| Five decades of scientific
research in the 3500-3100 million year old Barberton Greenstone Belt has
established the mountain ranges around the small and picturesque town of
Barberton as a world heritage site and a playground for international scientists
interested in early Earth processes.
The Barberton Greenstone
Belt represents relatively intact and undisturbed remnants of preserved
ancient seafloor and continental crust that have largely escaped tectonic
reworking since the time they formed. These rocks allow to test the physico-chemical
and biological processes that were operating during the formation of the
Earth’s early crust.
|
| There
are major outstanding questions about Early Earth that address our understanding
of geological, geophysical, chemical and biological processes.
These include research
related to:
-
Vertical (plume-driven)
versus horizontal (plate-tectonic-driven) type crustal mechanisms for the
early Archean
-
Chemical and tectonic make
up of the oldest greenstone belts
-
Earth’s early magnetic
field and magnetosphere
Addressing these questions
using analytical techniques, for example, stable isotope geochemistry
and paleomagnetic studies on surface outcrops has, however, some major
pitfalls:
-
Sparse and discontinuous
outcrops
-
Surface samples are open
weathering and/or other chemical alteration processes
-
lightning strikes and magnetic
overprints hinder obtaining records of unequivocal primary remnance
Clearly, the best way to
directly
access information
related to early Earth processes would be by diamond core drilling to retrieve
fresh, chemically representative samples from depth. |
Fig.
1 Barberton Greenstone Belt
Fig.
2 Location of BSDP drill cores
Illustrations
are from the AEON
- BSDP drilling report, see also the BSDP
drilling webpage. The BSDP project is also reported in EOS
and in Scientific Drilling by
Grosch et al. (2009a,b). |
Barberton Scientific
Drilling Program (BSDP)
| Drilling was aimed
on the mostly tholeiitic 3.47-3.44 Ga upper Onverwacht Group of the Swaziland
Supergroup in the southwesternmost BGB (Fig. 1), along the world renowned
Komati River (Fig. 2). The rocks exposed here include the Mendon, Kromberg
and Hooggenoeg Formations of the Onverwacht Group. Three diamond core boreholes
were drilled, namely KD1 (Kromdraai 1) and KD 2a and 2b (simplified
lithological log). |
Location and
block diagrams of the three drill sites in the Barberton Greestone Belt
(see also the report on Drilling
in 2008 from the Norwegian
Centre for Geobiology, in Bergen, Norway)
A core
orientation tool, EASYMARKTM, was
used to fix the orientation
of the drilled core in space, particularly for
paleomagnetic studies of basalts. |
In this project, we focus
on the paleomagnetism of the BSDP drill core. Anja Dijkhuizen has taken
small samples (8 mm cores) from this core for this purpose, using a specially
made diamond drill bit. She will focus on early Earth geomagnetic field
behaviour and on paleolatitudes of the formations, and depending on results
throughout the sampled intreval, possibly also for deriving (plate or plume)
tectonic processes. She is supervised by Cor
Langereis |
