Project highlights

  • Carry out research at the cutting edge of the rapidly developing field of impact-cratering.
  • Novel application of the latest understanding and techniques from physical volcanology to shed new geological understanding on the formation of impact ejecta deposits.
  • Studying world-class, well-preserved deposits of asteroid impact craters in Canada and Mexico, involving field visits, imagery and micro-analytic techniques.

Overview

When asteroids or comets collide with Earth they cause catastrophic shock, vaporisation, melting, fragmentation and ejection, significantly modifying the crust and devastating environments and biota. Such ‘hypervelocity collisions’ are a fundamental process of planetary evolution and arguably the greatest natural hazard. Significant advances in shock metamorphism, petrology and modelling have been made, but several geological aspects of what happens remain poorly understood. We need to better understand the processes of molten ejecta emplacement in order to account for the wider effects. A principle source of information lies in Earth’s geological record, but accessible, well-preserved large impact craters filled with clastic and melted products are rare.

This project will help decipher the fragmentation and emplacement processes of crater-fill material in very large impact craters on Earth, focussing on Manicouagan (Canada) and Chicxulub (Mexico). Both impacted continental crust, one on land the other at sea, and both have been drilled. The investigation will document, analyse and interpret the crater fills to shed new light on the physical processes of their formation. The student will draw upon state-of-the-art geological and physical volcanological techniques and understanding about how hot magma is fragmented, emplaced, and then deposited and agglutinated back together to form thick rock bodies that subsequently cool, and variously devitrify and crystallise. An objective is to develop a new facies scheme for large impact crater fills in order to help reconstruct the events by which they form.

The project will suit an enthusiastic geology student with interests in physical volcanology and planets, with a facility for rigorous documentation, and who thrives on original thinking, devising and testing hypotheses.

Host

University of Leicester

Theme

  • Dynamic Earth

Supervisors

Project investigator

  • Prof Michael Branney, University of Leicester

 

Co-investigators

  • Prof Jens Zinke
  • Dr Tiffany Barry, University of Leicester UK
  • Prof John Spray, University of New Brunswick, Canada.

How to apply

Methodology

The student will characterise the nature of crater-fill successions of large impacts, using field samples, core images and thin sections. The range of clastic, depositional and crystallisation facies will be distinguished, with an emphasis on possible former melt fragments, and their relationships to enclosing lithologies. Petrographic (optical microscopy and SEM) assessment of textures (clasts shapes and sorting; perlitic, palagonitic, spherulitic and axiolitic) and fabrics (welding, flow banding), alongside x-ray fluorescence (XRF) and laser-ablation inductively-coupled-plasma mass spectrometry (LA-ICP-MS) analysis. A new lithofacies scheme will be developed for large crater fills, and the succession of emplacement, depositional and post-depositional events will be deduced from the facies associations. Innovative interpretations will partly draw on the latest volcanological (field and experimental) understanding of ancient and modern glassy, and formerly glassy, volcanic tuffs and lavas in subaerial and subaqueous settings. Hypotheses that explain the various features will be devised and critically tested.

The student will undertake a supervised field visit to Manicouagan crater, and spend time at the University of New Brunswick, Canada, documenting drill core of the crater fill. They will benefit from being part of an international NERC-funded volcanoes and impact cratering group based at the University of Leicester, and studying welded tuffs (USA) and impact cratering at Ries (Germany), Sudbury (Canada) and Stac Fada (Scotland): lively discussion is anticipated.

Training and skills

The student will receive training in volcanic and sedimentary facies analysis, products of submarine volcanism, and welding and agglutination in tuffs, and in the analysis of suevites and breccias.  Guided in-depth reading of the volcanology literature will be complemented by field visits and access to hand specimens and thin sections to gain hands-on experience. Training will be provided in logging of volcanic, sedimentary and impact-related rocks, facies interpretation, core logging, optical and SEM microscopy and micro-analytic techniques, and scientific writing. By the end of the project the student will have gained expertise spanning submarine volcanic rocks, welded tuffs and impact cratering.

Partners and collaboration

A strength is that the student will benefit from joining a lively research group at Leicester, with international expertise (colleagues at Canada, Germany, USA, and Bristol) ranging from petrology, meteoritics, impacts, and physical volcanology. The student will actively participate in research group discussions, meetings, field trips and lab groups. Close collaboration with the University of New Brunswick in Canada will include an extended study visit. There will be outreach internship opportunities with UNESCO Geoparks (Scotland/and Bavaria) and museums (National Space Centre and Natural History Museum of Berlin).

Further details

Please contact Prof Michael Branney, University of Leicester (mjb26@le.ac.uk). For info Google: Volcanology at Leicester or see: https://www2.le.ac.uk/departments/geology/research/vtmrg

https://le.ac.uk/study/research-degrees/funded-opportunities/centa-phd-studentships

Possible timeline

Year 1

Learn about interpreting modern and ancient mass-flow sediments, glassy and formerly glassy volcanic rocks and their alteration products, including welded and non-welded vitroclastic textures, submarine lavas, hyalocastites, and welded and lava-like tuffs, on macroscopic and microscopic scales and crater fill deposits. Field visits to classic sites of aqueous volcanic successions (e.g. Wales, Italy, Sudbury) welded tuffs (Lake District), hand specimens and petrographic description and in-depth reading. Directed review fills of large impact crater deposits and training on quantitative faces association schemes. Aural presentation. Initial SEM work.

Year 2

Study visit to Canada, to examine the Manicouagan crater fill (Summer 2022) and drill core site at New Brunswick. Core logging, photography, facies definition, development of new textural lithofacies scheme. Quantitative analysis of facies associations. Conference participation.

Year 3

Study visit to the Texas (Autumn, 2022) Chicxulub core repository. Further development of lithofacies analysis, and writing-up. Presentation of results.

Further reading

Branney. M.J. and Brown, R.J. (2011) Impactoclastic density current emplacement of terrestrial meteorite-impact ejecta and the formation of dust pellets and accretionary lapilli: evidence from Stac Fada, Scotland. Journal of Geology, 119, p. 275-292

Gulick, S.P.S. Bralower, T.J., Ormo, J, Hall, B. et al. (2019) The first day of the Cenozoic. www.pnas.org/lookup/suppl/doi:10.1073/pnas.1909479116/-/DCSupplemental. Proceedings of the National Academy of Sciences of the United States of America, 116 (39), p. 19342-19341

Morgan, J.V., Gulick, S.P. Bralower, T., Chenot, E. et al. 2016. Science 345 (6314) 878-882.Siegert, S., Branney, M.J. and Hecht, L. (2017) Density current origin of a melt-bearing impact ejecta blanket (Ries suevite, Germany) Geology 45, p. 855-858

Siegert, S., Branney, M.J., and Hecht, L. (2017) Density current origin of a chemically zoned impact-generated melt-bearing ejecta blanket (Ries suevite, Germany). Geology 45 (9), pp. 855–858.

doi:10.1130/G39198.1

Thompson, L.M., Spray, J.G. (2017). Dynamic interaction between impact melt and fragmented basement at Manigouagan: the suevite connection. Meteoritics and Planetary Science 52 (7) 1300-1329

COVID-19

This research is primarily petrographic using existing drill core stored overseas. Should visits to Manicouagan and the drill stores at New Brunswick and Texas not be possible, excellent images of the entire Chicxulub core are publicly available online, and our collaborators in Canada will send photos and specimens of drill core to Leicester. Should international travel be excluded, gaining field expertise of subaqueous volcanism will be restricted to UK sites (Ramsay, Snowdonia, Llyn). Collaborators at Berlin Natural History Museum can make samples from other impact sites available should further change be required.