Carbonatite and Alkaline Magmatism in Taourirt (Morocco): Petrological, Geochemical and Sr-Nd Isotope Characteristics
2003; Oxford University Press; Volume: 44; Issue: 5 Linguagem: Inglês
10.1093/petrology/44.5.937
ISSN1460-2415
Autores Tópico(s)earthquake and tectonic studies
ResumoAlkaline lamprophyre dykes from Taourirt (North Morocco) contain numerous xenoliths, ranging from alkaline pyroxenites, kaersutitites, gabbros and nepheline syenites to a calcite carbonatite. The silicate xenoliths and the host rocks consist of Al- and Ti-rich diopside–salite, mica or kaersutitite, ± nepheline, ± plagioclase and K-feldspar, and ubiquitous apatite. Both the xenoliths and the lamprophyres are enriched in incompatible elements. The chemical composition of the lamprophyres cannot be accounted for by fractional crystallization alone. Moreover, the clinopyroxenes exhibit complex zoning, which requires repeated mixing of pulses of more or less fractionated melts. The carbonatite is a sövite cumulate with Sr-rich calcite, pyrochlore, fluorapatite, and rare salite. The Sr–Nd isotopic compositions of the Taourirt rocks indicate a depleted mantle source, the carbonatite having the most depleted composition, and define a linear trend similar to that of the East African carbonatites. The different rocks thus represent unrelated magmas, and the trend is interpreted as mixing between two components with HIMU and EM1 mantle end-member signatures. An EM2 mantle component could also be involved for a few samples; it may correspond to hydrous metasomatized mantle of the PP–PKP (phlogopite and phlogopite K-richterite peridotite) and MARID (mica, amphibole, rutile, ilmenite and diopside) type.
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