Abstract:The continental margins of East Africa and West Madagascar are a frontier for hydrocarbon exploration. However, the links between the regional tectonic history of sedimentary basins and margin evolution are relatively poorly understood. We use a plate kinematic model built by joint inversion of seafloor spreading data as a starting point to analyse the evolution of conjugate margin segments and corresponding sedimentary basins. By correlating megasequences in the basins to the plate model we produce a margin‐s… Show more
“…The N‐S trending DFZ (Figure l) in the TCB is a fossil transform fault that guided the southward drift of East Gondwana (Antarctica, Australia, India, and Madagascar) away from West Gondwana (Africa and South America) during the Jurassic and Early Cretaceous (e.g., Coffin & Rabinowitz, ). Following continental breakup at approximately 170 Ma (Geiger et al, ), an initial phase of NNW‐SSE plate separation resulted in the development of NNW‐SSE trending oceanic fracture zones offshore Tanzania (Figures g and h; e.g., Davis et al, ; Phethean et al, ; Sauter et al, ; Tuck‐Martin et al, ). By about 150 Ma, the strong continental cores of East and West Gondwana were no longer juxtaposed.…”
Section: Geological Backgroundmentioning
confidence: 99%
“…(c–f) Evolution of the Gulf of California from 20 Ma to present (modified from Bennett et al, ). (g)–(l) Evolution of the Tanzania Coastal Basin between 182 and 125 Ma (Phethean et al, ; Reeves et al, ; Tuck‐Martin et al, ).…”
Transform margins are first-order tectonic features that accommodate oceanic spreading.Uncertainties remain about their evolution, genetic relationship to oceanic spreading, and general structural character. When the relative motion of the plates changes during the margin evolution, further structural complexity is added. This work investigates the evolution of transform margins and associated rift-transform intersections, using an analogue modeling approach that simulates changing plate motions. We investigate the effects of different crustal rheologies by using either (a) a two-layer brittle-ductile configuration to simulate upper and lower continental crust, or (b) a single layer brittle configuration to simulate oceanic crust. The modeled rifting is initially orthogonal, followed by an imposed plate vector change of 7°that results in oblique rifting and plate overlap (transpression) or underlap (transtension) along each transform margin. This oblique deformation reactivates and overprints earlier orthogonal structures and is representative of natural examples. We find that (a) a transtensional shift in the plate direction produces a large strike-slip principal displacement zone, accompanied by en-echelon oblique-normal faults that accommodate the horizontal displacement until the new plate motion vector is stabilized, while (b) a transpressional shift produces compressional structures such as thrust fronts in a triangular zone in the area of overlap. These observations are in good agreement with natural examples from the Gulf of California (transtensional) and Tanzania Coastal Basin (transpressional) shear margins and illustrate that when these deformation patterns are present, a component of plate vector change should be considered in the evolution of transform margins.Plain Language Summary Tectonic plate boundaries on our planet are categorized by their relative motion with respect to each other. The three main categories are those moving away, toward, and parallel to one another. We study the processes occurring when two tectonic plates moving parallel begin to rotate and move away or toward each other. Currently, this is occurring in the Gulf of California, and in the past, it occurred in areas such as the Southern Atlantic, creating the segmented pattern along its midocean ridge. To study these tectonic plate boundaries, we use sandbox modeling. We make miniature models of the Earth's crust with silicone putty and sand and recreate the same movements that tectonic plates go through. This allows us to understand the structures created in such environments better. The pattern and the height or depth of these structures are related to how fast the plates move. This work can help recognize areas where similar deformation has occurred in the past, which is important for hydrocarbon exploration. It can also assist with geothermal energy exploration, as areas where plates move parallel and away from each other present good opportunities for hotter temperatures in the subsurface.
“…The N‐S trending DFZ (Figure l) in the TCB is a fossil transform fault that guided the southward drift of East Gondwana (Antarctica, Australia, India, and Madagascar) away from West Gondwana (Africa and South America) during the Jurassic and Early Cretaceous (e.g., Coffin & Rabinowitz, ). Following continental breakup at approximately 170 Ma (Geiger et al, ), an initial phase of NNW‐SSE plate separation resulted in the development of NNW‐SSE trending oceanic fracture zones offshore Tanzania (Figures g and h; e.g., Davis et al, ; Phethean et al, ; Sauter et al, ; Tuck‐Martin et al, ). By about 150 Ma, the strong continental cores of East and West Gondwana were no longer juxtaposed.…”
Section: Geological Backgroundmentioning
confidence: 99%
“…(c–f) Evolution of the Gulf of California from 20 Ma to present (modified from Bennett et al, ). (g)–(l) Evolution of the Tanzania Coastal Basin between 182 and 125 Ma (Phethean et al, ; Reeves et al, ; Tuck‐Martin et al, ).…”
Transform margins are first-order tectonic features that accommodate oceanic spreading.Uncertainties remain about their evolution, genetic relationship to oceanic spreading, and general structural character. When the relative motion of the plates changes during the margin evolution, further structural complexity is added. This work investigates the evolution of transform margins and associated rift-transform intersections, using an analogue modeling approach that simulates changing plate motions. We investigate the effects of different crustal rheologies by using either (a) a two-layer brittle-ductile configuration to simulate upper and lower continental crust, or (b) a single layer brittle configuration to simulate oceanic crust. The modeled rifting is initially orthogonal, followed by an imposed plate vector change of 7°that results in oblique rifting and plate overlap (transpression) or underlap (transtension) along each transform margin. This oblique deformation reactivates and overprints earlier orthogonal structures and is representative of natural examples. We find that (a) a transtensional shift in the plate direction produces a large strike-slip principal displacement zone, accompanied by en-echelon oblique-normal faults that accommodate the horizontal displacement until the new plate motion vector is stabilized, while (b) a transpressional shift produces compressional structures such as thrust fronts in a triangular zone in the area of overlap. These observations are in good agreement with natural examples from the Gulf of California (transtensional) and Tanzania Coastal Basin (transpressional) shear margins and illustrate that when these deformation patterns are present, a component of plate vector change should be considered in the evolution of transform margins.Plain Language Summary Tectonic plate boundaries on our planet are categorized by their relative motion with respect to each other. The three main categories are those moving away, toward, and parallel to one another. We study the processes occurring when two tectonic plates moving parallel begin to rotate and move away or toward each other. Currently, this is occurring in the Gulf of California, and in the past, it occurred in areas such as the Southern Atlantic, creating the segmented pattern along its midocean ridge. To study these tectonic plate boundaries, we use sandbox modeling. We make miniature models of the Earth's crust with silicone putty and sand and recreate the same movements that tectonic plates go through. This allows us to understand the structures created in such environments better. The pattern and the height or depth of these structures are related to how fast the plates move. This work can help recognize areas where similar deformation has occurred in the past, which is important for hydrocarbon exploration. It can also assist with geothermal energy exploration, as areas where plates move parallel and away from each other present good opportunities for hotter temperatures in the subsurface.
“…For the Falkland Plateau Basin to have opened along the same plate boundary, half rates implied by its magnetic reversal isochrons would therefore need to have been half as fast as modelled in Fig. 4 6 , 63 . The divergence rate discrepancy thus reveals the action of a third plate.…”
Section: Resultsmentioning
confidence: 99%
“…The greater (by > 4 km) depth to source and very sparse coverage of reliable magnetic track lines in the southern Weddell Sea 64 , 65 left us unable to identify a detailed set of conjugate magnetic reversal isochrons to those of the central Scotia Sea for the modelling. Table 1 lists the model rotations together with a set of Skytrain–East Gondwana rotations calculated for mutually-constrained chrons by addition in the regional plate circuit 6 , 63 , 77 – 79 . Figure 7 ( a ) Joint flowline-isochron visual-fit modelling for Skytrain-West Gondwana plate motion.…”
Section: Resultsmentioning
confidence: 99%
“…These ridges formed today's Riiser-Larsen Sea and Mozambique and Somali basins. Together, they accommodated the divergence of two large plates that was splitting Gondwana into eastern (bearing Antarctica, India and Australia) and western (bearing South America and Africa) parts at half spreading rates of 20-25 km/Myr 62,63 . For the Falkland Plateau Basin to have opened along the same plate boundary, half rates implied by its magnetic reversal isochrons would therefore need to have been half as fast as modelled in Fig.…”
Uncertainty about the structure of the Falkland Plateau Basin has long hindered understanding of tectonic evolution in southwest Gondwana. New aeromagnetic data from the basin reveal Jurassic-onset seafloor spreading by motion of a single newly-recognized plate, Skytrain, which also governed continental extension in the Weddell Sea Embayment and possibly further afield in Antarctica. The Skytrain plate resolves a nearly century-old controversy by requiring a South American setting for the Falkland Islands in Gondwana. The Skytrain plate’s later motion provides a unifying context for post-Cambrian wide-angle paleomagnetic rotation, Cretaceous uplift, and post-Permian oblique collision in the Ellsworth Mountains of Antarctica. Further north, the Skytrain plate’s margins built a continuous conjugate ocean to the Weddell Sea in the Falkland Plateau Basin and central Scotia Sea. This ocean rules out venerable correlation-based interpretations for a Pacific margin location and subsequent long-distance translation of the South Georgia microcontinent as the Drake Passage gateway opened.
The East African margin between the Somali Basin in the north and the Natal Basin in the south formed as a result of the Jurassic/Cretaceous dispersal of Gondwana. While the initial movements between East and West Gondwana left (oblique) rifted margins behind, the subsequent southward drift of East Gondwana from 157 Ma onwards created a major shear zone, the Davie Fracture Zone (DFZ), along East Africa. To document the structural variability of the DFZ, several deep seismic lines were acquired off northern Mozambique. The profiles clearly indicate the structural changes along the shear zone from an elevated continental block in the south (14°–20°S) to non-elevated basement covered by up to 6-km-thick sediments in the north (9°–13°S). Here, we compile the geological/geophysical knowledge of five profiles along East Africa and interpret them in the context of one of the latest kinematic reconstructions. A pre-rift position of the detached continental sliver of the Davie Ridge between Tanzania/Kenya and southeastern Madagascar fits to this kinematic reconstruction without general changes of the rotation poles.
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