Mantle heterogeneities: a combined isotope and trace element approach and evidence for recycled continental crust materials in some OIB sources

Combined with isotopes, the use of incompatible element ratios in the framework of ( C/ x C z , C/ y C z ) representations is a promising way of investigating the problem of mantle heterogeneity. This trace element approach is tested and validated: an extensive analysis of literature data shows that isotopically distinct OIB are characterized among other factors also by distinct incompatible trace element ratios. Good correlations are found between some incompatible trace element ratios and the 87 Sr/ 86 Sr isotopic composition of oceanic mantle materials. These correlations agree with the expected relations inferred from reservoir fractionation processes. The source reservoirs of low- 87 Sr/ 86 Sr oceanic basalts (MORB and OIB) appear depleted with respect to trace elements as a result of continental crust extraction. The question of the presence of recycled continental crust material in the source of high- 87 Sr/ 86 Sr oceanic basalts is then explored. The analysis developed on the basis of the proposed approach supports the existence of such material in some of these basalts.