ALBERT

Description: The alkaline lamprophyres and diabases from the Spanish Central System carry a heterogeneous suite of xenoliths including a group of highly altered ultramafic pyroxenites that contain CrMg-rich high-T hydrous minerals (Ti-phlogopite and pargasitic to kaersutitic amphibole), indicative of modal metasomatism. The trace element mineral compositions of these xenoliths show three patterns: type A xenoliths, with light rare earth element enriched clinopyroxenes with high field strength element (HFSE) negative anomalies; type B xenoliths, with clinopyroxenes and amphiboles with high incompatible trace element contents (large ion lithophile elements (LILE), HFSE and REE); type C xenoliths, with relatively REE- and HFSE-poor clinopyroxenes and amphiboles. These metasomatic signatures suggest the involvement of three different metasomatic agents: carbonate, silicate and hydrous fluids or melts, respectively. These agents could have been derived from the progressive differentiation of a CO2H2O-rich highly alkaline magma, genetically related to the Late Permian alkaline magmatism. Because of the original sub-alkaline nature of the pyroxenite xenoliths, they might have been formed originally as pyroxene-rich cumulates associated with underplated Hercynian calc-alkaline basic magmas. Metasomatism as a result of the infiltration of alkaline magmas within these cumulates might explain the relatively high radiogenic Nd composition of the altered ultramafic xenoliths.

Description: Spinel lherzolite xenoliths from the Cenozoic Calatrava volcanic field provide a sampling of the lithospheric mantle of central Spain. The xenoliths are estimated to originate from depths of 35-50 km. Trace element content of clinopyroxene and Cr-number in spinel indicate low degrees of partial melting ([≤] 5%) of the xenoliths. Although a major element whole-rock model suggests wider degrees of melting, the Calatrava peridotite chemistry indicates a moderately fertile mantle beneath central Spain. Calatrava peridotite xenoliths bear evidence for interaction with two different metasomatic agents. The enrichment in LREE(light rare earth element), Th, U and Pb, and the negative anomalies in Nb-Ta in clinopyroxene and amphibole from xenoliths of El Aprisco, indicate that the metasomatic agent was probably a subduction-related melt, whereas the enrichment in MREE in clinopyroxene from xenoliths of the Cerro Pelado centre suggests an alkaline melt similar to the host undersaturated magmas. These metasomatic agents are also consistent with the chemistry of interstitial glasses found in xenoliths of the two volcanic centres. Differences in metasomatism but also in mantle composition is supported by Sr-Nd whole-rock data which show a more radiogenic nature for Sr isotopes of samples from the El Aprisco centre (87Sr/86Sr ratios of 0.7035-0.7044 instead of 0.7032-0.7037 for samples from Cerro Pelado). The timing of the subduction-related metasomatic stage is unconstrained, although the Calatrava intraplate volcanism intrudes an old Variscan lithospheric section reworked during the converging plate system affecting SE Iberia in the Tertiary. The presence of wehrlite types within the Calatrava peridotite xenoliths is here interpreted as a reaction of host lherzolites with silica-undersaturated silicate melts that could be related to the Calatrava alkaline magmatism. The Sr-Nd isotopic composition of Calatrava peridotites plot within the European athenospheric reservoir(EAR) mantle, these values represent more enriched signatures than those found in the other Spanish Cenozoic alkaline province of Olot.

Description: 〈span〉We report the first attempt to date metasomatic events in peridotite xenoliths from the Subcontinental Lithospheric Mantle (SCLM) beneath the Cenozoic Calatrava volcanic field of central Spain. The most metasomatized xenoliths of the El Aprisco olivine melilitite maar were selected to perform a geochronological study on metasomatic apatite (U-Pb method) and amphibole (Ar-Ar), integrated with an enlarged chemical data set on these minerals. The metasomatic agents in studied samples are mainly carbonate-rich ultra-alkaline melts of probable asthenospheric derivation. Some samples have been overprinted by more than one metasomatic event. The geochronological data confirm three metasomatic events that occurred within the SCLM beneath central Spain in Cretaceous (118 Ma), Oligocene (29 Ma), and Miocene (16–4 Ma) times, much earlier than the host volcanic magmatism. To date, no magmatic events of those ages have been recorded in central Spain. However, a correlation with several cycles of sporadic intraplate magmatism of alkaline affinity in the Iberian microplate is suggested. This study illustrates that the SCLM preserves the memory of a complex history of melt and/or fluid percolation processes in a metasomatic record that is generally unrelated to shallower crustal magmatic events.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉We report the first attempt to date metasomatic events in peridotite xenoliths from the Subcontinental Lithospheric Mantle (SCLM) beneath the Cenozoic Calatrava volcanic field of central Spain. The most metasomatized xenoliths of the El Aprisco olivine melilitite maar were selected to perform a geochronological study on metasomatic apatite (U-Pb method) and amphibole (Ar-Ar), integrated with an enlarged chemical data set on these minerals. The metasomatic agents in studied samples are mainly carbonate-rich ultra-alkaline melts of probable asthenospheric derivation. Some samples have been overprinted by more than one metasomatic event. The geochronological data confirm three metasomatic events that occurred within the SCLM beneath central Spain in Cretaceous (118 Ma), Oligocene (29 Ma), and Miocene (16–4 Ma) times, much earlier than the host volcanic magmatism. To date, no magmatic events of those ages have been recorded in central Spain. However, a correlation with several cycles of sporadic intraplate magmatism of alkaline affinity in the Iberian microplate is suggested. This study illustrates that the SCLM preserves the memory of a complex history of melt and/or fluid percolation processes in a metasomatic record that is generally unrelated to shallower crustal magmatic events.〈/span〉

Description: Rhenium-depletion model ages ( T RD ) of sulfides in peridotite xenoliths from the subcontinental mantle beneath central Spain (the Calatrava volcanic field) reveal that episodes of mantle magmatism and/or metasomatism in the Iberia microplate were linked to crustal growth events, mainly during supercontinent assembly and/or breakup at ca. 1.8, 1.1, 0.9, 0.6, and 0.3 Ga. A synthesis of available in situ and whole-rock Os-isotope data on mantle-derived peridotites shows that this type of mantle (maximum T RD of ca. 1.8 Ga) is widespread in the subcontinental mantle of Europe and Africa outboard from the Betics-Maghrebides-Appenines front. In contrast, the mantle enclosed within the Alpine domain records T RD as old as 2.6 Ga, revealing a previously unrecognized Archean domain or domains in the central and western Mediterranean. Our observations indicate that ancient fragments of subcontinental lithospheric mantle have played an important role in the development of the present architecture of the Mediterranean lithosphere.

Description: Three Mn-Fe-rich fluorapatite types have been found in the highly evolved peraluminous and perphosphorous granites of the Belvís pluton. One of these apatite types includes abundant graphite microinclusions, suggestive of a magmatic origin for the graphite. The Belvís pluton is a reversely zoned massif composed by four highly fractionated granite units, showing a varied accessory phosphate phases: U-rich monazite, U-rich xenotime, U-rich fluorapatite, and late eosphorite-childrenite. The strong peraluminous character of the granites determines an earlier monazite and xenotime crystallization, so the three types of fluorapatite record late stages of phosphate crystallization. The earlier type 1 apatite is mostly euhedral, small and clear; type 2 apatite is dusty, large (〈2800 μm) and mostly anhedral, with strong interlobates interfaces with the main granite minerals, more abundant in the less fractionated units and absent in the most evolved unit; type 3 is subeuhedral to anhedral, shows feathery aggregate texture, and only appears in the most evolved unit. Apatite composition was acquired by electron microprobe analyses, laser ablation inductively coupled plasma-mass spectrometry and electron energy loss spectroscopy. Type 1 and type 2 apatite display similar broad compositional ranges showing high MnO (up to 4.30 wt%) and FeO (up to 2.88 wt%) contents, without traces of carbon in apatite structure. Type 2 differs from type 1 by having slightly higher LREE and Sr contents. REE spectra also differ, with type 1 displaying both variable LREE slope and negative Eu anomaly, whereas type 2 shows constant LREE slope and higher negative Eu anomaly, although both display similar HREE slope. Type 3 apatite displays higher FeO contents (up to 5.09 wt%), positively correlated with higher Cl-Na-Li-Be-B-Zn contents and extremely low Y-REE contents when compared to the other apatite types. Cation substitution indicates that part of the Fe content is as Fe 3+ . Graphite has been found exclusively as abundant microinclusions in type 2 apatite, parallel or randomly distributed, and heterogeneously grouped in clusters within the crystals. High-resolution electronic images show that graphite occurs with unusual habits: filaments of stacked hexagonal flakes up to 15 μm length and up to 0.5 μm width. Textural and chemical features suggest a highly crystallized melt, which favor compartmentalizing in compositional microdomains where the apatite types would have crystallized. The cocrystallization of type 2 apatite and graphite suggests a C-F-P-rich melt, sufficiently saturated to acquire an immiscible character with the highly evolved silicate melt in late-magmatic stages. As type 2 differs from type 1 apatite by higher LREE and Sr contents, we interpret that fluxing components were favorably concentrated in those residual less-depleted LREE-Sr fraction melts, once monazite and zircon (and xenotime) would have crystallized. Type 3 apatite records a change in the ultimate melt stage: an increase of the oxygen fugacity coupled with high undercooling by volatile lost of highly fractionated residual Cl-richer melts. The presence of biogenic carbon in granite peraluminous melts derived from metasedimentary sources and its later crystallization as graphite filaments opens a discussion on the carbon behavior during magma evolution, especially in highly polymerized melt framework.