چكيده فارسي :
The Libombo volcanic complex is part of the Mozambique basin in the southern part of Save river. According to Madeira (2011), the basin of Mozambique is located in passive continental margin that is part of Cenozoic Mesozoic sedimentary basins, which are located along the East African coast and is bounded by the Mozambique belt to the North, Zimbabwe craton in the Northwest and by the Kaapvaal craton in southwest. The study area belongs to the upper group Karoo and has as main characteristic the succession of Basalts and Rhyolites, because they are more resistant to the weathering in comparison with the basalts, tend to form zones topographically higher (the most prominent ones), while the Basalts because of their less resistance for the weathering, tend to form the valleys that intersects the Rhyolites. (NHATUGUÊS, 2003). According to the GTK consortium (2006), the Libombo volcanic chain forms a monocline orienting 15-30 to the East. In the Libombo mountains, rhyolitic flows form smoothly (10o– 15°) east-tilting terraces, with the thickness of single flows probably ranging from some tens of meters up to 200–300 m. Although the rhyolitic rocks generally show gentle dips, patterns developed during the emplacement and cooling of single flows, including shrinkage, jointing and ramp structures, show variably steep, or even vertical attitudes. (GTK consortium, 2006). The estimated maximum thickness of this succession, known formerly as Sica Beds (Cle verly et al.1984) ranges from some tens of meters in the area of Portela Mountain to a few hundred meters east of the Sica Mountain and the proper Pequenos Libombos mountains. The unit, which stands out as a resistant cap in the Movene basalt terrain, is cut by several NW–SEtrending faults and fractures, while a NW–SE-trending sinistral strike-slip fault has separated the ridge into two major parts. At many points visited, some of the faults mapped by GTK consortium were observed, and the faults were filled with brechas, which leads to the conclusion the moniclinal of Libombos was affected by a tectonic event of regional extension that originated the Normal faults oriented in North- South direction. At the field was observed that the most of the diaclases of the study area had the same preferential orientation with the faults. This observation suggests that the whole region suffered the same stress tectonic.
