IAP2-22-335

What’s in your basement? Controls on post-orogenic extensional basins

Back-arc basins are a fundamental part of active plate margins and like many rift basins show evidence for having experienced a strong influence by pre-existing orogenic structures and fabrics (structural inheritance). In continental rifts and passive margins such as East Africa, North Sea, Great South Basin, NZ, basement structures and terrane boundaries have been shown to influence the early evolution (eg. Phillips & McCaffrey 2019; Mulaya et al 2022). In back-arc systems the rheological properties of the crust, i.e. the basement units themselves, which can include exhumed high-pressure rocks, domes and orogenic boundaries are possibly of more significance (e.g. Fodor et al 2021). The student will test the hypothesis that the initiation and early evolution of back-arc basin systems is predominantly by detachment-style extensional deformation controlled by basement rheology before switching to steep fault mode. The project will be a collaborative project between Durham University, Leeds University and BGS in the UK and Dokuz Eylül Üniversity in Turkey and will target the western Anatolian/Aegean region where post-orogenic extension in the back-arc related to the Hellenic arc is focused. Detachment-style extension is well documented in the Aegean Islands and horst/graben style normal faulting in onshore Western Turkey. The student will investigate how damaging earthquakes on steep normal faults may be influenced by the evolution of deformation on large scale detachments.

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Image Captions

Figure 1 Tectonic map of Aegean Sea and surrounding regions
Figure 2. Basement units in western Anatolia and examples of structures formed at the contact between the Cycladic basement unit (CBU and the Menderes Massif (MM) (see red box in Fig 1) Map from Cetinkaplan et al (2020)

Methodology

  • Using the latest field and lab-based structural geology methods, you will determine the structural evolution (geometry, kinematics) at key localities in Western Turkey.
  • You will collect samples from rheological boundaries, shear zones and faults for microstructural study and U/Pb calcite dating in Durham and BGS.
  • You will also interpret seismic reflection datasets and active seismicity spatial and temporal patterns in the eastern Aegean region to tie onshore and offshore regions and provide sub-surface constraints that will allow you to create cross section reconstructions and 3D models.
  • There is an option to add a numerical modelling component using ASPECT to this project to test some of the underlying concepts depending on your background and experience.

Project Timeline

Year 1

Literature review, Project planning, Fieldwork 1, microstructural work

Year 2

U/Pb dating -1, fieldwork 2, microstructural, seismic interpretation and/or numerical modelling manuscript/chapter prep

Year 3

U/Pb dating-2, data analysis and synthesis, 3D model building and/or numerical modelling manuscript/chapter prep

Year 3.5

Thesis writing and submission

Training
& Skills

Mapping and Field structural geology, microstructural analysis, sample preparation and U/Pb dating (at BGS). Optional geodynamic modelling component

References & further reading

Phillips, T.B. & McCaffrey, K.J.W. 2019.  Terrane boundary reactivation, barriers to lateral fault propagation and reactivated fabrics – Rifting across the Median Batholith Zone, Great South Basin, New Zealand. Tectonics. 38, 4027-4053.

Mulaya, E., Gluyas, J., McCaffrey, K., Phillips, T. and Ballentine, C., 2022. Structural geometry and evolution of the Rukwa Rift Basin, Tanzania: Implications for helium potential. Basin Research, 34, 938-960.

Fodor, L. et al, 2021. Crustal exhumation and depocenter migration from the Alpine orogenic margin towards the Pannonian extensional back-arc basin controlled by inheritance. Global and Planetary Change, 201, p.103475.

Çetinkaplan, M., Candan, O., Oberhänsli, R., Sudo, M. and Cenki‐Tok, B., 2020. P–T–t evolution of the Cycladic Blueschist Unit in Western Anatolia/Turkey: Geodynamic implications for the Aegean region. Journal of Metamorphic Geology, 38, 379-419.

Roberts, N.M.W. & Holdsworth, R.E. 2022. Timescales of faulting through calcite geochronology: a review. Journal of Structural Geology, 158, 104578

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.

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