抄録
Mantle xenoliths hosted by the Canastra-1 kimberlite, located in the southwestern margin of the São Francisco Craton (SFC), Brazil, represent heterogeneous fragments from a stratified mantle column within the garnet stability field (>80 km). Here we report the first noble gas isotopes data for samples from the deep cratonic lithosphere-asthenosphere. Our results show that the upper mantle underneath the SFC registered a complex geological evolution. Helium isotopic ratios are strongly radiogenic, with low 3He/4He ratios. No significant variation is observed in the 3He/4He ratios with an increasing number of strokes. In the neon three-isotope diagram, most xenoliths present composition indistinguishable from the atmospheric ratio. However, some samples plot within the air-MORB line, whereas the hydrated websterites plot along the air-crustal mixing line. The 40Ar/36Ar isotopic ratios indicate mixing between the air and a mantle component (313-1211), with a strong atmospheric contribution. Therefore, we suggest that an ancient oceanic crust, probably related to the Gondwana amalgamation, was responsible for the effective recycling of a subducted-related noble gas component.
