Lithostratigraphy of the Vuurdood Subsuite, an early mafic-ultramafic phase of the Palaeoproterozoic Vioolsdrif Intrusive Suite, Richtersveld Magmatic Arc, Northern Cape Province

Mafic-ultramafic plutonic intrusions form an early phase in the emplacement of the predominantly granitic Vioolsdrif Suite, which together with its extrusive carapace, the Orange River Group, form the Richtersveld Magmatic Arc, a Palaeoproterozoic crustal segment formed between 1910 and 1865 Ma. Their lithologic character and distinctive dark weathering features in the mountain desert landscape of the Richtersveld, neighbouring regions of the Northern Cape Province and southern Namibia, make them a separate mappable unit in what is a predominantly granitic terrain. The name of the subsuite is taken from a spectacular twin peak massif near Goodhouse (Vuurdoodberg), while the type locality is one of the best preserved central-type intrusive bodies at Swartkop, situated 2 km off the N7 highway about 20 km south of the border town of Vioolsdrif, where the rock types present include gabbro, metagabbro, quartz-metagabbro, peridotite and troctolite.

Topographic stress influences on bedrock landslides

<p>Bedrock landslides are a major hazard, with influences on erosion, weathering, and organic carbon transfer. Understanding the controls of the magnitudes of bedrock landslides is central for predicting and managing landslide hazards. Previous studies hypothesize that the geometric sizes of bedrock landslides are controlled by bedrock fractures that set the strength of subsurface materials. Recent studies show that topographic stress, resulted from the interplay between tectonics stress and topography, sets the extent of subsurface open-fracture zones, but how topographic stress affects bedrock landslides remains less well understood. Here, we investigate whether topographic stress influences the magnitudes of bedrock landslides in a granitic terrain in the eastern Tibetan mountains where landslides prevail. We constructed two new landslide inventories of earthquake- and rainfall-induced landslides in the study area. We examine the relationships between landslide sizes and the proxies for topographic stress, topography, and landslide triggers (i.e. seismic shaking and rainfall). We demonstrate that topographic stress exerts a dominant control on the sizes of large bedrock landslides. Our study provides new insights into how landslides occur in different topographic and tectonic conditions, as well as how topographic stress influences earth surface processes.</p>

Distribution of aquifer characteristics in different geomorphologic units in a granitic terrain

Knowledge of aquifer characteristics is essential for groundwater development and management studies. Detailed hydrological studies were carried out in a granitic terrain consisting of different geomorphologic units to resolve the coverage, performance, and characteristics of the aquifer parameters through the application of the pumping test method. An interpretation was performed by different methods, viz., Theis, Jacob, Hantush, and Rushton and Redshaw (numerical finite difference method) to ascertain the aquifer parameters. These parameters are vital for future groundwater development and management studies. Transmissivity (T) values estimated by Theis method range from 3.83 to 436 m2/day; 3.77 to 718 m2/day; and 16 to 160 m2/day, by Jacob method it ranges from 3.90 to 436 m2/day; 3.73 to 769 m2/day; and 17.3 to 152 m2/day, by Hantush method it ranges from 1.63 to 189 m2/day; 0.53 to 755 m2/day; and 19.3 to 118 m2/day, while by numerical method it ranges from 3 to 455 m2/day, 3 to 700 m2/day, and 17 to 148 m2/day in pediplain with moderate weathering (PPM), pediplain with shallow weathering (PPS), and buried pediplain with shallow weathering (BPPS) geomorphologic units, respectively. Similarly, a radius of influences ranges from 9.75 to 1391.0 m; 8.0 to 698.09 m, and 380.78 to 433.76 m in PPS, PPM, and BPPS geomorphologic units, respectively. The aquifer parameters obtained by the pumping tests were correlated with the structural features and different geomorphologic units. It was found that these parameters have wide variations within each geomorphologic feature. The radius of influence of each test well was calculated and compared with the in situ measured discharge of various wells within the area. The high values of transmissivity (T) are attributed to aquifer controlled by fractured zone in the area.