Abstract
The scoria cones of the Quarternary maarvolcanoes of the Westeifel, Federal Republic of Germany, contain abundant ultramafic nodules, among which the lherzolites of the Dreiser Weiher are very well studied. This work deals with ultramafic nodules from some other maar-type volcanoes of the same district. The nodules are pyroxenites and hornblendites. A petrographic description of the nodules and chemical analyses of their constituent phases are given. The main constituents are olivine (fo 83–91 mol %), Ti- and Al-rich salitic clinopyroxene, titaniferous pargasitic amphibole, and titaniferous phlogopite. The nodules are interpreted as low pressure cognate cumulates of an undersaturated nephelinitic magma. Clinopyroxens and olivines of some nodules, however, are presumably early high pressure, high temperature phases. The mechanism of nodule formation is discussed.
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