No direct contribution of recycled crust in Icelandic basalts

Using Melt-PX to model the decompression melting of a heterogeneous mantle, I investigated the role of major-element composition of the lithologies present in the source on magmatic productivity, and trace element and isotopic melt compositions, independently of the bulk mantle composition. My calculations demonstrate that the volume of magma produced is not significantly affected by the nature of the lithological heterogeneity, but depends on the bulk mantle composition. However, an isochemical bulk mantle can produce contrasting trace element and isotopic melt compositions depending on the major-element compositions of the lithologies present in the source. Results show that the observed crust thickness of the Icelandic rift zones is consistent with about 10 % of recycled crust in the source, but also demonstrate there is no need to involve the contribution of melts derived from a recycled basalt component to explain the compositional variability of the Icelandic basalts in rift zones, and rather advance the contribution of olivine-bearing hybrid lithologies formed by solid-state reactions between the recycled crust and the peridotite

Quantifying lithological variability in the mantle

We present a method that can be used to estimate the amount of recycled material present in the source region of mid-ocean ridge basalts by combining three key constraints: (1) the melting behaviour of the lithologies identified to be present in a mantle source, (2) the overall volume of melt production, and (3) the proportion of melt production attributable to melting of each lithology. These constraints are unified in a three-lithology melting model containing lherzolite, pyroxenite and harzburgite, representative products of mantle differentiation, to quantify their abundance in igneous source regions. As a case study we apply this method to Iceland, a location with sufficient geochemical and geophysical data to meet the required observational constraints. We find that to generate the 20 km of igneous crustal thickness at Iceland's coasts, with 30±10%30±10% of the crust produced from melting a pyroxenitic lithology, requires an excess mantle potential temperature (ΔTp) of ⩾130 °C (View the MathML sourceTp⩾1460°C) and a source consisting of at least 5% recycled basalt. Therefore, the mantle beneath Iceland requires a significant excess temperature to match geophysical and geochemical observations: lithological variation alone cannot account for the high crustal thickness. Determining a unique source solution is only possible if mantle potential temperature is known precisely and independently, otherwise a family of possible lithology mixtures is obtained across the range of viable ΔTp. For Iceland this uncertainty in ΔTp means that the mantle could be >20% harzburgitic if View the MathML sourceΔTp>150°C (View the MathML sourceTp>1480°C). The consequences of lithological heterogeneity for plume dynamics in various geological contexts are also explored through thermodynamic modelling of the densities of lherzolite, basalt, and harzburgite mixtures in the mantle. All lithology solutions for Iceland are buoyant in the shallow mantle at the ΔTp for which they are valid, however only lithology mixtures incorporating a significant harzburgite component are able to reproduce recent estimates of the Iceland plume's volume flux. Using the literature estimates of the amount of recycled basalt in the sources of Hawaiian and Siberian volcanism, we found that they are negatively buoyant in the upper mantle, even at the extremes of their expected ΔTp. One solution to this problem is that low density refractory harzburgite is a more ubiquitous component in mantle plumes than previously acknowledged

Corrigendum to “Testing pyroxenite versus peridotite sources for marine basalts using U-series isotopes” [Lithos 332–333 (2019) 226–244]

The authors regret that a small error in the dynamic melting Matlab script used for this paper produced erroneous results for some of the included modeling outcomes. We have written an updated modeling program in python, which can be accessed in the ENKI and pyUserCalc public data repository (https://gitlab.com/ENKI-portal/pyUsercalc/). Although the corrected results shown in revised versions of Figs. S3, S4, S8, S9, and S10 now appear quite different from the original publication, however, we find that when restricted to plausible scenarios of interest, our conclusions overall have not significantly changed. Some details of our results and discussion require corrections, however

La Triada Oscura de la Personalidad y tácticas de retención de pareja

Una versión preliminar de este trabajo fue presentada como Trabajo Fin de Grado en Psicología en la Universidad de Huelva, siendo dirigido por la segunda autora y defendido por la primera autora.El objetivo principal de este estudio ha sido analizar la «Triada Oscura de la Personalidad» y las tácticas de retención de pareja en una muestra de población general. Asimismo, como objetivos específicos se plantea determinar la incidencia de los rasgos de la Triada en dicha muestra, así como estudiar la existencia de diferencias en las tácticas de retención de pareja utilizadas en función del sexo, situación sentimental y orientación sexual de los participantes.Se ha realizado un diseño transversal y se siguió una metodología selectiva ex post facto. La muestra estuvo compuesta por 229 personas de edades comprendidas entre 17 y 62 años y fue seleccionada mediante un muestreo accidental online. Para la recogida de datos se aplicaron tres cuestionarios; The Dirty Dozen (DD), Mate Retention Inventory-Short Form (MRI-SF) y Protocolo de recogida de información sociodemográfica. Los resultados obtenidos muestran que los hombres presentan mayor TRIOPE que las mujeres, que éstos aplican mayores tácticas de retención de pareja, y que las personas que conviven con su pareja utilizan más tácticas de retención de pareja.The main objective of this study has been analyzed in the Dark Triad Personality and the retention tactics of couple in a sample of general population. Likewise, specific objectives are to determine the incidence of Triada traits in the sample, as well as to study the existence of differences in the retention tactics of couples based on sex, the emotional situation and the sexual orientation of the participants. A cross-sectional design was carried out and an ex post facto selective methodology was followed. The sample consisted of 229 people aged between 17 and 62 years and was selected by means of an accidental online sampling. For data collection, three questionnaires were applied; The Dirty Dozen (DD), Mate Retention Inventory Short-Form (MRI-SF) and Protocol for the Collection of Sociodemographic Information. The results obtained show that men present a greater TRIOPE than women, these apply greater retention tactics of couple, and that the people who live with their partner they use more retention tactics of couple

Testing pyroxenite versus peridotite sources for marine basalts using U-series isotopes

Geochemically enriched signatures in global oceanic basalts have long indicated a heterogeneous mantle source, but the role of lithologic heterogeneity in producing mantle partial melts, particularly fertile pyroxenite rocks, remains unclear. Uranium-series disequilibria in basalts are particularly sensitive to the increased garnet mode and melting rates of pyroxenite rocks, making the system a useful indicator of mantle lithologic heterogeneity in the melt region for oceanic basalts. Here we summarize evidence for the presence and importance of pyroxenite rocks in the upper mantle and their role in melt generation of mid-ocean ridge basalts and ocean island basalts, with a synthesis of U-series disequilibrium systematics in oceanic basalts and implications for global lithologic heterogeneity of the upper mantle. We further synthesize the melt modeling approaches for the interpretation of U-series disequilibria in basalts and demonstrate the use of numerical solution models for time-dependent reactive porous flow and dynamic melting during decompression of a two-lithology mantle in thermal equilibrium. Our model outcomes corroborate prior interpretations in favor of reactive porous flow and two-porosity transport for relatively homogeneous, peridotite-dominated mantle regimes, and further support contributions of pyroxenite partial melts to aggregated melts in order to reproduce the heterogeneous global basalt data. To most accurately predict the conditions of melting by comparison with measured data, two-lithology melting calculations should carefully consider the role of thermal equilibrium, mineral/melt partitioning, non-linear variations in mineral modes, and degree of melting during the melting process

The role of pyroxenite in basalt genesis: Melt-PX, a melting parameterization for mantle pyroxenites between 0.9 and 5 GPa

Geochemical and isotopic data suggest that the source regions of oceanic basalts may contain pyroxenite in addition to peridotite. In order to incorporate the wide range of compositions and melting behaviors of pyroxenites into mantle melting models, we have developed a new parameterization, Melt-PX, which predicts near-solidus temperatures and extents of melting as a function of temperature and pressure for mantle pyroxenites. We used 183 high-pressure experiments (25 compositions; 0.9–5 GPa; 1150–1675°C) to constrain a model of melt fraction versus temperature from 5% melting up to the disappearance of clinopyroxene for pyroxenites as a function of pressure, temperature, and bulk composition. When applied to the global set of experimental data, our model reproduces the experimental F values with a standard error of estimate of 13% absolute; temperatures at which the pyroxenite is 5% molten are reproduced with a standard error of estimate of 30°C over a temperature range of ~500°C and a pressure range of ~4 GPa. In conjunction with parameterizations of peridotite melting, Melt-PX can be used to model the partial melting of multilithologic mantle sources—including the effects of varying the composition and the modal proportion of pyroxenite in such source regions. Examples of such applications include calculations of isentropic decompression melting of a mixed peridotite + pyroxenite mantle; these show that although the potential temperature of the upwelling mantle plays an important role in defining the extent of magma production, the composition and mass fraction of the pyroxenite also exert strong controls

Gondwana break-up related magmatism in the Falkland Islands

Jurassic dykes (c. 182 Ma) are widespread across the Falkland Islands and exhibit considerable geochemical variability. Orthopyroxene-bearing NW–SE-oriented quartz-tholeiite dykes underwent fractional crystallization at >1 GPa, and major element constraints suggest that they were derived by melting of a pyroxenite-rich source. They have εNd182 in the range –6 to –11 and 87Sr/86Sr182 >0.710 and therefore require an old lithospheric component in their source. A suite of basaltic andesites and andesites exhibit geochemical compositions transitional between Ferrar and Karoo magma types, and are similar to those seen in the KwaZulu-Natal region of southern Africa and the Theron Mountains of Antarctica. Olivine-phyric intrusions equilibrated at 182 1.6–3.6 and 87Sr/86Sr182 0.7036–0.7058) that require limited interaction with old continental lithosphere. A suite of plagioclase-phyric intrusions with 87Sr/86Sr182 c. 0.7035 and εNd182 c. +4, and low Th/Ta and La/Ta ratios (c. 1 and c. 15, respectively) also largely escaped interaction with the lithosphere. These isotopically depleted intrusions were probably emplaced synchronously with Gondwana fragmentation and the formation of new oceanic lithosphere. Estimates of mantle potential temperature from olivine equilibration temperatures do not provide unequivocal evidence for the presence of a plume thermal anomaly beneath the Falkland Islands at 182 Ma

Evidence for Low‐Pressure Crustal Anatexis During the Northeast Atlantic Break‐Up

While basaltic volcanism is dominant during rifting and continental breakup, felsic magmatism may be a significant component of some rift margins. During International Ocean Discovery Program (IODP) Expedition 396 on the continental margin of Norway, a graphite‐garnet‐cordierite bearing dacitic unit (the Mimir dacite) was recovered in two holes within early Eocene sediments on Mimir High (Site U1570), a marginal high on the Vøring Transform Margin. Here, we present a comprehensive textural, petrological, and geochemical study of the Mimir dacite in order to assess its origin and discuss the geodynamic implications. The major mineral phases (garnet, cordierite, quartz, plagioclase, alkali feldspar) are hosted in a fresh rhyolitic, vesicular, glassy matrix that is locally mingled with sediments. The major element chemistry of garnet and cordierite, the presence of zircon inclusions with inherited cores, and thermobarometric calculations all support an upper crustal metapelitic origin. While most magma‐rich margin models favor crustal anatexis in the lower crust, thermobarometric calculations performed here show that the Mimir dacite was produced at upper‐crustal depths (<5 kbar, 18 km depth) and high temperature (750–800°C) with up to 3 wt% water content. In situ U‐Pb analyses on zircon inclusions give a magmatic crystallization age of 54.6 ± 1.1 Ma, consistent with emplacement that post‐dates the Paleocene‐Eocene Thermal Maximum. Our results suggest that the opening of the Northeast Atlantic was associated with a phase of low‐pressure, high‐temperature crustal anatexis preceding the main phase of magmatism

Systematic LREE enrichment of mantle harzburgites: The petrogenesis of San Carlos xenoliths revisited

We are grateful to K. Itano for fruitful discussion of the ideas developed in this paper and K. Ozawa for support on the use of his opensystem melting model. The manuscript benefited from constructivecomments provided by Q. Xiong and three anonymous reviewers as well as from the editor X.-H. Li. This work was funded by a Japan Society for the Promotion of Science (JSPS) fellowship.The dichotomy between partial melting and metasomatism is a paradigm of mantle geochemistry since the pioneering work of Frey and Prinz (1978) on the occurrence of LREE-enriched harzburgites. However, the thermo-chemical implications of such two-stage scenarios are often poorly considered, and the latter fail to explain why trace-element enrichment and major-element depletion are often proportional.We here re-envisage the petrogenesis of the famous San Carlos peridotites based on new petrographic observations and detailed modal, major- and trace-element compositions. The lherzolites (and pyroxenites) are characterized by homogeneously fertile mineral chemistry and LREE-depleted patterns consistent with low degrees of partial melting of the lherzolitic protolith. Bulk compositions and mineral zoning suggest that opx-rich pyroxenites formed by pressure-solution creep during melt-present deformation, locally accompanied by magmatic segregations of cpx. The harzburgites are characterized by stronger mineral zoning with low-Mg# and Na-, Al- and Cr-rich cpx rims, and can be discriminated in a low-Jd and high-Jd cpx groups. The high-Jd group is interpreted as the result of local elemental redistribution in the presence of a low-degree hydrous melt, in good agreement with their wide range of LREE enrichment. In contrast, the MREE-to-HREE fractionation and increasing Cr# in spinel of the low-Jd group indicate that they experienced higher degrees of melting. Open-system melting simulations of trace-element fractionation during hydrous flux melting suggests that the high-Jd harzburgites are the result of low fluid influx producing poorly extracted melt, while higher influx led to higher melting degrees and efficient melt extraction in the low-Jd harzburgites; the lherzolites mostly remained below or near solidus during that process. The lithological and chemical heterogeneity of San Carlos mantle is thus compatible with a single-stage evolution, which is also supported by the striking consistency between Fe-Mg exchange and REE thermometric estimates (1057 and 1074 °C on average, respectively), indicating that harzburgites and lherzolites probably followed a similar P-T path and relatively little sub-solidus re-equilibration. These interpretations suggest that the development ofmelt extraction pathways promoted by reactive channeling instability is able to produce complex lithological heterogeneities during hydrous flux melting. This process provides a self-consistent explanation for the systematic enrichment of harzburgites observed in many mantle terranes and xenoliths worldwide. We argue that San Carlos is one of such examples where a ca 1.5-Ga continental lithosphere experienced localized flux melting and deformation during the tectonic reactivation of a Proterozoic subduction zone, providing new constraints on the mantle sources of volcanic activity in the Jemez Lineament.Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Scienc