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How and why is deformation localised in continental crust?

Prof. Tim Wright (SEE), Sandra Piazolo (SEE), Greg Houseman (SEE)

Contact email: t.j.wright@leeds.ac.uk

Summary

In this project you make and use geological field investigations of the exhumed lower crust to constrain models of strain localisation, and these against modern geodetic data from the India-Asia collision. 

Over the last few years, geodetic observations of strain from the continents have revealed two modes of behaviour. At fault zones such as the Himalayan Frontal Thrust, Altyn Tagh and Xianshuihe Faults in the India-Eurasia collision zone high geodetic strain rates are observed at the faults themselves. In other regions, including Western Tibet and Mongolia, present-day deformation is diffuse, with little evidence for localisation on the major structures (e.g. Zheng et al., JGR 2017). The underlying reasons for this bi-modal behaviour remain unclear and are highly debated. Understanding processes responsible for the presence or absence of strain localisation in the continents is important for diverse problems ranging from seismic hazard to the distribution of resources.

To address the question of strain localisation, the student will make new observations from exhumed lower-crustal rocks in Greenland, where bi-modal behaviour also appears to be present, and use the geological and geodetic observations to assess proposed mechanisms for strain (de-)localisation in continental crust by running numerical models.

The Nagssugtoqidian Orogen in SW Greenland is characterised by geological “blocks” that differ in whether strain localization is present or absent. These exhibit striking similarities to areas of different behaviour seen in the present day India-Eurasia collision zone. Compilation of structural and metamorphic data from over 20 years of mapping in the area allow identification of areas of interest that represent the areas of strain localization, largely undeformed regions and areas of diffuse strain. Using this unique dataset, freely available to us, as a guide, the student will conduct additional targeted field work to investigate the rheological, chemical and pre-deformation properties of the rocks outcropping today. They will use the results to build models that test whether the metamorphic, deformation and igneous history of areas involved in present day collisions is a deciding factor in the rheological behaviour of the whole orogeny

Specifically, the student will:

1. Analyse existing geological data from the Nagssugtoqidian belt of West Greenland to characterise strain localisation.

2. Geologically map, collect and analyse new samples from key sites to estimate viscosity distributions (in space) at locations with/without strain localisation and to establish plausible hypotheses for strain localisation.

3. Quantify the degree of strain localisation in the India-Eurasia collision zone using the latest geodetic data from InSAR and GPS, and assess how it varies in space.

4. Build geodynamic models to test the geological hypotheses against the geodetic observations and predictions built from the Greenland case study area.

The student will be supported by the supervisory team whose expertise covers all aspects of the projects. Depending of progression of the project, a visit to a second field area in Central Australia representing an ancient intercontinental orogen (Raimondo et al. Earth Science Reviews 2014) may be organised.

This project is highly innovative as it brings together fields of research that are traditionally separated, even though their main aim is the same: Understanding of the rheological behaviour of the Earth’s continental crust. At Leeds we can offer this unique project as expertise exists in all field necessary. This project promises to produce cutting-edge research markedly advancing our knowledge and understanding of Earth’s deformation behaviour and the validity of classic “rigid” plate tectonic theory in the continents. This knowledge is urgently needed to be able to refine current models used to predict geohazards such as earthquake frequency. We expect research to be presented at international conferences and published in international journals.

The project would suit a numerate student with a background in earth sciences, geology, or geophysics who is enthusiastic about geological fieldwork in remote and challenging areas. The student will be provided with training in state of the art geological and geodetic methods, including microstructural and large geological data analysis. The student will be part of the UK Natural Environmental Research Council’s Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET) and would have the opportunity to interact with COMET students with different skills and backgrounds from across the UK.

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Related undergraduate subjects:

  • Applied mathematics
  • Computer science
  • Computing
  • Earth science
  • Geological science
  • Geology
  • Geophysical science
  • Geophysics
  • Geoscience
  • Materials science
  • Mathematics
  • Natural sciences
  • Physical geography
  • Physical science
  • Physics
  • Remote sensing