Abstract
Mantle xenoliths from a Pliocene (∼2 Ma) pyroclastic cone of the Jabal Eghei Volcanic Complex (south Libya) are studied for unravelling depletion-, deformation- and metasomatic events within this part of the Saharan Metacraton. The xenoliths are fertile Cpx-rich spinel lherzolites texturally distinguished into protogranular (hereafter: undeformed – UX) and porphyroclastic/equigranular (deformed – DX) types. The extent of depletion is estimated at 5–10% (olivine-spinel compositions) and 3–13% (HREE contents in clinopyroxene) of melt extraction; all parameters of depletion indicate that the UX are slightly more depleted than the DX. Calculated equilibrium temperatures range 800–1100 °C and generally overlap with temperatures obtained for other xenolith suites in Libya and for other off-cratonic xenoliths worldwide. The temperature estimates for the UX are slightly higher (857–1091 °C) than those for the DX (800–923 °C) and the former xenolith types are better equilibrated. The studied xenoliths exhibit evidence of stealth (high abundances of modal Cpx in some samples) and cryptic metasomatism (LREE-enriched patterns on whole-rock and Cpx REE diagrams) with metasomatic agents most likely akin to alkaline mafic melts similar in composition to host magmas. The study provides a simplified 2D model assuming that: a) the Jabal Eghei lithospheric mantle was roughly stratified with more depleted undeformed peridotite in deeper and less depleted deformed peridotite in shallower regions, b) in the Miocene, normal faulting caused ductile and brittle deformations in the lower and the upper parts of the lithosphere, respectively, and produced small-scale mafic alkaline melts that moved upward and metasomatized the overlying mantle, and c) the advancing extension produced mafic alkaline magma that captured xenoliths and brought them to the surface.
Published Version
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