Depleted lherzolite xenoliths from the leucititic Morrón de Villamayor volcano (Calatrava volcanic field, Spain)

Abstract

This work reports petrographical, mineralogical and geochemical data of a suite of mantle xenoliths from the Morrón de Villamayor volcanic centre (MVM), which belongs to the Calatrava Volcanic Field (CVF), a part of the Circum-Mediterranean Anorogenic Cenozoic Igneous Province. The MVM volcano is the only centre belonging to the first stage of the CVF magmatism, an ultrapotassic stage that provides a sampling of the subcontinental lithospheric mantle beneath central Spain. The MVM peridotites record a variable host melt interaction (spongy texture and reaction zones), more intense toward xenolith-host leucitite contacts that it was formed during transport within the volcanic melt. The studied mantle xenoliths are spinel lherzolites equilibrated at lower temperatures (618-942°C) and similar pressure ranges (8.8-13.6 kbar) than other studied CVF mantle xenoliths, and record a lithospheric mantle before the main volcanic Calatrava event. The MVM lherzolites could be classified in two groups by their chondrite-normalized rare earth element (REE) clinopyroxene patterns: group-1 lherzolites show flat pattern, and group-2 lherzolites display a LREE-depleted (N-MORB like) pattern. Group-1 lherzolites represent a more residual lithospheric mantle (up to 9 partial melting %) than group-2 lherzolites (~5%), the latter with similar partial melting degrees than other mantle xenoliths from the CVF. Moreover, group-1 lherzolites have undergone a post partial melting refertilization by different metasomatic agents: silicate and alkaline silicate melts different in composition to host leucitite. A primary clinopyroxene concentrate from these MVM lherzolites provides high Sr ( 87 Sr/ 86 Sr = 0.706104) and intermediate Nd ( 143 Nd/ 144 Nd = 0.512830) initial radiogenic ratios, not previously recorded in this volcanic field. This sampling proves the presence of an enriched isotope mantle pole in xenolith suites of the Calatrava area, trending in composition to an intermediate DMM-EMII component.

Alkaline Silicate Metasomatism Recorded through Fe-Ti-Rich Mantle Xenoliths from the Calatrava Volcanic Field (Spain)

“…To estimate the partial-melting degree of this mantle source, the variation in the clinopyroxene trace-element contents was used to obtain a more reliable calculation, as it is the main mineral that hosts the greatest HREE-Y amount in spinel peridotites [39]. Therefore, primary clinopyroxene from the lherzolites-g2 indicates that the most primitive peridotites from the Cerro Pelado and El Palo volcanoes would have undergone a low degree of partial melting (≤5%) (Supplementary Figure S3), which is similar to that obtained in other poorly metasomatized peridotite suites from the CVF [9,10].…”

“…Spinel from lherzolites-g1 shows higher Cr# and TiO 2 and correlatively lower Mg# contents than those of lherzolites-g2, except for spinel from the lherzolite-g2 117491, which is highlighted for its high Cr# and TiO 2 contents (Figure 10a and Table S4). Spinel of the websterite shows very high Al 2 O 3 (up to 62 wt%) and low Cr 2 O 3 (3.6-5.8 wt%) contents compared to all other ultramafic xenoliths from the CVF [8][9][10] or from other volcanic fields [32,36]. Its TiO 2 content is similar to the spinel from the lherzolites-g2 (Figure 10a).…”

“…The Cerro Pelado and El Palo mantle xenoliths have a wide compositional range, although most of them, except for the wehrlite 117203, have a geochemical affinity with the EAR component [33], also called the common mantle reservoir (CMR) of the CiMACI province [17] (Figure 7), and some of them show affinities to the HIMU source of ocean island basalts (OIBs). The isotopic composition of these ultramafic xenoliths is far from the compositional field of the lherzolite unmetasomatized Calatrava SCLM [9,10], which defines a kind of mixing mantle array between the DM compositional fields (MORB-type) and the EMII component, although with slightly higher 87 Sr/ 86 Sr ratios (Figure 7).…”

“…Harker diagrams show that peridotite xenoliths have a varied major element composition (Figure 5). The compositional field of unmetasomatized lherzolites of the CVF [9,10] was included as the protolithic SCLM beneath Calatrava (Figure 5). Lherzolites, including those previously sampled in El Palo [2], have compositions close to the primitive mantle and the unmetasomatized lithospheric protolith of Calatrava.…”

“…Therefore, ultramafic xenoliths brought to the surface by alkaline and ultraalkaline magmas of the Calatrava Volcanic Field (CVF) represent a probe of the SCLM composition under the central part of the Iberian Peninsula. Previous studies in the CVF [2][3][4][5][6][7][8] have identified spinel-bearing lherzolites, with scarce or negligible evidence of refertilization as the primordial lithospheric mantle [9,10].…”