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Gurenko et al. (Contrib Mineral Petrol 162:349-363, ) report laser-assisted fluorination (LF) and secondary ionization mass spectrometry (SIMS) O/O datasets for olivine grains from the Canary Islands of Gran Canaria, Tenerife, La Gomera, La Palma and El Hierro. As with prior studies of oxygen isotopes in Canary Island lavas (e.g. Thirlwall et al. Chem Geol 135:233-262, ; Day et al. Geology 37:555-558, , Geochim Cosmochim Acta 74:6565-6589, ), these authors find variations in δO (~4.6-6.0 ‰) beyond that measured for mantle peridotite olivine (Mattey et al. Earth Planet Sci Lett 128:231-241, ) and interpret this variation to reflect contributions from pyroxenite-peridotite mantle sources. Furthermore, Gurenko et al. (Contrib Mineral Petrol 162:349-363, ) speculate that δO values for La Palma olivine grains measured by LF (Day et al. Geology 37:555-558, , Geochim Cosmochim Acta 74:6565-6589, ) may be biased to low values due to the presence of altered silicate, possibly serpentine. The range in δO values for Canary Island lavas are of importance for constraining their origin. Gurenko et al. (Contrib Mineral Petrol 162:349-363, ) took a subset (39 SIMS analyses from 13 grains from a single El Hierro lava; EH4) of a more extensive dataset (321 SIMS analyses from 110 grains from 16 Canary Island lavas) to suggest that δO is weakly correlated ( R = 0.291) with the parameter used by Gurenko et al. (Earth Planet Sci Lett 277:514-524, ) to describe the estimated weight fraction of pyroxenite-derived melt ( Xpx). With this relationship, end-member δO values for HIMU-peridotite (δO = 5.3 ± 0.3 ‰) and depleted pyroxenite (δO = 5.9 ± 0.3 ‰) were defined. Although the model proposed by Gurenko et al. (Contrib Mineral Petrol 162:349-363, ) implicates similar pyroxenite-peridotite mantle sources to those proposed by Day et al. (Geology 37:555-558, , Geochim Cosmochim Acta 74:6565-6589, ) and Day and Hilton (Earth Planet Sci Lett 305:226-234, ), there are significant differences in the predicted δO values of end member components in the two models. In particular, Day et al. (Geochim Cosmochim Acta 74:6565-6589, ) proposed a mantle source for La Palma lavas with low-δO (<5 ‰), rather than higher-δO (c.f. the HIMU-peridotite composition of Gurenko et al. in Contrib Mineral Petrol 162:349-363, ). Here we question the approach of using weakly correlated variations in δO and the Xpx parameter to define mantle source oxygen isotope compositions, and provide examples of why this approach appears flawed. We also provide reasons why the LF datasets previously published for Canary Island lavas remain robust and discuss why LF and SIMS data may provide complementary information on oxygen isotope variations in ocean island basalts (OIB), despite unresolved small-scale uncertainties associated with both techniques. [ABSTRACT FROM AUTHOR]

The comment by Day et al. (Contrib Mineral Petrol, ) (1) discusses the validity of the previously obtained oxygen isotope data for El Hierro and La Palma (Canary Island) olivines, (2) questions the approach by Gurenko et al. (Contrib Mineral Petrol 162:349-363, ) of using weakly correlated variations of δO values with X (proportion of pyroxenite-derived melt in the parental magma), and (3) provides reasons why oxygen isotope data by secondary ion mass spectrometry (SIMS) 'offer sensitive means for detecting melt-crust interactions.' We respond these comments and report a new set of oxygen isotope measurements performed by SIMS and single-grain laser fluorination methods. These measurements confirm our previous data and conclusions and demonstrate the ability of the SIMS technique to analyze O isotopes in terrestrial samples with 2-sigma uncertainty better than ±0.25 ‰. [ABSTRACT FROM AUTHOR]

Gabbro xenoliths reported in this paper were collected in northern Fuerteventura, the Canary Island located closest to the coast of Africa. The xenoliths are very fresh and consist of Ti–Al-poor clinopyroxene + plagioclase (An87–67) + olivine (Fo72–86) ± orthopyroxene. Clinopyroxene and orthopyroxene are constantly and markedly depleted in light rare earth elements (LREE) relative to heavy REE (HREE), as expected for cumulus minerals formed from highly refractory N-MORB-type melts. In contrast, whole-rock Primordial Mantle-normalized trace element patterns range from mildly S-shaped (mildly depleted in Pr–Sm relative to both the strongly incompatible elements Rb–La and the HREE) to enriched. Estimates show that the trace element compositions of the rocks and their minerals are compatible with formation as N-MORB gabbro cumulates, which have been infiltrated at various extents (≤1% to >5%) by enriched alkali basaltic melts. The enriched material is mainly concentrated along grain boundaries and cracks through mineral grains, suggesting that the infiltration is relatively recent, and is thus associated with the Canary Islands magmatism. Our data contradict the hypothesis that a mantle plume was present in this area during the opening of the Atlantic Ocean. No evidence of continental material that might reflect attenuated continental crust in the area has been found. Gabbro xenoliths with REE and trace element compositions similar to those exhibited by the Fuerteventura gabbros are also found among gabbro xenoliths from the islands of La Palma (western Canary Islands) and Lanzarote. The compositions of the most depleted samples from these islands are closely similar, implying that there was no significant change in chemistry during the early stages of formation of the Atlantic oceanic crust in this area. Strongly depleted gabbros similar to those collected in Fuerteventura have also been retrieved in the MARK area along the central Mid-Atlantic Ridge. The presence of N-MORB oceanic crust beneath Fuerteventura implies that the continent–ocean transition in the Canary Islands area must be relatively sharp, in contrast to the situation both further north along the coast of Morocco, and along the Iberian peninsula. [ABSTRACT FROM AUTHOR]

Phonolite and trachyte are the felsic magmas of the alkaline magma suites, which characterize the Canary Islands. The October 2011 submarine eruption off El Hierro, the westernmost island, nevertheless, produced a small volume of rhyolitic magma. The rhyolite occurred as highly vesicular, white coloured pumices enveloped in and mingled with darker coloured basanitic pumice. The basanitic pumice is relatively crystal poor with a few euhedral olivines (mostly Fo), clinopyroxenes and Fe-rich spinels, whereas very rare olivine of same composition is found together with equally rare Fe-sulphide and FeTi-rich oxides in the rhyolite. The Fe-Mg exchange equilibrium in the oxides permits to calculate an equilibrium temperature of 970-890 °C for the rhyolite, in agreement with quartz-melt equilibrium at ca. 930 °C. A striking mineralogical feature of the rhyolite is the presence of rounded to contorted grains of milky quartz, which are xenocrysts incorporated and partly dissolved into the magma. Analyses of residual volatile concentrations in the glasses show that the rhyolite melt was highly degassed, whereas the basanitic glass still has important halogen concentrations. Trace element patterns of the mafic glasses and their elevated incompatible element concentrations are typical of the western Canary Island basanites. In contrast, the trace element composition of the rhyolite shows surprisingly low concentrations for all elements except the most incompatible ones (e.g. Rb, Ba, K and Th). All other measured LILE, HFSE and REE have significantly lower concentration than the basanitic counterpart that can be explained by fractionation of accessory phases (1 % apatite, 1 % sphene and 0.1 % zircon). Surprisingly, low U concentration is presumably related to elevated oxygen fugacity in the rhyolite, causing U to be in a hexavalent state, and fluxing of F-rich gas leading to volatilization of UF, known to emanate at low temperature. The results suggest that a gas-rich basanitic melt remobilized a small volume of stagnant rhyolitic melt formed by incorporation of approximately 10 % quartz-rich sediment into a late differentiate of trachytic composition. Sediments at the interface of an old oceanic crust adjacent to a continental shield and younger volcanic island are likely to act as magma traps were sediment assimilation may alter the mantle-derived magma composition. Quartz assimilation thus explains the production of rhyolite magma in a volcanic island characterized by an alkaline magma series from primitive basanites to trachytes. [ABSTRACT FROM AUTHOR]

The composition of S-rich apatite, of volatile-rich glass inclusions in apatite, and of interstitial glasses in alkaline xenoliths from the 1949 basanite eruption in La Palma has been investigated to constrain the partitioning of volatiles between apatite and alkali-rich melts. The xenoliths are interpreted as cumulates from alkaline La Palma magmas. Apatite contains up to 0.89 wt% SO (3560 ppm S), 0.31 wt% Cl, and 0.66 wt% CeO. Sulfur is incorporated in apatite via several independent exchange reactions involving (P, Ca) vs. (S, Si, Na, and Ce). The concentration of halogens in phonolitic to trachytic glasses ranges from 0.15 to 0.44 wt% for Cl and from <0.07 to 0.65 wt% for F. The sulfur concentration in the glasses ranges from 0.06 to 0.23 wt% SO (sulfate-saturated systems). The chlorine partition coefficients (D) range from 0.4 to 1.3 (average D = 0.8), in good agreement with the results of experimental data in mafic and rhyolitic system with low Cl concentrations. With increasing F in glass inclusions D decreases from 35 to 3. However, most of our data display a high partition coefficient (~30) close to D determined experimentally in felsic rock. D decreases from 9.1 to 2.9 with increasing SO in glass inclusions. The combination of natural and experimental data reveals that the S partition coefficient tends toward a value of 2 for high S content in the glass (>0.2 wt% SO). D is only slightly dependent on the melt composition and can be expressed as: SO (wt%) = 0.157 * ln SO (wt%) + 0.9834. The phonolitic compositions of glass inclusions in amphibole and haüyne are very similar to evolved melts erupted on La Palma. The lower sulfur content and the higher Cl content in the phonolitic melt compared to basaltic magmas erupted in La Palma suggest that during magma evolution the crystallization of haüyne and pyrrhotite probably buffered the sulfur content of the melt, whereas the evolution of Cl concentration reflects an incompatible behavior. Trachytic compositions similar to those of the (water-rich) glass inclusions analyzed in apatite and clinopyroxene are not found as erupted products. These compositions are interpreted to be formed by the reaction between water-rich phonolitic melt and peridotite wall-rock. [ABSTRACT FROM AUTHOR]

The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units), Hf/Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic Hf isotopic compositions (Hf/Hf up to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend on the Nd vs. Hf isotope diagram (stretching over > 10 εHf units) between a depleted N-MORB-like endmember and a moderately enriched composition located on, or slightly below, the Nd-Hf mantle array, which overlaps the proposed 'C' mantle component of Hanan and Graham (). In contrast, all samples from the Canary hotspot track plot below the mantle array (Hf/Hf = 0.282943-0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between (1) a low Hf isotope HIMU-like endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic. Both domains, however, seem to share a common, moderately enriched endmember that has 'C'-like isotope compositions and is believed to represent subducted, <1-Ga-old oceanic lithosphere (oceanic crust and possibly minor sediment addition). The lower Hf/Hf ratio of the enriched, HIMU-like Canary domain endmember indicates the contribution of oceanic lithosphere with somewhat older recycling ages of ≥1 Ga. [ABSTRACT FROM AUTHOR]

A thermobarometric and petrologic study of basanites erupted from young volcanic cones along the submarine portions of the three El Hierro rift zones (NE-Rift, NW-Rift and S-Ridge) has been performed to reconstruct magma plumbing and storage beneath the island. Mineral-melt thermobarometry applied to naturally quenched glass and clinopyroxene rims yields pressures ranging from 350 to 1070 MPa with about 80% of the calculated pressures being in the range of 600–800 MPa. This corresponds to a depth range of 19–26 km, implying that the main level of final crystal fractionation is within the uppermost mantle. No systematic dependence between sample locality and fractionation pressures could be observed. Olivine and clinopyroxene crystals in the rocks are complexly zoned and have, on an inter-sample as well as on an intra-sample scale, highly variable core and rim compositions. This can best be explained by mixing of multiply saturated (olivine, magnetite, clinopyroxene, ilmenite), moderately evolved magmas with more mafic magmas being either only saturated with olivine + spinel or with olivine + spinel + clinopyroxene. The inter-sample differences indicate derivation from small, isolated magma chambers which have undergone distinct fractionation and mixing histories. This is in contrast to oceanic intraplate volcanoes situated on plumes with high melt supply rates, e.g. Kilauea Volcano (Hawaii), where magma is mainly transported through a central conduit system and stored in a shallow magma chamber prior to injection into the rift zones. The plumbing system beneath El Hierro rather resembles the magma storage systems beneath, e.g. Madeira or La Palma, indicating that small, intermittent magma chambers might be a common feature of oceanic islands fed by plumes with relatively low fluxes, which results in only limited and periodic magma supply. [ABSTRACT FROM AUTHOR]

Segregation veins are common in lava sheets and result from internal differentiation during lava emplacement and degassing. They consist of evolved liquid, most likely replaced by gas-filter pressing from a ∼50% crystallised host lava. Pairs of samples, host lavas and associated segregation veins from the Reykjanes Peninsula (Iceland), Lanzarote (Canary Islands) and the Masaya volcano (Nicaragua) show extreme mineralogical and compositional variations (MgO in host lava, segregation veins and interstitial glass ranges from 8–10 wt%, 3–6 wt%, and to less than 0.01 wt%, respectively). These samples allow the assessment of the internal lava flow differentiation mechanism, since both the parental and derived liquid are known in addition to the last magma drops in the form of late interstitial glasses. The mineralogical variation, mass-balance calculated from major- and trace element composition, and transitional metal partition between crystals and melts are all consistent with fractional crystallisation as the dominant differentiation mechanism. The interstitial glasses are highly silicic (SiO2 = 70–80 wt%) and represent a final product of high-degree (75–97%) fractional crystallisation of olivine tholeiite at a pressure close to one atmosphere. The tholeiitic liquid-line-of-decent and the composition of the residual melts are governed by the K2O/Na2O of the initial basaltic magma. The granitic minimum is reached if the initial liquid has a high K2O/Na2O whereas trondhjemitic composition is the final product of magma with low initial K2O/Na2O. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated a harzburgite xenolith from La Palma in the Canary Islands. Composition of the xenolith; Diffusion zones of the xenolith in orthopyroxene and olivine; Details on the formation of the orthopyroxene selvages.

Investigates the production of silicic melts by reaction between peridotite and infiltrating basaltic melts in veined xenoliths from La Palma, Canary Islands. Changes in the trace element compositions of basaltic to highly silicic glasses; Expected metasomatic effect of silicic melts with that of other transport agents.

Provides evidence of multi-stage magma ascent beneath the Canary Islands. Identification of some of the geographic features of the Canary Islands; Factors which attributed to the survival of fluid inclusions in the Canary Islands; Information on the Canary Islands.

Studies the variations in cooling rates of natural volcanic glasses from Tenerife, Canary Islands. Physical behaviors of silicate melts; Thermodynamic properties; Structural relaxation.

Studies the formation of silicon-potassium-sodium-rich melt in the upper mantle under La Palma, Canary Islands and its importance as a metasomatic agent. Two groups of mantle xenoliths hosted by the Historic Volcan de San Antonio; Specific soil compositions.