Controls by rheological structure of the lithosphere on the temporal evolution of continental magmatism: Inferences from the Pannonian Basin system

Abstract

Physical-chemical controls of continental magmatism evolution remain enigmatic. Of prime and controversial nature is the temporal transition from calc-alkaline magmas to alkali basalts, correlated with a switch in tectonic regime from extension to compression. We perform 1D thermo-kinematic modelling to analyze the evolution of the thermo-rheological structure of the lithosphere in such settings using the Northwestern Pannonian Basin as a test-bed. Given well-known evidence for major reduction of brittle deformation parameters due to melt-related softening, we use a relatively low internal angle of friction. We demonstrate that at the termination of extension, the presence of intra-crustal low-viscosity layers in the lithosphere provides optimal condition for emplacement and differentiation of intermediate crustal magmatic chambers along the pathway of deep-sourced basaltic melts. In contrast, subsequent lithosphere cooling after the end of extension combined with tectonic and magmatic thickening lead to a disappearance of the low-viscosity layers and formation of lithospheric-scale faults. The latter serve as conduits for rapid ascent of uncontaminated alkali basaltic melts from the mantle to the surface. These findings shed new light on the geodynamic controls of magmatism in extensional settings.