Revised Eburnean geodynamic evolution of the ... - Tectonique.net

4.5. Forward modelling
Forward-modelled geological cross-sections (Fig. 16) across
the Ashanti Belt and Tarkwa Basin were constructed in order
to understand and illustrate the structural relationship between
the Birimian and Tarkwaian units produced during D1 and D3
shortening events. These sections are geologically consistent with
the regional interpretation and the field observations. Forwardmodelling
was performed to ensure that geological cross-sections
were also geophysically consistent with aeromagnetic, gravity and
petrophysical data. Not all features within these models produce
a perceptible geophysical contrast but are otherwise in agreement
with the geological observations made within the study
area.
Modelling was performed using Oasis Montaj GM-SYS software
that utilises the algorithm of Talwani et al. (1959) and
S. Perrouty et al. / Precambrian Research 204– 205 (2012) 12– 39 29
Fig. 10. (Continued)
Talwani and Heirtzler (1964) to calculate the gravity and magnetic
response of two-dimensional polygons. Construction of these
integrated geological and geophysical models involved creating
a traditional geological cross-section that was assigned values of
magnetic susceptibility and density. The different fold trends in
the Birimian and Tarkwaian units are represented in 2D by different
fold wavelengths, amplitudes and positions of fold axes as
they occur in the plane of the section. The geophysical response
of this model was then calculated and compared to the observed
aeromagnetic and gravity anomalies. The geometry and magnetic
susceptibility/density values assigned to each rock package were
then manipulated within geologically reasonable limits to improve
the agreement between the model response and the observed
response.
Magnetic susceptibility ranges for the modelled rock packages
were based on field and laboratory susceptibility measurements