Back to Abstract Index
Paper Number: 92
The gravity derived Moho
depth of Botswana and its implications in the recent geodynamic
activities
Chisenga, C.1, Van Der Meidje, M.2 and
Fadel, I.2
1Malawi
university of Science and Technology, P.O.Box 5196 limbe, Malawi, cchisenga@must.ac.mw
2University
of Twente, Faculty ITC, P.O box 6, 7500 AE, Enschede, Netherlands.
___________________________________________________________________________
Botswana remains one of the least understood countries despite having
diamond and other resources underneath its crust [1]. The country
comprises of some of the interesting cratons e.g. Congo craton, Zimbabwe
craton and Kaapvaal craton, cratonic margins and intra-cratonic
boundaries. A supposed buried micro craton called Maltahohe craton is
also found in the western Botswana within the Rehoboth belt [2]. The 3D
structure of Botswana remains not well understood. The SH body wave
tomography of the area did not provide any significant insight into the
area which up to date remain unresolved [2]. Important information like
crustal thickness, Moho depth, and geodynamic of the crust as well as
tectonic activities is still poorly understood in Botswana.
In this study we utilise the ground and airborne gravity data of
Botswana to produce the crustal thickness map of Botswana. We assume a
two layer model of earth crust and upper mantle, the lithospheric
mantle, with a density contrast in between and model our crustal
thickness using the parker-Oldenburg equation [3]–[5]. The inversion
result from the model was constraints against seismic depth estimates in
Botswana [6]. We added ETOPO1 data to the Moho depth values to produce
the crustal thickness map. The final model was compared to the crustal
thickness extracts of both satellite gravity and seismic derived models
[7]–[9] of Botswana to see the improvement and how our model fairs
against existing models.
Overall, our model produces a good crustal thickness map of Botswana.
Despite that no other crustal thickness of Botswana exists. We used an
extract from the crustal thickness map of Africa for comparison. Our
model, considering the parameters and inversion parameters, compares
well with Tugume et al. (2013) model. A new insight into the structure,
tectonic and geodynamic underneath Botswana is understood. The failed
incipient rift in the Okavango area, major faulting that resulted into
dykes swarms and tectonically active areas that represent recent dynamic
activities of Botswana are well defined by the thickness and thinning of
the crust underneath Botswana. Uncertainty in seismic inversion is also
highlighted which defines the southern African earth structure.
Reference
[1] Schluter (2006), Springer Berlin Heidelberg.
[2] Begg G.C. (2009), Geosphere, vol. 5, no. 1, pp.
23–50.
[3] Oldenburg, D.W (1974) Soc. Explor. Geophys., vol. 39,
no. 4, pp. 526–536.
[4] Parker, R.L. (1973) Geophys. J. R. Astron. Soc., vol.
31, no. 4, pp. 447–455
[5] Gomez-Ortiz D. and Agarwal, B.N.P (2005) Comput.
Geosci., vol. 31, no. 4, pp. 513–520
[6] Youssouf, et al (2013) Tectonophysics, vol. 609, pp.
267–287
[7] Laske, G. (2013) Geophysics, vol. Abstract E, no. Res.
Abstracts, 15
[8] Tugume F. et al (2013) Tectonophysics, vol. 609, pp.
250–266
[9] Tedla G.E. (2011) Geophys. J. Int., vol. 187, no. 1, pp.
1–9
