Computer modeling of granite gneiss diapirism in the Earth's crust: Controlling factors, duration, and temperature regime

This paper is devoted to the modeling the granite gneiss formation by means of diapiric upwelling. The natural examples of granitic diapirism in the Precambrian granite-greenstone belts and complexes of metamorphic cores are described. A new approach is proposed to describe the partial melting and development of gravity instability in the crustal granitic layer, which experienced heat impact and melting during intrusion of basaltic melt. Rheology of partially melted material and surrounding medium is regarded to be temperature-dependent, following either plasticity or creep (non-Newtonian viscosity) law. Modeling results show that crustal rheology plays a significant role in the character of diapirism (shape of upwelling bodies, duration of the process, and width of thermal aureole). The rates of upwelling within the crust behaving as elastoplastic body are orders of magnitude higher (meters to tens meters per year) than those obtained for creep (viscous) liquid model (0.8 cm/yr). Modeling results revealed that the limiting depth of upwelling of partially crystallized melt, with allowance for temperature dependence of creep, corresponds to the isotherm of 400A degrees C.