Search

The volcanism of the Arasbaran region, northwest Iran, is characterized by multiple magmatic pulses from Cretaceous to Quaternary related to the consumption of the Neotethys oceanic basin and the subsequent continental collision between the Arabia and the Eurasian plates. In this paper we focus on the Eocene igneous products, which show wide compositional variations, ranging from shoshonite to tephrite and phonolite. They may be further grouped into leucite (analcime)-bearing and leucite-free rock types on the basis of their rock-forming minerals. Leucite-bearing and leucite-free Eocene magmatic rocks are geographically separate outcropping in the WNW and ESE part of the Ahar-Arasbaran region, respectively. K Ar dating show leucite-bearing rocks (39.4–39.6 +/− 1.0 Ma) being slightly younger with respect to leucite-free rocks (41.0–41.9 +/− 1.0 Ma). The two rock types are differentiated by each other in terms of silica saturation degrees but display similar incompatible trace elements distributions, typical of subduction-related volcanic rocks. Indeed, clear depletions in HFSE (e.g., Nb, Ta, Ti, Zr) and enrichments in LILE (e.g., Ba, K) and Pb are shown. The leucite-bearing volcanic rocks are strongly silica-undersaturated (Δq ca. -35) and show higher LILE/HFSE, LILE/REE, Ba/La (30–90) and Ba/Th (up to 520) values with respect to leucite-free rocks (Δ q from 0 to −15; Ba/La up to 30). Leucite-bearing and -free groups also show distinct Sr-Nd-Pb isotopic compositions, with the former having less radiogenic Sr (87Sr/86Sr 0.704424–0.704634) and Pb (206Pb/204Pb 18.58–18.65, 207Pb/204Pb 15.57–15.60, 208Pb/204Pb 38.63–38.71) and more radiogenic Nd (143Nd/144Nd 0.512695–0.512791), with respect to the latter ones (87Sr/86Sr 0.704481–0.705669, 206Pb/204Pb 18.65–18.75, 207Pb/204Pb 15.61–15.64, 208Pb/204Pb 38.65–38.87, 143Nd/144Nd 0.512572–0.512623). Geochemical and isotopic compositions, coupled with the strong silica-undersaturated character, of leucite-bearingrocks suggest in their mantle source the involvement of metasomatizing partial melts from subducted altered oceanic crust and subordinate carbonate-bearing sediments. On the other hand, the compositions of leucite-free igneous rocks are compatible with the involvement of a relatively higher contribution of partial melts from terrigenous (carbonate-poor) subducted sediments. The close spatial association and the relative geographical/stratigraphic position of these products indicate diachronous metasomatic events in the mantle wedge underlying the Arasbaran area that could have been originated by the late arrival of carbonate-rich sediments at depth during slab steepening and incipient roll-back preceding the continental collision. K Ar dating indicates that the Arasbaran magmatism was triggered by a late geodynamic event, during middle Eocene, plausibly consisting of re-adjusting of isotherms that heated the veined mantle wedge following the slab migration after roll-back. The slightly younger age of leucite-bearing rocks with respect to leucite-free rocks, coupled with the lower melting degree of the former may suggest an evolution of the local thermal regime with the progressive involvement of portions of the mantle wedge closer to the subducted plate. • A subduction-related magmatic pulse occurred in NW Iran at ca. 40 Ma. • Shoshonite leucite-free slightly preceded UK leucite-bearing volcanism. • Leucite-free magma source was metasomatised by dominant LC-sediment melts. • Leucite-bearing magmas was metasomatised by dominant HC-sediment melts. • Leucite-bearing rocks share similarities with Neapolitan Roman-type UK rocks. [ABSTRACT FROM AUTHOR]

A new analytical approach (Thermally Based Separation, TBS) for the characterisation of inorganic (IC) and organic (OC) carbon pools in alluvial soils has been tested. The method does not involve any chemical pre-treatment of samples and relies on different thermal stabilities of IC and OC pools, which can be accurately determined with an EA-IRMS analytical system. Elemental (C, g/kg) and isotopic (δ 13 C, ‰) carbon data were used to check the reliability of the TBS method by calculating the mass balances using the measured IC and OC fractions and total carbon (TC). TBS was applied to 7 soil samples from the Padanian alluvial plain (NE Italy) that were collected from different depths and characterised by textural/geochemical heterogeneity. The method allowed for a mean carbon elemental recovery of 99% (SD = 2%), and mean isotopic deviation (Δ 13 C) between theoretical (δ 13 C OC X OC  + δ 13 C IC X IC )/( X OC  +  X IC ) and measured δ 13 C TC of 0.2‰ (SD = 0.3‰). A comparison of TBS with other conventional methods for carbon separation provided insights into the possible effects of sample acidification on the soil organic pools. The results suggest a higher robustness of TBS compared to conventional methods in the determination of organic and inorganic carbon pools in soils. This is because TBS bypasses any possible fractionation derived from the hydrolysis of soil organic matter and therefore accurately determines the carbon isotopic composition of the OC and IC fractions. TBS appears to be more robust than conventional methods and is independent from the IC/OC ratio of the samples, from the unpredictable complexity of soil organic matter and from the arbitrary application of the acidification routine. On this basis, TBS represents a very promising approach for a correct and complete characterisation of soil carbon pools. [ABSTRACT FROM AUTHOR]

This paper demonstrates that geochemistry is useful for the identification of sediment origin and provenance in alluvial plains characterised by a complex hydrographic evolution. The study is focused on the northeastern Padanian plain (Italy), an area primarily characterised by sedimentary contributions from the two largest Italian river systems (Po and Adige), which intimately interacted during the last millennia. X-ray fluorescence analyses of 120 soils and alluvial sediments define three diverse geochemical affinities that have distinctive siderophile/chalcophile elemental ratios. The sample group characterised by high Ni/Zn and Cr/Pb values conforms to modern Po River sediments, whereas a second group showing low Ni/Zn and Cr/Pb values conforms to the geochemical signature of modern Adige River sediments. A third sample group defines a “transitional” affinity that represents a geochemical mixture of Po (70%) and Adige (30%) sedimentary end-members. Based on these geochemical features, it is possible to distinguish alluvial sediments of the Po River basin (Ni/Zn > 1.0 and Cr/Pb > 4.2) from those of the Adige River basin (Ni/Zn < 0.6 and Cr/Pb < 1.9) and to provide evidence of the migration of these rivers during the evolution of the Padanian plain. The interpretation of transitional samples is less constrained and could imply an ancient connection between the two fluvial systems, possibly due to the development of wetlands where both the Po and Adige rivers variably delivered their sedimentary contributions. This study approach, therefore, provides important implications for palaeohydrographic and palaeoenvironmental reconstructions in a complex area that is characterised by significant geomorphological modifications during the last millennia. [ABSTRACT FROM AUTHOR]

The carbon elemental concentration (C wt%) and isotopic (δ 13 C ‰) composition of mantle xenoliths from the Tallante and Calatrava volcanic occurrences (in South-East and Central Spain, respectively) have been investigated to identify carbon sources and processes occurring in distinct geodynamic settings of the Iberian Peninsula. The peridotitic mantle xenoliths from Calatrava show elemental C ranging from 0.11 to 2.87 wt% which is coupled with a continuous isotopic variation from very negative values (δ 13 C − 26.1‰) to typical mantle values (δ 13 C − 5.9‰). On the other hand, the Tallante mantle xenolith suite displays lower C contents (0.06–0.15 wt%) showing a tighter variation with 13 C-depleted values ranging between − 20.1 and − 23.7‰; higher elemental C up to 0.41 wt% displaying distinctly less negative isotopic values (δ 13 C between − 13.8 and − 11.9‰) have been recorded in veins crosscutting Tallante peridotites, plausibly representing the product of metasomatic reactions. The data from the two investigated xenolith suites invariably display a good correlation between elemental and isotopic composition, suggesting a mantle origin for carbon and Rayleigh-type fractionation as the process responsible for the observed C-δ 13 C variation. However, the correlation between the carbon isotopic data with other isotopic tracers (e.g. 87 Sr/ 86 Sr, 3 He/ 4 He) used to identify distinct mantle components and metasomatic reactions, indicates systematic differences between the two xenolith suites suggesting that beneath the Betic Cordillera (where Tallante is located) the deep C-cycle involves recycling, via subduction preceding/accompanying continental collision, of crustal components back in the mantle. Coherently, geochemical trends observed in the Tallante xenoliths seem to be influenced by metasomatic agents generated by melting of crustal lithologies that according to the analysis of a metasedimentary xenolith can contain C up to 1.2 wt% having δ 13 C of ca. − 18.0‰. [ABSTRACT FROM AUTHOR]

Abstract: Mantle xenoliths from Pliocene-Quaternary volcanic diatremes in the Azrou area (Middle Atlas, Morocco) include protogranular to porphyroclastic spinel lherzolites with superimposed metasomatic textures involving pyroxenes and spinel as the main reacting phases. Thermobarometric estimates on these xenoliths show pressure (P)–temperature (T) equilibrium conditions in the range 1.1–1.4 GPa and 900–1090 °C. Bulk rocks have flat heavy rare earth element (HREE) patterns (0.6–2.2 times chondrite) and are variably enriched in light REE (LREE; LaN/YbN between 1.1 and 15.6). The constituent clinopyroxenes are characterized by flat HREE distributions (5.1–11.9 times chondrite) and variable LREE enrichment with LaN/YbN from 0.4 to 25, which generally conform to the bulk rock chemistry. Trace elements characteristics of the metasomatised clinopyroxenes suggest that the metasomatasing agents were highly alkaline carbonate-rich melts such as nephelinites/melilitites or, as extreme, silico-carbonatites. Sr–Nd isotopic composition analyses carried out on clinopyroxene separates yield 87Sr/86Sr = 0.70243–0.70335, 143Nd/144Nd = 0.51273–0.51325. The helium isotope composition of olivines ranges from 6.2 to 6.8 Ra. These values, coupled with the radiogenic lead isotopic composition available in the literature, suggest that the Middle-Atlas lithospheric mantle interacted with HIMU-like metasomatic components. These are in turn related to local mantle upwellings along pre-existing tectonic lineaments – located at the northern border of the West African Craton – that were reactivated as far-field foreland reaction of the Africa-Europe collisional system. [Copyright &y& Elsevier]

The paper presents a first approach to the analysis of the dynamic behaviour of a pre-mixed hydrogen/air jet flame using near-IR imaging. In this kind of flames spectral lines are observed in the infrared, visible, and ultraviolet regions; emissions of visible light are however not so strong as in other wavelengths, especially in the near-infrared and infrared portions of the spectrum. Using a video camera, coupled with an optical filter, it is possible to capture images of the flame in a burner and then acquire sequences of images of the near-infrared emission during the combustion process. In this work, carried out in the frame of a collaboration between ENEL Produzione Ricerca and ISTI CNR, we propose a method suitable to process and analyse maps of near-infrared emissions in order to characterize the flame morphology and compute geometric and densitometric features useful to describe the combustion dynamics. The map of the emissions presents in some cases different unconnected sources with interesting distribution. In our analysis, we considered two different layers: the single images, as a distribution of near-IR emission, and the complete sequence of images in a dynamical evolution of the whole process. [Copyright &y& Elsevier]

• The application of DIN 19539 allows the discrimination of three soil carbon pools. • Two organic (TOC400 and ROC) and one inorganic (TIC900) carbon pools. • TOC400 at 300−400 °C, ROC at 510−600 °C, TIC900 at 700−900 °C. • TOC400/ROC ratio vsδ 13C TOC links SOM thermal and compositional features. • Temperature of carbonate breakdown vsδ 13C TIC reflects mineralogical differences. The quantification of soil carbon pools is a pressing topic both for the agriculture productivity and to evaluate the Greenhouse Gases (GHG) sequestration potential, therefore a rapid and precise analytical protocol for carbon speciation is needed. Temperature-dependent differentiation of soil carbon in compliance with the DIN (German Institute for Standardization) 19539 standard has been applied for the first time on 24 agricultural soil samples from the Po River Plain (Italy), with the aim of investigate their thermal behavior in the 50−900 °C interval. The results invariably show the existence of three soil carbon pools having different thermal stabilities, namely, thermally labile organic carbon (TOC400), residual oxidizable carbon (ROC) and total inorganic carbon (TIC900), in the intervals of 300−400 °C, 510−600 °C and 700−900 °C, respectively. Significant relationships have been observed between the above mentioned organic and inorganic carbon pools and the associated isotopic composition: 1) inverse correlation between TOC400/ROC and δ 13C links thermal stability and soil organic matter (SOM) composition; 2) direct correlation between carbonate breakdown temperature and δ 13C denotes the mineralogical association of the inorganic pool. The results give clues regarding the nature and evolution of soil carbon pools. [ABSTRACT FROM AUTHOR]

Active locomotion of wireless capsule endoscopes has the potential to improve the diagnostic yield of this painless technique for the diagnosis of gastrointestinal tract disease. In order to design effective locomotion mechanisms, a quantitative measure of the propelling force required to effectively move a capsule inside the gastrointestinal tract is necessary. In this study, we introduce a novel wireless platform that is able to measure the force opposing capsule motion, without perturbing the physiologic conditions with physical connections to the outside of the gastrointestinal tract. The platform takes advantage of a wireless capsule that is magnetically coupled with an external permanent magnet. A secondary contribution of this manuscript is to present a real-time method to estimate the axial magnetic force acting on a wireless capsule manipulated by an external magnetic field. In addition to the intermagnetic force, the platform provides real-time measurements of the capsule position, velocity, and acceleration. The platform was assessed with benchtop trials within a workspace that extends 15 cm from each side of the external permanent magnet, showing average error in estimating the force and the position of less than 0.1 N and 10 mm, respectively. The platform was also able to estimate the dynamic behavior of a known resistant force with an error of 5.45%. Finally, an in vivo experiment on a porcine colon model validated the feasibility of measuring the resistant force in opposition to magnetic propulsion of a wireless capsule. [ABSTRACT FROM AUTHOR]

Abstract: The genetic relationships between orogenic (i.e. subduction related) and anorogenic (i.e. intra-plate) Cenozoic igneous phases have been investigated in two regions of the western Mediterranean area: Sardinia and Southern Spain. In Sardinia the ‘orogenic’ magmatism (38–12Ma) is followed by the ‘anorogenic’ volcanism, mostly since about 6Ma, whereas in Southern Spain the ‘anorogenic’ volcanism follows the ‘orogenic’ phase (34–6Ma) after a gap of 0–4Ma in the Betic–Calatrava districts. The older orogenic magmatism (tholeiitic, calcalkaline and more potassic products) of both areas is related to the subduction of the Ionian oceanic lithosphere which developed beneath the Paleo-European-Iberian continental margin probably since Middle-Late Eocene. This subduction system migrated southeastwards with time up to its present position in the Eolian–Calabrian Arc and the Betic–Alboran regions along the Apennine–Maghrebide belt. Relics of subducted lithosphere are geophysically recorded as nearly-vertical bodies down to 500–600km, flattening for several hundreds of kilometres under the Tyrrhenian–Sardinia and Betic–Calatrava areas, respectively. These relics of subducted slabs, which pond over large areas of the mantle transition zone, appear to play a significant role also in the genesis of the younger anorogenic magmas, whose major volcanic fields lie above the frontal part of the subducted slab where convective instabilities and upward mantle flow components are geophysically supported by laboratory and 3D numerical models. This dynamic response to subduction, involving localised mantle upwellings and remobilization of pre-existing mantle components, may have been a fundamental factor in the generation of anorogenic magmas. Due to slab roll-back and inter-arc extension in both Eolian–Tyrrhenian and Betic–Alboran regions, the magma sources of the previous orogenic phases can be completely replaced by “fresh” mantle diapirs from whic\h anorogenic magmas will be generated. These magmas are invariably characterised by OIB isotopic signatures (HIMU and EMI) which are classically interpreted as long-term recycling of oceanic crust (plus variable sedimentary components) via ‘ancient’ pre-Paleozoic subduction events. We propose that the ‘recent’ Cenozoic subduction from which the orogenic series was generated, also had a dynamic influence on the younger anorogenic magmatism by remobilization of long-term isolated mantle components which resulted in the secular evolution of OIB-type magmas. In this view, the on-going subduction processes of the Mediterranean orogenic belts did not provide chemical “ingredients” to the mantle sources of the anorogenic magmas, but induced reactivation of older metasomatised mantle domains ultimately triggering magma genesis. [Copyright &y& Elsevier]

Using qualitative data from Ghana, this article explores the role of information in the formation of expectations of migrants and their families back home, with specific reference to the return experience. We develop a typology to illustrate (1) how information influences expectations throughout the migration experience; (2) the ability of the migrant and their family to adapt to those changing expectations, given differing levels of information; and (3) the implications (1) and (2) have for return. Latent tensions and conflicts emerge in which expectations of migrants and migrant families are not harmonious. The evidence shows that the pace of adaptation and change is regulated by access to information; information flow between migrant at destination and home; and the propensity of the migrant to adapt, which is related to the level of financial dependency (or strength of obligation) between migrant and home. The article raises policy questions around information access and information flows, community sensitisation and returnee reintegration, especially in poorer areas.Cet article utilise des données qualitatives sur le Ghana pour étudier le rôle que joue l’information dans la formation des attentes des migrants et de leurs familles, en ciblant plus particulièrement l’expérience du retour. Nous développons une typologie dans le but d’illustrer (1) comment l’information détermine les attentes dans le cas de l’expérience migratoire, (2) la capacité des migrants et de leurs familles à s’adapter à de nouvelles attentes dues à des niveaux d’information différents; et (3) les conséquences que les deux premiers points peuvent avoir sur les conditions du retour. Des tensions latentes se manifestent et des conflits émergent quand les attentes des migrants et de leurs familles ne vont pas dans le même sens. Les témoignages montrent que le rythme d’adaptation et de changement est régulé par l’accès à l’information, que l’information circule entre les migrants arrivés à destination et le pays d’origine, et que la propension des migrants à s’adapter est liée au niveau de dépendance financière (ou au poids des obligations) entre les migrants et le pays d’origine. L’article soulève des questions à propos de l’accès à l’information et les flux d’information, la sensibilisation des communautés, et la réintégration de ceux qui sont de retour, plus particulièrement dans les régions pauvres. [ABSTRACT FROM AUTHOR]

This work reports an ab initio study on the carbon (C), nitrogen (N), and sulphur (S) elemental and isotope compositions of the Padanian Plain sediments collected in the province of Ferrara (Northern Italy). The investigated sediments were already characterized by previous research that highlighted a bimodal provenance, as some sediments are from the Alpine chain and were conveyed to the plain by Po River, whereas others are from the Apennine chain and were conveyed to the plain by the Reno River. This information was obtained considering the concentration of heavy metals retrieved from hundreds of X-ray fluorescence analyses available in the literature, whereas CNS elemental and isotope compositions are unknown. These tracers are generally considered scarcely useful to identify the sediment provenance, as influenced by multiple environmental factors. However, this work challenges these assertions observing that 13C/12C, 15N/14N, 34S/32S are significantly different in Po and Reno River sediments. Our hypothesis is that the CNS geochemical signal is 1) mainly regulated by the organic fraction included in the alluvial sediments, and 2) these organic fraction have in turn a specific composition in the distinct source catchments. More in general, the presented data increase the knowledge on the local elemental and isotopic backgrounds. This is important because many pollutants contain significant CNS concentration and specific isotope composition. Therefore, they serve as baseline and will provide new tools to recognize possible anthropogenic anomalies in the studied area. • 13C/12C, 15N/14N, 34S/32S could be used to assess sediment provenance. • The utility of CNS isotopes is tested on Padanian Plain alluvial sediments. • CNS isotopes demonstrate that there are two distinct sediment populations. • The new data provide elemental and isotopic backgrounds. • The new data are useful for the recognition of possible anthropogenic anomalies. [ABSTRACT FROM AUTHOR]

A critical review of the available multidisciplinary data on the Paranà-Etendeka Province allows for the reconciliation of the controversial aspects of its origin in a coherent tectonomagmatic scenario, in which continental flood basalt (CFB) magmatism evolved from the Paranà plateau s.s. (Stage 1) to progressive continental rifting in Etendeka (Stage 2), and then opened to the South Atlantic at the same latitude; the CFB magmatism is triggered by the prolonged impingement of the proto Tristan plume on the western Gondwana lithosphere. The provinciality of the CFB is evidenced by the incompatible element distribution and Sr-Nd-Pb isotopic data, where the Paranà and Etendeka magmas are more akin to lithospheric and asthenospheric (plume-related) components, respectively. Stage 1 consisted of the rapid outpouring of the Paranà Plateau s.s. CFB (135–134 Ma, ~ 800,000 km3, and eruption rate ~0.8 km3/a) that was zonally arranged with prevailing high-TiO 2 (HT) basalts in the central-northern part and low-TiO 2 (LT) suites at the southern periphery. The differentiated nature (MgO = 8–4%) of these plateau magmas suggests the variable extent of fractional crystallisation during rise through a relatively thick lithosphere. Petrological modelling, isotopic signatures (87Sr/86Sr 0.70483–0.70620, and εNd (t) from −1.27 to −5.78), and incompatible element distributions approaching the EM1 mantle component suggest that the HT and LT Paranà basalts may be derived from mantle sources located in the lower lithosphere at P 3–4 GPa and a potential temperature (T p) of 1500–1550 °C. The high T p recorded (and the relative T excess 250–300 °C thermal anomaly) can be attained after several million years of lithospheric heating, beginning from the first plume impact, which is represented by precursor alkaline events (145–138 Ma) at the westernmost border of the Paranà plateau. The subsequent rifting (Stage 2 , mostly 134–128 Ma) developed SE of the Paranà plateau in relation to the NW drifting of the Gondwana plate over the rising plume and was accompanied by progressive lithospheric arching, thinning, and rifting, which culminated in continental breakup close to the Etendeka border. The concomitant and exclusive appearance, in both the HT and LT suites of this region, of the hottest and deepest (T p up to ~1590 °C and P up to ~5 GPa) high-MgO sub-lithospheric magmas (87Sr/86Sr 0.70319–0.70533 and εNd (t) from 9.08 to 0.53) is consistent with their generation from the axial zone of the upwelling plume. The basic–acidic bimodal character of CFB magmatism, since the beginning of this stage, must be related to the intensive block faulting of the rifted margins that favoured magma trapping and crystal fractionation to trachydacite and dacite-rhyolite differentiates from the respective HT and LT basalts. Owing to the higher SiO 2 and viscosity, the prevailing dacite-rhyolite magmas were more prone to pond in crustal magma chambers, where they experienced assimilation fractional crystallisation (87Sr/86Sr 0.71466–0.72558 and εNd (t) from −5.50 to −9.31) before erupting as extensive rheo-ignimbrites. During the final rifting stage, CFB activity continued until 128 Ma (with sporadic episodes until 122 Ma), and the plume dynamic support gradually vanished beneath the two conjugate South American/South African continental margins, up to the opening of the South Atlantic and hot-spot volcanism of the Rio Grande and Walvis Ridges. • Paranà-Etendeka LIP developed in two stages, triggered by a plume impingement • In the first stage, Paranà plateau s.s. CFB derived from lithospheric sources • In the second stage, Etendeka CFB formed from plume-related sources during rifting [ABSTRACT FROM AUTHOR]

The Pontine Islands form a volcanic archipelago in the Tyrrhenian Sea. It consists of two edifices, the islands of Ponza, Palmarola and Zannone and the islands of Ventotene and Santo Stefano, respectively. The Archipelago developed during two main volcanic cycles in the Plio-Pleistocene: 1) the Pliocene episode erupted subalkaline, silica-rich volcanic units, which constitute the dominant products in the western edifice (Ponza and Zannone Islands); 2) the Pleistocene episode erupted more alkaline products, represented by evolved rocks (trachytes to peralkaline rhyolites) in the islands of Ponza and Palmarola and by basic to intermediate rocks in the eastern edifice (Ventotene and Santo Stefano Islands). In this paper we present new geochemical and petrological data from submarine rock samples collected in two oceanographic cruises and a scuba diving survey. The main result is the recovery of relatively undifferentiated lithotypes that provide further insights on the magmatic spectrum existing in the Pontine Archipelago, allowing modelling of the whole suite of rocks by fractional crystallization processes. New major and trace element data and thermodynamic constrains (by the software PELE) indicate the existence of three distinct evolutionary trends corresponding to a HK calcalkaline series in the Pliocene, followed by a transitional and then by a shoshonite series in the Pleistocene. In particular, the transitional series, so far overlooked in the literature, is required in order to explain the genesis of several peralkaline felsic rocks recognized in the Archipelago. On the whole, the new geochemical data i) confirm the orogenic signature of the suites, ii) allow to rule out an anatectic origin for both subalkaline and peralkaline rhyolites and iii) indicate highly heterogeneous mantle sources, due to crustal components variously recycled in the mantle via subduction. [ABSTRACT FROM AUTHOR]

Detailed petrological and geochemical investigations of an extensive sampling of mantle xenoliths from the Neogene–Quaternary Bir Ali diatreme (southern Yemen) indicate that the underlying lithospheric mantle consists predominantly of medium- to fine-grained (often foliated) spinel-peridotites (85–90%) and spinel-pyroxenites (10–15%) showing thermobarometric estimates in the P–T range of 0.9–2.0 GPa and 900–1150 °C. Peridotites, including lherzolites, harzburgites and dunites delineate continuous chemical, modal and mineralogical variations compatible with large extractions of basic melts occurring since the late Proterozoic (~ 2 Ga, according to Lu–Hf model ages). Pyroxenites may represent intrusions of subalkaline basic melts interacting and equilibrated with the host peridotite. Subsequent metasomatism has led to modal changes, with evidence of reaction patches and clinopyroxene and spinel destabilization, as well as formation of new phases (glass, amphibole and feldspar). These changes are accompanied by enrichment of the most incompatible elements and isotopic compositions. 143 Nd/ 144 Nd ranges from 0.51419 to 0.51209 (ε Nd from + 30.3 to − 10.5), 176 Hf/ 177 Hf from 0.28459 to 0.28239 (ε Hf from + 64.4 to − 13.6), and 208 Pb/ 204 Pb from 36.85 to 41.56, thus extending from the depleted mantle (DM) towards the enriched OIB mantle (EM and HIMU) components. 3 He/ 4 He (R/R A ) ratios vary from 7.2 to 7.9 with He concentrations co-varying with the most incompatible element enrichment, in parallel with metasomatic effects. These metasomatic events, particularly effective in harzburgites and dunites, are attributable to the variable interaction with alkaline basic melts related to the general extensional and rifting regime affecting the East Africa–Arabian domain during the Cenozoic. In this respect, Bir Ali mantle xenoliths resemble those occurring along the Arabian margins and the East Africa Rift system, similarly affected by alkaline metasomatism, whereas they are distinctly different from xenoliths located within the Ethiopian–Yemen continental flood basalt province that are pervasively refertilized by plume-related subalkaline melts. [ABSTRACT FROM AUTHOR]

• Uncertainty in slopes of mixed waters is not explained by the experimental error. • Stream and spring isotopic data have significant differences in the slopes. • Evaporated soil water does not significantly affect the δ2H-δ18O relationship. The Ordinary Least Squares (OLS) regression is the most common method for fitting the δ2H-δ18O relationship. Recently, various studies compared the OLS regression with the Reduced Major Axis (RMA) and Major Axis (MA) regression for precipitation data. However, no studies have investigated so far the differences among the OLS, RMA, and MA regressions for water types prone to evaporation, mixing, and redistribution processes. In this work, we quantified the differences in terms of slopes and intercepts computed by the OLS, RMA, and MA methods for rainfall, snow and ice, stream, spring, groundwater, and soil water, and investigated whether the magnitude of such differences is significant and dependent on the water type, the datasets statistics, geographical or climatic characteristics of the study catchments. Our results show that the differences between the regression methods were largest for the isotopic data of some springs and some stream waters. Conversely, for rainfall, snow, ice, and melt waters datasets, all the differences were small and, particularly, smaller than their standard deviation. Slopes and intercepts computed using the different regression methods were statistically different for stream water (up to 70.4%, n = 54), followed by groundwater, springs, and soil water. The results of this study indicate that a thorough analysis of the δ2H-δ18O relationship in isotope hydrology studies is recommended, as well as considering the measurement errors for both δ2H and δ18O, and the presence of outliers. In case of small measurement errors and no significant differences between the slopes computed through the three methods, we suggest the application of the widely used OLS regression. Conversely, if the computed slopes are significantly different, we recommend investigating the possible reasons for such discrepancies and prefer the RMA over the MA approach, as the latter tends to be more sensitive to data with high leverage (i.e., data points with extreme δ18O values). [ABSTRACT FROM AUTHOR]