Littérature scientifique sur le sujet « ΕNd »
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Articles de revues sur le sujet "ΕNd"
1
Kerr, Andrew, George A. Jenner et Brian J. Fryer. « Sm–Nd isotopic geochemistry of Precambrian to Paleozoic granitoid suites and the deep-crustal structure of the southeast margin of the Newfoundland Appalachians ». Canadian Journal of Earth Sciences 32, no 2 (1 février 1995) : 224–45. http://dx.doi.org/10.1139/e95-019.
Texte intégralRésumé :
In the Eastern Central Mobile Belt of the Newfoundland Appalachians, late Precambrian basement inliers have εNd from −3 to +2, but Cambro-Ordovician metasedimentary rocks have initial εNd below −7. This region is inferred to have an "inverted" crustal residence structure, which influenced subsequent Appalachian-cycle magmatism. Ordovician and Silurian granitoid suites have εNd of −8 to −2, bracketing both basement and cover, but peraluminous, "S-type" granites have the lowest εNd. Devonian granites have initial εNd values from −5 to +1, and low εNd is associated with peraluminous character. These Paleozoic granites show geographic trends, with lowest εNd values in areas where metasedimentary rocks are abundant. They are suggested to contain anatectic material from both Precambrian basement and metasedimentary cover, but some "I-type" suites probably also include a mantle-derived component. In the adjacent Avalon Zone, Precambrian plutonic suites mostly have εNd from +1 to +6, but there are negative εNd values (−8 to −4) in the westernmost Avalon Zone. Devonian plutonic suites mostly have εNd from +2 to +5. Thus, the Precambrian crust of the Avalon Zone is largely "juvenile," except at its westernmost edge. Contrasts across the Eastern Central Mobile Belt–Avalon Zone boundary, defined by the Dover–Hermitage Bay fault system, indicate a major, crustal-scale structure, and suggest an isotopically distinct "central block" beneath the central Appalachian Orogen, rather than a simple extension of "Avalonian" crust. Similar geographic–isotopic patterns have been reported in Nova Scotia and New Brunswick, suggesting that this pattern represents a first-order deep-crustal subdivision of the northern Appalachian Orogen.
2
Arsouze, T., J. C. Dutay, M. Kageyama, F. Lacan, R. Alkama, O. Marti et C. Jeandel. « A modeling sensitivity study of the influence of the Atlantic meridional overturning circulation on neodymium isotopic composition at the Last Glacial Maximum ». Climate of the Past 4, no 3 (4 septembre 2008) : 191–203. http://dx.doi.org/10.5194/cp-4-191-2008.
Texte intégralRésumé :
Abstract. Using a simple parameterisation that resolves the first order global Nd isotopic composition (hereafter expressed as εNd in an Ocean Global Circulation Model, we have tested the impact of different circulation scenarios on the εNd in the Atlantic for the Last Glacial Maximum (LGM), relative to a modern control run. Three different LGM freshwater forcing experiments are performed to test for variability in the εNd oceanic distribution as a function of ocean circulation. Highly distinct representations of the ocean circulation are generated in the three simulations, which drive significant differences in εNd, particularly in deep waters of the western part of the basin. However, at the LGM, the Atlantic is more radiogenic than in the modern control run, particularly in the Labrador basin and in the Southern Ocean. A fourth experiment shows that changes in Nd sources and bathymetry drive a shift in the εNd signature of the basin that is sufficient to explain the changes in the εNd signature of the northern end-member (NADW or GNAIW glacial equivalent) in our LGM simulations. All three of our LGM circulation scenarios show good agreement with the existing intermediate depth εNd paleo-data. This study cannot indicate the likelihood of a given LGM oceanic circulation scenario, even if simulations with a prominent water mass of southern origin provide the most conclusive results. Instead, our modeling results highlight the need for more data from deep and bottom waters from western Atlantic, where the εNd change in the three LGM scenarios is the most important (up to 3 εNd. This would also aid more precise conclusions concerning the evolution of the northern end-member εNd signature, and thus the potential use of εNd as a tracer of past oceanic circulation.
3
Mikhailik, P. E., I. A. Vishnevskaya, E. V. Mikhailik, M. G. Blokhin, M. V. Chervyakovskaya, V. A. Rashidov et X. Ren. « Genesis and Nd Isotope Composition of Ferromanganese Deposits of the Sea of Okhotsk and the Kuril Island Arc ». Russian Geology and Geophysics 62, no 9 (1 septembre 2021) : 1074–87. http://dx.doi.org/10.2113/rgg20194142.
Texte intégralRésumé :
Abstract —The Nd isotope composition of ferromanganese deposits (FMD) from the central part of the Sea of Okhotsk and the Kuril island arc has been studied. The results showed that diagenetic samples from the Deryugin Basin have a heterogeneous Nd isotope composition. The positive εNd values here might be both due to the input of a terrigenous impurity and due to diffuse endogenetic element supply. The FMD samples from the Sonne underwater ridge show a εNd value specific to seawater (–3.2). The εNd value of hydrogenetic FMD from Volcano 7.14 is –3.4, which corresponds to the εNd value of the Pacific water. The FMD samples from Volcano 5.5 are characterized by εNd = –2.0. The higher εNd value might be due to a moderate dilution of the hydrothermal fluid by seawater and might also indicate the presence of volcanic fragments in the FMD samples. The highest εNd value (+4.4) has been established for volcaniclastic sandstone saturated with Fe and Mn hydroxides. It points to a mixing of volcanomictic and hydrothermal materials.
4
Bock, B., S. M. McLennan et G. N. Hanson. « The Taconian orogeny in southern New England : Nd-isotope evidence against addition of juvenile components ». Canadian Journal of Earth Sciences 33, no 12 (1 décembre 1996) : 1612–27. http://dx.doi.org/10.1139/e96-122.
Texte intégralRésumé :
Nd-isotope data for pre-Taconian (meta)sedimentary and igneous rocks, syn-Taconian (meta)sedimentary rocks, and Late Ordovician–Silurian plutonic rocks indicate that the Ordovician Taconian orogeny did not add significant amounts of juvenile crust to the Laurentian margin in southern New England. Nd-isotope compositions of Grenvillian crust and Late Proterozoic to Early Cambrian rift sediments range from εNd of −3.1 to −6.6 at 450 Ma. Sedimentary rocks deposited during the Cambrian and the early Middle Ordovician, which represent the drift stage of Laurentia, and earliest Taconian sedimentary rocks show more negative εNd(450 Ma), with a range from −11.7 to −13.3. Sedimentary rocks deposited in response to the Taconian orogeny have uniform εNd(450 Ma) values of about −8. Middle to Late Ordovician and Permian plutonic rocks from southwestern Connecticut have εNd(450 Ma) values of −2 to −5, which indicates that these rocks contain older crustal components. Rocks with juvenile Nd characteristics are the early Paleozoic Maltby Lake Volcanics (εNd(450 Ma) +8) from southwestern Connecticut, and Middle Ordovician igneous samples from the Hawley Formation (εNd(450 Ma) +6 to −0.6) in Massachusetts.
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Khim, Boo-Keun, Keiji Horikawa, Yoshihiro Asahara, Ji-Eun Kim et Minoru Ikehara. « Detrital Sr–Nd isotopes, sediment provenances and depositional processes in the Laxmi Basin of the Arabian Sea during the last 800 ka ». Geological Magazine 157, no 6 (23 novembre 2018) : 895–907. http://dx.doi.org/10.1017/s0016756818000596.
Texte intégralRésumé :
Abstract87Sr/86Sr ratios and εNd values of detrital particles at International Ocean Discovery Program (IODP) Site U1456 in the Laxmi Basin of the Arabian Sea were measured to trace changes in sediment provenance over glacial–interglacial cycles. Based on the correlation of planktonic foraminiferal (Globigerinoides ruber) δ18O fluctuations with the LR04 stack of benthic foraminifera δ18O values, combined with shipboard biostratigraphic and palaeomagnetic data, the studied interval spans ∼1.2 Ma. Over the past 800 ka, 87Sr/86Sr values ranged from 0.711 to 0.726 while εNd values ranged between −12.5 and −7.3 in the detrital particles. By comparing 87Sr/86Sr ratios and εNd values of the possible sources of river sediments with our data, we found that sediments in the Laxmi Basin were influenced to various degrees by proportions of at least three sediment sources (i.e. Tapi River, Narmada River and Indus River). The Indus River might be a more important contributor to glacial sediments. Although 87Sr/86Sr ratios and εNd values varied quasi-cyclically, this pattern did not correspond precisely to the glacial–interglacial cycles. In particular, low-magnetic-susceptibility (low-MS) intervals coinciding with pelagic carbonates were characterized by low 87Sr/86Sr ratios and high εNd values, whereas high-MS intervals matching turbidite deposits showed high 87Sr/86Sr ratios and low εNd values. Thus, this study reveals that differences in the depositional processes between glacial and interglacial periods, governed by changes in sea level and monsoon activity, are an important factor in deciding 87Sr/86Sr ratios and εNd values of the detrital fraction in the Indus Fan of the Arabian Sea.
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Dubois-Dauphin, Quentin, Paolo Montagna, Giuseppe Siani, Eric Douville, Claudia Wienberg, Dierk Hebbeln, Zhifei Liu et al. « Hydrological variations of the intermediate water masses of the western Mediterranean Sea during the past 20 ka inferred from neodymium isotopic composition in foraminifera and cold-water corals ». Climate of the Past 13, no 1 (10 janvier 2017) : 17–37. http://dx.doi.org/10.5194/cp-13-17-2017.
Texte intégralRésumé :
Abstract. We present the neodymium isotopic composition (εNd) of mixed planktonic foraminifera species from a sediment core collected at 622 m water depth in the Balearic Sea, as well as εNd of scleractinian cold-water corals (CWC; Madrepora oculata, Lophelia pertusa) retrieved between 280 and 442 m water depth in the Alboran Sea and at 414 m depth in the southern Sardinian continental margin. The aim is to constrain hydrological variations at intermediate depths in the western Mediterranean Sea during the last 20 kyr. Planktonic (Globigerina bulloides) and benthic (Cibicidoides pachyderma) foraminifera from the Balearic Sea were also analyzed for stable oxygen (δ18O) and carbon (δ13C) isotopes. The foraminiferal and coral εNd values from the Balearic and Alboran seas are comparable over the last ∼ 13 kyr, with mean values of −8.94 ± 0.26 (1σ; n = 24) and −8.91 ± 0.18 (1σ; n = 25), respectively. Before 13 ka BP, the foraminiferal εNd values are slightly lower (−9.28 ± 0.15) and tend to reflect higher mixing between intermediate and deep waters, which are characterized by more unradiogenic εNd values. The slight εNd increase after 13 ka BP is associated with a decoupling in the benthic foraminiferal δ13C composition between intermediate and deeper depths, which started at ∼ 16 ka BP. This suggests an earlier stratification of the water masses and a subsequent reduced contribution of unradiogenic εNd from deep waters. The CWC from the Sardinia Channel show a much larger scatter of εNd values, from −8.66 ± 0.30 to −5.99 ± 0.50, and a lower average (−7.31 ± 0.73; n = 19) compared to the CWC and foraminifera from the Alboran and Balearic seas, indicative of intermediate waters sourced from the Levantine basin. At the time of sapropel S1 deposition (10.2 to 6.4 ka), the εNd values of the Sardinian CWC become more unradiogenic (−8.38 ± 0.47; n = 3 at ∼ 8.7 ka BP), suggesting a significant contribution of intermediate waters originated from the western basin. We propose that western Mediterranean intermediate waters replaced the Levantine Intermediate Water (LIW), and thus there was a strong reduction of the LIW during the mid-sapropel ( ∼ 8.7 ka BP). This observation supports a notable change of Mediterranean circulation pattern centered on sapropel S1 that needs further investigation to be confirmed.
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Samson, Scott D., Sandra M. Barr et Chris E. White. « Nd isotopic characteristics of terranes within the Avalon Zone, southern New Brunswick ». Canadian Journal of Earth Sciences 37, no 7 (1 juillet 2000) : 1039–52. http://dx.doi.org/10.1139/e00-015.
Texte intégralRésumé :
Nd isotopic data are presented for rock units in four terranes within the traditional Avalon Zone of southern New Brunswick. Initial εNd values for igneous rocks within the Caledonia terrane range from -1.6 to +4.6, whereas values for sedimentary rocks range from -8.4 to +3.6. A granite within the Kingston terrane has εNd(438 Ma) = +4.0. Nd isotopic compositions for the Kingston and Caledonia terranes are similar to those of the Mira terrane in Cape Breton Island, the Antigonish Highlands of Nova Scotia, and plutonic rocks of eastern Newfoundland. Each of these regions may be a dismembered part of a single terrane, the Avalon terrane sensu stricto. Initial εNd values for rocks from the Brookville terrane range from -1.3 to +2.8. The Coverdale anorthosite within the Brookville terrane has a present day εNd value of -12.1 and a depleted mantle model age of 1.3 Ga, similar to Mesoproterozoic anorthosites in Laurentia. Clastic sedimentary rocks in the Green Head Group have εNd(750 Ma) values of -2.0 and -10.9. Viewed as a whole, the Brookville terrane is isotopically more evolved than the Caledonia terrane. Initial εNd values for rocks in the New River terrane range from -2.9 to 0.0. The Nd isotopic composition of the Brookville and New River terranes are thus similar to one another and have isotopic character similar to that of the Bras d'Or terrane of Cape Breton Island. It is suggested that all three regions belong to a single terrane (Bras d'Oria).
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Garzione, Carmala N., P. Jonathan Patchett, Gerald M. Ross et JoAnne Nelson. « Provenance of Paleozoic sedimentary rocks in the Canadian Cordilleran miogeocline : a Nd isotopic study ». Canadian Journal of Earth Sciences 34, no 12 (1 décembre 1997) : 1603–18. http://dx.doi.org/10.1139/e17-129.
Texte intégralRésumé :
Nd isotopes and trace elements in sedimentary rocks of the Yukon, the Northwest Territories, and northern British Columbia are used to examine the source of sediments in the Canadian Cordilleran miogeocline. Previous Nd isotope studies in southern Alberta demonstrated that strata of Neoproterozoic to Late Ordovician age were derived from Archean and Proterozoic Canadian Shield sources, whereas by the Late Devonian, a shift of 6 εNd units to younger crustal sources (εNd (T) = −6 to −9) had occurred. In this study, we found that the shift to younger crustal Nd isotopic signatures in the Yukon and Northwest Territories occurred much earlier than in southern Alberta. Cambrian and older strata have εNd(T) values of −10.0 to −21.1, consistent with derivation from Canadian Shield sources. Lower Ordovician through Permian strata in the Yukon and Northwest Territories, including the Innuitian-derived Imperial Assemblage, have εNd(T) values of −5 to −11.4. In northern British Columbia, the shift to a younger source reflects a wider range of εNd(T) values, from -−8.7 to −14.6 in Middle Ordovician through Middle Devonian strata, suggesting continued input from Canadian Shield sources. By the Middle Devonian, a complete shift to younger crustal signatures (εNd(T) = −5.9 to −10.5) had occurred in northern British Columbia. Several sources for the more juvenile sediments include (1) a mixture of locally erupted volcanic rocks with Canadian Shield sources, (2) a Grenville source, and (3) an Innuitian source. We propose that Ordovician to Lower Devonian strata were derived from a mixture of locally erupted, juvenile volcanics and pre-Cambrian Canadian Shield sources, and post-Middle Devonian strata were sourced from the Innuitian orogen in the Canadian Arctic.
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Chauvel, C., N. T. Arndt, S. Kielinzcuk et A. Thom. « Formation of Canadian 1.9 Ga old continental crust. I : Nd isotopic data ». Canadian Journal of Earth Sciences 24, no 3 (1 mars 1987) : 396–406. http://dx.doi.org/10.1139/e87-042.
Texte intégralRésumé :
A Nd isotopic study was carried out on 1.9−1.8 Ga rocks from two parts of the Trans-Hudson Orogen in northern Canada. The first part is the Reindeer Lake Zone in the Churchill Province in Saskatchewan, where a variety of volcanic, granitoid, and sedimentary rocks are preserved in several lithotectonic belts that border a reworked Archean craton to the northwest. The second area comprises the Ottawa and Belcher islands, in Hudson Bay, and the Fox River volcanics, in Manitoba. These form part of the Circum-Superior Belt, a band of basaltic volcanics and sedimentary rocks that overlies the Archean Superior craton.From U–Pb zircon ages, Pb–Pb ages, and Sm–Nd ages, Nd initial isotopic compositions were calculated for all analyzed samples. In the Saskatchewan terrains, we obtained a large range of εNd values, from +5 to −8. The highest values (+4 to +5) come from two volcanic-dominated belts (Flin Flon and Western la Ronge), lower values (~+2) characterize intervening sediment-dominated domains (Eastern La Ronge, Glennie Lake, and Kisseynew), and still lower values (−1 to −4) were found in migmatitic and granitoid belts adjacent to the reworked Archean craton in the northwest. Each lithotectonic belt has its own characteristic, restricted range of εNd values, and, with few exceptions, there is no correlation between εNd and rock type; i.e., in individual belts, volcanics, granites, and sediments have very similar εNd values.In the Circum-Superior Belt, three lava flows from the Ottawa Islands have εNd values ranging from +4.5 to 0, and samples from the Belcher Islands have values ranging from +3.5 to −9.These results are explained by mixing between mantle-derived rocks and variable amounts of Archean continental crustal rocks. Assuming that 1.9 Ga ago the mantle had an εNd value of +5 and Archean crust had an εNd value of −12, we calculate proportions of Archean crustal material in Trans-Hudson rocks ranging from ~2 to 35 %, increasing systematically toward the Archean platform. The mean Archean component is about 8%: this area of Proterozoic continental crust is clearly dominated by material derived directly from the mantle.The similarity between the εNd values of sediments, granites, and volcanics in the Trans-Hudson Orogen suggests that sedimentary processes played a dominant role in transporting Archean detritus from eroding Archean continental areas into basins, where it mixed with mantle-derived volcanic material and melted to form granitoids.
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Fryer, Brian J., John D. Greenough et J. Victor Owen. « Iapetus Ocean floor stuffed into a suture zone : xenolith Nd isotopic evidence for Dunnage-equivalent basement in central Newfoundland ». Canadian Journal of Earth Sciences 34, no 10 (1 octobre 1997) : 1392–400. http://dx.doi.org/10.1139/e17-111.
Texte intégralRésumé :
Granulite-facies xenoliths from Late Jurassic alkaline lamprophyres may represent basement to the Dunnage Zone in north-central Newfoundland (Notre Dame Bay area). At 143 Ma the xenoliths had positive εNd values between 0.9 and 4.7. They give Nd depleted mantle model ages around 700 Ma and have trace element and major element compositions reminiscent of oceanic arc-related intermediate volcanic and sedimentary rocks. Their positive εNd values and associated "young" Nd model ages argue against their representing Grenvillian crust. Similarly, Gander Zone basement to the east produced granitic rocks with strongly negative εNd values unlike those of the xenoliths. Positive εNd values for Avalonian granites indicate that the xenoliths could represent Avalon-type basement; however, there are 100–200 km of Gander and Dunnage zone rocks between the xenoiith locality and the Avalon Zone. Early orogenic volcanic rocks and some late orogenic to postorogenic granitic rocks in the central to northern portion of the Gander Zone have positive εNd values, consistent with extraction from a depleted mantle at the same time as material forming the xenoliths. Similarities between the xenolith chemistry and that of early orogenic (Cambrian) arc-related intermediate volcanic rocks of the Dunnage Zone indicate that the xenoliths and basement in the Notre Dame Bay area are composed of Iapetus Ocean floor relics (volcanic or volcanic-rich sedimentary rocks) stuffed into a collisional suture zone during ocean closure.
Thèses sur le sujet "ΕNd"
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Gao, Guohui. « Variations in the North African climate and in the hydrology of intermediate- and deep-water masses of the Mediterranean Sea during the late Quaternary : sedimentological, mineralogical and geochemical investigations of marine sediments ». Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASJ025.
Texte intégralRésumé :
La circulation thermohaline méditerranéenne influence l'AMOC et les dépôts de sapropels. Cette étude examine les méthodes d'extraction des compositions isotopiques de Nd de l'eau de mer passée et la variabilité de la formation des eaux profondes pendant le dernier cycle climatique. Nos résultats montrent que l'εNd des foraminifères n'est pas affecté par la diagenèse des téphras. L'extraction séquentielle avec hydroxylamine hydrochloride donne des valeurs d'εNd cohérentes avec celles des foraminifères. L'εNd des eaux profondes de la mer Adriatique est resté constant durant les 16 derniers ka. L'étude de carottes de la Méditerranée orientale a permis de contraindre la variabilité de la formation des eaux profondes adriatique et égéenne pendant le dernier cycle climatique, notamment durant les dépôts des sapropels S1 et S5. La formation d'eau profonde adriatique (AdDW) s'est arrêtée pendant le dépôt du S1a et S1b. L'événement froid à ~8,2 cal kyr BP coïncide avec une diminution de l'εNd, impliquant une formation active d'AdDW, responsable de la ré-ventilation des eaux profondes et de l'interruption du S1 dans le nord de la mer Ionienne. Pour le S5, l'apport initial d'eau douce a entraîné une stratification des eaux profondes, limitant leur formation et induisant une signature locale d'εNd due à un échange prolongé entre l'eau de mer et les sédiments. Au cours du dépôt, les enregistrements d'εNd indiquent un mélange des eaux profondes et une diminution du gradient d'εNd entre les marges nord et sud du bassin Levantin, associés à la baisse des températures et à la diminution de l'apport du Nil. Cela a facilité la formation d'eaux profondes égéennes et renforcé légèrement la circulation profonde. Des analyses minéralogiques et géochimiques sur une carotte au sud de la Sardaigne ont permis de reconstituer les variations des apports détritiques d'Afrique du Nord et les processus climatiques associés sur 600 ka. Les périodes glaciaires et de faible insolation estivale sont liées à une augmentation des flux terrigènes, des teneurs en smectite et des rapports illite/kaolinite (I/K) plus élevés, suggérant une source de poussière principale dans le nord de l'Afrique du Nord (PSA1).Les périodes humides africaines montrent un rapport I/K plus faible et des compositions isotopiques en Sr et Nd indiquant une source sédimentaire principale dans la région tropicale méridionale, en accord avec un déplacement vers le nord de la ZCIT et l'extension de la végétation. Les émissions de poussières sont réduites et le matériel détritique est transporté vers le sud de la mer Tyrrhénienne par les paléo-fleuves tunisiens. Les apports de poussières de PSA1 résultent d'une interaction complexe entre les climats des hautes et basses latitudes de l'hémisphère Nord, pas uniquement de la migration de la ZCIT. Les variations des apports éoliens n'induisent pas de modifications de l'εNd des eaux profondes du sud de la mer TyrrhénienneThe Mediterranean Sea's thermohaline circulation, which is sensitive to high and low latitude climate changes, influences the AMOC and the occurrence of sapropel layers in Eastern Mediterranean Sea (EMS). The depositions of sapropels are attributed to stagnant deep-water conditions and increased biological production during specific orbital cycles. However, debates persist concerning the complex interaction between climatic processes, circulation dynamics, and sapropel depositions. In this study, we have firstly investigated different methods for extracting past seawater Nd isotope compositions (εNd) from a core collected in the Adriatic Sea whose tephra layers have been previously well documented. Our results show that foraminiferal εNd values remain unaffected by the diagenesis of tephra and that sequential extraction with hydroxylamine hydrochloride yields εNd values that are more consistent with those obtained on planktonic foraminifera. We then demonstrated that εNd of the Adriatic deep-water remained constant throughout the past 16 kyr. In a second step, we investigated foraminiferal εNd of several cores located at intermediate and deep-water depths in the south of the Aegean Sea on the pathway of the Aegean Deep-Water (AeDW) and in the northern Ionian Sea. This permits us to constrain deep-water formations in the Adriatic Sea and the Aegean Sea during the last climatic cycle and, more particularly, during the deposition of sapropels S1 and S5. We have then demonstrated from cores of the northern Ionian Sea that the formation of Adriatic Deep-Water (AdDW) collapse during the deposition of S1a and S1b. The cold events at ~8.2 cal kyr BP are coeval to an obvious decrease in εNd value, implying an active AdDW formation, which is responsible for the re-ventilation of deep-water masses and the interruption of the deposition of the sapropel S1 in the northern Ionian Sea. When combined with previous εNd records from the EMS, our results indicate for the S5 that the initial freshwater influx led to strong water stratification, limited deep-water formation and shifted foraminiferal εNd towards a local signature due to a longer duration of Nd exchange between seawater and marginal sediments. As deposition of S5 progresses, εNd records of all cores of the EMS indicate a mixing of deep-water masses accompanied by a decrease in the εNd gradient between the northern and southern margins of the Levantine Basin. This is associated with the global decrease in temperatures and lower input of Nile River water, favoring deep-water formation in the north and enhancing basin-wide circulation. Foraminiferal εNd records show a great sensitivity to bottom water recirculation levels after prolonged stratification during periods of sapropel depositions. Finally, mineralogical and geochemical analyses (clay mineralogy, 87Sr/86Sr, εNd, major and trace elements) on a core south of Sardinia reconstructed detrital input variations from North Africa over the last 600 kyr. Glacial MIS and low summer insolation periods correlate with increased terrigenous flux, higher smectite content, and higher illite/kaolinite (I/K) ratios, indicating northern North Africa (PSA1) as the dust source. Conversely, African Humid Periods (AHPs) show lower I/K ratios, pointing to southern tropical North Africa as the sediment source, aligned with northward ITCZ movement and vegetation expansion, reducing dust emissions and transporting detrital material to the southern Tyrrhenian Sea via paleo-rivers from Tunisia
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Lee, Yi-Lin, et 李宜霖. « The Comparison of Inclined Planar Dual-Jet Interaction by k-εand k-ω Tubulent Models ». Thesis, 2001. http://ndltd.ncl.edu.tw/handle/15132579281645816568.
Texte intégralRésumé :
碩士中原大學
土木工程研究所
89
The numerical simulation results of the flows of two parallel/inclined planar turbulent jets are presented in this paper. This study adopts the control volume method for simulating the mean quantities of the two-dimensional averaged Navier-Stokes equations associated with and turbulent models. The computational results of these two turbulent models were validated with the experimental investigations and compared each other for the related physical quantities. The comparison includes mean flow direction, turbulent intensities and Reynolds stress; and demonstrates that (1) background flow is needed for the numerical simulation to reinforce entrainment and ensure the stability of the flow field. There exists a third order polynomial relationship between the background flow and the deflected angles. (2) The relationship of Merged Point (M.P.), Combined Point (C.P.) with dimensionless deflected angle shows that a linear relationship exists between the M.P. and deflected angels. Nevertheless the relationship of C.P. and the deflected angels is a second order polynomial. By comparing the experimental measurements, the numerical results of turbulent model is more closed to experimental results than turbulent model. (3) When the deflected angle increases, vortex center will shift upstream with the increase of the inclined angle of the dual jets in the converged region until 27 degree. Beyond this critical angel (27degree), the vortex profile will not change any more, it agrees well with the experimental result. General comparison of the experimental and numerical results show that the mean velocity profiles approach self-preserving in the combined region, also show that the fluid formal, jet track, mean velocity characteristics, turbulence stresses and turbulence shear stresses all have the same developing trend. Overall, the simulation of k-εturbulent model is much more closed to the experimental measurement than that of the k-ωturbulent model.
Chapitres de livres sur le sujet "ΕNd"
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Jin, Lu, Yuequan Yang, Chunbo Ni, Yifei Kong et Zhiqiang Cao. « Study on Online εNN Q-Learning for Multi-Robot System Based on Community Perception Network ». Dans Lecture Notes in Electrical Engineering, 861–68. Berlin, Heidelberg : Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-38524-7_96.
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Gottlieb, Eric S., Elizabeth L. Miller, John W. Valley, Christopher M. Fisher, Jeffrey D. Vervoort et Kouki Kitajima. « Zircon petrochronology of Cretaceous Cordilleran interior granites of the Snake Range and Kern Mountains, Nevada, USA ». Dans Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.2555(02).
Texte intégralRésumé :
ABSTRACT We addressed fundamental questions about the lithology, age, structure, and thermal evolution of the deep crust of the retroarc hinterland of the North American Cordilleran orogen through systematic investigation of zircons from Cretaceous plutons in the Snake Range and Kern Mountains of east-central Nevada. Geochronological (U-Pb) and geochemical (trace element, O and Hf isotopes) characterization of pre- and synmagmatic growth domains of zircons, coupled with traditional petrologic methods (petrography, field relationships, and whole-rock major-element, trace-element, and Sr-Nd and Pb isotope geochemistry), fingerprinted temporal variations in crustal contributions to magmatism. The samples are typical felsic, peraluminous Cordilleran interior granitoids that formed between 102 ± 2 Ma and 71 ± 1 Ma (95% confidence). Over the entire time span of magmatism, 87Sr/86Srinitial, εNd(t), 208Pb/204Pb, and εHf(t) exhibit incrementally more “crustal” ratios. The oldest and youngest samples, respectively, predate and postdate all published timing constraints of Cretaceous peak metamorphism in the region and exhibit the least and most radiogenic whole-rock isotopic results in the study (87Sr/86Srinitial = 0.7071 vs. 0.7222; εNd(t) = −3.4 vs. −18.8; 208Pb/204Pb = 38.8 vs. 40.1). Accordingly, the least intrasample variability of εHf(t), δ18OZrc, and trace-element ratios in magmatic zircon domains is also observed in these oldest and youngest samples, whereas greater intrasample variability is observed in intermediate-age samples that intruded during peak metamorphism. The geochemistry of zircon growth in the intermediate-age samples suggests assimilation of partially molten metasedimentary crust led to increased heterogeneity in their magma chemistry. Interaction of magmas with distinctive crust types is indicated by contrasts between four categories of inherited zircon observed in the studied intrusions: (1) detrital zircon with typical magmatic trace-element ratios; (2) zircon derived from high-grade 1.8–1.6 Ga basement; (3) zircon with anomalously low δ18O of uncertain origin, derived from 1.7/2.45 Ga basement (or detritus derived thereof); and (4) zircon from variably evolved Jurassic–Early Cretaceous deep-seated intrusions. The progression of zircon inheritance patterns, correlated with evolving geochemical signatures, in Late Cretaceous granitic plutons is best explained by early, relatively primitive intrusions and their penecontemporaneously metamorphosed country rock having been tectonically transported cratonward and superposed on older basement, from which the later, more-evolved Tungstonia pluton was generated. This juxtaposition consequentially implies tectonic transport of synorogenic plutonic rocks occurred in the Cordilleran hinterland during the Sevier orogeny as a result of the interplay of retroarc magmatism and convergent margin tectonism.
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Maslov, A. V., N. V. Politova, N. V. Kozina, A. B. Kuznetzov, M. D. Kravchishina, A. N. Novigatsky, V. P. Shevchenko et T. N. Alexeeva. « Rare and trace elements in modern bottom sediments of the Barents sea. Nd, Pb and Sr isotopic composition ». Dans THE BARENTS SEA SYSTEM, 444–72. Shirshov Institute of Oceanology Publishing House, 2021. http://dx.doi.org/10.29006/978-5-6045110-0-8/(32).
Texte intégralRésumé :
The article presents a brief lithological description of the modern bottom sediments of the Barents Sea, selected in the 67th voyage of the R/V “Akademik Mstislav Keldysh” at the polygons: 1) “Pechora Sea”; 2) “Western slope of Kaninskoe shoal”; 3) “Central Barents Sea (Shtokman area)”; 4) “Russkaya Gavan’ fjord”; 5) “Medvezhinsky Trench”; 6) in the area to the south of Spitsbergen; 7) “Kola meridian”; 8) “Spitsbergen – Franz Josef Land archipelago”; 9) “Cambridge Strait”. The distribution of Cr, Ni, Cu, Zn, Cd, and Pb in samples of bottom sediments (pelitic, aleurite-pelitic and sandy-aleuritic-pelitic ooze) is compared with the background concentrations and contents of these elements in the Post-Archean Average Shale (PAAS). The data obtained are consistent with the notion that the distribution of heavy metals and other elements in the bottom sediments is controlled primarily by the global geochemical background. The relationship of the Sc, V, Cr, Ni, Y, Zr, Nb, Mo, Hf, Th, U and rare-earth elements concentrations with content of fine pelite (< 0.001 mm) fraction and organic carbon (Corg) is considered. It was found that most of these elements are characterized by a moderate positive correlation with the amount of fine pelite fraction in samples. By the magnitude of the correlation coefficient with the Corg content, all elements are attributed into three groups: (1) with moderate positive correlation, (2) weak positive correlation, (3) practically not pronounced correlation. The distribution in the bottom sediments of the Barents Sea of the element-indicators of the source rocks composition (Sc, Th, Co, Cr, La and Sm), as well as of rare earths, make it possible to consider that the majority of bottom sediments is mature in geochemical terms material, the sources of which were rocks of the Kola Peninsula and Spitsbergen (?). The bottom sediments of the Cambridge Strait are represented by geochemically less mature material, which, apparently, entered the sea as a result of erosion of the Franz Josef Land archipelago rocks. The established isotopic characteristics (εNd, 207Pb/206Pb and 87Sr/86Sr) of 17 samples of surface sediments suggest that the main contribution to the formation of bottom deposits of the central regions of the Barents Sea is made by rocks of the mainland part located in the influence zone of the North Cape Current. Archipelagos and islands (Franz Josef Land, Novaya Zemlya, etc.) that frame the Barents Sea supply a relatively small amount of clastic material that is carried by Arctic currents. The values of εNd and 87Sr/86Sr in the surface sediments of the central part of the Barents Sea and in the ice-rafted sediments carried by the Transpolar Drift showed a significant difference. This suggests that the contribution of such material to the formation of surface sediments of the Barents Sea is relatively small
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Vogel, Thomas A., F. William Cambray, Leeann Feher et Kurt N. Constenius. « Petrochemistry and Emplacement History of the Wasatch Igneous Belt ». Dans Geology and Ore Deposits of the Oquirrh and Wasatch Mountains, Utah, 35–46. Society of Economic Geologists, 1998. http://dx.doi.org/10.5382/gb.29.03.
Texte intégralRésumé :
Abstract Exposures in and around the mid-Tertiary Wasatch Igneous Belt (WIB) provide an opportunity to investigate the mechanisms associated with the emplacement of the stocks. They are associated in time and place with northeast-trending dikes, indicating that the area was undergoing extension at the time. Studies elsewhere show that at best, distortion of the country rock around igneous intrusions can only account for 40 percent of the space required. We propose a model in which part of the space is made available where faults associated with the extension change strike (releasing bends) or dip (releasing steps). Evidence for this is in the form of kinematic indicators associated with minor intrusions, the map scale geometry of the stocks and the pattern of dikes. The Little Cottonwood, Alta, and Clayton Peak stocks are chemically distinct, lending support to the concept of separately generated and separately emplaced magma bodies. The eastern stocks and the Keetley Volcanics have some similarities with the Alta stock. The stocks and volcanic rocks of the WIB are all high-K calc-alkaline rocks with K2O, εSr and εNd values that are difficult to generate from the mantle wedge overlying a subducting plate, but are consistent with magmas derived by partial melting of the lower crust (Proterozoic meta-igneous). The intrusive and volcanic rocks in the WIB range in age from 30.5 ± 0.6 Ma (Little Cottonwood) to 35.5 ±1.5 Ma (Clayton Peak) with most of the intrusions and volcanic deposits occurring in the 32 to 36 Ma range.
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Dostal, Jaroslav, Pierre Jutras et Reginald A. Wilson. « Geochemical and Nd isotopic constraints on the origin of uppermost Silurian rhyolitic rocks in the northern Appalachians (northern New Brunswick) : Tectonic implications ». Dans New Developments in the Appalachian-Caledonian- Variscan Orogen. Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2554(06).
Texte intégralRésumé :
ABSTRACT Voluminous bimodal volcanic rocks of the Silurian (ca. 422–420 Ma) Dickie Cove Group in the Ganderia domain of northern New Brunswick, Canada, are subaerial units that were deposited in an extensional setting, with the mafic types corresponding to continental tholeiites. Felsic rocks are rhyolites with calc-alkaline affinities. They exhibit geochemical characteristics that are typical of A2-type felsic magmas, such as enrichments in the incompatible elements Zr, Nb, and Y, as well as high FeO*/(FeO* + MgO) and Ga/Al ratios. Their εNd(t) values are positive (+0.7 to +3.4) but lower than those of the associated basalts. Saturation thermometry has yielded average zircon crystallization temperature estimates for the rhyolites that are well above 900 °C. The geochemical data indicate that the felsic melts were likely sourced from heterogeneous Neoproterozoic lower crust and generated by dehydration melting triggered by heat derived from underplated mafic magma. Parent melts of the rhyolites underwent fractional crystallization in a complex magma chamber prior to eruption. The Nd isotopic data suggest that the lower crust of Ganderia is similar to that of Avalonia in northern mainland Nova Scotia, and that the two microcontinents shared a common Neoproterozoic history and origin as continental blocks rifted from neighboring parts of Gondwana. The tectono-magmatic setting of the Dickie Cove Group volcanic rocks is interpreted as being related to Pridolian, post-Salinic relaxation and slab breakoff, which generated volcanism initially constrained within the Chaleur zone of the Chaleur Bay synclinorium, a large domain of the northern Appalachians. This was followed later in the Pridolian by extensional collapse and widening of the area of magmatic activity, which then prograded into the Tobique zone farther to the southwest.
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« The Space εn ». Dans Metric Spaces of Fuzzy Sets : Theory and Applications, 37–49. WORLD SCIENTIFIC, 1994. http://dx.doi.org/10.1142/9789814447010_0006.
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« Metrics on εn ». Dans Metric Spaces of Fuzzy Sets : Theory and Applications, 51–70. WORLD SCIENTIFIC, 1994. http://dx.doi.org/10.1142/9789814447010_0007.
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Chapman, Jonathan, et Frederick Rowbottom. « The theory of a topos In S ». Dans Relative Category Theory and Geometric Morphisms, 140–71. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780198534341.003.0010.
Texte intégralRésumé :
Abstract In this chapter, we employ the canonical set theory of a topos ε in S, to give a set-theoretic description of the structure of εand to construct exponentials and finite colimits. If εhas copowers then (set-indexed) disjunctions, V, are available in the language.
Actes de conférences sur le sujet "ΕNd"
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Kalashnikov, A. O., P. A. Serov, J. A. Mikhailova et V. N. Yakovenchuk. « Neodymium isotopes do fractionate in magmatic environments ». Dans Project KO5125 ARLIN Arctic Layered Intrusions as a Source of Critical Metals for Green Economy European Neighbourhood Instrument Cross-Border Cooperation Programme Kolarctic 2014-2020. GI KSC RAS, 2022. http://dx.doi.org/10.31241/arlin.2022.006.
Texte intégralRésumé :
We have revealed that εNd(T) changes from positive to negative near magmatic contacts, in the gabbro-norite Nyud and the peralkaline Lovozero massifs (NW Russia). We suppose that these reversions are caused by fractionation of neodymium isotopes by thermal diffusion near the contacts.
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Rakhimov, I. R., et E. L. Kunakkuzin. « PETROLOGICAL AND GEOCHEMICAL FEATURES OF THE TASHLY-TAU ORE-BEARING MASSIF (KHUDOLAZ COMPLEX, SOUTH URALS) ». Dans Проблемы минералогии, петрографии и металлогении. Научные чтения памяти П. Н. Чирвинского. Пермский государственный национальный исследовательский университет, 2021. http://dx.doi.org/10.17072/chirvinsky.2021.197.
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Petrographic and petrological-geochemical studies of the Tashly-Tau ore-bearing massif rocks of the Khudolaz complex have been carried out. It was revealed that the rocks are rich in hornblende and can be called olivine plagiogornblendites. They are characterized by high concentrations of LILE (Cs, Rb, Sr, Ba) and low concentrations of HFSE (Nb, Ta, Zr, Hf, REE). It was established by geochemical thermometry that the parental magma was a water-saturated, moderate magnesian melt containing olivine phenocrysts in an amount of 16–18 wt.%. Sr-Nd isotopic data (εNd (Т) = + 5.2… + 10.3, εSrUR (Т) = 0… + 3.72) indicate a weak crustal contamination of the parental melt by upper crust. The source of the parental melt could be a PREMA-type mantle reservoir.
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Larkin, Max. « QUANTIFYING CRUSTAL CONTAMINATION : RELATING SIO2AND εND AS A PROXY FOR THE DEGREE OF CRUSTAL CONTAMINATION IN WESTERN NORTH AMERICA ». Dans 112th Annual GSA Cordilleran Section Meeting. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016cd-274600.
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ГУСЕВ Н, И., Ю. РОМАНОВА Л et Г. СКУБЛОВ С. « GEOCHEMISTRY AND AGE OF ZIRCON FROM KHAPCHAN ACCRETIONAL OLISTOSTROM OF ANABAR SHIELD ». Dans ГЕОЛОГИЯ И МИНЕРАЛЬНО-СЫРЬЕВЫЕ РЕСУРСЫ СЕВЕРО-ВОСТОКА РОССИИ 2024, 302–8. Crossref, 2024. http://dx.doi.org/10.53954/9785604990100_302.
Texte intégralRésumé :
Chaotic breccias in carbonate rocks of the Paleoproterozoic Khapchan series of the Anabar Shield were characterized for the first time. Breccias belong to the flysch-carbonate subtype of accretionary olistostrome and confirm the existence of a subduction zone in the Paleoproterozoic in the east of the Anabar Shield. The olistostrome was formed in connection with underwater thrusts during the destruction of an accretionary uplift composed of weakly lithified and loose sedimentary material. The Sm-Nd isotope system of olistostrome rocks indicates a Paleoproterozoic age (TNd(DM2) = 2.34-2.42 Ga) and a juvenile (εNd(T) = 0.6-1.5) proximal nature of the rock source. U-Pb dating of zircon from detrital material and olistostrome matrix constrains the lower temporal boundary of the accretionary stage in the Khapchan Belt. Based on detrital zircon from the carbonate matrix of the olistostrome, the age of accretion is no older than 2009 ± 11 Ma. Granulite metamorphism with an age of 1898 ± 5 Ma is caused by collision events that followed accretion.
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Rey, Fernando, Matthew A. Malkowski et Hideki Masago. « ISOTOPIC VARIATIONS IN DETRITAL (ΕHF) AND WHOLE ROCK (ΕND) RECORDS ALONG RETREATING ACCRETIONARY MARGINS : INSIGHTS FROM SOUTHERN PATAGONIA AND JAPAN ». Dans GSA Connects 2023 Meeting in Pittsburgh, Pennsylvania. Geological Society of America, 2023. http://dx.doi.org/10.1130/abs/2023am-395987.
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Henderson, Miles A., Linda C. Kah, Guillermo L. Albanesi, Nicolás A. Feltes, Fernanda Serra, Victor J. Polyak et Yemane Asmerom. « 87SR/86SR AND εND STRATIGRAPHY OF MIDDLE ORDOVICIAN CARBONATE SEDIMENTS IN ARGENTINA : A POTENTIAL LINK BETWEEN BIOGEOCHEMICAL AND PHYSIOCHEMICAL CHANGES IN OCEAN CHEMISTRY ». Dans GSA Annual Meeting in Seattle, Washington, USA - 2017. Geological Society of America, 2017. http://dx.doi.org/10.1130/abs/2017am-297832.
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Heinonen, Jussi S., Arto V. Luttinen, Saku K. Vuori, Wendy A. Bohrson, Frank J. Spera et Melissa A. Scruggs. « TWO GABBROIC DIKES FROM THE KAROO LIP EXHIBIT INCREASING εND TOWARDS THE CONTACT WITH THE WALLROCK AND RECORD TWO DISTINCT STORIES OF DIFFERENTIATION ». Dans GSA Annual Meeting in Seattle, Washington, USA - 2017. Geological Society of America, 2017. http://dx.doi.org/10.1130/abs/2017am-302987.
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Bassom, Neil J., et Tung Mai. « Modeling and Optimizing XeF2-enhanced FIB Milling of Silicon ». Dans ISTFA 1999. ASM International, 1999. http://dx.doi.org/10.31399/asm.cp.istfa1999p0255.
Texte intégralRésumé :
Abstract Wide variations in the dose enhancement factor observed when milling silicon using Focused Ion Beam (FIB) XeF2 Gas Assisted Etching (GAE) prompted the development of a simple model of the GAE process. The model accounts for three material removal mechanisms: regular sputtering; gas-assisted sputtering; and spontaneous chemical reactions. An expression linking the dose enhancement factor, εd, to the gas and milling parameters has been derived. Experiments show that εd behaves as predicted; good quantitative agreement is achieved over wide ranges of milling parameters for εd values between 20X and 2500X. Conditions required to minimize variations in d and maximize material removal rates, M, are derived. It is shown that if the dose per unit area per raster is below a threshold value then εd and M depend only on the average current density J (the area of the box divided by the beam current). A consideration of the J regimes used for front-side and back-side FIB work shows why changes in εd have not previously been a problem but are inevitable when milling the large trenches characteristics of Flip Chip circuit modification work. While εd changes dramatically there is a region of J values for which M is approximately constant.
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Černičková, Ivona, Marek Mihalkovič, Libor Ďuriška, Peter Švec, Peter Švec et Jozef Janovec. « Atomic models of εn structural variants - Overview ». Dans APPLIED PHYSICS OF CONDENSED MATTER (APCOM 2022). AIP Publishing, 2023. http://dx.doi.org/10.1063/5.0135821.
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Makino, Toshiro, et Hidenobu Wakabayashi. « Experimental Verification of Kirchhoff’s Thermal Radiation Law on Surfaces With Emittance Spectra Characterized by Optical Interference Phenomena ». Dans 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22718.
Texte intégralRésumé :
This paper discusses Kirchhoff’s law on thermal radiation. The logic of derivation of the law is reconsidered, first. Then, spectra of normal emittance εN and normal incidence hemispherical reflectance RNH are measured on surfaces whose microstructure changes in a non-equilibrium experimental system to examine the validity of the complementary relation between εN and RNH, which is the suggestion of Kirchhoff’s law. As the results of the examination, it is illustrated experimentally on a variety of surfaces that the complementary relation is valid within an experimental uncertainty. Provided this conclusion is admitted, the followings are suggested. If a surface is designed so that it does not reflect a narrow spectral region of radiation to any direction and reflects the other spectral regions of radiation much over the hemisphere, then the surface can be a new spectrally-functional emitter of radiation. It is also suggested that thermal radiation emitted at a surface is considered as the emission of plane waves at the surface rather than as the emission of spherical waves by electric dipoles.