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Paleostress analysis of the Nyasa / Malawi Rift: implication for the present-day regional dynamics
  • Athanas Simon MACHEYEKI,
  • Hassan Mdala
Athanas Simon MACHEYEKI
University of Dodoma

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Hassan Mdala
Geological Survey of Malawi
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The Nyasa/ Malawi rift is characterized by poor magma with relatively large earthquakes. There has been a controversy as to the stress kinematics of the rift, some considering it as part of the transform fault and some considering it as a rift structure characterized by normal faulting. To review this controversy, we collect fault slip data from the central to the southern end of the rift and integrate our results with published focal mechanisms fault slip data on the rift. Results show that the central part of the rift is under radial extension whereas the southern half is under oblique NNE-SSW transtensive tectonic regime with the horizontal axis of minimum extension = 020˚. Further south, the obliquity extension rotates by about 15˚ reaching N-S with Shmin = 175˚. The level of structural penetration and intensity of faulting show that the N-S opening is more important and prominent in the south than towards the north. We also find that the faults that dip to the east and trending NW-SE are characterized by sinistral sense of movement whereas those that dip to the southwestern side are characterized by dextral sense of movements. This implies that regionally, the rift is essentially under normal faulting regime but with a significant strike –slip component – hence the obliquity kinematics. Tectonic regimes obtained from fault-slip data are related to lithospheric scale and involve both the crust and the upper mantle. Thus, the pure NNW-SSE extension related to focal mechanism data are crust deformation related events.