Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011geoji.187.1135w&link_type=abstract
Geophysical Journal International, Volume 187, Issue 3, pp. 1135-1145.
Mathematics
Logic
Numerical Approximations And Analysis, Continental Tectonics: Extensional, Dynamics Of Lithosphere And Mantle, Rheology: Crust And Lithosphere, Africa
Scientific paper
Rift induced delamination (RID) was favoured as a geodynamic process explaining the special situation of an extremely elevated old crustal block located in a continental rift system, the Rwenzori Mountains. The concept of RID is an upwelling asthenosphere encircling stiff lithosphere. If temperature- and stress-dependent viscosity of the undermost lower crust is reduced and strength fails, the detachment of cold and dense mantle-lithosphere root is trigged. Surface expressions are propagating rift tips surrounding an uplifting less dense crustal block. This study was performed to test the scope of application of RID hypothesis. Characteristic features of the numerical models are kept constant, whereas parameters controlling the initial temperature anomaly, rheological properties and the background geotherm are varied systematically. The system answer is a bifurcation, either the anomaly cools down or the central mantle lithosphere detaches and sinks down, or, rather an unsuccessful and successful RID. The excess temperature of the prescribed initial anomaly is most sensitive and serves at the transition from cooling to delamination as a critical temperature. Delamination works only in certain ranges. The anomaly full width ranges between 20 and 50 km, the offset of the symmetric anomalies lies between 64 and 180 km and the top anomaly has to reach into the lower crust. The corresponding geometric characteristics of the Rwenzori region always lies inside the found parameter ranges for the delamination regime, even near the optimum. Quantitative parameters concerning rheology are uncertain but, qualitatively, conform to the available findings. Thus, we establish RID as a possible mechanism coinciding roughly with the local observations, such as, an old crustal horst inside a young rift system, a missing mountain root, the high seismicity, low seismic velocities in the lower crust, minor volcanism and extreme topography. If RID is valid for the very special situation of the Rwenzoris and by now the sole example, one ought to generalize it and the parameter regimes explored can be used as a pattern for searching similar geological situations.
Schmeling Harro
Wallner Herbert
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