Richterite-bearing peridotites and MARID-type inclusions in lavas from North Eastern Morocco: Mineralogy and D/H isotopic studies

K-richterite/phlogopite-bearing peridotite xenoliths and MARID inclusions have been found in Late Cretaceous (67 +/- 0.2 million years) monchiquites and an olivine nephelinite from North Eastern Morocco. It is the first evidence of MARID rocks and K-richterite/phlogopite-bearing peridotites outside the kimberlitic context. In the hydrous xenoliths, textural features suggest that K-richterite, phlogopite and Al-poor diopside are replacement minerals. K-richterites contain 2-5 wt% FeO, 0.1-1.5 wt% TiO2 and <0.5 wt% Cr2O3. Micas contain 5.4-7.4 wt% FeO and 0.3-2.2 wt% TiO2, with Cr and Ni contents <0.2 wt%. Diopsides are Al-poor (<0.2 wt% Al2O3) and contain 0.1-0.2 wt% TiO2, 0.9-1.1 wt% Na2O and 1.3-1.7 wt% Cr2O3. Compared to known K-richterites and micas from metasomatised peridotite nodules (PKP types), the Moroccan minerals are more Fe rich, K-richterites have higher Ti and micas less Cr and Ni. They are thus closer to MARID than to PKP minerals. K-richterites and mica from the MARID inclusions show typical characteristics, e.g. high FeO (4.3-4.7 wt% in richterite and 7.2 wt% in mica), low NiO and/or Cr2O3 and the incomplete filling of the tetrahedral site by Si+Al. Ion probe D/H analyses of amphiboles and micas from both xenolith types give high delta D values ranging from -8 to -73, with large variations within single grains (up to 50 parts per thousand). Both the D-enrichment and the FD variations are inherited from the mantle. The similar chemical composition and delta D values of K-richterite/phlogopite from the hydrous peridotites and MARID minerals suggest a genetic link between the two types of xenoliths. The conditions required for producing MARIDs and K-richterite/phlogopite-bearing peridotites may thus exist in contexts other than stable cratonic settings. MARID rocks and the associated metasomites may result from a hydrous fluid interaction with a peridotite, the metasomatic agent being characterised by a high K and low Al signature and a high FD value. A D-rich source is involved in the metasomatic event producing the hydrous minerals, and the scatter observed in the delta D values suggests a mixing between this source and another one with typical upper mantle D/H composition. As indicated by the low delta D (-74) values of micas from the host lava, metasomatism predated and is unrelated to the alkaline volcanism.