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2010-01-20 – SEMINAR by Mohammednur Desissa: Magnetotelluric Survey in the Dabbaho Volcanic Segment, Afar Depression, Northern Ethiopia

20 January, 2010 (16:00 GMT), 5 Merrion Square, Dublin 2.

Speaker: Mohammednur Desissa – University of Edinburgh, UK/ Geological Survey of Northern Ireland / Geological Survey of Ethiopia, Ethiopia.
Title: Magnetotelluric Survey in the Dabbaho Volcanic Segment, Afar Depression, Northern Ethiopia.

Abstract:

The Afar depression provides an ideal laboratory to study the evolution of rift segmentation as rifting proceeds to breakup. The three riftarms of the Afar Triple junction formed within the palaeogene flood basalt province associated with the Afar mantle plume (Yirgu et al, 2006; Aquater, 1996). The NW trending rift structure comprises the currently active Arta Ale-Manda Hararo rift system, which extends the active tectonics of the Red sea to the south. The Arta Ale-Manda Haro rift system, which includes Dabbaho, Alayta, Tat Ale, and Hararo is marked by axial volcanic ranges with aligned basaltic cones and fissural flows. The Dabbaho magmatic segment is currently active; the Hararo segment is currently inactive, but dyking appears to be propagating southwards. Magnetotellurics (MT) survey was aimed at locating partial melt in the crust and topmost mantle and determining crustal structure across the currently active Dabbaho magmatic segment by determining subsurface conductivity variations. The MT data modeled using 2D inversion scheme revealed detailed subsurface conductivity architecture underneath the Debaho magmatic segment. Prominent high conductivity bodies were found, interpreted to represent partial melt. Lateral and vertical extents of the partial melt have been mapped at two different depths. A shallower melt at depth ranges of 2-7km is delineated incorporating conduit structure through which the melt would arrive to the surface. The most significant conductive zone/partial melt has been mapped in depth ranges of 15-27km covering a width of 20-22km both in the lower crust and the uppermost mantle (deeper magma chamber).