Mafic alkaline metasomatism in the lithosphere underneath East Serbia: evidence from the study of xenoliths and the host alkali basalts

Abstract

Effects of mafic alkaline metasomatism have been interpreted by study of East Serbian (SE Europe) mantle xenoliths and petrogenesis of their host alkaline rocks. Fertile xenoliths (addition of >10 %vol. of metasomatic clinopyroxene) and tiny assemblages found in depleted xenoliths are distinguished. The fertile lithology contains Ti-Al-Cr-rich clinopyroxene, Fe-rich olivine, Fe-Al-rich orthopyroxene and Al-rich spinel. The composition of this lithology is modeled by addition of 5-20 wt% of a basanitic-like melt to a refractory mantle. The small-scale assemblages occur as pocket-like, symplectitic or irregular deformation-assisted accumulations of metasomatic phases, generally composed of Ti-Al-and incompatible elements-rich Cr-diopside, Cr-Fe-Ti-rich spinel, altered glass, olivine, apatite, ilmenite, carbonate and feldspar, as well as relicts of a high-TiO2 (~11 wt%) phlogopite. Textural relationships imply the following reaction: opx + Cr-rich sp ±phlogopite + Si-poor alkaline melt = Ti-Al-cpx + Ti-rich sp ± ol ± other minor phases. The inversion modeling, performed on least contaminated and most isotopically uniform host basanites, implies a source which is enriched in highly and moderately incompatible elements (~35-40xchondrite for U-Th-Nb-Ta, 2xchondrite for heavy rare earth elements) suggesting that the primary magma of the host basanites was not derived by melting of a homogeneous asthenospheric source. D0 values of the calculated basanitic source are similar to D0 values of anhydrous metasomatized mantle with small additions of metasomatic clinopyroxene and carbonate (~5 %) and with traces of ilmenite (~1 %) and apatite (~0.05 %). A schematic two-phase model involves percolation of CO2-and H2O-rich fluids, precipitation of metasomatic hydrous minerals and their subsequent breakdown due to the further uplift of hot asthenospheric mantle. This model uses a general idea of linking intraplate alkaline magmatism to lithospheric mantle sources enriched by sub-lithospheric melts at some time in the past. Mantle metasomatism is generally believed to be responsible for small-scale heterogeneities within the lithosphere (Dawson 1984; Harte 1984Harte , 1987Menzies et al. 1987). Evidence from the study of mantle xenoliths entrained in alkali basalts proved to be particularly important for understanding the origin of such heterogeneities. Studies have shown that the major metasomatic agents are: (i) carbonatitic melts (Baker et al. 1998;Yaxley et al. 1998;Gorring & Kay 2000; Wang & Gasparik 2001), (ii) silicate melts (Menzies et al. 1987;Vannucci et al. 1998;Zangana et al. 1999;Gregoire et al. 2000;Kepezhinskas et al. 1995Kepezhinskas et al. , 1996Schiano et al. 2002) and (iii) fluids (O'Reilly & Griffin 1988;Baker et al. 1998;Gorring & Kay 2000;Larsen et al. 2003), the latter two having a wide range of compositions. All these agents produce different metasomatic styles recognized by changes in primary mantle mineralogy and specific enrichments in trace element composition. It is widely accepted that mafic al...

Orthopyroxene-enrichment in the lherzolite-websterite xenolith suite from Paleogene alkali basalts of the Poiana Ruscă Mountains (Romania)

“…Xenolith Ce6-15 is a dunite, whereas the Ce6-20 sample has a lherzolite modal composition and very similar in mineral composition to the Ce6-15 dunite and to the pyroxenite sample analysed by Downes et al (1995). Similar Fe-rich dunites were also reported from E-Serbia (Cvetković et al 2010). These samples are displaced from the main residual trend (OSMA) of mantle xenoliths (Fig.…”

“…1) form a north-south line within the Carpatho-Balkan tectonic terrain as a continuation of the volcanic chain of the Apuseni Mts (Cvetković et al 2004). Jovanović et al (2001) and Cvetković et al (2004Cvetković et al ( , 2007Cvetković et al ( , 2010Cvetković et al ( , 2013 presented detailed descriptions of the magmatism and the mantle xenoliths. They suggested that the lithospheric mantle underneath East Serbia is more depleted than the normal European lithosphere and described two different types of orthopyroxene-rich lithologies.…”

“…Binns et al 1970;Wilshire & Shervais 1975;Frey & Prinz 1978;Dobosi & Jenner 1999;Cvetković et al 2010). The Fe-rich xenoliths may have crystallized from the older basaltic andesitic magmas of Poiana Ruscă or from similar magmas and subsequently entrained by the younger host basaltic magmas.…”

“…Some studies have proposed the origin of these orthopyroxene-enriched rocks as mantle-depth crystallization products from boninitic melts (Embey-Isztin et al 1989;Cvetković et al 2007;Bali et al 2007Bali et al , 2008. Some recent papers (Cvetković et al 2004(Cvetković et al , 2010Embey-Isztin & Dobosi 2011) suggested the possibility of orthopyroxene-rich (poikilitic) lithologies as resulting from magmatic modification of the lithospheric mantle via infiltrating (alkaline) mafic melt.…”

Variability of orogenic magmatism during Mediterranean-style continental collisions: A numerical modelling approach

“…Xenoliths found in these magmatic rocks suggest lithospheric temperatures of ~1000 °C (e.g., Cvetković et al, 2004bCvetković et al, , 2007a. This magmatism was shown to have formed by partial melting of hydrous mantle (Cvetković et al, 2010). Although, similar to the source of the European Cenozoic anorogenic provinces (e.g., Lustrino and Wilson, 2007;Cvetković et al, 2007a), these small volumes of melts rather reflect a secondary direct sourcing of melts by asthenosphere in the hinterland of the subduction zones, as observed for instance elsewhere in the Mediterranean system (Seghedi and Downes, 2011;Faccenna et al, 2014).…”