Seafloor spreading of the third arm of the Afar triple junction: A review.

The only place within the East African Rift System where seafloor spreading is being manifested along with new crust being formed is at the Afar triple junction, a seismically active area defined by latitude 9°N to 14°N and longitude 43E° to 49E°. Previous seafloor spreading studies have primarily concentrated on the Aden-Owen Carlsberg Ridge (AOCR). The AOCR defines the boundary between the Eastern Gulf of Aden and the Western Gulf of Aden. Although the previous studies have provided insight into seafloor spreading rates, the timing of seafloor spreading, particularly in the Western Gulf of Aden (encompassing the study area) remains unclear. This study seeks to estimate the rates of seafloor spreading by reviewing data from previous studies and integrating geophysical (paleomagnetic anomalies), geological data and systematically estimating seafloor spreading rates and determining the timing of the initial seafloor spreading in the Afar region using advanced geo-software (Gplates). The results from our modeling show that the initial seafloor spreading began approximately 16 million years ago, with spreading rates varying from 12.29 to 20.12 mm/yr (average = 15.75 mm/yr). The average seafloor spreading rates in the study area are nearly 1.5-fold lower than the average seafloor spreading in the Eastern Gulf of Aden (23 mm/yr). The predominant seafloor spreading in the study area is East-West. Further, the angular rotation of the Somalian plate against the Arabian plate has been estimated to be 0.5353°/Ma. The study enhances understanding of plate tectonics, seismic hazards, volcanism and hydrocarbon systems in the Afar region.

Stress dynamics associated with the Nyasa / Malawi rift: Implication for the present-day East African Rift System dynamics.

The Nyasa/Malawi rift (NMR), known for its poor magma and notable seismic activity, has sparked a debate regarding its stress kinematics. It is on one hand viewed as a transform fault, while on other hand as a rift structure characterized by normal faulting. In order to address this controversy, we conducted paleostress analysis that involved collecting fault slip data along the central to southern region of the rift. We integrated our findings with published kinematic data on focal mechanisms in the rift. Our results reveal that the central part of the rift experiences radial or sub-radial extension, while the southern half is subject to oblique NNE-SSW transtensive tectonic forces. The minimum horizontal principal stress axis aligns with an orientation of 020°. As we move further south, the extension direction changes by approximately 25°, resulting in a predominantly north-south opening with a minimum horizontal stress axis direction of 175° (Shmin = 175°). The degree of structural penetration and intensity of faulting indicate that the north-south opening is more significant and pronounced in the southern region compared to the northern region. Additionally, we observed that faults dipping to the east and trending NW-SE exhibit sinistral (left-lateral) movement, while faults dipping to the southwestern side display dextral (right-lateral) movement. This suggests that, regionally, the NMR primarily experiences a normal faulting regime, albeit with a significant strike-slip component, which accounts for the oblique kinematics observed. The tectonic regimes identified through our fault slip data encompass the crust and upper mantle, spanning a lithospheric scale.

Strain accommodation by slow slip and dyking in a youthful continental rift, East Africa.

Continental rifts begin and develop through repeated episodes of faulting and magmatism, but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented. In highly evolved rifts, tensile stresses from far-field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions. These rifting crises are rarely observed in thick lithosphere during the initial stages of rifting. Here we show that most of the strain during the July-August 2007 seismic crisis in the weakly extended Natron rift, Tanzania, was released aseismically. Deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping. This event provides compelling evidence for strain accommodation by magma intrusion, in addition to slip along normal faults, during the initial stages of continental rifting and before significant crustal thinning.