Integrated Geophysical Investigations of the Central Main Ethiopian Rift and Adjacent Plateaus: An Implication to Crustal Structure and Moho Depth Determinations
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Date
2016-06
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Addis Ababa Universty
Abstract
Compilation of newly acquired magnetic and existing gravity, magnetic and seismic data were carried out to examine nature of the crustal structure, probable depth to Moho and density distributions of the crust in the central Main Ethiopian Rift and adjacent plateaus. Data enhancement (filtering) techniques have been applied to the observed gravity and magnetic data in order to highlight the effects of deep seated and shallow origin geologic sources. The compiled Bouguer gravity anomaly map and its derivatives (regional, residual maps) and gravity profiles constructed along selected lines reveal minimum anomalies over the south east and south west plateaus, superimposed with relatively high values over the major volcanic centers and high density rift floor. Correspondingly, the compiled magnetic anomaly map including its derivatives (regional and residual maps) and magnetic profiles constructed along selected lines reveal that the volcanic centers residing the rift floor are associated with relatively high magnetic anomalies as compared to the relatively low magnetic anomalies associated with the sediment dominate rift lakes and parts of the highlands. Close examination of the regional and residual gravity and magnetic anomaly maps and enhancement techniques reveal that the Quaternary volcano-tectonically active zones of the Wonji Fault Belt (WFB) and Silti DebreZeit Fault Zone (SDZFZ) with a general NNE - SSW to N - S trending anomaly zones are interpreted to underlie by shallow magmatic intrusions and/or magmatic chambers. In addition, our result confirms the presence of deep and regional E-W trending anomaly zone in the south west of the study area which is assumed to be coincident with the Goba-Bonga transverse tectonic lineament and associated Wagebeta caldera complexes. Based on the evidences derived from 2-dimensional gravity modeling and seismic data, the crustal thickness (Moho depth) in the study area varies from 35 – 40 km beneath SW plateau, 38 - 39 km under the rift floor and ranges from 42 - 43 km beneath the SE plateau. Our investigation results generally support the idea which suggests that rift extension and crustal deformation in the central Main Ethiopian Rift are currently concentrated in the Quaternary volcano-tectonically active zones of the Wonji Fault Belt, Silti DebreZeit Fault Zone and the Goba-Bonga tectonic lineaments. Keywords: Central Main Ethiopian Rift; Bouguer gravity anomaly; magnetic anomaly; receiver function; crustal thickness.
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Keywords
Central Main Ethiopian Rift, Bouguer gravity anomaly, Magnetic anomaly, Receiver function, Crustal thickness