Geodynamic modelling of extreme uplift in the Rwenzori Mountains

Aims of the geodynamic modelling

I. Identify the mechanisms responsible for extreme uplift in rifting environments and apply them to the Western African Rift and the Rwenzori Mountains.

Three subtopics, each of which poses a different hypothesis as cause for extreme uplift in rifting environments will be pursued:

  • The effect of melt dynamics and the extraction of melt for the dynamics of rifting. Magma accumulation at crustal level or magmatic underplating in combination with dehydration and water release are responsible for block or flank uplift.
  • The role of inherited chemical heterogeneities, in particular water, and pre-existing lithospheric and asthenospheric structures on rift dynamics. Remobilisation of deep seated crustal fragments are responsible for block or flank uplift.
  • 3-D interactions in lithospheric processes caused by rift-rift interaction, transtension and local secondary transpression are responsible for block or flank uplift.

The relative importance of each of these processes for extreme block or flank uplift will be evaluated and possibly combinations of them might be applied to the African Rift. Constraints from other geophysical and geological projects will be accounted for.

II. Perform coupled climate-tectonics calculations to assess:
  • The role of erosion on uplift rate and total amount of uplift, testing different erosion and climate scenarios
  • Estimate the impact of such a dynamic rift model and topography evolution on the regional climate evolution with application to East Africa
  • The full bi-directional feedback between climate and tectonics with application to East Africa.

A strong interaction between geodynamic modelling, erosion/sedimentation studies and topography evolution is required.

Model 1: Rifting with melt crustal injection and underplating

To evaluate the effect of melt dynamics and the extraction of melt for the dynamics of rifting and the associated uplift, modelling will invoke active rifting due to a plume influx into the asthenosphere in addition to passive rifting due to externally applied extension

Model 2: Reactivation of paleo-suture zone due rifting
The paleo-suture-model considers the Pan-African suture as starting condition and investigates processes that are triggered by incipient extension. Modelling of continental collision and root delamination will be carried out to producing the starting model. Thereafter, modelling will go on including extension (due to release of stored energy) and melting of the water-rich root. The role of water in the root formation and the subsequent delamination or root detachment process shall be included into the collisional models.

Model 3: Extension and Rotation
The model is inspired by the global tectonic context and local tectonic observations.
A flip of the rift shoulders and a significant strike slip component of faulting within the Rwenzori is inferred.

  • At ~ 12-10 Ma, abortion of the Eastern Rift Branch due to propagation into the Tanzania craton
  • Extension is transmitted into the mobile belt around the craton
  • Rotation of the Tanzania craton
  • The Western Rift branch begins to develop

A 3-D modelling by the Finite Element Method will be carried out to:

  • Investigate the interaction of the Western and the Eastern Rift branch
  • Predict the strike-slip faulting component (transtension)
  • Predict the possible flip of the rift shoulders
  • Estimate the maximum implied rift flank uplift

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Harro Schmeling & Team (Institut für Meteorologie und Geophysik, J.W. Goethe Universität, Frankfurt)

Klaus Regenauer-Lieb & Evariste Sebazungu (Institut für Geowissenschaften, Johannes Gutenberg-Universität, Mainz)