Open Session - SWISS GEOSCIENCE MEETINGs
Open Session - SWISS GEOSCIENCE MEETINGs
Open Session - SWISS GEOSCIENCE MEETINGs
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which seems to be consistent with the uplift of the Rhenish Shield as seen in earlier levelling results.<br />
Having continued with the GPS observations and carried out an extension of the network as a coverage of the Northern<br />
Rhenish Massif up to 50 measuring points can be analysed which also include the observations in the Ardennes on Belgian<br />
territory (Demoulin et al. 2005).<br />
As a recent example, the measurements of the local deformation GPS network ‘Donatussprung’, a section of the Erft Fault<br />
system where the surface trace can be identified from topography and effects on buildings and roads, have revealed displacements<br />
of up to 6 mm/y in horizontal and 22 mm/y in vertical direction with high accuracy (Görres & Kuhlmann 2008).<br />
Vertical and horizontal motions due to recent tectonics in this region are smaller by at least an order of magnitude. The<br />
observed pattern of vertical and horizontal velocity vectors shows a remarkable difference in the motion of point groups on<br />
either side of the fault. The scenario suggested by these measurements indicates that the sediment layers on the Erft Block<br />
are indeed sinking in proportion to the groundwater withdrawal, but that near the fault the pattern of motions is strongly<br />
influenced by the fault geometry. Modelling options include mining subsidence troughs as well as fault slip motion.<br />
There is reasonable hope that after 15 years of annual GPS observations in an entire reprocessing of all points and all observation<br />
epochs (currently worked on) the indications (Extension and Uplift) can be clarified.<br />
REFERENCES<br />
Campbell, J., Kümpel, H.-J., Fabian, M., Fischer, D., Görres, B., Keysers, Ch., & Lehmann, K. 2002: Recent movement pattern of<br />
the Lower Rhine Basin from tilt, gravity and GPS data, Netherlands Journal of Geosciences/ Geologie en Mijnbouw, Vol.<br />
81 (2), 223-230.<br />
Demoulin, A., Campbell, J., De Wulf, A., Muls, A., Arnould, R., Görres, B., Fischer, D., Kötter, T., Brondeel, M., Van Damme, D.,<br />
& Jacqmotte, J.M. 2005: GPS monitoring of vertical ground motion in northern Ardenne-Eifel: five campaigns (1999-<br />
2003) of the HARD project, Int. J. Earth Sci (Geolog. Rundsch) 94: 515-524.<br />
Görres, B. & Kuhlmann, H. 1998: How groundwater withdrawal and recent tectonics cause damages of the earth’s surface:<br />
Monitoring of 3D site motions by GPS and terrestrial measurements, Journal of Applied Geodesy, 1(2008), 223-232,<br />
deGruyter Berlin, DOI 10, 1515/JAG.2007.024.<br />
1.1<br />
Terrestrial core formation aided by flow channelling instabilities induced<br />
by iron diapirs<br />
Golabek Gregor*, Tackley Paul* & Schmeling Harro**<br />
*Institut für Geophysik, Geophysical Fluid Dynamics, Schafmattstrasse 30, CH-8093 Zürich (gregor.golabek@erdw.ethz.ch)<br />
**Institut für Geowissenschaften, Facheinheit Geophysik, Altenhöferallee 1, D-60438 Frankfurt am Main<br />
The terrestrial core formation process remains poorly known. Isotopic constraints by Hf/W systematics indicate a fast process<br />
which was largely completed within 33 Ma for the Earth. An unstable gravitational configuration of dense molten metallic<br />
ponds overlying a chondritic protocore is predicted by most studies at latest for the time a planetary embryo reaches Mars<br />
size. This leads to the formation of Rayleigh-Taylor instabilities. We propose the application of Stevenson's stress-induced<br />
melt channelling mechanism in the regions surrounding incipient iron diapirs. We therefore perform numerical experiments<br />
solving the two-phase, two compositions flow equations within a 2D rectangular box. We apply the Compaction<br />
Boussinesq Approximation (CBA) and include a depth-dependent gravity. We use a temperature and stress-dependent viscosity<br />
for the solid phase and melt fraction dependent rheology for the partially molten region around the diapir. We investigate<br />
the development of the channelling instability in cases with and without interaction with surrounding diapirs. In interactive<br />
cases we vary the distance between the diapir centres between 1 and 5 diapir radii and apply pseudoplasticity with<br />
power law exponents ranging from 1 to 6. As a result for single diapirs we observe for sufficiently small retention numbers<br />
the development of iron-rich melt channels within a region of approximately twice the diapir's radius. This could lead to<br />
effective draining of the surrounding region and might initiate cascading daughter diapirs or iron dykes. For small distances<br />
between interactive diapirs the channelling mechanism is delayed for several million years compared with models without<br />
2<br />
Symposium 1: Structural Geology, Tectonics and Geodynamics