Research Foci in 2011:

• ACTIVE AND NEO-TECTONICS OF THE WESTERN CAPE
  Despite its location in a quiet, stable, continental interior, the Western Cape experiences relatively frequent micro-earthquakes, and have a history of intraplate events up to local magnitude 6.9 (in Tulbagh, 1969). Little is known of active and recent seismicity in the region, largely because of lack of observations. In a new project under the umbrella of the Inkaba ye Afrika program we ar setting up a new seismic monitoring station to monitor current seismic activity in the Ceres-Tulbagh region, where the current South African Seismic Network has registered activity of at least one magnitude 3 per month. Focussing on small earthquakes in the aftershock zone of the Tulbagh 1969 event, we hope to characterise the current level of activity on active faults in the region, their focal mechanisms, and make some inferences about current stress states in the area.

  In addition to the active monitoring, investigations are underway in areas where recent (which in South African terms means post-Cretaceous!) seismic events are suspected.

• THE MATCHLESS AMPHIBOLITE, KUISEB SCHIST, NAMIBIA
  The Kuiseb Schist may represent one of the largest, best preserved, accretionary prisms on Earth. Within these rocks, which form the Southern Zone of the Damara Orogen, the Matchless Amphibolite is observed as a tens of meters thick layer of basalt and gabbro, almost continuous for upwards of 400km along strike. With a team from the University of Stellenbosch, I am inverstigating the structure and composition of the Matchless Amphibolite, and the nature of deformation and fluid-rock interaction within the Matchless and in surrounding rocks.

• THE NAUKLUFT FAULT, NAMIBIA
  The Naukluft Fault, central Namibia, accommodated > 10 km displacement of Damara Group sediments over Nama Group sediments during the Pan-African assembly of Gondwana. This terrane-boundary fault comprises predominantly carbonate fault rocks in a metres thick, granular, cataclasite cross-cutting mylonitic textures. In collaboration with a research team at Univ. California Santa Cruz, we are:
  • Characterising the "sole dolomite" of the basal thrust and exploring its geometry and relation to the nappe-bounding thrusts
  • Investigating deformation and fluid-flow in the vicinity of fault-ramps and intersections between the basal thrust and inferred splay-faults
  • Exploring chemical and mechanical changes related to the fluid-driven transition from calcite to dolomite fault rocks

• FRACTURE AND SOLUTION TRANSFER PROCESSES RELATED TO SLICKENFIBRE GROWTH
  Slickenfibres appear to grow at a low angle from the shear surface on which they form, and parallel to the least principal compressive stress. Consequently slickenfibre shear surfaces are interpreted to accommodate shear displacement at a very high angle to the greatest compressive stress, defying classical Coulomb fault mechanics. Based on samples from the Chrystalls Beach Complex, work on slickenfibres involve:
  • Field and microstructural investigations of geometrical relationships between slickenfibres and other structures.
  • Determination of total and incremental displacement accommodated on slickenfibre shear surfaces, and comparison of fault dimensions with analogous active slip styles
  • Geochemical analyses of veins and wallrock in order to determine fluid and material sources.
  • Numerical modelling approaches applied to estimate the rate of vein growth.

• HETEROGENEITY IN INTERSEISMIC COUPLING ALONG THE HIKURANGI SUBDUCTION MARGIN, NEW ZEALAND
  The Hikurangi subduction margin, along the east coast of the North Island, New Zealand, is inferred to be strongly coupled in the south and interseismically creeping in the north. It has been determined that temperature is not a major factor controlling this heterogeneous fault behaviour (McCaffrey et al. 2008; Fagereng & Ellis 2009). On-going investigations of factors affecting fault behaviour involve:
  • Explore potential along-strike variations in fault zone fluid pressure
  • Investigate accretionary prism geometry in order to infer relative fault strength along different fault segments
  • Compare physical parameters of the Hikurangi margin with other well-studied subduction thrust interfaces

Wallace, L.M, Fagereng, A. and Ellis, S. (2012) Upper plate tectonic stress state may influence interseismic coupling on subduction megathrusts, Geology, in press.

Rowe, C.D., Fagereng, A., Miller, J.A. and Mapani, B. (2012) Signature of coseismic decarbonation in dolomitic fault rocks of the Naukluft Thrust, Namibia, Earth and Planetary Science Letters, 333-334, 200-210, doi:10.1016/j.epsl.2012.04.030

Fagereng, A. (2012) A note on folding mechanisms in the Cape Fold Belt, South Africa, South African Journal of Geology, in press.

Fagereng, A. (2012) On stress and strain in a continuous-discontinuous shear zone undergoing simple shear and volume loss, Journal of Structural Geology, in press, download pdf

Fagereng, A., Remitti, F. and Sibson, R.H., (2011) Incrementally developed slickenfibres - geological record of repeating low stress-drop seismic events? Tectonophysics, 510, 381-386, 10.1016/j.tecto.2011.08.015.

Fagereng, A. (2011) Geology of the Seismogenic Subduction Thrust Interface, In Fagereng, A., Toy, V.G., Rowland, J. (eds.), Geology of the Earthquake Source - a Volume in Honour of Rick Sibson, Geological Society of London, Special Publication, 359, 55-76.Available from Geol Soc. London (depending on subsciptions)

Fagereng, A. and Toy, V.G. (2011) Geology of the Earthquake Source - An Introduction, In Fagereng, A., Toy, V.G., Rowland, J. (eds.), Geology of the Earthquake Source - a Volume in Honour of Rick Sibson, Geological Society of London, Special Publication, 359, 1-16. Open Access from Geol Soc. London

Fagereng, A. and Diener, J.F.A. (2011) San Andreas Fault tremor and retrograde metamorphism. Geophysical Research Letters, 38, L23303, doi:10.1029/2011GL049550.

Fagereng, A. and Diener, J.F.A. (2011) Non-volcanic tremor and discontinuous slab dehydration. Geophysical Research Letters, 38, L15302, doi:10.1029/2011GL048214.

Fagereng, A. (2011) Wedge geometry, mechanical strength, and interseismic coupling of the Hikurangi subduction thrust, New Zealand. Tectonophysics, 507, 26-30, 10.1016/j.tecto.2011.05.004. download pdf

Fagereng, A. (2011) Fractal vein distributions within a fault-fracture mesh in an exhumed accretionary melange, Chrystalls Beach Complex, New Zealand, Journal of Structural Geology, 33, 918-927. download pdf

Fagereng, A. (2011) Frequency-size distribution of competent lenses in a block-in-matrix melange: imposed length scales of brittle deformation?, Journal of Geophysical Research, 116,B05302, doi:10.1029/2010JB007775. download pdf

Fagereng, A. and Cooper, A.F., (2010) The metamorphic history of rocks buried, accreted and exhumed in an accretionary complex: an example from the Otago Schist, New Zealand, Journal of Metamorphic Geology, 28, 935-954. download pdf

Fagereng, A. and Sibson, R.H., (2010) Melange rheology and seismic style, Geology, 38, 751-754. download pdf

Fagereng, A. Remitti, F. and Sibson, R.H., (2010) Shear veins observed within anisotropic fabric at high angles to the maximum compressive stress, Nature Geoscience, 3, 482-485. download pdf

Fagereng, A. and Cooper, A.F., (2010) Petrology of metabasalts from the Chrystalls Beach accretionary melange - Implications for tectonic setting and terrane origin, New Zealand Journal of Geology and Geophysics, 53, 57-70. download pdf

Wallace, L., Reyners, M., Cochran, U., Bannister, S., Barnes, P.M., Berryman, K.R., Downes, G., Eberhart-Phillips, D., Fagereng, A. Ellis, S., Nicol, A., McCaffrey, R., Beavan, J., Henrys, S., Sutherland, R., Barker, D.H.N., Litchfield, N., Townend, J., Robinson, R., Bell, R., Wilson, K. and Power, W., (2009). Characterising the seismogenic zone of a major plate boundary subduction thrust: the Hikurangi Margin, New Zealand, Geochemistry Geophysics Geosystems, 10, Q10006, doi:10.1029/2009GC002610.

Scott, J.M., Palin, J.M., Cooper, A.F., Fagereng, A. and King, R.P., (2009). Polymetamorphism, zircon growth and retention of early assemblages through the dynamic evolution of a continental arc in Fiordland, New Zealand, Journal of Metamorphic Geology, 27, 281-294.

Fagereng, A. and Ellis, S., (2009) On factors controlling the depth of interseismic coupling on the Hikurangi subduction interface, New Zealand, Earth and Planetary Science Letters, 278, 120-130. download pdf

Fagereng, A., Harris, C., la Grange, M. and Stevens, G., (2008). Stable isotope study of the Archean rocks of the Vredefort impact structure, central Kaapvaal Craton, South Africa, Contributions to Mineralogy and Petrology, 155, 63-78. download pdf

• Second-year structural geology: Introduction to structural description of rocks, stress, and strain
• Second-year field camp: Laingsburg, Cape Fold Belt
• Third-year structural geology: Rheology, deformation mechanisms, interpretation of geometries, microstructure
• Honours: Tectonics & Geodynamics
• Honours: Evolution of the African Plate

Last Update: May 2012