Understanding geophysical imprints of suture zones: Development of 2D constraint inversion for electrical anisotropy

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Between 2004 - 2006 several high resolution magnetotelluric (MT) experiments along a 650 km long continental scale transect imaged various structural details in the upper and lower crust of South African mobile belts and associated suture zones. With isotropic 2D inversion the main regional features can be explained: (i) the transition of the unexpectedly conductive Namaqua-Natal Mobile Belt (NNMB) into the highly resistive Kaapvaal Craton, which is located 70 km farther southwest than expected, (ii) a sub-vertical zone of high electrical conductivity in the NNMB basement, likely an image of a large crustal scale shear zone, (iii) an extensive shallow sub-horizontal high conductivity layer which correlates with a prominent black shale horizon in the Karoo Basin, (iv) a previously unknown conductive synformal structure in the NNMB basement in 10 - 25 km depth , and (v) the conductive deep basins of the Cape Fold Belt (CFB), which (vi) are sandwiched between the resistive, intensely folded mountain ranges. Some confined areas along the profile exhibit three-dimensional (3D) effects in the MT impedance tensor, likely caused by electrical anisotropy. Modelling and quantifying electrical anisotropy in suture zones has been one of the major goals of my previous application and was part of a PhD project. Unfortunately, the PhD student got severely ill and the position could only be filled again in October 2008. The new PhD student is currently working towards anisotropic inversion. With this proposal we intend to (i) model the effects of electrical anisotropy in the MT data which are currently not explained, (ii) quantify the electrical anisotropy to derive structural details of the associated fault systems and (iii) derive a more complete image of the complicated evolution of Gondwana’s accretion processes preserved in the lithosphere, by putting together the regional information and structural details of anisotropic zones.