Abdelkader Mokhtari
Moulay Ismail University, Meknes, Morocco, Geologie, Faculty Member
Résumé / Abstract A calcite carbonatite inclusion has been found in a camptonite from Taourirt (Morocco). Major phases are SrO-rich (2.8 wt%) calcite, pyrochlore (66-67 wt% Nb2O5) in large zoned crystals and in small MnO-rich (2.3 wt%)... more
Résumé / Abstract A calcite carbonatite inclusion has been found in a camptonite from Taourirt (Morocco). Major phases are SrO-rich (2.8 wt%) calcite, pyrochlore (66-67 wt% Nb2O5) in large zoned crystals and in small MnO-rich (2.3 wt%) grains, SrO-rich (1.7 wt%) fluorapatite (3.5 wt% F) and rare salite. The carbonatite composition shows high contents of Sr, Nb, Ta and LREE. The carbonatite and the camptonites have similar REE patterns which suggests a common parental magma. The Taourirt carbonatite and lamprophyres show chemical characteristics similar to those of the known Tamazert carbonatite complex situated 300 km to the South. The Taourirt lamprophyres contain numerous pyroxenite and syenite inclusions which could indicate the presence of an underlying alkaline complex.
ABSTRACT: The north-eastern Morocco, is a peculiar area which is suspected to be a large impact site. It has a conspicuous ring structure with an apparent diameter of about 200 km of which half is in the sea. Jurassic mountains... more
ABSTRACT: The north-eastern Morocco, is a peculiar area which is suspected to be a large impact site. It has a conspicuous ring structure with an apparent diameter of about 200 km of which half is in the sea. Jurassic mountains Taourirt-Oujda-Tlemcen showing an arc form correspond to the outer ring. Mesozoic and Palaeozoic bedrock units are locally brecciated and cut by pseudotachylite breccia dykes. Kebdana mounts with its intense and unusual deformation, form probably the central uplift of a complex crater. A wide variety of breccias is located inside and outside of the crater, many of which contain fragments exhibiting shock metamorphic features. The age of the impact is estimated to be toward the late of Messinian.
Research Interests:
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... more
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 δD values ranging from –8 to –73, with large variations within single grains (up to 50‰). Both the D-enrichment and the δD variations are inherited from the mantle. The similar chemical composition and δD 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 δD value. A D-rich source is involved in the metasomatic event producing the hydrous minerals, and the scatter observed in the δD values suggests a mixing between this source and another one with typical upper mantle D/H composition. As indicated by the low δD (–74) values of micas from the host lava, metasomatism predated and is unrelated to the alkaline volcanism.