Evidence for felsic plumes in the Alps

In the Alps, the current view is that the Monte Rosa granite batholith and the Zermatt-Saas ophiolite have been exhumed in a subduction channel. The Monte Rosa granite batholith is an inherited Paleozoic lens and was not produced by the Alpine subduction. Here, I show that the Zermatt-Saas ophiolite has been transformed into hornblende + albite amphibolite, high-pressure phengite-garnet micaschists, and eventually into albitic lithologies at transition with the Monte Rosa granite batholith. The transformation is characterized by the omnipresence of albite. This suggests that a metamorphic front developed into the Zermatt-Saas ophiolite during its exhumation in the Cenozoic. Subsolidus conditions show that the transformation of the Zermatt-Saas ophiolite into albitic lithologies has been generated by aqueous fluids. These considerations show the occurrence of large felsic plumes containing a significant amount of water in the mantle. These felsic plumes have generated a metamorphic front into the Zermatt-Saas ophiolite. They produced the Monte Rosa granite batholith in the Cenozoic.