People at Fort Hoofddijk

Tanja Zegers
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Dr. T.E. Zegers
Postdoc 1997-2003
(1999-2000 University of Michigan)
Now at:
European Space Agency (ESA)
European Space & Technology Centre (ESTEC)
P.O.Box 299, 2200 AG Noordwijk
The Netherlands
ESA Home page
Phone:  +31 71 565 6585
E-mail: t.zegers@rssd.esa.int

Research
Publications

 



Research of Tanja Zegers

Remagnetization processes in the Belgian Ardennes 
The Ardennes form part of the Variscan foreland fold and thrust belt in Western Europe. Devonian/Carboniferous units of low metamorphic grade in the Ardennes  have been shown to contain at least two remagnetised NRM components: a low-temperature post-folding component and a pre-folding high-temperature component(Molina Garza and Zijderveld, 1996). This research project is aimed at understanding the process of remagnetization and its relationship with geological processes, and formed part of a larger program on the natural remanent magnetisation (NRM) in sedimentary rocks as a record of the Earth’s magnetic field led by Dr. Mark Dekkers

The following topics were addressed:
  • Which minerals are the carriers of the NRM components in the limestone and red beds ?
  • Is the magnetic behaviour different for different rock types and what causes this difference ?
  • Is there a relationship between NRM components and fluid flow processes ? A number of small Mississippi Valley Type ore bodies occur in the Ardennes, is there a relationship between those and the low-temperature remagnetization ?
  • Is there a relationship between deformation, in particular major thrust zones, and NRM components ?
  • Which mechanisms caused the remagnetisations ?
 
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Structural and kinematic evolution of the early Archean Pilbara Craton

This project was part of the Pilbara study group at the Structural Geology Department of Utrecht University (Prof. Stan White) and the Isotope Lab of the Free University in Amsterdam (Dr. Jan Wijbrans) and resulted in my PhD thesis.

Major results were that three main deformation events have been recognised in the area of the Shaw Batholith (eastern Pilbara): 

  • extension in a core-complex type setting (3.47-3.42 Ga)
  • compression involving folding and trusting (3.3-3.2 Ga)
  • pan-cratonic strike-slip deformation at ca. 2.93 Ga.
The timing of these events has been established by a combination of 40Ar/39Ar dating of hornblende and U-Pb SHRIMPII dating of zircons. U-Pb dating was done in collaboration with Dr. Nelson at Curtin University, Perth, Australia.

In addition, a structural and geochemical study of one of the major gold mines in the eastern Pilbara, the Bamboo Creek Deposit, showed that gold mineralization occurred prior to ca. 3.3 Ga, and was related to deformation of carbonate altered boudins in an, originally komatiitic, shear zone. This study was done in collaboration with Dr. Mark Barley and Prof. David Groves at the University of Western Australia.
If interested, my thesis can be ordered, write me an e-mail.

Did a pre 2.7 Ga Vaalbara exist ?

The Pilbara and Kaapvaal Craton are the only two remaining pristine early Archean terrains. The evolution of both cratons between 3.5 and 2.8 Ga show a surprising amount of similarities. It has been proposed that the two cratons were part of one major continent between 2.7 and 2.1 Ga (Cheney et al., 1988) called Vaalbara.
By combining structural, geological and paleomagnetic data we evaluate the possibility of a Vaalbara continent for the 3.5-2.8 Ga period. In collaboration with Prof. Maarten de Wit and Dr. Jesse Dann, University of Cape Town, South Africa.

Paleomagnetism of the lower Mt. Bruce Supergroup, Pilbara Craton
MSc-student project by Geert Strik on samples from the lower Mt. Bruce Supergroup in the Nullagine area, in collaboration with Tim Blake. The research has resulted in a PhD project for Geert Strik, which started in 1999. The project is a study of igneous and sedimentary sequences from the well-preserved Pilbara (Australia) and Kaapvaal (South Africa) Cratons. 

publications Publications of Tanja Zegers
2003
  • Strik, G., Blake, T.S., Zegers, T.E., White, S.H. and Langereis, C.G. (2003). Palaeomagnetism of flood basalts in the Pilbara Craton, Western Australia: late Archaean continental drift and the oldest known reversal of the geomagnetic field, J. Geophys. Res., 108(B12), 2551, doi:10.1029/2003JB002475 
  • Zegers, T.E., Dekkers, M.J. and Bailly, S. (2003). Late Carboniferous to Permian remagnetization of Devonian limestones in the Ardennes: Role of temperature, fluids and deformation. J. Geophys. Res.Vol. 108, No. B7, 2357, doi: 10.1029/2002JB002213 
2002
  • Kloppenburg, A. White, S.H. and Zegers, T.E. (2002). Erratum to "Structural evolution of the Warrawoona Greenstone Belt and adjoining granitoid complexes, Pilbara Craton, Australia: implications for Archaean tectonic processes"; [Precambrian Res. 112 (2001) 107-147], Precambrian Res., 116,165-166.   [PDF]
  • Zegers, T.E., Barley, M.E., Groves, D.I., McNaughton, N.J. and White, S.H. (2002). Deformation and hydrothermal alteration in the Early Archean Shear zone-hosted Bamboo Creek Deposit, Pilbara, Western Australia, Economic Geology, 97, 757-773.
2001
  • Zegers, T.E. and Van Keken, P.E. (2001). Mid Archean continent formation by crustal delamination, Geology, 29, 1083-1086.   [PDF]
  • Zegers, T.E., Nelson, D.R., Wijbrans, J.R. and White, S.H. (2001). SHRIMP U-Pb zircon dating of Archean core complex formation and pancratonic strike-slip deformation in the East Pilbara Granite-Greenstone Terrain, Tectonics, 20, 883-908.   [PDF]
  • Kloppenburg, A. White, S.H. and Zegers, T.E. (2001). Structural evolution of the Warrawoona Greenstone Belt and adjoining granitoid complexes, Pilbara Craton, Australia: implications for Archaean tectonic processes, Precambrian Res., 112, 107-147.    [PDF]
1999
  • Zegers, T.E., Wijbrans, J.R. and White, S.H. (1999). 40Ar/39Ar age constraints on tectonothermal events in the Shaw Area of the eastern Pilbara granite-greenstone terrain (W. Australia): 700 Ma of Archean tectonic evolution, Tectonophysics, 311, 45-81   [PDF]
1998
  • Zegers, T.E., de Keijzer, M., Passchier, C.W. and White, S.H. (1998). The Mulgandinnah Shear Zone; an Archean  crustal scale shear zone, Pilbara Craton, Western Australia. (Special Issue on Pilbara Craton), Precambrian Res., 88, 233-247. [PDF]
  • Zegers, T.E., de Wit, M.J., Dann, J. and White, S.H. (1998). Vaalbara, Earth's oldest assembled continent ? A combined structural, geochronologic and paleomagnetic test, Terra Nova, 10, 250-259.   [PDF]
1997
  • Zegers, T.E., Wijbrans, J., Nelson, D. and White, S.H. (1997). 40Ar/39Ar and U-Pb dating in the eastern Pilbara: temporal constraints on structural and metamorphic events between 3.5 and 2.8 Ga, Geologie en Mijnbouw (extended abstract), 76, 353-355.
  • White, S.H., Zegers, T.E., de Keijzer, M. and Dirks, P. (1997). Tectonic evolution of the eastern Pilbara, Australia, Geologie en Mijnbouw (extended abstract),74, 343-347.
1996
  • Zegers, T.E., White, S.H., De Keijzer, M. and Dirks, P. (1996). Extensional structures during deposition of the 3460 Ma Warrawoona Group in the eastern Pilbara Craton, Western Australia. Precambrian Res., 80, 89-105[PDF]
  • Zegers, T.E. (1996). Structural, kinematic and metallogenic evolution of selected domains of the Pilbara granitoid-greenstone terrain; implications for mid archean tectonic regimes. (PhD thesis, Utrecht University) Geologica Ultraiectina, 146, 208 pp.