Les xénolites ultramafiques du volcanisme alcalin quaternaire d'Oranie (Tell, Algérie occidentale), témoins d'une lithosphère cisaillée et enrichie

Abstract

Ultramafic xenoliths from Quaternary alkali volcanism from Oranie (Tell, western Algeria): witnesses of a sheared and enriched lithosphere. Numerous ultramafic xenoliths occur within the Aïn-Temouchent volcanic complex (Northwestern Oranie, Algeria). Most of them are type I mantle tectonites (lherzolites and harzburgites) and composite xenoliths (harzburgite/clinopyroxenite) are rare. Only a few samples of spinel lherzolites display relatively fertile compositions when the major part of type I xenoliths have refractory major element compositions but enriched LREE contents showing that they have been affected by mantle metasomatism. The composite xenoliths are witnesses of reactions of alkaline magmas with the upper mantle. An asthenospheric rising, in relation with the large strike slip fault affecting the North African plate margin at Trias time is proposed as a possible geodynamical setting. To cite this article: M. Zerka et al., C. R. Geoscience 334 (2002) 387-394.  2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS xenoliths / upper mantle / mantle metasomatism / lithospheric thinning / Oranie / AlgeriaRésumé -Le complexe volcanique alcalin quaternaire d'Aïn-Témouchent (Oranie, Algérie nord-occidentale) a remonté de nombreuses enclaves de lherzolite et de harzburgite, ainsi que de rares enclaves « composites » harzburgite/clinopyroxénite. Quelques lherzolites, rééquilibrées dans le domaine de stabilité des péridotites à spinelle, ont des compositions relativement fertiles ; les autres, qui apparaissent réfractaires au niveau des éléments majeurs, mais enrichies en terres rares légères, correspondent à des produits de réactions entre manteau et magmas (métasomatisme mantellique). Un amincissement lithosphérique en régime distensif, favorisé par de profonds cisaillements et situé dans une ancienne zone de subduction, serait actif sur la bordure septentrionale de la plaque Afrique au cours du Néogène et, probablement, dès le Trias. Pour citer cet article : M. Zerka et al., C. R. Geoscience 334 (2002) 387-394.  2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS xénolites / manteau supérieur / métasomatisme mantellique / amincissement lithosphérique / Oranie / Algérie

Lithosphere tearing along STEP faults and synkinematic formation of lherzolite and wehrlite in the shallow subcontinental mantle

“…Indications for the presence of interstitial glass has also been found, although the current state of preservations of the xenoliths did not allow their further investigation. These petrographic features, the observed lithologies and their abundances are nevertheless consistent with earlier reports from the same volcanic field (e.g., Zerka et al, 2002;Lahmer et al, 2018).…”

“…The volcanic rocks crosscut and overlie the Tell sedimentary nappes overthrust during the Miocene on the northern part of the African plate (Coulon et al, 2002). The alkaline lavas contain a large number of mantle xenoliths (Zerka et al, 2002;Lahmer et al, 2018 and references therein). In Solid Earth Discuss., https://doi.org/10.5194/se-2019-32 Manuscript under review for journal Solid Earth Discussion started: 27 February 2019 c Author(s) 2019.…”

“…The Plio-Pleistocene basaltic volcanism in the Oran volcanic field transported a large number of mantle xenoliths to the surface, mostly in the Aïn Témouchent volcanic complex. Earlier works on the peridotite suite have shown that the SCLM records metasomatic events in the shallow spinel-and plagioclase-facies due to channeling of reactive alkaline magmas in ductile shear zones (Zerka et al, 2002;Lahmer et al, 2018). However, due to the lack of microstructural data, the reconstruction of deformation mechanisms and the relationship between the melt percolation and deformation along the Rif-Tell STEP fault have remained unexplored.…”

Heterogeneity and anisotropy in the lithospheric mantle

“…Montferrier, S France (Cabanes and Briqueu, 1987), (ii) convergent plate boundaries, such as the Persani mountains (Falus et al, 2008) and Oran in Algeria (Zerka et al, 2002), or (iii) intraplate settings were deformation is associated with reactivation of preexisting lithospheric-scale faults as M A N U S C R I P T…”

Mantle metasomatism by melts of HIMU piclogite components: new insights from Fe-lherzolite xenoliths (Calatrava Volcanic District, central Spain)

“…Pearson & Wittig (2008) emphasized these characteristics in mantle xenoliths from cratonic regions, which typically display very high Mg# olivine (92.6-92.8), and, to lesser extent, in peridotite xenoliths from OIB (ocean island basalt) settings (where the Mg# of olivines is mostly between 91 and 92: Simon et al 2008). Within offcraton localities, such as the European circum-Mediterranean region (Downes 2001), the olivine Mg# in peridotite xenoliths is 89.3 -91.3 in Sardinia (Beccaluva et al 2001a), 89.3 -90.8 in the Hyblean area, Sicily (Perinelli et al 2007), 89.0 -89.7 in the Gharyan volcanic field (Beccaluva et al 2008), 89.0-91.5 in Oranie, Tell, Algeria (Zerka et al 2002), mostly between 89.0 and 92.0 in peridotite xenoliths from the Massif Central (Werling & Altherr 1997;Touron et al 2008), and mostly between 89.0 and 91.5 in peridotite xenoliths from the Veneto volcanic province, where rare samples display olivine Mg# values down to 87.0 (Beccaluva et al 2001b). Similar values are also recorded in mantle xenoliths from the Iberian peninsula, with olivine Mg# 89.4 -90.9 in anhydrous peridotite xenoliths from Tallante (Beccaluva et al 2004) and 89.2-91.8 in peridotite xenoliths from the Olot volcanic district .…”