Petrology of mantle xenoliths hosted in tertiary magmas of the Hessian Depression, Germany: A comaprison to xenoliths from Quaternary magmas of the West Eifel.

摘要

A suite of twenty-three mantle xenoliths hosted in Tertiary alkali-basaltic lavas of the Hessian Depression, Germany were studied in order to document field relations, petrography, mineral chemistry and petrogenesis. Xenoliths from three locations (Stopfling, Altenburg and Druseltal) were chosen to characterize any heterogeneity within the Hessian mantle. Rock types are entirely anhydrous Group 1 xenoliths that consist of lherzolite (57%), harzburgite (22%), wehrlite (17%), and websterite (4%). Rock texture is dominantly protogranular whereas xenoliths with porphyroclastic and tabular equigranular textures are minor and restricted to Druseltal.;Mineral chemistry varies systematically with respect to rock type. Inherent minerals from wehrlites are distinctively depleted in MgO and enriched in FeO compared to minerals from co-existing orthopyroxene-rich xenoliths. Lower mg;A broad similarity between the Hessian and other xenolith-bearing Tertiary volcanic fields in the area (e.g. Vogelsberg, Rhon, Siebengebirge) indicates a relative homogeneity of mantle metasomatic processes during the Tertiary beneath the Rhenish Massif. However, metasomatic indicators from lavas and xenoliths from the nearby Quaternary West Eifel imply that the mantle source region during the Quaternary was substantially more enriched than it was in the Tertiary. (Abstract shortened by UMI.)