TY - JOUR A1 - Heckenbach, Esther Lina A1 - Brune, Sascha A1 - Glerum, Anne C. A1 - Bott, Judith T1 - Is there a speed limit for the thermal steady-state assumption in continental rifts? JF - Geochemistry, geophysics, geosystems : G 3 ; an electronic journal of the earth sciences N2 - The lithosphere is often assumed to reside in a thermal steady-state when quantitatively describing the temperature distribution in continental interiors and sedimentary basins, but also at active plate boundaries. Here, we investigate the applicability limit of this assumption at slowly deforming continental rifts. To this aim, we assess the tectonic thermal imprint in numerical experiments that cover a range of realistic rift configurations. For each model scenario, the deviation from thermal equilibrium is evaluated. This is done by comparing the transient temperature field of every model to a corresponding steady-state model with an identical structural configuration. We find that the validity of the thermal steady-state assumption strongly depends on rift type, divergence velocity, sampling location, and depth within the rift. Maximum differences between transient and steady-state models occur in narrow rifts, at the rift sides, and if the extension rate exceeds 0.5-2 mm/a. Wide rifts, however, reside close to thermal steady-state even for high extension velocities. The transient imprint of rifting appears to be overall negligible for shallow isotherms with a temperature less than 100 degrees C. Contrarily, a steady-state treatment of deep crustal isotherms leads to an underestimation of crustal temperatures, especially for narrow rift settings. Thus, not only relatively fast rifts like the Gulf of Corinth, Red Sea, and Main Ethiopian Rift, but even slow rifts like the Kenya Rift, Rhine Graben, and Rio Grande Rift must be expected to feature a pronounced transient component in the temperature field and to therefore violate the thermal steady-state assumption for deeper crustal isotherms. KW - basin analysis KW - geodynamics KW - numerical modeling KW - rifting KW - thermal KW - modeling Y1 - 2021 U6 - https://doi.org/10.1029/2020GC009577 SN - 1525-2027 VL - 22 IS - 3 PB - Wiley CY - Hoboken, NJ ER - TY - JOUR A1 - Brune, Sascha A1 - Corti, Giacomo A1 - Ranalli, Giorgio T1 - Controls of inherited lithospheric heterogeneity on rift linkage: Numerical and analog models of interaction between the Kenyan and Ethiopian rifts across the Turkana depression JF - Tectonics N2 - Inherited rheological structures in the lithosphere are expected to have large impact on the architecture of continental rifts. The Turkana depression in the East African Rift connects the Main Ethiopian Rift to the north with the Kenya rift in the south. This region is characterized by a NW-SE trending band of thinned crust inherited from a Mesozoic rifting event, which is cutting the present-day N-S rift trend at high angle. In striking contrast to the narrow rifts in Ethiopia and Kenya, extension in the Turkana region is accommodated in subparallel deformation domains that are laterally distributed over several hundred kilometers. We present both analog experiments and numerical models that reproduce the along-axis transition from narrow rifting in Ethiopia and Kenya to a distributed deformation within the Turkana depression. Similarly to natural observations, our models show that the Ethiopian and Kenyan rifts bend away from each other within the Turkana region, thus forming a right-lateral step over and avoiding a direct link to form a continuous N-S depression. The models reveal five potential types of rift linkage across the preexisting basin: three types where rifts bend away from the inherited structure connecting via a (1) wide or (2) narrow rift or by (3) forming a rotating microplate, (4) a type where rifts bend towards it, and (5) straight rift linkage. The fact that linkage type 1 is realized in the Turkana region provides new insights on the rheological configuration of the Mesozoic rift system at the onset of the recent rift episode. Plain Language Summary The Turkana depression in the Kenya/Ethiopia borderland is most famous for its several million years old human fossils, but it also holds a rich geological history of continental separation. The Turkana region is a lowland located between the East African and Ethiopian domes because its crust and mantle have been stretched in a continent-wide rift event during Cretaceous times about 140-120 Ma ago. This thin lithosphere exerted paramount control on the dynamics of East African rifting in this area, which commenced around 15 Ma ago and persists until today. Combining analog "sandbox" experiments with numerical geodynamic modeling, we find that inherited rift structures explain the dramatic change in rift style from deep, narrow rift basins north and south of the Turkana area to wide, distributed deformation within the Turkana depression. The failed Cretaceous rift is also responsible for the eastward bend of the Ethiopian rift and the westward bend of the Kenyan rift when entering the Turkana depression, which generated the characteristic hook-shaped form of present-day Lake Turkana. Combing two independent modeling techniques-analog and numerical experiments-is a very promising approach allowing to draw robust conclusions about the processes that shape the surface of our planet. KW - continental rifting KW - east African rift KW - numerical modeling KW - analog modeling KW - tectonic inheritance KW - Turkana depression Y1 - 2017 U6 - https://doi.org/10.1002/2017TC004739 SN - 0278-7407 SN - 1944-9194 VL - 36 SP - 1767 EP - 1786 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Baes, Marzieh A1 - Sobolev, Stephan V. A1 - Gerya, Taras V. A1 - Brune, Sascha T1 - Subduction initiation by Plume-Plateau interaction BT - insights from numerical models JF - Geochemistry, geophysics, geosystems N2 - It has recently been demonstrated that the interaction of a mantle plume with sufficiently old oceanic lithosphere can initiate subduction. However, the existence of large lithospheric heterogeneities, such as a buoyant plateau, in proximity to a rising plume head may potentially hinder the formation of a new subduction zone. Here, we investigate this scenario by means of 3-D numerical thermomechanical modeling. We explore how plume-lithosphere interaction is affected by lithospheric age, relative location of plume head and plateau border, and the strength of the oceanic crust. Our numerical experiments suggest four different geodynamic regimes: (a) oceanic trench formation, (b) circular oceanic-plateau trench formation, (c) plateau trench formation, and (d) no trench formation. We show that regardless of the age and crustal strength of the oceanic lithosphere, subduction can initiate when the plume head is either below the plateau border or at a distance less than the plume radius from the plateau edge. Crustal heterogeneity facilitates subduction initiation of old oceanic lithosphere. High crustal strength hampers the formation of a new subduction zone when the plume head is located below a young lithosphere containing a thick and strong plateau. We suggest that plume-plateau interaction in the western margin of the Caribbean could have resulted in subduction initiation when the plume head impinged onto the oceanic lithosphere close to the border between plateau and oceanic crust. KW - subduction zone KW - plume KW - plateau KW - numerical modeling KW - plume-induced KW - subduction initiation (PISI) Y1 - 2020 U6 - https://doi.org/10.1029/2020GC009119 SN - 1525-2027 VL - 21 IS - 8 PB - American Geophysical Union CY - Washington ER -