Crustal xenoliths and their evidence for crustal structure underneath the Eifel volcanic district.

Abstract

From a study of 1000 xenoliths in volcanic rocks the following profile has been deduced (downwards): 5 km Devonian; 10 km greenschist facies phyllites; 5 km low amphibolite-facies mica schists; and 5-10 km medium- to high-grade amphibolite-facies gneisses. A thin layer of granulite-facies metabasites between these and the Moho are regarded as the remains of an older series, the other rocks having suffered Variscan Barrovian regional metamorphism. Many xenoliths display young contact metamorphism in deep chambers and superimposed pyrometamorphism. The crust has suffered rotational deformation, increasing downwards in amount and complexity. The T has not been >300oC at 15 km below the recent surface since Variscan times.-J.M.H.