Extinct isotope heterogeneities in the mantles of Earth and Mars: Implications for mantle stirring rates          下载免费PDF全文

Stein B. Jacobsen  Gang Yu 《Meteoritics & planetary science》2015,50(4):555-567

Heterogeneities in terrestrial samples for ¹⁸²W/¹⁸³W and ¹⁴²Nd/¹⁴⁴Nd are only preserved in Hadean and Archean rocks while heterogeneities in ¹²⁹Xe/¹³⁰Xe and ¹³⁶Xe/¹³⁰Xe persist to very young mantle‐derived rocks. In contrast, meteorites from Mars show that the Martian mantle preserves heterogeneities in ¹⁸²W/¹⁸³W and ¹⁴²Nd/¹⁴⁴Nd up to the present. As a consequence of the probable “deep magma ocean” core formation process, we assume that the Earth and Mars both had a very early two‐mantle‐reservoir structure with different initial extinct nuclide isotopic compositions (different ¹⁸²W/¹⁸³W, ¹⁴²Nd/¹⁴⁴Nd, ¹²⁹Xe/¹³⁰Xe, ¹³⁶Xe/¹³⁰Xe ratios). Based on this assumption, we developed a simple stochastic model to trace the evolution of a mantle with two initially distinct layers for the extinct isotopes and its development into a heterogeneous mantle by convective mixing and stretching of these two layers. Using the extinct isotope system ¹⁸²Hf‐¹⁸²W, we find that the mantles of Earth and Mars exhibit substantially different mixing or stirring rates. This is consistent with Mars having cooled faster than the Earth due to its smaller size, resulting in less efficient mantle mixing for Mars. Moreover, the mantle stirring rate obtained for Earth using ¹⁸²Hf‐¹⁸²W is consistent with the mantle stirring rate of ~500 Myr constrained by the long‐lived isotope system, ⁸⁷Rb‐⁸⁷Sr and ¹⁴⁷Sm‐¹⁴³Nd. The apparent absence of ¹⁸²W/¹⁸³W isotopic heterogeneity in modern terrestrial rocks is attributed to very active mantle stirring which reduced the ¹⁸²W/¹⁸³W isotopic heterogeneity to a relatively small scale (~83 m for a mantle stirring rate of 500 Myr) compared to the common sampling scale of terrestrial basalts (~30 or 100 km). Our results also support the “deep magma ocean” core formation model as being applicable to both Mars and Earth.  相似文献   

Isotopic climate record in a Holocene stalagmite from Ursilor Cave (Romania)     

Bogdan Petroniu Onac  Silviu Constantin  Joyce Lundberg  Stein‐Erik Lauritzen 《第四纪科学杂志》2002,17(4):319-327

The PU‐2 stalagmite from Ursilor Cave provides the first dated Romanian isotope record for the Holocene. The overall growth rate of the speleothem was 3.5 cm kyr^?1, corresponding to a temporal resolution of 142 y between each isotope analysis. The ‘Hendy’ tests indicate that isotopic equilibrium conditions occurred during the formation of PU‐2, and hence that it is suitable for palaeoclimatic studies. The relationship between δ¹⁸O and temperature was found to be positive. This can be interpreted either as rain‐out with distance from the west‐northwest ocean source of evaporation or shifts in air mass source with changing North Atlantic Oscillation indices. Applying five U–Th thermal ionisation mass spectrometric (TIMS) dates to a 17.5 cm isotope profile (δ¹⁸O and δ¹³C) along the stalagmite growth axis enabled a tentative interpretation of the palaeoclimate signal over the past 7.1 kyr. Spikes of depleted isotopic δ¹⁸O values are centred near ca. 7, ca. 5.2 and ca. 4 ka, reflecting cool conditions. The record shows two warm intervals between ca. 3.8 and ca. 3.2 ka (the maximum warmth) and from ca. 2 to ca. 1.4 ka, when the δ¹⁸O values were less negative than present. The ‘Holocene Climate Optimum’ spanning the time interval from ca. 6.8 to ca. 4.4 ka is not well expressed in the PU‐2 stalagmite. Individual spikes of lighter δ¹³C are interpreted as indicative of periods of heavy rainfall, at ca. 7, ca. 5.5, and ca. 3.5 ka. The overall trend to lighter δ¹³C in the PU‐2 stalagmite may reflect a gradual decrease in water–rock interaction. The results demonstrate that the effect of North Atlantic oceanic changes extended to the investigated area. Nevertheless, some differences in temporal correlation and intensity of stable isotopic response to these climatic events have been found, but the exact nature of these differences and the underlying mechanism is yet to be determined. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Source apportionment for African dust outbreaks over the Western Mediterranean using the HYSPLIT model     

M. Escudero  A.F. Stein  R.R. Draxler  X. Querol  A. Alastuey  S. Castillo  A. Avila 《Atmospheric Research》2011,99(3-4):518-527

A source apportionment technique has been applied to determine the geographical distribution of emissions in Northern Africa contributing to dust outbreaks that yield high PM10 levels at Spanish regional background stations. Seven dust episodes have been analyzed in this study. Total suspended particles have been sampled and chemically analyzed for these events at La Castanya background station (Montseny, NE Spain) and differences in the composition of airborne dust have been studied. The dominant role of northern and western source areas (Tunisia, Algeria, Mauritania and the Western Sahara) contrasted with the negligible contribution of major emission source areas such as the Bodelé depression, Libya, Niger, and Sudan. During the simulated events using the dust module of the HYSPLIT model, material from the latter regions is persistently transported across the Atlantic but not towards Western Europe. As a consequence, the composition of the dust turned out to be quite homogeneous since the mixing of dust occurs from various source areas with similar chemical composition. However, differences in Ca/Al ratios have been found in a number of samples that are mainly explained by vertical transport segregation of clay minerals (relatively richer in Al) from coarser dust particles (Ca-carbonate).  相似文献   

Experimental data on SOA formation from mixtures of anthropogenic and biogenic organic compounds     

M.G. Vivanco  M. Santiago  M. Sánchez  M.A. Clavero  E. Borrás  M. Ródenas  F. Alacreu  M. Vázquez  E. Clemente  R. Porras  A. Muñoz  A. Stein 《Atmósfera》2013,26(1):59-73

Secondary organic aerosols (SOA) constitute a significant fraction of the atmospheric particulate matter. Theses particles are formed as a consequence of the oxidation reaction of certain organic gases that leads to the formation of low-volatility compounds. As for other pollutants, air quality models allow the simulation of particle levels and thus models constitute a powerful tool in air quality management. Nevertheless, the accepted use of models must be based on the validation of its capacity to reproduce observed concentrations. Air monitoring sites provide measured information of a large variety of ambient pollutants. Unfortunately, measurements on SOA are not normally available, as current monitoring networks do not include instrumentation to distinguish primary from secondary sources of organic carbonaceous aerosol. This paper presents a set of photooxidation experiments performed in the European Photorreactor (EUPHORE) smog chamber (CEAM, Spain) under different experimental conditions to investigate SOA formation. The use of chambers allows the isolation of atmospheric chemistry and aerosol formation processes. Thus, although these measurements were obtained at initial precursor concentrations higher than those in atmospheric conditions, they constitute a valuable set of information for SOA model evaluation purposes.  相似文献   

Application of Re-Os Geochemistry to Sedimentary Basin: Stratigraphic Correlation, Oil - Source Correlation and Paleo-Environment Condition     

XU Guangping  Judith L. Hannah  Holly J. Stein  Svetoslav Georgiev 《《地质学报》英文版》2013,87(Z1):602-604

  相似文献   

Assessment of a conceptual hydrological model and artificial neural networks for daily outflows forecasting     

M. Rezaeianzadeh  A. Stein  H. Tabari  H. Abghari  N. Jalalkamali  E. Z. Hosseinipour  V. P. Singh 《International Journal of Environmental Science and Technology》2013,10(6):1181-1192

Artificial neural networks (ANNs) are used by hydrologists and engineers to forecast flows at the outlet of a watershed. They are employed in particular where hydrological data are limited. Despite these developments, practitioners still prefer conventional hydrological models. This study applied the standard conceptual HEC-HMS’s soil moisture accounting (SMA) algorithm and the multi layer perceptron (MLP) for forecasting daily outflows at the outlet of Khosrow Shirin watershed in Iran. The MLP [optimized with the scaled conjugate gradient] used the logistic and tangent sigmoid activation functions resulting into 12 ANNs. The R ² and RMSE values for the best trained MPLs using the tangent and logistic sigmoid transfer function were 0.87, 1.875 m³ s^?1 and 0.81, 2.297 m³ s^?1, respectively. The results showed that MLPs optimized with the tangent sigmoid predicted peak flows and annual flood volumes more accurately than the HEC-HMS model with the SMA algorithm, with R ² and RMSE values equal to 0.87, 0.84 and 1.875 and 2.1 m³ s^?1, respectively. Also, an MLP is easier to develop due to using a simple trial and error procedure. Practitioners of hydrologic modeling and flood flow forecasting may consider this study as an example of the capability of the ANN for real world flow forecasting.  相似文献   

Dolomitic slates from Uruguay: petrophysical and petromechanical characterization and deposit evaluation     

Manuela Morales Demarco  Pedro Oyhantçabal  Karl-Jochen Stein  Siegfried Siegesmund 《Environmental Earth Sciences》2013,69(4):1361-1395

Slates are internationally known as roof and façade-cladding material since prehistoric times. The methods required to mine and manufacture these dimensional stones are relatively simple in comparison to those utilized in granitic dimensional stones. This has led to a worldwide rentable commercialization of slate in the last centuries and also to the development of characteristic cultural landscapes. In Uruguay several slates are mined and used in architecture, especially as façade cladding and floor slabs. The most important slates regarding their production and utilization are the dolomitic slates. These dolomitic slates are associated with the Neoproterozoic thrust and fold belt of the Dom Feliciano belt. Representative samples have been geochemically and petrographically characterized, as well as petrophysically and petromechanically analyzed. The petrophysical and petromechanical properties were investigated in a very systematic way with respect to the new European standards, showing values comparable to those registered for internationally known slates. Detailed structural and deposit analysis were carried out in Uruguay in order to evaluate the dolomitic slate deposits. The slates are linked to calc-silicate strata in a greenschist facies volcano-sedimentary sequence and the deposits are located in the limb of a regional fold, where bedding and cleavage are parallel. The main lithotype is a layered and fine-grained dolomitic slate with a quite diverse palette of colors: light and dark green, gray, dark gray, reddish and black. The mined slate is split into slabs 0.5–2 cm thick. In the past, the average production in Uruguay was around 4,000 tons/year and a historical maximum of 13,000 tons was reached in 1993 (Oyhantçabal et al. in Z dt Ges Geowiss 158(3):417–428, 2007). The oscillations in the regional demand were the cause of several flourishing and decay cycles in the activity, but our investigation shows a considerable volume of indicated resources and therefore a very good potential.  相似文献   

Comparing the Hawkes and Trigger Process Models for Aftershock Sequences Following the 2005 Kashmir Earthquake     

K. Türkyilmaz  M. N. M. van Lieshout  A. Stein 《Mathematical Geosciences》2013,45(2):149-164

In an earlier study (Van Lieshout and Stein in Math Gesoci 44(3):309–326, 2012) we postulated the existence of two major earthquakes in the 2005 Kashmir disaster instead of a single one, based upon the pattern of aftershocks. In this study, we explore this hypothesis further by fitting several spatial point pattern models. In particular, we discuss the Hawkes and the trigger process models for earthquake aftershock sequences following the Kashmir catastrophe in 2005. The minimum contrast method is used for estimation of the parameters. The study shows that the trigger model fits better than the Hawkes model. The most likely number of main shocks is rounded to 2 generating the almost 200 aftershocks, whereas the Hawkes model would estimate a parent process of approximately 18 parents with on average about 10 descendants. We conclude that the spatial pattern of aftershocks can best be understood as a mixture of two bivariate normal distributions centered around two major shocks and estimate the parameters.  相似文献   

Identifying factors of influence in the spatial distribution of domestic fires     

Olga Špatenková  Alfred Stein 《International journal of geographical information science》2013,27(6):841-858

Domestic fires at the city level, being causes for casualties and causing significant material damages, are stored as a point pattern in a GIS. In this paper we apply a statistical point pattern analysis to derive major causes from related layers of information. We fit a G-function to analyse neighbourhood relations and a Strauss process for inferring causal relations. Using open-source software we find significant differences in patterns and explaining factors between the different parts of the day, in particular for different building types and income groups. We conclude that a quantitative spatial model can be fitted and that this provides a useful opportunity for fire brigades to improve planning their efforts.  相似文献   

Forsterite‐bearing type B refractory inclusions from CV3 chondrites: From aggregates to volatilized melt droplets     

Emma S. BULLOCK  Glenn J. MacPHERSON  Kazuhide NAGASHIMA  Alexander N. KROT  Michail I. PETAEV  Stein B. JACOBSEN  Alexander A. ULYANOV 《Meteoritics & planetary science》2012,47(12):2128-2147

Abstract– Detailed petrologic and oxygen isotopic analysis of six forsterite‐bearing Type B calcium‐aluminum‐rich inclusions (FoBs) from CV3 chondrites indicates that they formed by varying degrees of melting of primitive precursor material that resembled amoeboid olivine aggregates. A continuous evolutionary sequence exists between those objects that experienced only slight partial melting or sintering through objects that underwent prolonged melting episodes. In most cases, melting was accompanied by surface evaporative loss of magnesium and silicon. This loss resulted in outer margins that are very different in composition from the cores, so much so that in some cases, the mantles contain mineral assemblages that are petrologically incompatible with those in the cores. The precursor objects for these FoBs had a range of bulk compositions and must therefore have formed under varying conditions if they condensed from a solar composition gas. Five of the six objects show small degrees of mass‐dependent oxygen isotopic fractionation in pyroxene, spinel, and olivine, consistent with the inferred melt evaporation, but there are no consistent differences among the three phases. Forsterite, spinel, and pyroxene are ¹⁶O‐rich with Δ¹⁷O ～ ?24‰ in all FoBs. Melilite and anorthite show a range of Δ¹⁷O from ?17‰ to ?1‰.  相似文献