Thorium isotope composition in volcanic rocks of continental rift zone

The ratio 230Th/232Th in volcanic rocks of rift zones in the East Africa (Kenya and Tanganyika areas) and Baikal region is studied. The ratio value varies within wide limits 0.34-1.26. Continental rift zone rocks as to Th isotopic content are similar to volcanites of alkali series of oceanic isles. According to the decrease in 230Th/232Th value a series of volcanic rocks is pinpointed: medium - oceanic ridges - Island - Baikal - Kenya rift - Tanganyika rift. The presence of correlation bonds between Th, Sr, Nd isotopic ratios is explained from the viewpoint of the mantle heterogeneity and mixing of various pallial sources of various composition. The pallial substratum of the continental rift zones is characterized by higher Th/U ratios as compared with oceanic rift zones