HR: 0800h
AN: T11D-0404    [Abstracts]
TI: Tectonic Evolution of the Northern Malawi rift, East Africa: Structural Controls on Sediment Dispersal in a Large Lake Basin.
AU: * Mortimer, E
EM: estellem@geo.uni-potsdam.de
AF: University of Potsdam, Inst. f. Geowissenschaften Haus 25 Karl-Liebknecht Str. 24/25, Potsdam, 14476 Germany
AU: Paton, D
T11D-0404 AF: Colorado School of Mines, Department of Geology and Geological Engineering, Golden, CO 80401 United States
AU: Scholz, C
T11D-0404 AF: Syracuse University, Department of Earth Sciences, Syracuse, NY 13244 United States
AU: Strecker, M
EM: strecker@geo.uni-potsdam.de
AF: University of Potsdam, Inst. f. Geowissenschaften Haus 25 Karl-Liebknecht Str. 24/25, Potsdam, 14476 Germany
AB: The Malawi Rift is an integral part of the East African Rift system (EARs), the type example of a rift system in its youthful stages of development. Understanding the spatio-temporal evolution of this rift system provides insights into the past histories and controls on more ancient rift basins. Fundamental questions remain regarding the structural styles, partitioning, and sediment dispersal patterns within large lacustrine basins that are common to young rifts. Such basins are particularly useful recorders of climatic fluctuations. In areas with pronounced climatic variability and high evaporation/precipitation ratios this may lead to, often transient, basin isolation that may dramatically affect sediment and facies distribution. We investigate the structural evolution and sedimentation patterns of the North basin, Malawi Rift. We utilise two seismic reflection data sets: the first, collected by project PROBE, records the entire basin-fill (Sequences 1-3) at medium resolution; the second provides a closely-spaced high-resolution survey of the past ~1 Ma (Sequence 3). These data document the development of the basin-bounding and intra-basin faults. Throughout its history, the basin-bounding fault has accommodated the greatest strain and therefore exerted the fundamental control on the distribution of sediment within the rift. Present-day sediments enter the basin axially, although there is evidence that transverse supply was also important in the past. We identify 11 intra-basin structures that strike parallel or sub-parallel to this border fault. These intra-basin faults, active from the earliest stages, have initial segment lengths of ~30 km, but rapidly reach lengths in excess of 80 km in the north of the basin, and 60 km in the south. Much of the sedimentation along the faults occurred during Sequence 2 (~2.7-1.6 Ma), a period of relative over-filling of the basin. While the basin-bounding fault controls the overall sediment architecture, all 11 intra-basin structures have remained active and have, in particular during the most recent depositional history, played an important role in sediment dispersal within the basin during lake-level lowstands. Such long-lengths and long-lived activity on almost exclusively synthetic intra-basin faults is, however, unusual. This pattern is possibly attributed to one or a combination of factors including: underlying structural fabrics; the geometry of the detachment at depth; sediment loading at the mouths of feeder systems; or loading by a volcanic centre to the north.
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: Fall Meeting 2005