered for at least three years (for UK/EU applicants). Applicants require to have (by the time of starting) a Masters level degree (either undergraduate or postgraduate) in Geology, Geophysics, Physics, or a closely related field and an enthusiasm to work in computational geophysics. Good programming skills in Matlab/Python/C/Fortran or a similar language, as well as familiarity with LINUX operating systems, are highly beneficial.

Contact:  Dr. Maxim Ballmer, m.ballmer <at> ucl.ac.uk

The seismic signals of the heterogeneous Earth mantle

Geophysical imaging of the Earth’s deep interior, and hence our understanding of present-day mantle structure and long-term evolution, is subject to fundamental limitations. For example, the deep mantle is interrogated by Earthquake-generated sound waves through seismic tomography, but the true resolution of any releated tomography model is limited to 10s-100s km. On the other hand, geochemical data has little-to-no spatial resolution power. Based on such limited information, the mantle has been suggested to be anything between a rather well-mixed “marble cake” of recycled mafic (basaltic) and ultramafic (harzburgitic) heterogeneities, or a poorly-mixed “plum pudding” with prevalent blobs of ancient material [Ballmer et al., 2015, 2017]. Within uncertainties in terms of mantle material properties and initial condition, both these scenarios are viable and can be reproduced by numerical models of mantle convection.

In this project, we will quantitatively test the predictions of such godynamic models by comparison with seismic data. While comparison of geodynamic model predictions with seismic tomography models is performed routinely (but subject to intrinsic limitations), we will focus on direct comparison with data. This approach will involve forward-modeling of a huge dataset of synthetic waveforms [Nissen-Meyer et al., 2014], and application of a machine-learning technique (to be newly developed) in order to compare these synthetic waveforms with real seismograms. Such an integrated geodynamic-seismological effort will serve to quantify, and potentially distinguish, the geophysical signals of the marble-cake vs. plum-pudding mantles.

Material cycles through the Earth's mantle set up life-sustainable conditions on the surface. Geophysical imaging of the mantle and geodynamic modeling provide two avenues to study mantle structure and evolution, and thus to better understand planetary habitability in general. This project aims to quantitatively integrate these two complementary approaches.

citations: https://protect-au.mimecast.com/s/HEuRCYW8Nockw2qVHVB9Bv?domain=doi.org, https://protect-au.mimecast.com/s/xZCrCZY1NqiP09LKIxZ9Jr?domain=doi.org, https://protect-au.mimecast.com/s/Wtd8C1WLPxcnlNoJU1HSxK?domain=doi.org<https://protect-au.mimecast.com/s/dRQVC2xMQziKgzX5fXZgL2?domain=doi.org>

Potential collaborators: Ana Ferreira, CSML, John Brodholt (UCL), Tarje Nissen-Meyer (Univ. Oxford), Paula Koelemeijer (RHUL), Paul Tackley (ETH)

The initial condition for the long-term evolution of terrestrial planets

Early in their history, terrestrial planets evolve through stages of large-scale melting, or magma oceans, due to the energy release during accretion and differentiation. Any magma ocean is thought to become progressively enriched in FeO and incompatible elements during fractional crystallization. The resulting upwards enrichment of the cumulate (=crystal) package(s) drives gravitational over-turn(s) of the incipiently solid mantle, and ultimately stabilizes a FeO-enriched molten layer at the core-mantle boundary (CMB), or “basal magma ocean” (BMO). The BMO itself will freeze by fractional crystallization, ultimately stabilizing a thick FeO-enriched layer at the CMB. Such a layer, however, would be too dense to be entrained by mantle convection, a scenario that is ruled out by geophysical observations, at least for Earth.

In this project, we will investigate the consequences of a previously neglected mechanism, BMO reactive crystallization, on long-term planetary evolution. Reaction is driven by chemical disequilibrium between the mantle and BMO. The related BMO reactive cumulates should range from Mg-enriched bridgmanite (MgSiO3) to FeO-enriched pyrolite, but the detailed compositions will be calculated using available thermodynamic models. The long-term thermochemical evolution of the mantle (e.g., fate of the cumulate package) will be addressed by geodynamic modeling. The predicted thermochemical mantle structures will be compared to lower-mantle seismic signature of Earth, using available constraints for physical properties of mantle materials at high pressure-temperature conditions. Finally, results will be applied to terrestrial planets in general. Such an effort is expected to yield systematic relationships between planet mass/composition, deep-mantle structure and long-term thermal evolution.

On Earth, long-term material cycles through the mantle set up life-sustainable conditions at the surface. This cycling is controlled by the initial condition after planetary accretion and differentiation. Indeed, studying mantle evolution is key to understand the conditions for habitability, and gauge the potential for extraterrestrial life in our galaxy.

citations: https://protect-au.mimecast.com/s/Xyc7C3QNPBi7OzlDSElscA?domain=doi.org, https://protect-au.mimecast.com/s/xZCrCZY1NqiP09LKIxZ9Jr?domain=doi.org, https://protect-au.mimecast.com/s/j35oC4QOPEiYqKO4i3LaXB?domain=doi.org

Potential collaborators: Ana Ferreira, John Brodholt, Dave Dobson, Andy Thomson (UCL); Oliver Shorttle (Cambridge); John Hernlund, Christine Hernlund (ELSI, Tokyo Tech); Kei Hirose (ELSI, Tokyo Tech; Univ. Tokyo); Razvan Caracas (ENS Lyon)

The dynamics of mantle plumes, and their geophysical and geochemical expressions

While magmatic activity along plate boundaries is well explained by plate-tectonic theory, the expressions of intraplate volcanism may inform about deep-mantle processes. Mantle upwellings, or “plumes”, are thought to sustain major intraplate volcanism at oceanic hotspots, but the explicit upwelling dynamics as well as the chemistry of materials carried that are by plumes remain poorly understood. For example, a range of plume parameters can account for geophysical observations such as hotspot swell geometry or distribution of volcanism [Ballmer et al., 2011, 2013].

In this project, we will explore the dynamics of plumes as a function of the composition and properties of these materials using 3D numerical models of mantle convection. Model predictions in terms of the geophysical expression of plumes (seismic tomography, dynamic topography, …) and geochemical signatures of ocean-island basalts (major-element and trace-element signatures) will be compared to observations such as for the Hawaiian Islands or Iceland hotspots. Incorporation of multiple datasets, including those from geochemistry, is critical to put constraints on plume upwelling dynamics [e.g., Ballmer et al., 2011]. Such an integrated approach will exploit the coupled controls of plume composition on both upwelling dynamics and lava chemistry, and hence provide new quantitative constraints on the structure of mantle plumes, and thus on the make-up of the plume-source region near the core-mantle boundary [Weis et al., 2011].

While volcanism along plate boundaries reflects surficial tectonic processes, the study of intraplate volcanism helps to understand mantle structure, composition and evolution. Mantle plumes feed intraplate hotspots, transporting heat and volatiles from the deep mantle. Indeed, long-term material cycles through the Earth's mantle stabilize life-sustainable conditions at the surface.

citations: https://protect-au.mimecast.com/s/uClRC5QPXJig2L7kH97_Pe?domain=doi.org, https://protect-au.mimecast.com/s/8AJjC6XQ4LfVqYvLtvDOSY?domain=doi.org, https://protect-au.mimecast.com/s/88QYC71R2NTEw1KGSP3Ykv?domain=doi.org

Potential collaborators: Ana Ferreira, John Brodholt, Dave Dobson, Andy Thomson (UCL); Kate Rychert (Univ. Southampton); Lara Kalnins (Univ. Edinburgh); Oliver Shorttle (Cambridge); Mark Hoggard (Harvard); Antonio M.-C. Cordoba (ETH)

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