INFLUENCE OF PRE-EXISTING STRUCTURES ON STRAIN LOCALIZATION AND EVOLUTION AT THE SOUTHERN TERMINATION OF THE MALAWI RIFT

The Malawi rift is the youngest segment of the East Africa Rift System (EARS) and has been suggested to be the southern termination of the western branch of the EARS. Rifting in Malawi mostly occurs in the Precambrian basement rock, which is well exposed at the surface. The Malawi rift is an ideal location to determine the controls of pre-existing structures on incipient rifting. Our objectives include mapping the rift surface structures in southern Malawi using remote sensing in the form of Shuttle Radar Topography Mission (SRTM) digital elevation model, which records elevation over the rift; Landsat, an Earth imaging satellite that records the electromagnetic radiation resulting from reflected and emitted energy from Earth; and Radio Detecting And Ranging Satellite (RADARSAT), which measures surface roughness. We will map the basement structures over the southern portion of Malawi using a magnetic anomaly map, produced from aeromagnetic data. Magnetic anomalies are often reflected through the distribution of magnetic minerals, primarily magnetite. The Precambrian basement is rich with magnetite and this high concentration, juxtaposed against rocks with lower concentrations of magnetite can produce a sharp boundary, showing as a linear trend. Preliminary remote sensing analysis show a northeast-southwest trend, truncated against the border faults, largely from the Mesozoic Karoo rifting, and Precambrian basement structures showing a WNW-ESE trend as well as a similar northeast-southwest trend to that of the Karoo rifting events. There are also some north-south trends that side step along pre-existing Precambrian faults, showing that current structural evolution is influenced by pre-existing structures. By comparing basement structures to superficial surface structural expression, we can better understand how pre-existing basement structures influence the initiation, evolution, and termination of amagmatic rifting, which will contribute to hazard mitigation, rift modeling, and the construction of more accurate geologic maps of southern Malawi.