New observations from the European Palaeozoic belt indicate significant material
transfers, far from plate boundaries, which are incompatible with the current
concepts of collision tectonics. These material and heat transfer called “laterally
forced overturns” (LFO) are enhanced by grain-scale melt-induced softening
reducing significantly the strength of orogenic lower crust. The LFO is
accomplished by vertical extrusion of the OLC from the bottom of the crustal root
along steep channels of variable dimension and, by lateral viscous spreading of
partially molten OLC in supra-crustal levels. Detailed structural and geophysical
characterization of LFO records (e.g., vertical and horizontal channel flows) is
shown in the Variscan orogenic root. This model is suplemented by thermodynamic
modelling (Thermocalc, Perplex) of PTt evolutions aiming to determine transient
thermal evolutions of orogenic roots. The thermodynamic modelling is also applied
to evaluate melting processes as well as the equilibrium between infiltrated melts
and host rocks. The extruded orogenic lower crust is significantly compositionally
modified by melt infiltration process, so that it becames more felsic and
radiogenic. In addition, the new vertical and horizontal distribution of crustal
material favour high proportion of felsic material in supracrustal levels and
melting of buried supracrustal material. It will be shown, how the vertical
material transfer process modify the radiogenic heat production, thereby
influencing possible heat flow pattern in Varszican orogenic belt.
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