Editing Geology of the Alps (section)

===Metamorphism===
The rocks of the Helvetic and Austroalpine nappes and the southern Alps did not experience high grade [[metamorphism]] in the major Alpine phases in the Cenozoic. Any high grade [[metamorphic rocks]] in these units will not have become metamorphic due to the formation of the Alps. Other possibilities are:
* they were originally from lower regions of the crust and got to the surface by [[Tectonic uplift|uplift]], which gives them [[amphibolite facies]] at most.
* in the Austroalpine nappes [[eclogite]]s occur that were formed during the [[Cretaceous]] period, in an early phase of mountain building called the Eo-Alpine orogeny. These are high-grade metamorphic rocks, but their metamorphism is unrelated to the (later) formation of the Alps.

Cenozoic eclogites do occur in the Penninic nappes, which contain material that has been through [[blueschist facies|blueschist]] or [[eclogite facies]]. These nappes show a [[Metamorphism#Regional|Barrovian field gradient]]. This type of metamorphism can only occur when a rock is in [[pressure]]–[[temperature]] conditions that normally occur in the Earth's [[Mantle (geology)|mantle]]. This means the Penninic nappes consist of material that was [[subduction|subducted]] into the mantle and was later [[obduction|obducted]] onto the crust.

Alpine ([[Cenozoic]]) [[Contact metamorphism|contact-]] or Buchan metamorphism is rare in the Alps, because intrusions are rare.