|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
in sedimentary rocks as a record of the Earth’s magnetic field led by Dr.
following topics were addressed:
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
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 ?
a relationship between deformation, in particular major thrust zones, and
NRM components ?
caused the remagnetisations ?
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):
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.
extension in a core-complex
type setting (3.47-3.42 Ga)
folding and trusting (3.3-3.2 Ga)
deformation at ca. 2.93 Ga.
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
If interested, my
thesis can be ordered, write me an e-mail.
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
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
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)
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,
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
J. Geophys. Res.Vol. 108, No. B7, 2357, doi: 10.1029/2002JB002213
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)
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,
Zegers, T.E. and Van Keken,
P.E. (2001). Mid Archean continent formation by crustal delamination,
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,
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.
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,
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.
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,
Nova, 10, 250-259. [PDF]
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
Geologie en Mijnbouw (extended abstract),74,
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,