Source components of the Gran Canaria (Canary Islands) shield stage magmas: evidence from olivine composition and Sr–Nd–Pb isotopes     

Andrey A. Gurenko  Kaj A. Hoernle  Alexander V. Sobolev  Folkmar Hauff  Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2010,159(5):689-702

The Canary Island primitive basaltic magmas are thought to be derived from an HIMU-type upwelling mantle containing isotopically depleted (NMORB)-type component having interacted with an enriched (EM)-type component, the origin of which is still a subject of debate. We studied the relationships between Ni, Mn and Ca concentrations in olivine phenocrysts (85.6–90.0 mol.% Fo, 1,722–3,915 ppm Ni, 1,085–1,552 ppm Mn, 1,222–3,002 ppm Ca) from the most primitive subaerial and ODP Leg 157 high-silica (picritic to olivine basaltic) lavas with their bulk rock Sr–Nd–Pb isotope compositions (⁸⁷Sr/⁸⁶Sr = 0.70315–0.70331, ¹⁴³Nd/¹⁴⁴Nd = 0.51288–0.51292, ²⁰⁶Pb/²⁰⁴Pb = 19.55–19.93, ²⁰⁷Pb/²⁰⁴Pb = 15.60–15.63, ²⁰⁸Pb/²⁰⁴Pb = 39.31–39.69). Our data point toward the presence of both a peridotitic and a pyroxenitic component in the magma source. Using the model (Sobolev et al. in: Science 316:412–417, 2007) in which the reaction of Si-rich melts originated during partial melting of eclogite (a high pressure product of subducted oceanic crust) with ambient peridotitic mantle forms olivine-free reaction pyroxenite, we obtain an end member composition for peridotite with ⁸⁷Sr/⁸⁶Sr = 0.70337, ¹⁴³Nd/¹⁴⁴Nd = 0.51291, ²⁰⁶Pb/²⁰⁴Pb = 19.36, ²⁰⁷Pb/²⁰⁴Pb = 15.61 and ²⁰⁸Pb/²⁰⁴Pb = 39.07 (EM-type end member), and pyroxenite with ⁸⁷Sr/⁸⁶Sr = 0.70309, ¹⁴³Nd/¹⁴⁴Nd = 0.51289, ²⁰⁶Pb/²⁰⁴Pb = 20.03, ²⁰⁷Pb/²⁰⁴Pb = 15.62 and ²⁰⁸Pb/²⁰⁴Pb = 39.84 (HIMU-type end member). Mixing of melts from these end members in proportions ranging from 70% peridotite and 30% pyroxenite to 28% peridotite and 72% pyroxenite derived melt fractions can generate the compositions of the most primitive Gran Canaria shield stage lavas. Combining our results with those from the low-silica rocks from the western Canary Islands (Gurenko et al. EPSL 277:514–524, 2009), at least four distinct components are required. We propose that they are (1) HIMU-type pyroxenitic component (representing recycled ocean crust of intermediate age) from the plume center, (2) HIMU-type peridotitic component (ancient recycled ocean crust stirred into the ambient mantle) from the plume margin, (3) depleted, MORB-type pyroxenitic component (young recycled oceanic crust) in the upper mantle entrained by the plume, and (4) EM-type peridotitic component from the asthenosphere or lithosphere above the plume center.  相似文献   

Importance of diffuse nutrient loading and lake level changes to the eutrophication of an originally oligotrophic boreal lake: a palaeolimnological diatom and chironomid analysis     

Jarmo J. Meriläinen  Juhani Hynynen  Arja Palomäki  Pasi Reinikainen  Anssi Teppo  Kaj Granberg 《Journal of Paleolimnology》2000,24(3):251-270

The recent environmental history of Lake Lappajärvi in western Finland (63°00 N, 23°30 E, area 149 km²), a humic, brown water lake with an average phosphorus content of ca. 20 g l^–1, was studied from short core sediment samples taken from the two main basins of the lake. Based on the stratigraphy of diatoms and chironomids and the sediment quality it was possible to distinguish four developmental stages during the past century: (1) a pre-industrial stage covering the time up to about 1935; (2) a stage of increasing nutrient loading (ca. 1936–1960); (3) a stage of pronounced erosion from lake level regulation and extensive ditching of the catchment area (ca. 1960–1970); and (4) a meso-eutrophic stage from ca. 1970 onwards.Acidophilous Aulacoseira distans coll. and other species typical of dystrophic, nutrient-poor lakes characterized the diatom assemblages during the first stage, and the profundal zoobenthic assemblages, characterized by Heterotrissocladius subpilosus and Micropsectra, indicated good hypolimnetic oxygen conditions and a low sedimentation of organic matter (approx. less than 50 g m^–2 a^–1). The increased loading rapidly led to changes both in diatoms and chironomids (e.g., to an early extinction of H. subpilosus in the 1950s). The process finally led to eutrophication with a successive proliferation of diatom species such as Asterionella formosa followed by Aulacoseira ambigua, Fragilaria crotonensis, and finally Melosira varians. The relative proportion of alkaliphilous species reached a maximum in the final stage and the original profundal chironomid fauna was replaced by Chironomus anthracinus gr. and C. plumosus which are typical of profundal areas suffering from temporal oxygen deficit. It is notable that the considerable decrease in waste water loading from the point sources (80–86% ) during the past two decades has not led to a recovery in the lake. This highlights the importance of diffuse loading from agriculture, forestry and other human activities even to this comparatively large lake.  相似文献   

Comparative analysis of pollution of the surface atmospheric layer in such megalopolises as Moscow and Beijing     

A. V. Andronova  M. A. Iordanskii  A. V. Trefilova  V. A. Lebedev  V. M. Minashkin  Yu. I. Obvintsev  M. S. Artamonova  I. G. Granberg 《Izvestiya Atmospheric and Oceanic Physics》2011,47(7):819-827

The results of simultaneous investigations of atmospheric aerosol in two large megalopolises—Moscow and Beijing—are presented. The purpose of these investigations was to compare parameters and reveal common characteristics of urban aerosols. Aerosol parameters were measured in the megalopolises simultaneously from October 23, 2007, through November 2, 2007. The mass concentrations of aerosols were measured continuously with a nephelometer (Mosscow) and discretely with the use of aspiration samplers according to the weight method (Moscow, Beijing). The number concentration and the particle size distribution function were determined with analyzers of the size spectrum in the interval 0.15–15.0 μm and were measured synchronously with sampling for elementary analysis. The elementary compositions of samples were determined by mass spectrometry, which made it possible to identify 60 chemical elements.  相似文献   

The age of Earth’s largest volcano: Tamu Massif on Shatsky Rise (northwest Pacific Ocean)   总被引：1，自引：0，他引：1  

Jörg Geldmacher  Paul van den Bogaard  Ken Heydolph  Kaj Hoernle 《International Journal of Earth Sciences》2014,103(8):2351-2357

This study presents laser step-heating ⁴⁰Ar/³⁹Ar age determinations of basaltic lava samples from Tamu Massif, the oldest and largest edifice of the submarine Shatsky Rise in the northwest Pacific and Earth’s proposed largest volcano. The rocks were recovered during Integrated Ocean Drilling Program Expedition 324, which cored 160 m into the igneous basement near the summit of Tamu Massif. The analyzed lavas cover all three major stratigraphic groups penetrated at this site and confirm a Late Jurassic/Early Cretaceous age for the onset of Shatsky Rise volcanism. Lavas analyzed from the lower and middle section of the hole yield plateau ages between 144.4 ± 1.0 and 143.1 ± 3.3 Ma with overlapping analytical errors (2σ), whereas a sample from the uppermost lava group produced a significantly younger age of 133.9 ± 2.3 Ma suggesting a late or rejuvenated phase of volcanism. The new geochronological data infer minimum (average) melt production rates of 0.63–0.84 km³/a over a time interval of 3–4 million years consistent with the presence of a mantle plume.  相似文献   

Optical Changes in a Eutrophic Estuary During Reduced Nutrient Loadings     

Troels Møller Pedersen  Kaj Sand-Jensen  Stiig Markager  Søren Laurentius Nielsen 《Estuaries and Coasts》2014,37(4):880-892

Loss of water clarity is one of the consequences of coastal eutrophication. Efforts have therefore been made to reduce external nutrient loadings of coastal waters. This paper documents improvements to water clarity between 1985 and 2008–2009 at four stations in the microtidal estuary Roskilde Fjord and find significant relationships to freshwater nutrient loadings. The paper then investigates to which extent changes in phytoplankton biomass (chlorophyll a (Chl a)), non-algal particulate organic matter (POM*), and residual attenuation in the water (K _b), respectively, can account for this optical improvement. Vertical light attenuation (K _d) declined, on average, by 34 %, accompanying a 71 % reduction of Chl a and an 80 % reduction of POM*. Residual attenuation declined by 26 % over the period in accordance with a measured 34 % decline of dissolved organic nitrogen. Analysis of simultaneous changes in light attenuation and Secchi depth also suggested a reduction of the scatter-to-absorption ratio over time. Considering the stronger reductions of particle concentrations than dissolved organic matter, the contribution of residual attenuation to vertical attenuation increased from 54 to 74 % in 1985 to 78 to 85 % in 2008–2009. Overall, efforts to reduce nutrient loading and improve water clarity appeared to have had a larger impact on POM* than on Chl a and colored dissolved organic matter concentrations in the estuary, which can account for the decrease in the scatter-to-absorption ratio. These optical changes lead to larger improvements of Secchi depth than of vertical light attenuation. The consequence of this is an overestimation (0.45–1.48 m) of the predicted increase of potential seagrass depth limits when based on Secchi depth rather than K _d.  相似文献   

六元体系Li–Na–K–Mg–Cl–SO₄–H₂O多温相平衡预测          下载免费PDF全文

崔瑞芝  聂国亮  Kaj Thomsen  李军  李武 《盐湖研究》2022,30(2)

采用基于扩展UNIQUAC模型的AQSOL027软件针对水盐体系Li–Na–K–Mg–Cl–SO₄–H₂O的六个五元子体系进行相平衡理论计算,首次报道了多个五元子体系在多个温度条件下的相图,将计算相图与已有实验相图以及基于其它热力学模型的计算相图进行了比较。结果表明：AQSOL027在相图计算中具有较好的准确性和可靠性。AQSOL027是一款基于Excel、用于计算复杂多温水-盐体系Li–Na–K–Mg–Ca–H–Cl–(HSO₄/SO₄)–(CO₂/HCO₃/CO₃)–(H₃BO₃/B₄O₇/BO₂)–OH–H₂O的计算机软件,集成了扩展UNIQUAC模型和相平衡算法,该软件可结合SysCAD和Aspen过程模拟器,实现盐田工艺过程的计算机辅助设计。  相似文献   

Time-scales for magmatic differentiation at the Snaefellsjökull central volcano, western Iceland: Constraints from U-Th-Pa-Ra disequilibria in post-glacial lavas     

Thomas Find Kokfelt  Kaj Hoernle  Folkmar Hauff 《Geochimica et cosmochimica acta》2009,73(4):1120-136

We present major and trace element and Sr-Nd-Pb and U-Th-Pa-Ra isotope data for a small sample suite of primarily post-glacial, mildly alkalic volcanic rocks from the Snaefellsjökull central volcano situated off the main rift systems in western Iceland. The volcanic rocks are crystal-poor and range from olivine alkali basalt to trachyte and show tight correlations of major and trace elements that are explained by fractional crystallization involving removal of olivine, plagioclase, clinopyroxene, Fe-Ti oxide and apatite. Sr-Nd-Pb isotopes are practically invariant, consistent with derivation from the same source region. During fractionation from primitive basalt to evolved trachyte, (²³⁰Th/²³²Th), (²³⁰Th/²³⁸U) and (²³¹Pa/²³⁵U) decrease progressively at broadly constant (²³⁸U/²³²Th). A continuous closed-system fractionation model that assumes constant initial (²³⁰Th/²³²Th) in the basaltic precursor melt indicates that hawaiite was derived from olivine basalt by ∼50% fractional crystallization within and trachyte by ∼80% fractionation within . An overrepresentation of evolved basalts and hawaiites with young inferred magma ages in the dataset is consistent with the parental precursor to these magmas intruded into the sub-volcanic magma plumbing system as a consequence of lithospheric rebound caused by deglaciation. Lavas affected by apatite removal have higher (²³¹Pa/²³⁵U) than predicted for simple radioactive decay, suggesting apatite significantly fractionates U from Pa. The proposed fractionation model consistently explains our U-series data assuming and and . If applicable, these D values would indicate that the effect of apatite fractionation must be adequately considered when assessing differentiation time scales using (²³¹Pa/²³⁵U) disequilibria data.  相似文献   

The role and conditions of second-stage mantle melting in the generation of low-Ti tholeiites and boninites: the case of the Manihiki Plateau and the Troodos ophiolite     

Roman?Golowin  Maxim?PortnyaginEmail author  Kaj?Hoernle  Alexander?Sobolev  Dimitry?Kuzmin  Reinhard?Werner 《Contributions to Mineralogy and Petrology》2017,172(11-12):104

High-Mg, low-Ti volcanic rocks from the Manihiki Plateau in the Western Pacific share many geochemical characteristics with subduction-related boninites such as high-Ca boninites from the Troodos ophiolite on Cyprus, which are believed to originate by hydrous re-melting of previously depleted mantle. In this paper we compare the Manihiki rocks and Troodos boninites using a new dataset on the major and trace element composition of whole rocks and glasses from these locations, and new high-precision, electron microprobe analyses of olivine and Cr-spinel in these rocks. Our results show that both low-Ti Manihiki rocks and Troodos boninites could originate by re-melting of a previously depleted lherzolite mantle source (20–25% of total melting with 8–10% melting during the first stage), as indicated by strong depletion of magmas in more to less incompatible elements (Sm/Yb < 0.8, Zr/Y < 2, Ti/V < 12) and high-Cr-spinel compositions (Cr# > 0.5). In comparison with Troodos boninites, the low-Ti Manihiki magmas had distinctively lower H₂O contents (< 0.2 vs. > 2 wt% in boninites), ~ 100 °C higher liquidus temperatures at a given olivine Fo-number, lower fO₂ (ΔQFM < + 0.2 vs. ΔQFM > + 0.2) and originated from deeper and hotter mantle (1.4–1.7 GPa, ~ 1440 °C vs. 0.8–1.0 GPa, ~ 1300 °C for Troodos boninites). The data provide new evidence that re-melting of residual upper mantle is not only restricted to subduction zones, where it occurs under hydrous conditions, but can also take place due to interaction of previously depleted upper mantle with mantle plumes from the deep and hotter Earth interior.  相似文献   

Whole-stream metabolism in nutrient-poor calcareous streams on Öland,Sweden     

Anette B. Alnoee  Tenna Riis  Mikkel R. Andersen  Annette Baattrup-Pedersen  Kaj Sand-Jensen 《Aquatic Sciences - Research Across Boundaries》2015,77(2):207-219

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Geochemistry of a new enriched mantle type locality in the northern hemisphere: Implications for the origin of the EM-I source     

Jörg Geldmacher  Kaj Hoernle  Andreas Klügel  Paul van den Bogaard  Ilya Bindeman 《Earth and Planetary Science Letters》2008,265(1-2):167-182

Late Cretaceous (66.2 ± 0.5 Ma amphibole and 66.7 ± 0.2 Ma phlogopite ⁴⁰Ar/³⁹Ar ages) nephelinitic volcanic rocks from Godzilla Seamount in the eastern North Atlantic (34°N latitude) have trace element and Sr–Nd–Pb–Hf-isotope compositions similar to the Enriched Mantle I (EM-I) endmember, except for their low ²⁰⁷Pb/²⁰⁴Pb relative to ²⁰⁶Pb/²⁰⁴Pb ratios (²⁰⁶Pb/²⁰⁴Pb_in = 17.7, ²⁰⁷Pb/²⁰⁴Pb_in = 15.34) plotting below the Northern Hemisphere Reference Line on the uranogenic Pb isotope diagram. O isotope data on amphibole separates are mantle-like (δ¹⁸O = 5.6–5.8‰). Age and location of the isolated Godzilla Seamount, however, preclude it from being derived from the Madeira or Canary hotspots, making a lower-mantle origin unlikely. Therefore we propose derivation from a shallow (lithospheric/asthenospheric) melting anomaly. As observed in mid-ocean-ridge and ocean-island basalts, there is a systematic decrease of ²⁰⁷Pb/²⁰⁴Pb ratios (and Δ7/4) in the individual EM-I endmember type localities towards northern latitudes with Godzilla lying on the extension of this trend. This trend is mirrored in ultra-potassic volcanic rocks such as lamproites and kimberlites, which reflect the composition of enriched subcontinental lithospheric mantle. Therefore, a global pattern in ²⁰⁷Pb/²⁰⁴Pb ratios and Δ7/4 is suggested. The geochemical composition of EM-I endmember type localities, including Godzilla lavas, and the enriched (DUPAL) anomaly in the southern hemisphere could reflect derivation from ancient, metasomatized subcontinental lithospheric mantle. We propose a two-stage model to explain the trace element and isotopic composition of the EM-I mantle endmember localities worldwide: 1) during the early history of the Earth, subcontinental lithosphere was metasomatized by melts from subducted slabs along convergent margins generating high μ (²³⁸U/²⁰⁴Pb) sources, and 2) as the Earth cooled, hydrous fluids replaced hydrous melts as the main slab component metasomatizing the subcontinental lithospheric mantle (generating EM-I sources with lower μ). In accordance with this model, the global variations in ²⁰⁷Pb/²⁰⁴Pb ratios and Δ7/4 could reflect geographic differences in μ and/or the age at which the transition from stages 1 to 2 took place in the Archaean lithosphere. The model would require a re-definition of the EM-I endmember to low ²⁰⁶Pb/²⁰⁴Pb, high ²⁰⁸Pb/²⁰⁴Pb (positive Δ8/4) but variable ²⁰⁷Pb/²⁰⁴Pb (positive and negative Δ7/4).  相似文献