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The geology of the angareb ring dike complex,northwestern ethiopia |
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| Authors: | G A Hahn R G H Raynolds R A Wood |
| Institution: | 1. Department of Earth Sciences, Dartmouth College, 03755, Hanover, N.H., U.S.A. 3. Dept of Applied Earth Sciences, Stanford University, 94306, Stanford, CA, USA 4. Dept of Geological Sciences, University of Texas at Austin, 78712, Austin, TX, USA |
| Abstract: | The Angareb Ring Dike Complex is located in Begemder Province in northwestern Ethiopia, 55 kilometers NNW of the provincial capital Gondar. The structure was first identified in 1973 from Landsat 1 satellite imagery analysis of the East African Rift System. The complex is exposed on the floor of the Tana Graben, a feature bearing structural affinity to the East African Rift. A post-early Miocene age is ascribed to the complex. Association with other as yet univestigated circular features may define a volcanic province of early continental rifting in Ethiopia. Contained within the ring structure is a heterogenous tuff breccia of over 100 cubic kilometers in volume, composed of massive agglomorates, ash flows, welded tuffs, and subaqueous tuffs. The tuff is interpreted as filling a subsiding caldron above an eviscerating magma chamber. Mineralogy and chemical analyses depict a fractionating basaltic magma of transitional-mildly alkaline composition. Partial melting of the Precambrian basement is envisioned to explain the subalkaline granites. Comparison of chemical data with regional petrochemical interpretations suggests that the complex represents the beginning of central vent activity in the waning stages of Tertiary volcanism in Ethiopia. |
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