Evidence for felsic plumes in the Alps

In the Alps, the Monte Rosa granite batholith is considered as an inherited Paleozoic lens and was not produced by the Alpine subduction. A large transition develops between Monte Rosa granite and the eclogite-facies Zermatt-Saas ophiolite. This transition is difficult to explain on the basis of current models. I show that a metamorphic front has transformed the Zermatt-Saas ophiolite into hornblende amphibolite, high-pressure micaschists, and albitic schists and gneiss. Aqueous fluids have played an important role in this transformation process. Large felsic plumes containing a significant amount of water have generated the metamorphic front into the Zermatt-Saas ophiolite during its exhumation. These felsic plumes produced the Monte Rosa granite batholith between 42.6 and 33 Ma in the Cenozoic.