The role of magmatic processes for Plume Craton Rift Interaction with application to the Tanzania craton and the East African Rift System: A physical approach

• Applicant: Professor Dr. Harro Schmeling
• Subject Area: Geophysics
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 245168320

• Final Report Year: 2018

Final Report Abstract

One of the major unresolved questions in geodynamics is the stability of cratons and the physical conditions for rifts to penetrate into a craton. We tested the hypothesis that magmatic processes at the base of a craton associated with a plume will lead to a melt infiltration front penetrating into the craton base, release volatiles at shallower depth, weaken it and finally assist destabilization and erosion of the craton and rifting of the lithosphere. The interaction of the East African rift system with the Tanzania craton is regarded as a prototype of such a process. The extreme scenario of the Rwenzori region is well observed and reveals the breaking of the still connected Congo and Tanzania cratons. In a simple model, related to the geological situation, even with a conservative approach, melting in the asthenosphere with melt extraction and intrusion considerably accelerates erosion, upwelling and weakening, hence rifting of the lithosphere. Thus, magmatic processes enable or even drive breaking of cratons. Physical fundamental of the numerical models is thermo-mechanics of visco-plastic flow. The conservation of mass, momentum and energy equations are solved for a multicomponent (crust–mantle) and two-phase (melt–matrix) system. Rheology is temperature-, pressure-, and stress-dependent. In consideration of depletion and enrichment melting and solidification are controlled by a simplified linear binary solid solution model. Melt is extracted and emplaced in predefined levels in the lithospheric mantle and crust. The Compaction Boussinesq Approximation (CBA) and the high Prandtl number approximation were applied; its validity was tested against the Full Compaction formulation and found fully satisfactory for models with low porosity. But because no analytical solutions exist, for verification of the algorithm and code a benchmark initiative on mantle convection with melting and melt segregation was initiated. The finding, that segregating melt can generate high viscous stress in models with Full Compaction – in contrast to CBA – provides reasonable approaches for more physical based mechanisms for a fast subsolidus melt transport. Concepts of intermediate dyke propagation or dyke swarms encourages to future investigations.

Publications

• (2014) : Modeling continental rifting with melting and melt extraction: Testing various mechanisms controlling the depth of the intrusion level. — 74. Jahrestagung der DGG in Karlsruhe, 10. - 13.03.2014, Poster S1-P.001, Abstract: 80
  Wallner, H.; Schmeling, H.
  
• (2014) : Probing depth dependencies of melt emplacement on time dependent quantities in a continental rift scenario with melting and melt extraction. — 11th EGU General Assembly 2014, Vienna, Austria, 27.4. – 2.5.2014, Abstract: Geophysical Research Abstracts, Vol. 14, EGU2014-5975, 2014
  Wallner, H.; Schmeling, H.
  
• (2015) : A benchmark initiative on mantle convection with melting and melt segregation. — 12th EGU General Assembly 2015, Vienna, Austria, 12.4. – 17.4.2015, Abstract: Geophysical Research Abstracts, Vol. 17, EGU2015-10795, 2015
  Schmeling, H.; Dohmen, J.; Wallner, H.; Noack, L.; Tosi, N.; Plesa, A.-C.; Maurice, M.
  
• (2015) : Melt emplacement induced stresses. — 12th EGU General Assembly 2015, Vienna, Austria, 12.4. – 17.4.2015, Abstract: Geophysical Research Abstracts, Vol. 17, EGU2015-12702, 2015
  Wallner, H.; Schmeling, H.
  
• (2016) : A benchmark initiative on mantle convection with melting and melt segregation. — 76. Jahrestagung der DGG und AEF in Münster, 14. - 17.03.2014, Vortrag S1-B.001, Abstract im Tagungsband
  Dohmen, J.; Schmeling, H.; Dannberg J.; Kalousová K.; Maurice M.; Noack L.; Plesa A.; Spiegelman M.; Thieulot C.; Tosi N.; Wallner, H.
  
• (2016) : Can compaction, caused by melt extraction and intrusion, generate tectonically effective stresses in the lithosphere?. — 13th EGU General Assembly 2016, Vienna, Austria, 17.4. – 22.4.2016, Abstract: Geophysical Research Abstracts, Vol. 18, EGU2016-8889, 2016
  Wallner, H.; Schmeling, H.
  
• (2016) : Numerical Models of Mantle Lithosphere Weakening, Erosion and Delamination Induced by Melt Extraction and Emplacement. — International Journal of Earth Sciences, 105(6), 1741-1760
  Wallner, H.; Schmeling, H.
  (See online at https://doi.org/10.1007/s00531-016-1343-y)
• (2017) : Modelling komatiitic melt accumulation and segregation in the transition zone. — Earth and Planetary Science Letters 472, 95-106
  Schmeling, H.; N. Arndt
  (See online at https://doi.org/10.1016/j.epsl.2017.05.021)