Rheological controls on slab delamination
Lead Research Organisation:
University College London
Department Name: Earth Sciences
Abstract
Subducted oceanic lithosphere displays a range of complex behaviours including penetration into the lower mantle, stagnation in the transition zone and ponding at, or just below, the 660 km seismic discontinuity, and intermediate behaviour between these end-members. At a finer scale, the MORB component is thought to mechanically decouple from the slab core to produce seismic scatterers in the lower mantle and potential reservoirs for enriched OIB material at the core-mantle boundary and the base of the transition zone. The exact behaviour of the slab and its different components will depend on their densities and strengths relative to each other and the surrounding mantle. While the densities of the various rocks and minerals in the mantle are well known our knowledge of their strengths is very poor; geodynamical simulations show a range of slab behaviours dependent on these properties. We will measure the relative strength of the main rocks which comprise the slab (mid-ocean-ridge basalt and depleted peridotite) under the range of pressure and temperature conditions of the subducting slab to ~1000 km depth. This will allow us to assess which phase assemblages of the two compositions along the slab geotherm show the main rheological contrasts and hence better understand the processes of slab deformation and delamination.
Planned Impact
This is curiosity-driven research with no direct relevance to industry or policy makers.
However, there is potential for technological spin offs:
1)The development of in-situ X-ray facilities for high-pressure research would be of interest to some UK industry, for example AWE who we are developing links with.
2)High-pressure mineralogy can be useful for informing novel crystallography at low pressure. Dobson is developing a new blue pigment based around the crystal structure of ringwoodite and a better understanding of its defect chemistry (as might be achieved through looking at the effects of deformation on ringwoodite's optical properties) might help this process. UK-based Colart is interested in commercialising this pigment when it reaches a sufficient level of development.
In addition, the Earth's interior catches the public imagination. Dobson has a strong collaboration with the Slade School of Art, having developed and pioneered their Scientist in Residence programme and we propose to continue this in the form of a public outreach symposium and high-quality publication based around the science and materiality of colour.
However, there is potential for technological spin offs:
1)The development of in-situ X-ray facilities for high-pressure research would be of interest to some UK industry, for example AWE who we are developing links with.
2)High-pressure mineralogy can be useful for informing novel crystallography at low pressure. Dobson is developing a new blue pigment based around the crystal structure of ringwoodite and a better understanding of its defect chemistry (as might be achieved through looking at the effects of deformation on ringwoodite's optical properties) might help this process. UK-based Colart is interested in commercialising this pigment when it reaches a sufficient level of development.
In addition, the Earth's interior catches the public imagination. Dobson has a strong collaboration with the Slade School of Art, having developed and pioneered their Scientist in Residence programme and we propose to continue this in the form of a public outreach symposium and high-quality publication based around the science and materiality of colour.
Publications
Dobson D
(2024)
Magma mixing between rhyolite and pseudotachylite as the origin for the Glencoe 'Flinty Crush Rock'
in Scottish Journal of Geology
Dobson DP
(2021)
The tungsten carbide-carbon monoxide-tungsten buffer and its use for synthesizing iron-bearing silicates in muffle furnaces.
in The Review of scientific instruments
Thomson A.R.
(2023)
Preliminary results from the new deformation multi-anvil press at the photon factory: Insight into the creep strength of calcium silicate perovskite
in Core-Mantle Coevolution: A Multidisciplinary Approach
Xu F
(2022)
Deformation of Post-Spinel Under the Lower Mantle Conditions
in Journal of Geophysical Research: Solid Earth
Description | Plate tectonics is driven by subduction of cold oceanic lithosphere into the convecting mantle. The lithosphere is made of two components - the crust (mainly basalt composition) and lithospheric mantle (peridotite composition like the rest of the mantle but much colder) - which can behave very differently during subduction into the mantle. This differenc in behaviour and ultimate fate of the two components has important implications for how mantl convection works and the sources of the different ignwouls rocks we see at the Earth's surface. We are measuring the relative flow strength of these two components under the conditions of Earth's transition zone and lower mantle where much of the convective complexity occurs. We find that in the transition zone the basaltic and peridotite components have similar strengths (within a factor of 2) but as the peridotite transforms to the lower mantle phases assemblage there is a significant weakeninf (bt a factor of 10 or more) which should aid separation of crustal components from mantle-lithospheric components of the sunducting slab. |
Exploitation Route | hese results will be important gor geodymanicists modelling mantl convection and for solid-Earth seismologisits |
Sectors | Education |
Title | WC-CO/W buffer |
Description | This is a nwe method to control oxygen fugacity at close to the Fe-FeO buffer in standard laboratory muffle furnaces. It opens the possibility of synthesising transition-element-bearing ceramics (ie geological materials) without recourse to dedicated gas mixing techniques which often requre hazardous gasses such as CO or H2. |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2021 |
Provided To Others? | Yes |
Impact | None yet |
Title | Deformation of post-spinel under the lower mantle conditions |
Description | Data used in Deformation of post-spinel under the lower mantle conditions F. Xu1, 2, D. Yamazaki1, S. A. Hunt3, 2, N. Tsujino1, Y. Higo4, Y. Tange4, K. Ohara4, D. P. Dobson2 1 Institute for Planetary Materials, Okayama University, Misasa, 682-0193 Tottori, Japan 2 Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom 3 Department of Materials, University of Manchester, Sackville Street Building, Manchester M1 3BB, United Kingdom 4 Japan Synchrotron Radiation Research Institute, SPring-8, Sayo, Hyogo 679-5198, Japan |
Type Of Material | Database/Collection of data |
Year Produced | 2021 |
Provided To Others? | Yes |
Impact | N/A |
URL | https://zenodo.org/record/5647995 |
Description | D111 experiments |
Organisation | Okayama University |
Country | Japan |
Sector | Academic/University |
PI Contribution | We travel to the Misasa Instiutute fir Planetary Materials and work with the D111 deformation press. This is an upscaled version of the D-T-cup press developed by Dobson and Hunt at UCL. We are performing relative-strengtyh ecperiments on MORB and ringwood/post-spinel assemblages at pressured of 22-25 GPa. |
Collaborator Contribution | They provide the equipment and consumables, and travel and accomodation costs (within budgetary limits). The staff at Misasa are international experts in high-pressure experiments and we have a close collaboration sith Yamazaki in particular who is engaged on a daily bais in discussing experimental design and results. In addition, ancilliart facilities for sampel prep and analysis are available while we are visitng Misasa. |
Impact | None yet |
Start Year | 2022 |
Description | Japan deformation press |
Organisation | Ehime University |
Country | Japan |
Sector | Academic/University |
PI Contribution | We have designed a new deformation press and provided access to the prototype, and help and support in performing experiments at UCL during August-November 2016. Dobson visied Japan during March 2016 to advise on the new press (based on our deformation design) being commissionned to go on a beamline at Photon Factory synchrotron in Tsukuba, Japan. |
Collaborator Contribution | A group of 4 researchers Visited UCL for 2 months in 2016 (August, November) to perform deformation experiments at the P-T conditions of the lower mantle. They provided all cells and hard anvils to reach the extreme pressures necessary. They have won a grant (approximately £200k) to install one of our (UCL design) presses on an existing multi-anvil beamline at the Photon Factory. |
Impact | The dfevelopment of a new high-pressure deformation beamline on Photon Factory synchrotron in Japan. |
Start Year | 2016 |
Description | SPring-8 deformation experiments |
Organisation | SPring-8 |
Country | Japan |
Sector | Public |
PI Contribution | SPring-8 has installed one of the UCL-designed deformation (D-111) presses. We collaboprate with colleagues from Japan and China to measure rheological properties of mantle rocks here. |
Collaborator Contribution | SPring-8 provides the beamtime and maintains the facility. |
Impact | Papers are in preparation. |
Start Year | 2022 |
Description | CPD workshops for potdoor professionals |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Other audiences |
Results and Impact | Geologically oriented CPD workshops for mountain leaders and mountain guides. These comprise one-day events where we go into the field and I shoe the geology of the areas the guides work in and give them the broader contex of what they are seeing. The aim is that this will equip guides to inform their clients about the geology as they are oit guiding, to enhance clients' understangding of the envorinments they are using for their leisure. While each workshop involves 5 guides it is expected that he reach is much further than this as tehy apply their new knowledge and skills to informing their clients. |
Year(s) Of Engagement Activity | 2022,2023 |
Description | One Minute Geology |
Form Of Engagement Activity | Engagement focused website, blog or social media channel |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | One Minute Geology is a You Tube channel and website (YouTube.com/c/oneminutegeology; www.oneminutegeology.net) which engages the general public and outdoors professionals in geology and environmental sciences subjects of relavence to the localities they find themselves in. On the website each video is geolocated on a clickable map so that users can easily find geological features near them. It was founded in October 2020 and currently has around 200 videos on UK and international geology and geological research, receiving over 100,000 unique views per year and over 1400 subscribers (1 March 2024). In addition to the channel and website have used my OMG videos in outreach talks to schools and to supplement university lectires while students have been unable to access field work during lockdown. |
Year(s) Of Engagement Activity | 2020,2021,2022,2023,2024 |
URL | http://www.youtube.com/c/oneminutegeology/ |
Description | Talks to geological societies |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Talks to the Norfolk Geological sicuety and the Sussex geological Society in October/Nivember 2022 about geology of the deep Earth. These talks included latest results from current research as well as an overviey of the topic. |
Year(s) Of Engagement Activity | 2022 |