Active Crustal Deformation Across a Nucleating Extensional Microplate, D. R. Congo, East Africa

Abstract Active tectonic fragmentation of continents is commonly accommodated by continental‐scale networks of rift basins and microplates along the evolving divergent plate boundaries. Yet, little is known about deformational processes that accompany the incipient stages of microplate development. We explore the East Africa's Western Rift, where the Nubian‐Victoria plate boundary is collocated with a ∼200‐km‐wide region of seismicity, low‐wave‐speed lithosphere, and hot springs that continue outboard of the commonly proposed active rift axis and westward into the Congo Craton, across the polydeformed Precambrian orogenic belts. We investigate a network of two contiguous, poorly studied rift basins in eastern DRC: the NW‐striking Luama Rift, commonly characterized as a “failed” Mesozoic rift, and its adjacent NE‐striking Kamituga Rift, located cratonward. We perform fault mapping, earthquake‐based stress inversion, reactivation tendency and fault attribute analyses to characterize the axes and mechanisms of active extension. In the two rift basins, we unveil and analyze previously unknown systems of 2–170‐km long active faults with 10–130‐m high scarps, and resolve their contemporary stress states and length‐scale attributes. The results reveal: (a) failure‐optimal orientation of faults in the contemporary EARS stress field, (b) fault‐length scale distribution that manifests rejuvenation of the Luama Rift, and incipient rifting in the Kamituga Rift as a southwestward continuation of the Kivu Rift. The axes of extension delineate a previously unknown microplate, herein named the “Itombwe Microplate”; however, we propose that diffuse seismicity across the microplate indicates its non‐rigidity or that microplate nucleation is still incipient.