Mantle models, global

Comparison with global mantle models for southern Africa... 

Fig. 8. Three-component waveform fits at three distance ranges for synthetic seismograms (dotted lines) computed from composite velocity model consisting of the seismic lithosphere of the southern African model of Priestley (1999) above 160 km depth and the southern Africa upper-mantle model derived from the global tomographic model S12WM13 below 160 km depth compared with the observed seismograms (continuous lines) of the 14 August 1994 earthquake (Fig. 1, event 8) recorded at three distance ranges.

This transfer most plausibly occurs by advection of mantle material (Kellogg and Wasserburg 1990) and so includes all the noble gases. The possibility that transfer of He from the lower mantle occurs by diffusion (Allegre et al. 1986), so that the principles of the residual mantle model can still be applied to the other noble gases, has not been shown to be reasonable for maintaining the present global flux. Also, this would result in substantial mantle He/Ne fractionations, which are not observed (see Neon isotopic compositions in the mantle section). 

The globally S5mchronous development of erosion surfaces and slow uplift rates of shields indicates that models based on localized heating of the crust and mantle are not adequate to explain the uplift process. To produce near simultaneous surfaces on separate continents. King (1967) invoked global epeirogeny - uplift... 

Heat production for the bulk continental crust in Table 7 is calculated using the crustal age distribution of model 2 in Rudnick and Fountain (1995) and is in the upper end of the range of values from global crust/mantle budgets (Table 2). 

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