**5.3 The depletion inheritance of the mantle beneath the continental border**

The depletion heritage of the mantle beneath the continental border considering that Nb and Ta are least effectively transferred from the subducted oceanic slab to the overlying mantle melting column, the ratio of elements to Nb (or Ta) would measure the non-conservative character of the elements (% sz), which expresses the extent of their displacement from the average MORB at a given Nb [125]. Calculations of % sz for the elements in La Conception show that Rb, Pb, Th, Ba, U, K, and Pb are strongly non-conservative with % sz > 80%; LREE, Sr., and P2O5 are moderately non-conservative with a % sz range of 80–40%; Sm and Nd are non-conservative to slightly non-conservative with % sz from 40% to the detection limit, whereas other elements exhibited negative % sz values (**Figure 4**) [20]. The negative % sz values suggest that the mantle beneath the Norfolk Ridge was relatively depleted before the onset of the Oligocene subduction zone, which may partially inhibit the arc magmatism.
