Continental fragment formation by rifting of orogenic belts

Overview

Continental slivers, ribbons, flakes and microplates are small fragments of the Earth’s continents that become isolated during plate tectonic movements but the processes by which they form are poorly understood.
At continental margins, many subduction systems show evidence for formation of tectonic slivers due to partitioning of oblique convergence into trench parallel and trench-perpendicular components, e.g. Cordilleran terranes in western US. Microcontinents are also known to form in the oceanic domain, e.g. Jan Mayen and Seychelles due to ridge jump processes or directional plate motion changes.

Recent modelling of the development of segmentation in rift systems has highlighted the role of mantle sutures or scars in controlling first order margin architectures (Heron et al 2019). This work also identified that rifting of collisional orogens can create continental slivers if the later extension is orthogonal to the earlier convergence (e.g. Fig. 1). This is due to an offset in the location of the younger rift axis relative to the collisional suture that produced the earlier lithospheric mantle features.

The aim of this project is to investigate what controls the formation and tectonic evolution of continental fragments in orthogonal rift systems using a combined structural, geophysical and modelling approach. A secondary aim will be to investigate whether the mechanism identified by Heron et al (2019) applies throughout Earth history or is restricted to the transition from Early Earth to modern plate tectonics.

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Image Captions

A scanning electron image of an apatite crystal (c. 300 µm long). Accumulation of helium, due to radioactive decay of U and Th within the crystal, and thermal diffusive loss of helium over geological time can be measured and used to infer the thermal history of the host rock and importantly its trajectory from depth to the surface Model set-up for West Greenland to study a Proterozoic relict subduction scar in the mantle and its control on inheritance in the Mesozoic – Cenozoic Labrador Sea, Baffin Bay ocean basins (Peace et al 2017, Heron et al 2019)

Methodology

Initially a comprehensive literature review will be undertaken. Undertake desktop GIS mapping and GPlates models to constrain the tectonic history of individual examples as input parameters for geological models.

GIS mapping and GPlates models will constrain the tectonic history of individual examples of continental fragments, which will be used to generate input parameters for geological models. Physical calculations in 2D and 3D will be performed using the open source community code ASPECT, which has been applied to a wide variety of relevant tectonic and geodynamical modeling projects (Heister et al., 2017). ASPECT uses cutting-edge numerical techniques for optimal performance, is extensible to tailor for individual needs, and runs on large supercomputers. Here you will work with Durham University’s Geodynamics Research Group (Prof Jeroen van Hunen and Dr Phil Heron) and the corresponding high-performance computing team (Advanced Research Computing). The study starts from existing models that have been set-up for West Greenland (Fig 2, Heron et al 2019) and will also build upon ongoing work on structural inheritance from the Structural Research Group (Prof McCaffrey).

The record of sedimentary rift basin fill, measured by seismic reflection and drilling for example, provides ideal observations that can be used to test model predictions of subsidence during rifting. The equivalent information for constraining uplift and erosion in the hinterland is often more difficult because erosion removes the geological record. Low temperature thermochronology can be used to solve this problem and provide quantitative estimates of the amount of uplift and erosion, and the thermal history of the shallow crust (e.g. Jess et al., 2019) which will help constrain the geodynamic models This project will capitalise on extensive existing thermochronology data sets, and new data generated for this project, coupled with novel 4D inverse thermal history modelling techniques developed by Prof. Rod Brown and the computational thermochronology group at the University of Glasgow.

Project Timeline

Year 1

Year 1 Literature review, desktop study including GIS and GPlates studies. Iapetus DTP training, attendance at national conference. Analysis of individual continental fragment examples, training on high performance computing and ASPECT modelling. Initial training in thermochronology laboratory techniques and thermal history inverse modelling techniques. Analysis of results, 9 month confirmation report and interview and preparation of first results for publication.

Year 2

Year 2. Completion of the basic software tools to be developed, and first major results for the project; preparation for publication of first key results in a peer-reviewed journal.

Year 3

Year 3. Application of the developed software and methodologies to different tectonic settings and areas; writing of further manuscript for publication.

Year 3.5

Year 3.5. Analysis and synthesis of results, final progression report and interview and preparation of further results for publication. Thesis preparation and submission.

Training
& Skills

The project will give the student an opportunity to gain skills in field-based structural geology, thermo-chronology analysis and interpretation, and numerical modelling and an understanding of early Earth and modern tectonics.

You will become part of the Structural and Geodymanics Research Groups at Durham, an established research unit of 20+ academic, postdoctoral and postgraduate structural geologists. At Glasgow you will be a member of the Dynamic Earth and Planetary Evolution theme.

Training will be provided in geodynamical and in thermal history inverse modelling (programming, code development, model setup, and usage) as well as data management of high-performance computing systems. The project is an opportunity for the student to become proficient in computer programming and large dataset analysis, with support from an enthusiastic ASPECT community. Training in laboratory based thermochronology analytical techniques (fission track and (U-Th)/He analysis) will also be provided.

The student will have opportunities to work with other partners in the UK and internationally and they are encouraged to travel to national and international scientific meetings to present results. The student will be expected to present posters and talks at conferences including at least one international conference.

You will also become part of the IAPETUS2. A Doctoral Training Programme which offers a multidisciplinary package of training focused around meeting the specific needs and requirements of each student who thus benefit from the combined strengths and expertise that is available across our partner organisations.

References & further reading

Heron, P.J., Peace, A.L., McCaffrey, K.J.W., Welford, J.K., Wilson, R., van Hunen, J. and Pysklywec, R.N., 2019. Segmentation of rifts through structural inheritance: Creation of the Davis Strait. Tectonics, 38, 2411-2430.

Heister, T., Dannberg, J., Gassmöller, R., Bangerth, W., 2017. High accuracy mantle convection simulation through modern numerical methods – II: realistic models and problems, Geophysical Journal International, 210(2), 833-851.

Jess, S., Stephenson, R., Roberts, D.H. and Brown, R., 2019. Differential erosion of a Mesozoic rift flank: Establishing the source of topography across Karrat, central West Greenland. Geomorphology, 334, 138-150.

Peace, A.L., McCaffrey, K. Imber, J. van Hunen, J. Hobbs, R. Wilson. R. The role of pre‐existing structures during rifting, continental breakup and transform system development, offshore West Greenland. Basin Research 30, 373-394

Schiffer, C. Doré, A.G. Foulger, G. Franke, D., Geoffroy, L., Gernigon, L. Holdsworth, R.E., Kusznir, N. Lundin, E. McCaffrey, K.J.W., Peace, A., Petersen, K.D. Phillips, T.B. Stephenson, R. Stoker, M. Welford. J.K., 2019. Structural inheritance in the North Atlantic. Earth Science Reviews.

Further Information

For further information contact Ken McCaffrey at k.j.w.mccaffrey@durham.ac.uk Twitter handle @kmccaffrey

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