Pyroxenite xenoliths and clinopyroxene megacrysts from the Cenozoic Jbel Saghro Volcanic Field (Anti-Atlas,Morocco): Petrography,mineral chemistry and equilibration conditions |
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| Institution: | 1. Department of Geology, Faculty of Sciences-Semlalia, Cadi Ayyad University, Prince Moulay Abdellah Boulevard, P.O. Box 2390, Marrakesh, Morocco;2. Faculty of Geology and Geography, Tomsk State University, 36 Lenin Avenue, Tomsk 634050, Russia;3. GET, Université de Toulouse, CNRS-CNES-IRD-Université Paul Sabatier, OMP, 14 Av.E. Belin 31400 Toulouse, France;4. Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal;5. Department of Geology, Faculty of Sciences, Ibno Zohr University, P.O. Box 28/S, Agadir, Morocco |
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| Abstract: | A suite of mafic pyroxenite xenoliths and clinopyroxene megacrysts was brought to the surface by Cenozoic nephelinites of the Jbel Saghro Volcanic Field (Anti-Atlas, Morocco). The large population of samples was subdivided into five groups: (i) clinopyroxenites sensu stricto; (ii) olivine clinopyroxenites; (iii) mica-bearing clinopyroxenites; (iv) kaersutite-bearing clinopyroxenites; (v) clinopyroxene megacrysts. These xenoliths display a cumulate texture (adcumulate, heteradcumulate with poikilitic clinopyroxene including olivine). The clinopyroxenes have the composition of augite and show an appreciable variation of MgO (7.02–14.80 wt.%), TiO2 (0.58–5.76 wt.%) and Al2O3 (2.81–12.38 wt.%) contents in grains. The clinopyroxenes are characterized by convex upward chondrite-normalized REE patterns, they display very similar trace element compositions with low contents of incompatible elements such as Rb (0?0.9 ppm), Ba (0.1–8.3 ppm), Th (0.1?0.3 ppm), U (0.01?0.04 ppm) and Nb (1.3–3.2 ppm). REE contents of the calculated melts in equilibrium with the clinopyroxene megacrysts and clinopyroxene from pyroxenite xenoliths are similar to those of the nephelinites exposed in Jbel Saghro. Crystallization temperatures of pyroxenite xenoliths and clinopyroxene megacrysts range from 950 °C to 1150 °C. Clinopyroxene barometry yielded pressure of crystallization ranging from 0.4 to 0.8 GPa for pyroxenite xenoliths and 0.3 to 0.7 GPa for clinopyroxene megacrysts. This pressure range is in agreement with pyroxenite xenoliths and clinopyroxene megacrysts being crystallized from their parental melts at the lower and upper crust. |
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| Keywords: | Xenoliths Pyroxenites Megacrysts Trace elements Nephelinite Morocco |
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