1,721,131 research outputs found
Petrogenesis and geodynamic significance of the volcanism of the Northern Ethiopian plateau
Full text linkAfter the pioneering works of Morgan during the Seventies (Morgan, 1971) a renewed interest on mantle plumes has arisen in the last decades with controversial hypotheses on depths of plume provenance, triggering mechanisms, shape and size of the convective mantle, as well as relationships with hot spots, Large Igneous Province (LIP), and rift volcanism (Ernst & Buchan, 2001; Foulger et al., 2005; Foulger & Jurdy, 2007).
In this regard, the Ethiopian-Yemen basaltic plateau represents a very convenient natural laboratory to study Continental Flood Basalts (CFB) and the tectonomagmatic processes that led to the
formation of the Red Sea, Gulf of Aden and East African rift system, from Oligocene to Present. This area is centred on the Afar hot spot which appears unequivocally related to a deep plume originating in the lower mantle (Courtillot et al., 2003, Davaille et al., 2005). A multidisciplinary study has been
developed on the Ethiopian Oligocene Plateau, integrating field data with detailed sampling of selected basaltic sections, geochemical and petrological results, as well as GIS processing, in order to provide new insights on the mantle plume region from which plateau basalts were generated. The integrated approach includes:
1. Digitalization, georeferentiation and projection in the UTM system WGS-84 Datum of the geological map 1:2.000.000 by Merla et al. (1973), and subsequent creation shapefiles for each geological formations related to the Oligocene CFB and a shapefile containing the UTM coordinates of the studied samples. The topographic values (z) were obtained by NASA Shuttle Radar Tomography Mission (SRTM) rasters.
2. Petrochemical analyses of samples collected along selected plateau sections and petrological classification allowed definition of a zonal arrangement of volcanics with Low-Ti tholeiites in the NW part and High-Ti transitional basalts (and picrites) in the SE sector of the Ethiopian plateau. Calculation of the erupted volumes of each magma-type was carried out.
3. Thermobarometric methods and the Niu & Batiza (1991) empirical model were applied to the various magmatypes in order to constrain their degree of partial melting (F), temperature (T), as well as initial (P ) and final (P ) pressures of melt generation in a mantle upwelling region. Calculations were carried out on selected representative near-primary magmas, i.e. in equilibrium with peridotite mantle sources. Petrogenetic modelling is also used to figure out the plume influenced mantle region from which northern Ethiopia CFB were generated
Thermally based isotopic speciation of carbon in complex matrices: a tool for environmental investigation
No full textElemental and isotopic analyses of carbon in environmental matrices usually highlight multiple pools of different composition and 13C/12C (δ13C ‰) isotopic ratio. Interpretation necessarily needs the characterization of the diverse end-members that usually are constituted by inorganic and organic components. In this view, we developed a routine protocol based on coupling of elemental and isotopic analyses that is able to discriminate the inorganic (IC) and organic (OC) contributions to the total carbon (TC) content. The procedure is only based on thermal destabilization of the different carbon pools and has been successfully applied on different environmental matrices (rocks, soils, biological samples) with a mean C elemental and isotopic recoveries of 99.5% (SD = 1.3%) and 0.2‰ (SD = 0.2‰), respectively. The Thermally Based Speciation (TBS) lead us to define precise isotopic end-members, which are unaffected by any chemical treatment of the sample, to be used for accurate mass balance calculation that represents a powerful tool to quantify the distinct carbon pools. The paper critically evaluates the method explaining the potentials and the current limits of the proposed analytical protocol
Carbon elemental and isotopic composition in mantle xenoliths from Spain: Insights on sources and petrogenetic processes
No full textThe carbon elemental concentration (C wt%) and isotopic (δ13C ‰) 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 (δ13C − 26.1‰) to typical mantle values (δ13C − 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 13C-depleted values ranging between − 20.1 and − 23.7‰; higher elemental C up to 0.41 wt% displaying distinctly less negative isotopic values (δ13C 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-δ13C variation. However, the correlation between the carbon isotopic data with other isotopic tracers (e.g. 87Sr/86Sr, 3He/4He) 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 δ13C of ca. − 18.0‰
Carbon budget in the Iberian mantle: Insights from Calatrava and Tallante xenoliths
No full textIn this contribution we present elemental and isotopic analyses of carbon (C) carried out on mantle xenoliths from the Calatrava and Tallante volcanic districts (Spain).
The C content of peridotite xenoliths from Calatrava, previously studied by [1], generally range between 1100 and 5500 ppm, with up to 2.9 wt% C in a single sample. The associated isotopic composition (δ13C) of most samples varies between -26.1 to -15.2 ‰, whereas the carbon-rich outlier displays a distincly less negative C isotopic composition (i.e. -6.2‰) that conforms with a typical mantle signature [2]. The C content of xenoliths from Tallante previously studied by [3], [4], varies from 600 to 1000 ppm in anhydrous peridotites, to 1500 ppm in an amphibole bearing peridotite; higher C content of 4000 ppm have been recorded in the felsic vein crosscutting a peridotite composite xenolith previously studied by [5]. The associated isotopic composition (δ13C) varies between -20.1 to -22.4 ‰ in peridotites, whereas the mentioned felsic vein displays the value of -11.9‰. In both xenolith suites a correlation is observed between the carbon contents and the respective δ13C values suggesting that analogous fractionation processes affected vast domains of the Iberian lithospheric mantle. Noteworthy, in the Tallante xenolith suite less negative δ13C values comparable to those of the Calatrava district are never recorded. The less negative isotopic composition recorded by Tallante xenoliths approaches that of the carbonate matrix of the xenolith-bearing volcanoclasic deposit (-9.8‰). On the whole, the available data suggest that the carbon of the studied xenoliths, host lavas and cabonate volcanoclastic matrices is juvenile, mostly originated deep in the mantle, and influenced by multiple episodes of degassing, that ultimately led to extremely explosive volcanic eruptions. References [1] Bianchini
et al (2010), GSL Sp. Pub. 337, 107-124. [2] Deines (2002), Earth Sc. Rev. 58, 247-278. [3] Beccaluva et al (2004), Lithos 75, 67-87. [4] Bianchini et al (2011), Lithos 124,308-318. [5] Bianchini et al (2015), Lithos 220-223, 191-199
Thermally based isotopic speciation of carbon pools in environmental matrices
No full textIn the last years several authors applied the thermal speciation techniques to different environmental matrices such as biological material (Boyle et al., 2004; Pallasser et al., 2013) and soils/sediments (Hsieh and Bugna 2008; Bisutti et al. 2007; Leifeld 2007), in order to identify the different carbon pools. The abovementioned methods have been improved by coupling the elemental content with the carbon isotope analysis, which represents a powerful tool for the discrimination of the distinct carbon pools in heterogeneous environmental materials (Lopez-Capel et al. 2006; Manning et al. 2005, 2008). Elemental and isotopic analyses of carbon in environmental matrices usually highlight multiple pools of different composition and 13C/12C (δ13C ‰) isotopic ratio. Interpretation necessarily needs the characterization of the diverse end-members that usually are constituted by inorganic and organic components. In this view, we developed a routine protocol based on coupling of elemental and isotopic analyses that is able to discriminate the inorganic (IC) and organic (OC) contributions to the total carbon (TC) content. The procedure is only based on thermal destabilization of the different carbon pools and has been successfully applied on different environmental matrices (rocks, soils, and biological samples) with a mean C elemental and isotopic recoveries of 99.5 % (SD= 1.3 %) and 0.2‰ (SD=0.2‰), respectively. The thermally based speciation (TBS) leads us to define precise isotopic end -members, which are unaffected
by any chemical treatment of the sample, to be used for accurate mass balance calculation that represents a powerful tool to quantify the distinct carbon pools. The paper critically evaluates the method explaining the potentials and the current limits of the proposed analytical protocol
Carbon budget in Calatrava and Tallante xenoliths: insights on sources and petrogenetic processes
No full textWe present elemental and isotopic analyses of carbon (C) carried out on mantle xenoliths from the Calatrava and Tallante volcanic districts (Spain). The C content of peridotite xenoliths from Calatrava, previously studied by Bianchini et al. (2010), generally range between 1100 and 5500 ppm, with up to 2.9 wt.% C in a single sample. The
associated isotopic composition (delta 13C) of most samples varies between -26.1 to -15.2 ‰, whereas the carbon-rich outlier displays a distincly less negative C isotopic composition (-6.2‰) that conforms with a typical “mantle signature” (Deines, 2002). The C content of xenoliths from Tallante previously studied by Bianchini et al. (2011), varies from 600 to 1000 ppm in anhydrous peridotites, to 1500 ppm in an amphibole bearing peridotite; higher C content of 4000 ppm have been recorded in the felsic vein crosscutting a peridotite composite xenolith previously studied by Bianchini et al. (2015). The associated isotopic composition (delta13C) varies between -20.1 to -22.4 ‰ in peridotites, whereas the mentioned felsic vein displays the value of -11.9‰. In both xenolith suites a correlation is observed between the carbon contents and the respective delta13C values suggesting that analogous fractionation processes affected vast domains of the Iberian lithospheric mantle. Noteworthy, in the Tallante xenolith suite delta13C values approaching the notional “mantle signature” are never recorded. The less negative isotopic composition recorded by Tallante xenoliths approaches that of the carbonate matrix of the xenolith-bearing volcanoclasic deposit (-9.8‰). On the whole, the available data suggest that the carbon of the studied xenoliths, host lavas and cabonate volcanoclastic matrices is juvenile, mostly originated deep in the mantle, and influenced by multiple episodes of degassing, that ultimately led to extremely explosive volcanic eruptions. Differences between the two suites are possibly related to distinct geodynamic settings, as the Tallante mantle section was interested by supra-subduction metasomatic fluids/melts that didn’t occur at Calatrava
Preliminary notes on C-N ppols in sediments from the Sacca di Goro coastal lagoon (Po delta, northern Italy)
Full text linkA very hot debate is currently focused on submerged substrates that can be classified either as sediments or subaqueous soils. In this paper, the controversy is contextualized on a specific case study, i.e. the Sacca di Goro coastal lagoon facing the North Adriatic Sea. The submerged substrate has been sampled along a a E-W transect and subsequently analyzed to investigate the C-N elemental and isotopic compositions. The recorded concentration of organic carbon (OC) and nitrogen is 0.26-0.50 and 0.02-0.06 wt%, respectively, and the spatial distribution of these parameters highlights a general decrease of concentration from W to E. The carbon isotopic composition of the organic matter (δ13COC) indicates the incorporation within the substrate of significant amount of seaweed and seagrass. Seaweed prevails in the west (δ13COC down to -19‰) due to a nutrient-rich freshwater inflow (Po di Volano), whereas seagrass is preponderant eastward (δ13COC up to -10‰) in a sector of the lagoon fed by riverine waters characterized by lower nutrient load (Po di Goro). The existence of these biological components plausibly implies a lush benthic vegetation, properly rooted on the submerged floor. For this reason, in our view the substrate of the investigated lagoon can be regarded as a subaqueous soil
An integrated GIS-based petrogenetic model for continental flood volcanism in a plume region: the case study of the Ethiopian plateau basalts.
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Geochemical proxies of sediment provenance in alluvial plains with interfering fluvial systems: A study case from NE Italy
No full textThis 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
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