Apatite, phosphorus and titanium in eclogitic garnet from the upper mantle

The existence of apatite exsolution lamellae in garnet supports earlier suggestions that garnet is a major repository for P in the mantle, and that P is strongly coupled to Na+Ti. The bulk P content (∼250 ppm) of mantle eclogites is unexpectedly similar to estimates for the P content (130–220 ppm) of the upper mantle; both rocks are depleted relative to chondrites and to ocean floor basalts. Eclogites have either equilibrated with the mantle at large, or have undergone secondary melting, and based on P contents are unlikely to have had subducted protoliths.