Specifics of global events with which alkaline magmatism
is associated
Erlich E. I.
Independent geological consultant,
š
Summary of radiometric dates of alkaline magmatic rocks show that they are formed in the course of short (several mln. years) global phases. Such phases are synchronous global wide. Areas of their distribution within certain phase are not limited by lithosphere plates’ boundaries. It is suggested that the source of magmatic activity is located below lower lithosphere probably at the boundary between core and lower mantle boundary.
High (0.8-0.95) correlation coefficients between radiometric dates of alkaline rocks on one hand and granitoids and rejuvenated metamorphic rocks on the other clearly indicate that both types of magmatism are generated by the same forces. Difference in chemical composition is associated with different tectonic nature of regions where magmatism occurred. Well known association of kimberlite magmatism with stable cratons (Clifford rule) belongs not to ancient platforms only but as well to median massifs with different timing of cratonization.