An analytical model concerning the possible initiation of subduction between the India and Africa plates, caused by the Morondova plume

Identifying the geodynamic processes that trigger the formation of new subduction zones is key to understand what keeps the plate tectonic cycle going, and how plate tectonics once started. Here we discuss the possibility of plume-induced subduction initiation. Previously, our numerical modeling revealed that mantle upwelling and radial push induced by plume rise may trigger plate motion change, and plate divergence as much as 15-20 My prior to LIP eruption. Here we show that, depending on the geometry of plates, the distribution of cratonic keels and where the plume rises, it may also cause a plate rotation around a pole that is located close to the same plate boundary where the plume head impinges: If that occurs near one end of the plate boundary, an Euler pole of the rotation may form along that plate boundary, with extension on one side, and convergence on the other.  This concept is applied to the India-Africa plate boundary and the Morondova plume, which erupted around 90 Ma, but may have influenced plate motions as early as 105-110 Ma. If there is negligible friction, i.e. there is a pre-existing weak plate boundary, we estimate that the total amount of convergence generated in the northern part of the India-Africa plate boundary can exceed 100 km, which is widely thought to be sufficient to initiate forced, self-sustaining subduction. This may especially occur if the India continental craton acts like an “anchor” causing a comparatively southern location of the rotation pole of the India plate. Geology and paleomagnetism-based reconstructions of subduction initiation below ophiolites from Pakistan, through Oman, to the eastern Mediterranean reveal that E-W convergence around 105 Ma caused forced subduction initiation, and we tentatively postulate that this is triggered by Morondova plume head rise. Whether the timing of this convergence is appropriate to match observations on subduction initiation as early as 105 Ma depends on the timing of plume head arrival, which may predate eruption of the earliest volcanics. It also depends on whether a plume head already can exert substantial torque on the plate while it is still rising – for example, if the plate is coupled to the induced mantle flow by a thick craton.