Crustal thinning beneath the Rwenzori region, Albertine rift, Uganda, from receiver-function analysis
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The Rwenzori mountains in western Uganda, with a maximum elevation of more than 5,000 m, are located within the Albertine rift valley. We have deployed a temporary seismic network on the Ugandan side of the mountain range to study the seismic velocity structure of the crust and upper mantle beneath this section of the rift. We present results from a receiver-function study revealing a simple crustal structure along the eastern rift flank with a more or less uniform crustal thickness of about 30 km. The complexity of inner-crustal structures increases drastically within the Rwenzori block. We apply different inversion techniques to obtain reliable results for the thickness of the crust. The observations expose a significantly thinner crust beneath the Rwenzori range with thickness values ranging from about 20–28 km beneath northern and central parts of the mountains. Our study therefore indicates the absence of a crustal root beneath the Rwenzori block. Beneath the Lake Edward and Lake George basins we detect the top of a layer of significantly reduced S-wave velocity at 15 km depth. This low-velocity layer may be attributed to the presence of partial melt beneath a region of recent volcanic activity.
KeywordsEast African Rift System Rwenzori mountains Receiver functions Lithosphere Crust
This research has been financed by Deutsche Forschungsgemeinschaft (DFG) within the framework of the RiftLink research group (FOR 703). We would like to thank the Geophysical Instrument Pool Potsdam (GIPP) of the GeoForschungsZentrum for providing seismic stations and W. Hanka and staff from the GEOFON data center for archiving the data. The support of the Ugandan National Council for Science and Technology and of the Ugandan Wildlife Authority is greatly appreciated. We thank Kitam Ali and Arthur Batte for help with the setup and servicing of seismic stations. Additional data from station MBAR was provided by the GSN-IRIS/IDA. We used the SeismicHandler software package (Stammler 1993) for data processing. The figures were generated using GMT software (Wessel and Smith 1998). We appreciate the detailed comments and suggestions of the two reviewers, James Hammond and Joachim R. R. Ritter, which helped to significantly improve the manuscript.
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