Paper No. 10-5
Presentation Time: 9:35 AM
GRAVITY AND MAGNETIC INVESTIGATIONS OF MAGMA-ASSISTED RIFTING IN CONTINENTAL RIFTS, AN EXAMPLE FROM THE MAIN ETHIOPIAN RIFT
MICKUS, Kevin, Geology, Missouri State University, Springfield, MO 65897, EMISHAW, Luel, Oklahoma State University, Stillwater, OK 74078, KATUMWEHE, Andrew, Kimbell School of Geosciences, Midwestern State University, 3410 Taft Boulevard, Wichita Falls, TX 76308, LESEANE, Khumo, Department of Geological Sciences, University of Cape Town, Rondebosch, none 7701, South Africa, DEMISSIE, Zelalem, Wichita State University, Department of Geology, 1845 Fairmount Ave., Wichita, KS 67260 and ABDELSALAM, Mohamed G., Boone Pickens School of Geology, Oklahoma State University, Stillwater, OK 74078
In continental rift systems, the extension is attributed to far field forces that create normal faults in the upper crust. However, recent studies conducted in the East African Rift, Main Ethiopian Rift, and Afar Depression have revealed an alternative mechanism for extension - magma-assisted rifting, which involves the intrusion of dikes into the crust. Geological and geophysical studies have indicated that magma-assisted rifting occurs in magmatic segments that are regions of concentrated extensional strain and volcanism separated by regions with little extension and volcanism. Geophysical studies including seismic, gravity, magnetic, and magnetotellurics, have indicated that under each magmatic segment within the central and northern Main Ethiopian Rift and the Afar Depression, there are regions of denser magmatic intrusions that may contain magmatic material. This magmatic material, added to the upper crust, provides the material that aids in dike intrusion thus causing additional extensional strain in the rift.
The analysis of gravity and magnetic data has played a critical role in uncovering the underlying structure of the Earth's crust beneath volcanic regions. Data transformation techniques, including wavelength filtering, upward continuation, and derivative analysis, have been used alongside depth analysis methods such as power spectra, two-dimensional forward modeling, and three-dimensional inversion. These methods were applied to investigate the structure beneath several volcanic complexes, including Aluto, Gedemsa, and Boseti. The findings reveal the existence of two distinct regions of magmatic intrusion. A larger, deeper (10-20 km), larger region and a smaller, shallower (3-5 km) region, where magma accumulates from the mantle. Within both regions, the mafic mantle, fractional crystallization provides the mechanism for the observed bimodal volcanic products at the surface. The forced intrusion of magma from these magmatic zones provides the necessary stress to cause the extension observed in the Main Ethiopian Rift.
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