Highly depleted Hadean mantle reservoirs in the sources of early Archean arc-like rocks, Isua supracrustal belt, southern West Greenland     

J. Elis Hoffmann  Carsten Münker  Ali Polat  Klaus Mezger  Minik T. Rosing 《Geochimica et cosmochimica acta》2010,74(24):7236-6628

Growing evidence from the accessible geological record reveals that crust-mantle differentiation on Earth started as early as 4.4 Ga. In order to assess the extent of early Archean mantle depletion, we obtained ¹⁷⁶Lu-¹⁷⁶Hf, ¹⁴⁷Sm-¹⁴³Nd, and high field strength element (HFSE) concentration data for the least altered, well characterized boninite-like metabasalts and associated metasedimentary rocks from the Isua supracrustal belt (southern West Greenland). The metasediments exhibit initial εHf₍₃₇₂₀₎ values from −0.7 to +1.5 and initial εNd₍₃₇₂₀₎ values from +1.6 to +2.1. Initial εHf₍₃₇₂₀₎ values of the least altered boninite-like metabasalts span a range from +3.5 to +12.9 and initial εNd₍₃₇₂₀₎ values from −0.3 to +3.2. These initial Hf-isotope ratios display coherent trends with SiO₂, Al₂O₃/TiO₂ and other relatively immobile elements, indicating contamination via assimilation of enriched components, most likely sediments derived from the earliest crust in the region. This model is also consistent with previously reported initial γOs₍₃₇₂₀₎ values for some of the samples. In addition to the positive εHf₍₃₇₂₀₎ values, the least disturbed samples exhibit positive εNd₍₃₇₂₀₎ values and a co-variation of εHf₍₃₇₂₀₎ and εΝd₍₃₇₂₀₎ values. Based on these observations, it is argued, that the most depleted samples with initial εHf₍₃₇₂₀₎ values of up to +12.9 and high ¹⁷⁶Lu/¹⁷⁷Hf of ∼0.05 to ∼0.09 tap a highly depleted mantle source with a long term depletion history in the garnet stability field. High precision high field strength element (HFSE) data obtained for the Isua samples confirm the contamination trend. Even the most primitive samples display negative Nb-Ta anomalies and elevated Nb/Ta, indicating a subduction zone setting and overprint of the depleted mantle sources by felsic melts generated by partial melting of eclogite. Collectively, the data for boninite-like metabasalts support the presence of strongly depleted mantle reservoirs as previously inferred from Hf isotope data for Hadean zircons and combined ¹⁴²Nd-¹⁴³Nd isotope data for early Archean rocks.  相似文献   

Optical Design of Multilayer Achromatic Waveplate by Simulated Annealing Algorithm   总被引：2，自引：0，他引：2  

Jun Ma  Jing-Shan Wang  Carsten Denker  Hai-Min Wang 《中国天文和天体物理学报》2008,8(3):349-361

We applied a Monte Carlo method-simulated annealing algorithm-to carry out the design of multilayer achromatic waveplate. We present solutions for three-, six-and ten-layer achromatic waveplates. The optimized retardance settings are found to be 89°51'39"±0°33'37" and 89°54'46"±0°22'4" for the six-and ten-layer waveplates, respectively, for a wavelength range from 1000nm to 1800nm. The polarimetric properties of multilayer waveplates are investigated based on several numerical experiments. In contrast to previously proposed three-layer achromatic waveplate, the fast axes of the new six-and ten-layer achromatic waveplate remain at fixed angles, independent of the wavelength. Two applications of multilayer achromatic waveplate are discussed, the general-purpose phase shifter and the birefringent filter in the Infrared Imaging Magnetograph (IRIM) system of the Big Bear Solar Observatory (BBSO). We also checked an experimental method to measure the retardance of waveplates.  相似文献   

Improvement of hydrodynamic forecasting of Danish waters: impact of low-frequency North Atlantic barotropic variations     

Bjarne Büchmann  Carsten Hansen  Johan Söderkvist 《Ocean Dynamics》2011,61(10):1611-1617

The Danish Maritime Safety Administration (DaMSA) provides forecast of elevations, currents, and other parameters to the maritime society. Accurate and reliable predictions are important to help navigate Danish waters in a safe manner, and the forecasts are routinely used by the Vessel Traffic Services in the Great Belt and the Sound. The DaMSA model setup includes three nested models, with coarse resolution in the North Atlantic and increasing to 600 m in the Belt Sea and South West Baltic. Observations of some special events in late 2009 drew attention to a possible relation between Atlantic-scale surge events and small-scale currents in the Danish Straits. During the special event with large-scale surge, the observed southward moving current in the Danish Straits was 0.5–2.0 m/s for several days, while the operational model showed a much smaller response. As a consequence, the entire DaMSA model complex was revised during 2010. Multi-annual reruns have showed that with the updated model, the explained variance of the current increases from 67% to 88%.  相似文献   

First record of Gzhelian and Asselian Fusulinids from the Vazhnan Formation (Sanandaj-Sirjan zone of Iran)     

E. Ja. Leven  M. N. Gorgij 《Stratigraphy and Geological Correlation》2011,19(5):486-501

The Vazhnan Formation, formerly attributed to the Sakmarian is now shown to be of the Gzhelian-Asselian age. Accordingly it is correlative with the concurrent Zaladou Formation of Central Iran and Dorud Group of Alborz. This suggests a vast transgression that covered the greater part of the Iranian territory in the terminal Carboniferous-initial Permian. The work includes brief characterization of fusulinids found in the formation section.  相似文献   

Comparison of approaches for the characterization of contamination at rural megasites     

Arno Rein  Steffen Popp  Steffen Zacharias  Carsten Leven  Martin Bittens  Peter Dietrich 《Environmental Earth Sciences》2011,63(6):1239-1249

The present work focuses on approaches for the characterization of subsurface contamination, which need to be reliable and cost-effective, particularly for extended and remote areas aimed at being redeveloped. Requirements are discussed with respect to specific conditions at megasites, in order to enable site valorization. In a case study, two approaches are compared, comprising (1) conventional site investigation based on historical surveys and concentration measurements at monitoring wells installed in areas suspected of being polluted and (2) the use of direct push (DP) methods covering the complete area. The DP investigation provided information on the contamination distribution and yielded also important information on hydraulic conditions. Statistical analysis of the results applying indicator kriging revealed that the conventional approach is markedly risky when decision-making relies solely on historical and sparse data. The DP campaign remarkably reduced the uncertainty concerning the estimated occurrence of polluted groundwater at the whole site. Furthermore, monitoring measurements are analyzed showing the possible importance of temporal variability. Taking economical consideration into account, DP-based groundwater screening is recommended to obtain either first or complementary information on the entire site. Based on these data, also locations for a long-term monitoring could be selected if temporal variability is assumed relevant.  相似文献   

Can CDM monitoring requirements be reduced while maintaining environmental integrity?     

Carsten Warnecke 《Climate Policy》2013,13(4):443-466

Monitoring, reporting, and verification (MRV) requirements in the Clean Development Mechanism (CDM) are perceived to be of high quality, but also complex and stringent. Only one-third of the registered projects successfully managed initial verification and already received carbon credits. The time required to achieve first issuance remains high despite considerable improvements in other CDM project cycle steps. This leads to the question of whether MRV provisions in the CDM represent barriers that could be lowered while ensuring the CDM's integrity. The CDM requirements are compared with the MRV provisions of the EU Emission Trading System (EU ETS). The comparison shows that CDM–MRV provisions are often stricter and less flexible compared to similar provisions in the EU ETS. Due to structural differences between the EU ETS and the CDM, some different MRV approaches are justified and reflect the CDM's disparate objectives and complexity. It is found that some CDM provisions result in barriers which seem avoidable and do not contribute to the CDM's environmental integrity. Recommendations are made for CDM-specific improvements and general structural changes to improve cost-efficiency and reduce uncertainty with relevance to policy developments around future market mechanisms.  相似文献   

An integrative hierarchical monitoring approach applied at a natural analogue site to monitor CO2 degassing areas     

Uta Sauer  Claudia Schütze  Carsten Leven  Stefan Schlömer  Peter Dietrich 《Acta Geotechnica》2014,9(1):127-133

This paper introduces an integrative hierarchical monitoring concept allowing for the detection and assessment of possible leakages from geological storage formations into the shallow subsurface or atmosphere. The concept introduced in this paper combines various investigation methods working at different scales and with varying resolutions. This approach will allow large spatial areas to be consistently covered, to enable efficient monitoring. Experience gained from the adoption of these tools for naturally occurring CO₂ deposits (analogue sites) is helpful for the evaluation and adoption of the methods to the requirements of storage projects.  相似文献   

Thermal tracer testing in a sedimentary aquifer: field experiment (Lauswiesen,Germany) and numerical simulation   总被引：1，自引：0，他引：1  

Valentin Wagner  Tao Li  Peter Bayer  Carsten Leven  Peter Dietrich  Philipp Blum 《Hydrogeology Journal》2014,22(1):175-187

An active and short-duration thermal tracer test (TTT) was conducted in a shallow sedimentary aquifer at the Lauswiesen test site, near Tübingen, Germany. By injecting 16  m³ of warm water at 22°C, a thermal anomaly was created, which propagated along the local groundwater flow direction. This was comprehensively monitored in five observation wells at a few meters distance. The purpose of this well-controlled experiment was to determine the practicability of such a TTT and its suitability to examine hydraulic characteristics of heterogeneous aquifers. The results showed that the thermal peak arrival times in the observation wells were consistent with previous observations from alternative field testing such as direct-push injection logging (DPIL). Combined analysis of depth-dependent temperatures and peak arrival times, and comparison with a numerical heat transport model, offers valuable insights into the natural flow field and spatial distribution of hydraulic conductivities. The study was able to identify vertical flow focusing and bypassing, which are attributed to preferential flow paths common in such sedimentary sand and gravel aquifers. These findings are fundamental for further development of experimental designs of active and short-duration TTTs and provide a basis for a more quantitative analysis of advective and conductive transport processes.  相似文献   

Nitrate reduction potential of a fractured Middle Triassic carbonate aquifer in Southwest Germany     

Osenbr&#;ck  Karsten  Blendinger  Eva  Leven  Carsten  R&#;gner  Hermann  Finkel  Michael  Jakus  Natalia  Schulz  Hartmut  Grathwohl  Peter 《Hydrogeology Journal》2022,30(1):163-180

Hydrogeology Journal - Nitrate reduction constitutes an important natural mechanism to mitigate the widespread and persistent nitrate contamination of groundwater resources. In fractured aquifers,...  相似文献   

The role of external forcing in prolonged trends in Australian rainfall     

Carsten S. Frederiksen  Simon Grainger 《Climate Dynamics》2015,45(9-10):2455-2468

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