Heat Flow and Geodynamics of the Kaapvaal Craton and its implications on the potential of Enhanced Geothermal Energy in South Africa

Dhansay T.

Africa Earth Observatory Network, Nelson Mandela Metropolitan University; Council for Geoscience, South Africa

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Being the leading carbon emissive nation in Africa; with more than 90% of all energy needs met by non-renewable energy sources¹, South Africa is now in the process of alleviating this scenario by implementing cleaner renewable forms of energy. This is affirmed by the South African Government’s renewable energy² and greenhouse gas mitigation targets³, which aims to produce more than 10,000 GWh of renewable energy and simultaneously generate a 15% decrease in greenhouse gas emissions by 2015. This is further compounded by the 2015 greenhouse gas mitigation deadline agreed upon during the recent COP17 climate change summit held in South Africa⁴. With a thick continental lithosphere and underlying mantle keel providing cold and dense mantle heat flow signatures⁵, notwithstanding the lack of active volcanism, geothermal energy is not considered as a large-scale alternative energy source in South Africa, however in this study I investigate the presence of anonymously high heat flow signatures along the Limpopo Mobile Belt and ascribe it towards Enhanced Geothermal Energy (EGS) potential through geodynamic and mantle heat flow evolutionary modeling compounded with hydrogeological groundwater aquifer modeling. Furthermore, I perform levelised cost of energy (LCOE) modeling to determine the economic viability and sustainability of EGS in South Africa. I conclude that while the Kaapvaal Craton does show relatively cold and dense mantle heat flow signatures, the high degrees of tectonic-lead deformation and plutonism with high concentrations of radioactive elements along the Limpopo Mobile Belt has resulted in an anonymously high heat flow zone sufficient for EGS harnessing. Furthermore, I deduce that while the cost of EGS in South Africa would be exponentially greater than current coal-generated energy, with an added policy amendment toward carbon reduction incentive for EGS, the LCOE of EGS decreases to a range that warrants further research and development of this technology toward possible future implementation in South Africa.

References:

1. Digest of South African Energy Statistics (2009), Department of Energy, Republic of South Africa (public domain)

2. White Paper on Renewable Energy (2003), Department of Minerals and Energy (public domain)

3. Energy efficiency strategy of the Republic of South Africa (2005), Department of Minerals and Energy (public domain)

4. Jacobs, M. (2012). Climate policy: Deadline 2015, Nature, 481, 137-138

5. Niu, R., et al. (2004). Seismic constraints on the depth and composition of the mantle keel beneath the Kaapvaal craton. Earth and Planetary Science Letters, 224, 337-346 (Elsevier)

Evolution of Zamiin-Uud – Hegenshan accretion-collisional zone in Middle Devonian – Early Carboniferous: accreted model of South Gobi microcontinent to active margin of Sibirian continent, SE Mongolia

Otgonbaatar D.^1,2, Buslov M.M.², Tomurtogoo O.³, Tomurhuu D.³

¹ Novosibirsk State University, Novosibirsk, Russia; ² V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia; ³Institute of Geology and Mineral Resources, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia

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Newly discovered Silurian-Lower Devonian ophiolite between Precambrian Hutag-Uul and Nuhetdavaa basements in SE Mongolia had been mapped with structural observations at Bayartiin-Ovoo (Bairam-Ovoo in old papers) area and furthermore distinguished as Zamiin-Uud – Hegenshan accretion-collisional zone. The zone composed of ultramafic rocks, rarely basalt, tuff and green- and black schist, which stratigraphically associated with Lower Devonian siliceous-terrigenous sequence. These complexes are totally overprinted by ductile deformation of greenschist-amphibolitie faceis. The rocks association, its criteria elements greatly support an accretionary wedge setting in Devonian. The structure is well compared northeastward with Hegenshan ophiolite of NE Chine. The accretionary system of the South Gobi microcontinent active margin represented by ophiolite association, particularly strongly deformed with early-middle Devonian crinoids bearing flyshoid succession (Toli-Uul area in Mongolia) and blueschist bearing unit (⁴⁰Ar-³⁹Ar age of 383±13Ma on Baolidao area in Chine).

The accretionary and microcontinent units were duplicated by large scale displacement in Later Devonian-Early Carboniferous. A collisional stage of duplicated Zamiin-Uud – Hegenshan accretion-collisional zone probably started at Tournaisian-Visean and completed by amalgamation into Sibirian continent in serpukhovian. The Zamiin-Uud accretion-collisional complex is uncomfortably overlaid by brittle deformed Upper Carboniferous-Early Permian flyshoid-terrigenous succession, which intruded by post-collision Early Permian granitoid.

Fig.(a) Location of the Central Asian Orogenic Belt (CAOB) and adjacent tectonic elements (modified after Buslov, 2011). (b) Simplified tectonic map of the southeastern part of the CAOB showing main lithotectonic zones and location of Fig. 2 (modified after Chen et al., 2009; Hsü et al., 1991; Miao et al., 2007; Ping Jian et al., 2010; Tomurtogoo, 2009; Xiao et al., 2003; Xu et al., 2001). Numbers in left of each box refer to geochronological constraints from: ⁽¹⁾Bao et al. (1994), ⁽²⁾Xu et al. (2001), ⁽³⁾Tomurhuu et al. (2009), ⁽⁴⁾Miao et al. (2007).

Finally, some ultramafic sheets were southward thrust over the lower Permian volcanic and lower-middle Jurassic sedimentary sequences in the Mesozoic. Also Sulinheer ophiolitoc rocks were removed into the Zamiin-Uud – Hegenshan accretion-collisional zone by the Mesozoic NE trending sinistral transpressional fault.

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