Abstract
The continental crust (CC) with an intermediate composition has been created along volcanic arcs. Mantle-derived arc magmas are, however, generally basaltic. A consequence of CC formation thus should be the corresponding production of refractory residue, referred to as 'anti-continent (AC)'. AC is likely to detach from arc crust by density inversion and descend into the upper mantle. High-pressure experiments demonstrate that sinking AC is, in contrast to the subducting oceanic crust, always denser than the surrounding mantle, suggesting that AC founders headlong and accumulates at the base of the mantle to form a 250km-thick mass known as the D" layer. Geochemical modeling further suggests the contribution of the accreted AC to deep-seated hotspot sources (EM1). In complementary processes, Earth creates buoyant CC and dense AC at the top and the base of the mantle, respectively, and has recycled portions of AC in mantle plumes.
