Petrological Origin, P-T Conditions And Mantle Heterogeneity Of OIB

As an important part of the rock assemblage within the oceanic plate,ocean island basalts?OIB?are often related to"hot spots"and"mantle plumes"in genesis,so the study of OIB should be regarded as a petrological probe and window to explore the mantle source lithology.Petrology generally considers that peridotite is the main source of basaltic rocks.But the change of P-T conditions and melting degree of peridotite is difficult to match such a wide variety of geochemical characteristics of basalts found in nature.There must be participation of other lithology components.In this article we used the FCKANTMS discriminant?Yang et al.,2019?to constrain the lithology and P-T conditions of Azores,Canary,Galagapos and Samoa.The Azores mantle lithology is partially melted by water-rich peridotite.Canary originated from a mix source which including Co₂-rich peridotite and pyroxenite in different proportions.The Samoa and Galagapos show distinct small-scale mantle heterogeneity,and both western archipelagoes are more fertile than the eastern ones.The FCKANTMS discriminant has a useful constraint to identify the source lithology of basaltic rock.Combined with the detailed exploration of 4 archipelagoes,we summarized how to use FCKANTMS diagrams exactly.We explored the mantle source lithology of 11 archipelagoes with restrained FCKANTMS discriminant.We found that the proportion of pyroxenite signals in the oceanic mantle is higher than estimated.We think that the signals is caused by the higher proportion in the initial melt of pyroxenite which has a higher melt degree instead of the underestimated pyroxenite components in the oceanic mantle.From the globel view,it's difficult to find out the regularity of the lithology characteristics of the mantle source.However,the heterogeneity is common in both oceans.It is worth noting that the archipelagoes near the continental margin shows more obvious small-scale mantle heterogeneity than the archipelagioes located in the oceanic intraplate,which may be due to the richer material sources and more active mantle convection at the plate boundary compared with the oceanic intraplate.