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91.
Jeroen T.M. de Jong Marie Boyé Maria D. Gelado-Caballero Klaas R. Timmermans Marcel J.W. Veldhuis Rob F. Nolting Constant M.G. van den Berg Hein J.W. de Baar 《Marine Chemistry》2007
Dissolved Fe, Mn and Al concentrations (dFe, dMn and dAl hereafter) in surface waters and the water column of the Northeast Atlantic and the European continental shelf are reported. Following an episode of enhanced Saharan dust inputs over the Northeast Atlantic Ocean prior and during the cruise in March 1998, surface concentrations were enhanced up to 4 nmol L− 1 dFe, 3 nmol L− 1 dMn and 40 nmol L− 1 dAl and returned to 0.6 nmol L− 1 dFe, 0.5 nmol L− 1 dMn and 10 nmol L− 1 dAl towards the end of the cruise three weeks later. A simple steady state model (MADCOW, [Measures, C.I., Brown, E.T., 1996. Estimating dust input to the Atlantic Ocean using surface water aluminium concentrations. In: Guerzoni. S. and Chester. R. (Eds.), The impact of desert dust across the Mediterranean, Kluwer Academic Publishers, The Netherlands, pp. 301–311.]) was used which relies on surface ocean dAl as a proxy for atmospheric deposition of mineral dust. We estimated dust input at 1.8 g m− 2 yr− 1 (range 1.0–2.9 g m− 2 yr− 1) and fluxes of dFe, dMn and dAl were inferred. Mixed layer steady state residence times for dissolved metals were estimated at 1.3 yr for dFe (range 0.3–2.9 yr) and 1.9 yr for dMn (range 1.0–3.8 yr). The dFe residence time may have been overestimated and it is shown that 0.2–0.4 yr is probably more realistic. Using vertical dFe versus Apparent Oxygen Utilization (AOU) relationships as well as a biogeochemical two end member mixing model, regenerative Fe:C ratios were estimated respectively to be 20 ± 6 and 22 ± 5 μmol Fe:mol C. Combining the atmospheric flux of dFe to the upper water column with the latter Fe:C ratio, a ‘new iron’ supported primary productivity of only 15% (range 7%–56%) was deduced. This would imply that 85% (range 44–93%) of primary productivity could be supported by regenerated dFe. The open ocean surface data suggest that the continental shelf is probably not a major source of dissolved metals to the surface of the adjacent open ocean. Continental shelf concentrations of dMn, dFe, and to a lesser extent dAl, were well correlated with salinity and express mixing of a fresher continental end member with Atlantic Ocean water flowing onto the shelf. This means probably that diffusive benthic fluxes did not play a major role at the time of the cruise. 相似文献
92.
93.
A new process-based approach is introduced for a more efficient computation of the overflow-induced growth of an erosional channel in a non-cohesive homogeneous narrow landmass such as the breach growth in a sand-dike. The approach is easy to incorporate in a 1D/2DV morphodynamic model to compute the channel growth both vertically and laterally. 相似文献
94.
J. D. Clemens 《Australian Journal of Earth Sciences》2020,67(2):175-200
AbstractInformation, mainly from the granitic and silicic volcanic rocks in the Stawell, Bendigo and Melbourne structural zones in the state of Victoria, shows that the sources of both the S- and I-type rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with the sources of similar granitic rocks in the Melbourne Zone, consistent with the absence of the mainly Proterozoic Selwyn Block beneath most of the SBZ. Below a mid-crustal décollement in the SBZ, the crust is evidently highly variable and possibly includes thinned Proterozoic crust. There is geochronological evidence for ca 400 and ca 370?Ma granulite-grade metamorphic events here, and, after this double bout of metamorphism, and depletion in the silicic melt component, the constituents of the entire deep crust of the SBZ would have densities similar to those of overlying, much lower-grade Cambrian metabasaltic to boninitic rocks. Thus, granitic magmas may have formed here by partial melting of a variety of rock types, probably with back-arc affinities, with ages that may extend back to the Proterozoic. Therefore, the basement of the SBZ is unlikely to consist solely of thick ocean-floor rocks, as in some current interpretations.
- KEY POINTS
The sources of the Devonian granitic rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with those of the Melbourne Zone granites.
Two Devonian granulite-facies events left the melt-depleted deep SBZ crust with densities similar to those of overlying Cambrian metabasaltic rocks.
The SBZ Devonian granitic magmas probably formed by partial melting of heterogeneous Proterozoic to Cambrian arc-related crust, below the mid-crustal décollement.
95.
Namık Aysal Marcel Guillong Tamara Bayanova Mayuko Fukuyama Nicole Leonard İsak Yılmaz Elif Varol Fatma Şişman Tükel Yusuf Kaan Kadıoğlu Nurullah Hanilçi Fulya Uzun Ersin Kaygısız 《Geostandards and Geoanalytical Research》2023,47(2):297-310
Gem quality andradite-rich garnet (IUC-1), obtained from the Miocene trachyte dome near Ankara city (Turkey), has been identified as a potential natural secondary reference material for U-Pb dating. In this study, U-Pb dating was performed in five different laboratories using isotope dilution TIMS and laser ablation ICP-MS to determine the homogeneity of euhedral garnet crystals. The U-Pb ID-TIMS data for IUC-1 yielded 207Pb/235U and 206Pb/238U ages of 20.9 ± 0.4 and 20.6 ± 0.8 Ma respectively, and these values are consistent with U-Pb LA-ICP-MS analyses, in which different garnet crystals yielded ages of 20.8 ± 0.1, 20.7 ± 0.1, 20.7 ± 0.2 and 20.2 ± 0.1 Ma. An andradite (IUC-2) from the Serçeören wollastonite skarn (Turkey) can be used as a secondary reference material provided detailed imaging of the crystals is undertaken. ID-TIMS data yielded 207Pb/235U and 206Pb/238U ages of 20.4 ± 0.4 and 20.9 ± 1.0 Ma respectively, and yielded U-Pb ages on different grains of 20.5 ± 0.1, 20.7 ± 1.0, 20.8 ± 1.7 and 20.9 ± 1.6 Ma. The assigned weighted mean age of IUC-1 (20.4 ± 0.5 Ma, 2s) is proposed as a 2023 reference value. IUC-1 garnet is expected to contribute significantly to rapidly developing garnet geochronology in the near future. 相似文献
96.
Clemens Reimann David B. Smith Laurel G. Woodruff Belinda Flem 《Applied Geochemistry》2011,26(9-10):1623-1631
Analytical results for Pb-concentrations and isotopic ratios from ca. 150 samples of soil A horizon and ca. 145 samples of soil C horizon collected along a 4000-km east–west transect across the USA are presented. Lead concentrations along the transect show: (1) generally higher values in the soil A-horizon than the C-horizon (median 21 vs. 16.5 mg/kg), (2) an increase in the median value of the soil A-horizon for central to eastern USA (Missouri to Maryland) when compared to the western USA (California to Kansas) (median 26 vs. 20 mg/kg) and (3) a higher A/C ratio for the central to eastern USA (1.35 vs. 1.14). Lead isotopes show a distinct trend across the USA, with the highest 206Pb/207Pb ratios occurring in the centre (Missouri, median A-horizon: 1.245; C-horizon: 1.251) and the lowest at both coasts (e.g., California, median A-horizon: 1.195; C-horizon: 1.216). The soil C-horizon samples show generally higher 206Pb/207Pb ratios than the A-horizon (median C-horizon: 1.224; A-horizon: 1.219). The 206Pb/207Pb-isotope ratios in the soil A horizon show a correlation with the total feldspar content for the same 2500-km portion of the transect from east-central Colorado to the Atlantic coast that shows steadily increasing precipitation. No such correlation exists in the soil C horizon. The data demonstrate the importance of climate and weathering on both Pb-concentration and 206Pb/207Pb-isotope ratios in soil samples and natural shifts thereof in the soil profile during soil-forming processes. 相似文献
97.
Dipl.-Geol. Clemens Marzela 《International Journal of Earth Sciences》1981,70(2):473-479
Zusammenfassung In Gesteinen des jüngsten Präkambriums und Unterkambriums (mit einer Diskordanz nach dem pC III) sind im Antiatlas Marokkos wiederholt Anzeichen für eine Sedimentation bei warmem (semiarid bis arid) Klima zu finden. Klimaindikatoren sind Rotsedimente, CaSO4- und NaCl-Pseudomorphosen sowie Sedimente vom Sabkha-Typ.Paläomagnetische Daten weisen zu dieser Zeit auf Südpolpositionen in diesem Gebiet hin.Vereisungsrelikte in Nachbargebieten entsprechen möglicherweise einer Sedimentationslücke nach dem pC III im Antiatlas.
In the Antiatlas region of Morocco rocks of Late-Precambrian and Lower-Cambrian age (with a discordance after the pC III) show evidence for sedimentation under warm (semiarid to arid) climate. Climate indicators are redbeds, sabkha-sediments and pseudomorphoses after CaSO4 and NaCl.Paleomagnetic data showed that at this time southpole positions were distributed in this area.In nearby regions documents of glaciation are possibly correspondend with a time of non-sedimentation after the pC III in the Antiatlas.
Résumé Les roches du Précambrien supérieur et du Cambrien inférieur de l'Antiatlas du Maroc (avec une discordance après le pC III) présentent de nombreuses évidences d'une sédimentation sous des conditions climatiques chaudes (semiarides à arides). Les indicateurs climatiques sont des couches rouges, des sédiments de sabkha et des pseudomorphoses de CaSO4 et NaCl.Les études paléomagnétiques démontrent que l'emplacement du pôle sud se trouvait à cette époque dans cette même région.Les restes de glaciation dans les régions voisines paraissent corréspondre à une periode de nonsédimentation après le pC III dans l'Antiatlas.
— III- ( ) . , CaSO4 NaCl, Sabkha. , . , , — 800–900 .相似文献
98.
99.
Over several years many partition coefficients have been measured between framework silicates, sheet silicates and hydrothermal solutions. Only trace alkaline cations are considered in the present work. It is well known that the difference between ionic radii of the trace cation and the major cation is replaces is not satisfactory for a good correlation with the partition coefficients PX. A structural parameter δc is therefore defined, taking into consideration the adaptation of the trace cation to the cavity in which it occurs. This cavity may be the entire site of the major element, or a part of this site in the case of small cations, or a structural cavity located out of the alkali-ion site. The adaptation parameter δc is the difference between the ionic radius of the trace cation and the radius of that cavity. This paper shows that the partition coefficient PX of the trace alkali-ion from the hydrothermal solution is an exponential function of the adaptation parameter δc, whatever the silicate may be. 相似文献
100.