Communication Dans Un Congrès Année : 2024

Temporal variation in counterclockwise vertical-axis block rotations across a rift overlap zone, southwestern Ethiopia, East Africa

Résumé

The southward propagation of the southern Main Ethiopian Rift (sMER) and the northward propagation of the Kenya Rift has generated the Broadly Rifted Zone (BRZ), a ~40-km-wide zone of extensional overlap between the Chew Bahir Basin-Gofa Province and the sMER, however, the tectonic interaction between these propagating rifts is not well-understood. We present new paleomagnetic and geochronologic data from the Eo-Oligocene (45–35 Ma) and Miocene (18–11 Ma) rocks. Rock magnetic, alternating field and thermal demagnetization experiments indicate simple titanomagnetite mineralogies carrying a characteristic remnant magnetization from which straightforward magnetization directions were obtained. Site-mean paleomagnetic directions obtained from the analyzed samples reflect stable normal and reversed polarity directions. A comparison of the mean directions obtained for the Eo-Oligocene and Miocene rocks relative to the pole for stable South Africa at the corresponding ages reveals a significant counterclockwise (CCW) rotation of ~11.1°± 6.4° and insignificant CCW rotation of ~3.2° ± 11.5°, respectively, reflecting a decrease in the extent of block rotations overtime. The result is consistent with the regional deformation migration patterns during rifting. In the context of the regional tectonic evolution toward a narrow zone, much of the deformation associated with block rotations probably occurred prior to the final emplacement of the Miocene volcanics. In light of the fabrics in the basement rocks exposed in sMER, the observed CCW block rotations were likely accompanied and aided by the reactivation of NW-SE-striking basement heterogeneities, supporting the notion that inherited crustal-scale structures play a significant role during rifting across the BRZ.

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Dates et versions

insu-04977359 , version 1 (05-03-2025)

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  • HAL Id : insu-04977359 , version 1

Citer

Asfaw Erbello, Guillaume Dupont-Nivet, Tesfaye Kidane, et al. Temporal variation in counterclockwise vertical-axis block rotations across a rift overlap zone, southwestern Ethiopia, East Africa. American Geophysical Union Annual Meeting 2024 (AGU24), American Geophysical Union, Dec 2024, Washington DC, United States. pp.T22A-02. ⟨insu-04977359⟩
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