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Quantitative structural analyses and numerical modelling of ...

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HEAT SOURCES AND EXHUMATION MECHANISMS 91Fig. 9. Results <strong>of</strong> <strong>numerical</strong> simulations showing distribution <strong>of</strong> lithologies <strong>and</strong> temperature field developed after 20 Myr. Light shade<strong>of</strong> the lower crustal colour marks places where removal <strong>of</strong> radioactive heat production occurred while light shade <strong>of</strong> the mantle colourmarks asthenosphere (adiabatic geotherm <strong>and</strong> no heat production). First column shows results for low radioactive heat production <strong>and</strong>lithology <strong>and</strong> temperature fields are identical for all switch-<strong>of</strong>f conditions as they are not reached during 20 Myr. The second columngives results for no switch-<strong>of</strong>f condition, whereas the third <strong>and</strong> fourth columns shows results <strong>of</strong> simulations with 900 <strong>and</strong> 1000 °Cswitch <strong>of</strong>f for the lower crustal layer.The metaigneous rocks from Fichtelgebirge yield anaverage radioactive heat production <strong>of</strong> 3.9 lW m )3obtained from the average elemental concentrations <strong>of</strong>K, U <strong>and</strong> Th (Siebel et al., 1997; Wieg<strong>and</strong>, 1997) usingEqn 1 (Table 1). However, the radioactive heat productionfor the average felsic granulites (SiO 2 > 70,Table 1) is extremely low (0.9 lW m )3 ), suggestingthat the radioactive elements were mostly lost duringÓ 2010 Blackwell Publishing Ltd193

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