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North-Central Section (44th Annual) and South-Central Section (44th Annual) Joint Meeting (11–13 April 2010)

Paper No. 3
Presentation Time: 4:15 PM

DETAILED MAGNETIC STUDY OF THE RED SEA PROPAGATOR WITHIN AFAR, ETHIOPIA: IMPLICATIONS FOR THE TRANSITIONING FROM CONTINENTAL RIFTING TO SEA FLOOR SPREADING


BRIDGES, David L.1, MICKUS, Kevin L.2, GAO, Stephen S.3, ABDELSALAM, Mohamed G.1 and HARO, Workineh4, (1)Geological Sciences and Engineering, Missouri University of Science & Technology, 129 McNutt Hall, Rolla, MO 65409, (2)Department of Geography, Geology, and Planning, Missouri State University, 901 S. National Avenue, Springfield, MO 65897, (3)Geosciences and Geological and Petroleum Engineering, Missouri University of Science & Technology, 129 McNutt Hall, Rolla, MO 65409, (4)Geological Survey of Ethiopia, Addis Ababa, Ethiopia, dlbr3d@mst.edu

A detailed magnetic study across the Tendaho Graben (the Red Sea propagator within the Afar Depression, Ethiopia) revealed features that can best be interpreted as a continental rift undergoing oceanization. This NW-trending extensional structure is ~50 km wide and it is confined within well-developed NW-trending boarder faults that deform the 2 km thick and ~ 2 Ma basalt flows of the Afar Stratoids. Faults within the graben are inward dipping and the deformed blocks show inward tilting. The age of the basaltic flows becomes progressively younger inward from the boarder faults until it reaches ~30,000 years close to the rift axis. The rift is filled with up to 2 km lacustrine sediments. A gravity analysis has indicated a gravity maximum over the center and thickest part of the graben that is caused by a thick zone of mafic dikes that extends into the basement rocks. Total-field magnetic measurements over the same region as the gravity study indicates that the central part of the Tendaho Graben has a 10 km wide magnetic minimum, which exhibits a narrow zone (~3 km) of a relatively higher magnetic values that coincides with the region of hydrothermal activities. This magnetic geometry is similar in dimension and magnitude to that observed from magnetic stripes of typical mid-ocean ridges. Forward modeling of the magnetic data (combined with geochronological data) shows that the basaltic rocks within the magnetic trough were crystallized after 0.78 Ma under normal magnetic polarity. Finally, the width of the magnetic trough (10 km) and the age of basaltic rocks (<0.78 Ma) indicate a spreading rate of ~ 0.64 cm/year. However, to achieve the ~50 km width of the Tendaho Graben which started opening ~1.6 Ma, a 2.4 cm/year spreading rate is needed between 1.6 and 0.78 Ma. This suggests that the spreading rate with Tendaho Graben is slowing down and extension within Afar is taken somewhere else.

Session No. 1

S1. They Say That “Breaking up Is Hard to Do”: Geological, Geophysical, and Remote Sensing Investigations of Continental Rifts
Sunday, 11 April 2010: 3:30 PM-5:00 PM
Compton Ferry (Branson Convention Center)
Geological Society of America Abstracts with Programs. Vol. 42, No. 2, p.37
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