Fracture Development Around Moshaneng and Kanye, Southeast Botswana

Abstract

<p> SE Botswana, located in the NW part of the Kaapvaal Craton is a long lived tectonically stable environment dominated by brittle deformation for more than 2.6 Ga. </p> <p> Relative chronologies in the development of fractures are rationalized according to major unconformities that developed during the Proterozoic in areas around Moshaneng and Kanye in SE Botswana. Periods of brittle deformation are divided into pre-Transvaal Supergroup, post-Transvaal Supergroup/ pre-Waterberg Group and post-Waterberg Group times. Pre-Transvaal lineaments trend ENE and NE and were probably formed as fractures in a rifting environment Dikes are intruded along some of these lineaments. Post-Transvaal/ pre-Waterberg fractures consist of strike-slip faults that form a conjugate system of two major sets trending NE and NW. These fractures probably formed as a result of E-W compression. The displacement along the NE trending faults depicts reactivation along pre-existing fractures. Regional patterns of fault termination are discemable. Epidermal folds and thrusts were produced in the Transvaal Supergroup rocks. Rotational bulk strain is locally significant. PostWaterberg deformation was dominated by dip-slip faults, vertical displacements and drape folds. </p> <p> An orthogonal system of bedding-normal joints predominates in the layered rocks. Inversion of the relative magnitudes of a2 and a3 probably accounts for a two phase tensile failure of layered rocks during the formation of the joint system. A diagonal system of bedding normal joints is superimposed on the orthogonal system possibly because of pre-existing folds that perturb the remote stress field. Joint spacings have a negatively skewed normal frequency distribution. Systematic joints show that spacing of set1 <set2 <set3 <set4. </p> <p> Relics of joint patterns in chert breccia provide insight about post-Transvaal/ pre-Waterberg karstification residuum. The joint pattern accounts for the initial process of fragmentation that resulted in the formation of chert breccia. </p> <p> On the subcontinental scale, high strain tectonic belts provide a chronology of large scale stress fields that could explain the intracratonic brittle deformations. </p>