303-6 Along-strike variability of deformation, tectonic stress, and kinematics of incipient intra-oceanic rifting, Davie Rift, Offshore East Africa

Session: Honoring the Late Professor Mohamed Abdelsalam: Outstanding Researcher, Generous Colleague, Legendary Mentor, and Ambassador for the Geosciences In Africa (Posters)

Poster Booth No.: 181

Presenting Author:

Andry Ramarolahy

Authors:

Ramarolahy, Andry¹, Kolawole, Folarin², Raveloson, Andriamiranto³, Ajala, Rasheed⁴, Leonard, Ohenhen⁵, Waldhauser, Felix⁶, Nettles, Meredith⁷, Lemna, Obeid Saitabau⁸, Jamal, Daud⁹

(1) Earth and Environmental Sciences, Columbia University, New York, New York, USA, (2) Earth and Environmental Sciences, Columbia University, New York, New York, USA, (3) Institute and Observatory of Geophysics of Antananarivo (IOGA), University Of Antananarivo, Antananarivo, Antananarivo, Madagascar, (4) Lamont-Doherty Earth Observatory, Columbia University, New York, New York, USA, (5) Department of Earth System Science, University of California Irvine, Irvine, California, USA, (6) Lamont-Doherty Earth Observatory, Columbia University, New York, New York, USA, (7) Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA, (8) School of Mines and Geosciences, University of Dar es Salaam, Dar es Salaam, Tanzania, (9) Department of Geology, Eduardo Mondlane University, Maputo, Mozambique,

Abstract:

New divergent plate boundaries form through rifting of existing plates at zones of mechanical weakness. We investigate the physics of rift initiation in the ancient oceanic lithosphere of the Mozambique Channel, where the Davie Rift, an offshore branch of the East African Rift System, exploits and propagates along the Mesozoic Davie Fracture Zone. Our goal is to elucidate how inherited rifted margins and oceanic structural fabrics influence the evolution of this incipient plate boundary. Here, we integrate (1) fault mapping from available high-resolution bathymetry data across the Mozambique Channel, and coastline topography data where the Davie Rift deformation hugs the adjacent continental margins, (2) computation of earthquake focal mechanisms and stress inversion of the rift segments from a newly developed earthquake catalog, and (3) time-series analysis of satellite geodetic data (InSAR) across the coastline faults. We develop a comprehensive rift-wide active fault database, delineating six distinct segments of the Davie Rift via en-echelon geometrical arrangement of fault clusters and major rift terminations. The results show distributed faults across a 70 - 90 km wide zone in each of the rift segments, but with a prominent rift-bounding fault or graben in only the three of the segments. These bounding faults and grabens ubiquitously localize on the eastern margin of the rift zones and are colocated with the gravity trace of the Davie Fracture Zone. Focal mechanism inversion show a prominence of ENE-to-NE-striking axes of minimum principal tectonic stress axis (sigma3), but with an along-strike variability in the tectonic stress regimes comprising pure normal faulting, transtensional, and transpressional regimes. The stress patterns show a pronounced heterogeneity of P-axes in the segments located at/near the continent-ocean boundaries, potentially reflecting the effects of tectonic inheritance. Further, InSAR time-series analysis resolves predominantly normal faulting on the shoreline faults that strike-obliquely and are adjacent to strike-slip offshore faults, consistent with oblique extensional kinematics on the associated  rift segments. These results highlight the along-rift heterogeneity of tectonic stress and kinematics in the earliest phase of rifting, potentially modulated by structural inheritance.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7869

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