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Earth and Planetary Science Letters
North-Holland
Earth and Planetary Science Letters

North-Holland

0012-821X

Earth and Planetary Science Letters/Journal Earth and Planetary Science LettersSCIEIAHCIISTP
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    Hydrous silicate melts and the deep mantle H2O cycle

    Drewitt, James W. E.Walter, Michael J.Brodholt, John P.Muir, Joshua M. R....
    13页
    查看更多>>摘要：We report ab initio atomistic simulations of hydrous silicate melts under deep upper mantle to shallow lower mantle conditions and use them to parameterise density and viscosity across the ternary system MgO-SiO2-H2O (MSH). On the basis of phase relations in the MSH system, primary hydrous partial melts of the mantle have 40-50 mol% H2O. Our results show that these melts will be positively buoyant at the upper and lower boundaries of the mantle transition zone except in very iron-rich compositions, where greater than or similar to 75% Mg is substituted by Fe. Hydrous partial melts will also be highly inviscid. Our results indicate that if melting occurs when wadsleyite transforms to olivine at 410 km, melts will be buoyant and ponding of melts is unexpected. Box models of mantle circulation incorporating the upward mobility of partial melts above and below the transition zone suggest that the upper mantle becomes efficiently hydrated at the expense of the transition zone such that large differences in H2O concentration between the upper mantle, transition zone and lower mantle are difficult to maintain on timescales of mantle recycling. The MORB source mantle with similar to 0.02-0.04 wt% H2O may be indicative of the H2O content of the transition zone and lower mantle, resulting in a bulk mantle H2O content of the order 0.5 to 1 ocean mass, which is consistent with geochemical constraints and estimates of subduction ingassing. (c) 2022 The Author(s). Published by Elsevier B.V.
      原文链接:
    • NSTL
    • Elsevier

    Martian hydrothermal fluids recorded in the Sm-Nd isotopic systematics of apatite in regolith breccia meteorites

    Shang, ShengHui, HejiuYang, YuehengChen, Tianyu...
    12页
    查看更多>>摘要：The observations of Martian orbiters and rovers have suggested that there were fluids on the surface of early Mars. However, the geochemical properties of those fluids are unclear. The Martian regolith breccia meteorites (MRB), the source materials of which are thought to have formed at 4.4 Ga, may have recorded interactions with fluids on Mars. Here, we have analyzed the in situ Sm-Nd isotopic compositions and trace element contents of apatite in MRB and have obtained a Sm-Nd isochron age of 1490 +/- 480 Ma. This young age indicates that the MRB apatites were altered by fluids and have exchanged trace elements with fluids. The very negative initial epsilon Nd-143, combined with the previously reported positive delta D and delta Cl-37 in the MRB apatites, indicate that Martian fluids originated from a geochemically enriched reservoir in the crust. The large ranges of rare earth element abundance (Sigma REE) and of the chondrite normalized ratio of La and Yb [(La/Yb)(N)] indicate the chemical complexity of the fluids that interacted with the apatites in the MRB. The apatite REE compositions were used to further determine the pH values of Martian fluids equilibrated with the MRB apatites, which varied from similar to 3 to similar to 8. The apatite X-site Cl contents indicate that the Cl contents in Martian fluids in equilibrium with the MRB apatites at 400 degrees C and 1 bar could be up to 1857 ppm, within the range of terrestrial hydrothermal fluids. Combined with previously reported geochemical data from Martian meteorites, our study suggests that fluids may have been present throughout the early geological history of Mars. (C) 2022 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Major Early-Middle Devonian oceanic oxygenation linked to early land plant evolution detected using high-resolution U isotopes of marine limestones

    Elrick, MayaGilleaudeau, Geoffrey J.Romaniello, Stephen J.Algeo, Thomas J....
    11页
    查看更多>>摘要：The middle Paleozoic (similar to 420-350 Myr) records a major increase in ocean-atmosphere oxygen levels; however, the timing and pattern of oxygenation are poorly constrained. Two well-dated North American locations in Nevada and Illinois were used to generate a high-resolution U-isotopic profile (delta U-238) spanning similar to 70 Myr of the middle Paleozoic. Stratigraphic and geochemical data support the interpretation that the Nevada profile represents a near-primary record of global-ocean redox variations. First-order delta U-238 trends indicate strongly reducing oceans during the late Silurian and Early Devonian, terminated by a major oxygenation event near the Emsian-Eifelian boundary (similar to 395 Ma). More oxic seawater conditions persisted for the next 30+ Myr, but were punctuated by multiple Myr-scale anoxic events during the Middle-Late Devonian and Early Mississippian that correlate with known global biotic crises, positive delta C-13 excursions, and widespread organic-rich facies deposition. The timing of the similar to 395 Ma oxygenation event suggests that the O-2 rise was the result of increased photosynthesis and organic carbon burial linked to diversification of late Silurian to earliest Middle Devonian terrestrial plants, rather than to subsequent Devonian increases in terrestrial plant root depth, tree height, lignin content, or seed reproduction. These findings demonstrate that early colonization of continents by relatively small, shallowly rooted plants with geographically limited ranges was sufficient to drive long-term oxygenation of the ocean-atmosphere system, paving the way for the evolution of large, mobile animals that have dominated the Earth's surface since the middle Paleozoic. (c) 2022 The Author(s). Published by Elsevier B.V.
      原文链接:
    • NSTL
    • Elsevier

    Mercury isotope evidence for regional volcanism during the Frasnian-Famennian transition

    Zhao, HeShen, JunAlgeo, Thomas J.Racki, Grzegorz...
    13页
    查看更多>>摘要：Mercury (Hg) concentrations and isotopes are widely used as proxies for volcanic inputs to paleodepositional systems. Enhanced volcanism during the Late Devonian was previously mainly inferred in the western Paleo-Tethys Ocean region from high Hg enrichments around the Upper Kellwasser horizon (UKW) and Frasnian-Famennian Boundary (FFB). In this study, we generated high-resolution Hg concentration data for four UKW-FFB sections (Walnut Creek and Dupont-GHS in the U.S.A., and Yangdi and Nandong in South China) and Hg isotope data for two of them (Walnut Creek and Nandong) in order to test the geographic distribution and stratigraphic range of volcanic inputs during the Frasnian-Famennian transition. Within the uppermost Frasnian Palmatolepis linguiformis Zone and the lowermost Famennian Lower Pa. triangularis Zone, Nandong (Paleo-Tethys Ocean) exhibits enrichment factors (HgEF > 2) and mass independent fractionations (MIF) of odd isotopes (Delta Hg-199 -0 parts per thousand) that are consistent with significant volcanic inputs. Positive Delta Hg-199 values and an absence of Hg enrichments in the equivalent stratigraphic intervals at Walnut Creek and Dupont-GHS (peri-Panthalassic region) indicate that Late Devonian volcanism was a regional rather than a global phenomenon, and that it may have been associated with subduction zones and/or a large igneous province (LIP) of limited size in the Paleo-Tethyan region rather than with a major continental LIP of potentially global significance. (c) 2022 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Delayed Be-10 dilution in detrital quartz following extensive coseismic landsliding: A 2016 Kaikoura earthquake case study

    Wilkinson, ClareStahl, TimothyJones, KatieFujioka, Toshiyuki...
    12页
    查看更多>>摘要：Large earthquakes play a major role in the topographic evolution of active orogens. Earthquake induced landslides can alter the mass balance of mountain belts for decades to centuries depending on how landslide material is transported and stored. In this study, we analysed in-situ Be-10 concentrations in fluvial sediments to capture a time series of post-earthquake denudation rates of the Tutae Putaputa vertical bar Conway River catchment, which experienced similar to 13 x 10(6) m(3) of landsliding in the 2016 Kaikoura earthquake. Be-10 concentrations were determined for detrital samples from the Conway River at the rangefront of the Seaward Kaikoura Mountains, South Island, New Zealand, and near the catchment outlet over three sampling intervals, including after significant precipitation events, 1-2 yr following the earthquake. Our results indicate somewhat higher apparent erosion rates at the rangefront (0.41-0.58 mm/yr) when compared to erosion rates incorporating lower-relief sub-catchments at the river outlet (similar to 0.28 mm/yr). No changes were found over the same time period in the Hurunui River, a neighbouring catchment that experienced negligible coseismic landsliding during the Kaikoura event. Apparent catchment-averaged erosion rates in the Conway River have remained similar to long-term exhumation rates from previously published thermochronology studies. To explain our results, we explore the observed controls on catchment-wide Be-10 concentrations in our study area, such as the spatiotemporal variability in landslide connectivity to the channel and storage within the catchment. Our results highlight that using in-situ cosmogenic Be-10 in fluvial deposits as a proxy for changes in sediment fluxes of earthquake-affected landscapes is complex and highly site-specific. (C) 2022 The Authors. Published by Elsevier B.V.
      原文链接:
    • NSTL
    • Elsevier

    Fractionation of rhenium isotopes in the Mackenzie River basin during oxidative weathering (vol 573, 117131, 2021)

    Dellinger, MathieuHilton, Robert G.Nowell, Geoff M.
    1页
      原文链接:
    • NSTL
    • Elsevier

    Ice age effects on the satellite-derived (J) over dot(2) : Mapping the sensitivity to 3D variations in mantle viscosity

    Kim, A. J.Crawford, O.Al-Attar, D.Lau, H. C. P....
    7页
    查看更多>>摘要：Studies of glacial isostatic adjustment (GIA) based on spherically symmetric viscoelastic Earth models have argued that the rate of change of the degree 2 zonal harmonic of the Earth's geopotential, or (J)over dot(2), provides an important constraint on mean viscosity in the deep mantle (Mitrovica and Peltier, 1993; Nakada et al., 2015; Lau et al., 2016). To refine this constraint, we compute Frechet kernels using an adjoint methodology that reveal the sensitivity of the datum to 3D variations in mantle viscosity. We demonstrate that the mantle sensitivity of the datum is largely limited to the region below the ancient Laurentide ice sheet that covered Canada and significant portions of the northeastern United States at Last Glacial Maximum (LGM). In the bottom half of the lower mantle, this region of maximum sensitivity lies outside the location of Large Low Shear Velocity Provinces (LLSVPs) imaged from seismic tomographic studies. Thus, if the low shear velocity of these provinces originates from thermal effects, previous inferences of viscosity based upon the (J)over dot(2) datum are likely higher than the actual mean viscosity of the lower mantle.(c) 2022 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Diffusive fractionation of K isotopes in molten basalts

    Zhang, Youxue
    10页
    查看更多>>摘要：The K-41/K-39 isotope ratio profiles in diffusion couple experiments have been measured by Secondary Ion Mass Spectrometry (SIMS). One goal of this research is to push the use of SIMS in measuring non-traditional stable isotope ratios. The second, more important goal, is to quantify for the first time diffusive fractionation of K isotopes and its dependence on temperature and different counter-diffusion elements. The data show that the precision in a single day-night session of SIMS measurements can reach 0.2 parts per thousand (1cr hereafter) with effort, and the long-term accuracy without using any isotope ratio standard is about 2.5 parts per thousand. At an initial concentration contrast (ratio of high concentration to low concentration) of about 70 in a diffusion couple, the total K-41/K-39 fractionation (maximum minus minimum) is about 10 parts per thousand. The 41K/39K ratio profiles were initially fit by assuming constant effective binary diffusivity (D) of K2O, which led to minor misfits and more importantly, to large disagreement between diffusivities based on chemical diffusion and isotope diffusion profiles. It was found that D for K2O varies with its concentration. The profiles were then fit by assuming D for K2O increases exponentially with K2O concentration, which resolved the misfits and disagreements. That is, combining concentration and isotope ratio profiles enables distinguishing subtle concentration-dependent diffusivity. For the SiO2-K2O interdiffusion couples, the empirical diffusive isotope fractionation parameter beta increases slightly with temperature from 0.104 +/- 0.003 at 1260 C to 0.116 +/- 0.003 at 1500 C. For the MgO-K2O interdiffusion couples, excluding an outlier point at 1260 C, beta increases from 0.090 +/- 0.005 at 1350 C to 0.100 +/- 0.003 at 1500 C. These beta values are roughly consistent with a diffusion mechanism of NaKO exchanging with SiO2 in the SiO2-K2O interdiffusion couples, or NaKO exchanging with MgO in the MgO-K2O interdiffusion couples. Applying the obtained beta value to model diffusive isotope fractionation in nature, diffusive K isotope fractionation during magma mixing is expected to be large enough to be resolvable by SIMS. When collecting samples for K-Ar or K-Ca dating, it is important to correct for the effect of possible K isotope fractionation by measuring K isotope ratio in the sample. When diffusive and convective diffusive modeling was applied to evaluate isotope fractionation during volatile loss through diffusion and evaporation, it is found that a loss of 80% potassium would lead to an increase of 841K by 6.3 parts per thousand to 8.9 parts per thousand , more than 10 times greater than the enrichment of 841K in the Moon relative to the Earth. Hence, the depletion of K and the associated enrichment of 841K in the Moon relative to the Earth are unlikely diffusion controlled. (c) 2022 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Diffusion rates of hydrogen defect species associated with site-specific infrared spectral bands in natural olivine

    Li, Yang (Will)Mackwell, Stephen J.Kohlstedt, David L.
    13页
    查看更多>>摘要：We investigated hydrogen transport in naturally occurring, iron-bearing samples of San Carlos olivine that were hydrogenated at confining pressures of 200 or 300 MPa and 1173 to 1303 K or dehydrogenated at room pressure and 1191 to 1358 K. Chemical diffusion coefficients were determined from diffusion profiles for individual O-H-stretching bands from series of infrared spectra in orthogonal directions across each sample. Within experimental uncertainty, the diffusivities associated with all the individual bands are in good agreement with one another in both the hydrogenation and the dehydrogenation experiments. Hydrogenation proceeds by two diffusion mechanisms, as reported previously. The faster process involves interstitial diffusion of protons coupled with a counter-flux of polarons, with proton diffusion rate-limiting hydrogenation. For this mechanism, diffusion is faster along the olivine [100] direction than along [010] and [001], consistent with the anisotropy reported for proton diffusion and conductivity in olivine. The slower process involves interstitial proton diffusion coupled with a parallel flux of metal vacancies, with vacancy diffusion rate-limiting hydrogenation. For this mechanism, diffusion is faster along [001] than along [100] and [010], consistent with the anisotropy previously reported for the diffusion of metal cations in olivine. Diffusivities from our new dehydrogenation experiments are identical in both magnitude and anisotropy to those determined in our earlier hydrogenation experiments. This agreement demonstrates the validity of studies that used the results of our hydrogenation experiments to analyze dehydrogenation profiles in olivine xenocrysts and olivine in mantle xenoliths to determine rates of magma ascent from the source regions in Earth's interior. (C) 2022 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Towards composition of carbonatite melts in peridotitic mantle

    Shatskiy, AntonBekhtenova, AltynaPodborodnikov, Ivan, VAreflev, Anton V....
    11页
    查看更多>>摘要：It is generally accepted that carbonatite metasomatism in the subcontinental lithospheric mantle (SCLM) inevitably causes wehrlitization of the primary lherzolite substrate. However, the K-rich carbonatite inclusions in kimberlitic diamonds containing orthopyroxene indicate that this is not always the case. In the present study, we equilibrated natural garnet lherzolite with carbonate melts containing 33-38 wt% K2O with various Ca# = 10, 20, 30, and 40 at 6 GPa and 1200-1500 degrees C, where Ca# = 100.Ca/(Ca+Mg+Fe). The original ratio of peridotite to carbonate was 58 to 42 by weight. In the studied temperature range, the melt retains essentially carbonate composition with silica content increasing from 1 to 11-12 wt%. The melt with Ca# 10 alters lherzolite to harzburgite, replacing clinopyroxene by orthopyroxene and decreasing CaO content in garnet below 4 wt%. The melts with Ca# 20-30 also consume clinopyroxene; although CaO content in garnet remains in the range of lherzolitic compositions. The melt with Ca# 40 yields wehrlitization, consuming orthopyroxene, increasing clinopyroxene fraction, and increasing CaO content in garnet above 6 wt%. After the interaction, the Ca# of the melt changes as follows 10 -> 16-28, 20 -> 20-33, 30 -> 27-34, and 40 -> 30-34. The olivine + orthopyroxene + clinopyroxene + garnet assemblage was found in equilibrium with carbonatite melt with Ca# 34 at 1200 degrees C and Ca# 30 at 1400 degrees C. Thus, K-rich (26-35 wt% K2O) carbonatite melts with Ca# = 30-34 can appear in equilibrium with garnet lherzolite, while the melts with Ca# < 30 and > 34 can be in equilibrium with harzburgite and wehrlite, respectively, at 6 GPa and 1200-1400 degrees C. Considering that Ca-Mg-Fe carbonates do not melt at the geothermal conditions of the SCLM, while sodic, dolomitic melt causes wehrlitization, high-Mg (Ca# < 35) K-rich dolomitic melt is the only possible carbonatite fluids that are thermodynamically stable in equilibrium with garnet harzburgites and lherzolites in the SCLM at a depth of about 200 km. At higher temperatures corresponding to the underlying asthenosphere, the high alkalinity ceases to be a requirement for the stability of the carbonate melt. Nevertheless, the regularities established here for the K-rich melts remain valid for less alkaline (4-15 wt% Na2O+K2O) primary kimberlite (i.e., mantle carbonatite) melts in the sublithospheric mantle. (C) 2022 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier