Archaean to Proterozoic Crustal Evolution in the Central Zone of the Limpopo Belt (South Africa-Botswana): Constraints from Combined U-Pb and Lu-Hf Isotope Analyses of Zircon   总被引：5，自引：0，他引：5  

Zeh  Armin; Gerdes  Axel; Klemd  Reiner; Barton  Jackson M.  Jr 《Journal of Petrology》2007,48(8):1605-1639

A combined set of U–Pb and Lu–Hf in situ laser ablationICP-(MC)-MS zircon analyses were obtained from orthogneissesand granitoids in the Central Zone of the Limpopo Belt, whichcomprises the Beit Bridge and Mahalapye complexes. The resultsindicate that by combining the two isotope systems primary magmaticzircon domains can be distinguished from those formed duringlater metamorphic events, even if the distinct zircon domainsunderwent multiple Pb loss and the texture–age relationships,as obtained by cathodoluminescence images and U–Pb analyses,are ambiguous. Furthermore, the applied technique allows distinctionof zircon grains formed in juvenile magmas from those generatedby melting of older continental crust or affected by substantialcrustal contamination. The combined U–Pb and Lu–Hfdata reveal that the Sand River gneiss suite of the Beit BridgeComplex was emplaced at 3283 ± 8 Ma and formed from meltingof an older Archaean crust, which was derived from a depletedmantle source at around 3·65 Ga. The hafnium model age(T_DM^Hf) is significantly older than those obtained from zirconsfrom numerous Neoarchaean granitoids of the Beit Bridge Complex,comprising the Singelele gneiss (2647 ± 12 Ma), the Bulaigranite (2612 ± 7 Ma), the Regina gneiss (2649 ±9 Ma) and two samples of the Zanzibar gneiss (2613 ±6 Ma). These granitoids show initial Hf(t) values between +0·5 and –7·1, which correspond to initialT_DM^Hf between 3·46 and 3·01 Ga. These variableT_DM^Hf_initial and Hf(t)_initial values are interpreted to be theresult of different mixtures of reworked 3·65 Ga Palaeoarchaeancrust with juvenile magmas extracted from the depleted mantleduring the Neoarchaean at 2·65 Ga. This conclusion issupported by results obtained from the Mahalapye Complex, whichwas affected by migmatization and granite intrusions duringthe Palaeoproterozoic at 2·02–2·06 Ga. TheMokgware granite (2019 ± 9 Ma) contains zircon xenocrystswith Pb–Pb ages of 2·52–2·65 Ga and2·93 Ga and hafnium model ages of 3·0–3·4Ga, indicating that this granite is derived from remelting ofArchaean crust. In contrast, uniform T_DM^Hf_initial ages of 2·61–2·67Ga obtained from a diorite gneiss (2061 ± 6 Ma) of theMahalapye Complex indicate that its protolith may have beenformed from remelting of a Neoarchaean juvenile crust. VariableHf(t)_initial values from –3·7 to +6·3 ofzircon cores (2711 ± 11 Ma) in an adjacent leucosomealso support a model of mixing of juvenile mantle derived matterwith older crust in the Neoarchaean. KEY WORDS: Archaean; Palaeoproterozoic; Limpopo Belt; zircon, U–Pb dating; Lu–Hf isotopes; LA-ICP-MS  相似文献   

Fluid Inclusions and Stable Isotopic Characteristics of the Yaoling Tungsten Deposit in South China: Metallogenetic Constraints     

Feng Yang  Wei Zhai  Xiaoming Sun  Reiner Klemd  Yanyan Sun  Yunshan Wu  Renmin Hua  Siqi Zheng 《Resource Geology》2019,69(1):107-122

The Yaoling tungsten deposit is a typical wolframite quartz vein‐type tungsten deposit in the South China metallogenic province. The wolframite‐bearing quartz veins mainly occur in Cambrian to Ordovician host rocks or in Mesozoic granitic rocks and are controlled by the west‐north‐west trending extensional faults. The ore mineralization mainly comprises wolframite and variable amounts of molybdenite, chalcopyrite, pyrite, fluorite, and tourmaline. Hydrothermal alteration is well developed at the Yaoling tungsten deposit, including greisenization, silicification, fluoritization, and tourmalinization. Three types of primary/pseudosecondary fluid inclusions have been identified in vein quartz, which is intimately intergrown with wolframite. These include two‐phase liquid‐rich aqueous inclusions (type I), two‐ or three‐phase CO₂‐rich inclusions (type II), and type III daughter mineral‐bearing multiphase high‐salinity aqueous inclusions. Microthermometric measurements reveal consistent moderate homogenization temperatures (peak values from 200 to 280°C), and low to high salinities (1.3–39 wt % NaCl equiv.) for the type I, type II, and type III inclusions, where the CO₂‐rich type II inclusions display trace amounts of CH₄ and N₂. The ore‐forming fluids are far more saline than those of other tungsten deposits reported in South China. The estimated maximum trapping pressure of the ore‐forming fluids is about 1230–1760 bar, corresponding to a lithostatic depth of 4.0–5.8 km. The δD_H2O isotopic compositions of the inclusion fluid ranges from ?66.7 to ?47.8‰, with δ¹⁸O_H2O values between 1.63 and 4.17‰, δ¹³C values of ?6.5–0.8‰, and δ³⁴S values between ?1.98 and 1.92‰, with an average of ?0.07‰. The stable isotope data imply that the ore‐forming fluids of the Yaoling tungsten deposit were mainly derived from crustal magmatic fluids with some involvement of meteoric water. Fluid immiscibility and fluid–rock interaction are thought to have been the main mechanisms for tungsten precipitation at Yaoling.  相似文献   

A Geodetic View on Isostatic Models   总被引：1，自引：0，他引：1  

Franziska Göttl  Reiner Rummel 《Pure and Applied Geophysics》2009,166(8-9):1247-1260

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Stef Proost and John B. Braden (eds.), Climate Change, Transport and Environmental Policy     

David Reiner  Andreas Schafer 《Climatic change》2000,47(1-2):217-224

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The Moho Structure in The Western Eger Rift: A Receiver Function Experiment     

Geissler  Wolfram  Plenefisch  Thomas  Kind  Reiner  Klinge  Klaus  Kämpf  Horst  Boušková  Alena  Nehybka  Vladimír  Skácelová  Zuzana  Jacob  Brian 《Studia Geophysica et Geodaetica》2000,44(2):188-194

We used teleseismic recordings of a temporary deployment of seismic stations and of permanent short period stations in the western Eger Rift system to study the lithosphere with the help of Receiver Functions. The crust-mantle boundary (Moho) is observed at almost all stations by strong P-to-S converted phases. The Moho is basically flat between about 26 – 30 km depth in the entire region. At one station in the Eger Rift (BOH-1, Loket castle) no Moho is observed. We interpret this with the existence of a broad gradient zone there, instead of a sharp discontinuity. This observation, however, needs to be confirmed by more data.  相似文献   

Analysis of the photometric and spectroscopic period of the symbiotic star AG Pegasi with consequences for the model     

Reiner Luthardt 《Astronomische Nachrichten》1990,311(2):141-141

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德国4站点极端降水频数和强度趋势变化分析   总被引：1，自引：0，他引：1  

杨靖文  孙即霖  Reiner Schlitzer 《中国海洋大学学报(自然科学版)》2010,(Z1)

根据不莱梅、波茨坦、卡尔斯鲁厄和楚格峰1901—2007年逐日降水量分析了各站极端降水的频数和强度趋势变化。结果表明:山区(楚格峰)出现的极端降水数量呈上升趋势,且强度显著增强,在冬、夏2季亦如此。这与全球变暖背景下,山区的积雪融化导致对流活动增强以及大气环流影响水汽输送增强有关;在超过绝对阈值的极端降水方面,北方地区(不莱梅和波茨坦)发生频数保持稳定,无显著趋势变化,南方地区(卡尔斯鲁厄)有显著减少的趋势,且不莱梅的频数变化趋势与波茨坦相似,具有强正相关,而此2站与卡尔斯鲁厄的频数变化趋势呈反位相,有较强的负相关;除楚格峰外,极端降水强度变化无显著趋势。低海拔地区在冬季极端降水的频数和强度上,大部分有显著上升的趋势,而夏季,在2方面均出现不同程度的下降;极端降水频数和强度呈强正相关。  相似文献   

On the spectral consistency of the altimetric ocean and geoid surface: a one-dimensional example     

Alberta Albertella  Reiner Rummel 《Journal of Geodesy》2009,83(9):805-815

Geoid models from the new generation of satellite gravity missions, such as GRACE and GOCE, in combination with sea surface from satellite altimetry allow to obtain absolute dynamic ocean topography with rather high spatial resolution and accuracy. However, this implies combination of data with fundamentally different characteristics and different spatial resolutions. Spectral consistency would imply the removal of the short-scale features of the altimetric sea surface height by filtering, to provide altimetric data consistent with the resolution of the geoid field. The goal must be to lose as little as possible from the high precision of the altimetric signal. Using a one-dimensional example we show how the spectrum is changing when a function defined only on a limited domain (ocean in the real case) is extended or not as to cover the complete domain (the whole sphere in the real case). The results depend on the spectral characteristics of the altimetric signal and of the applied filter. Referring to the periodicity condition, as it is requested in the case of Fourier analysis, the action of the two classical filters (Ideal Low Pass and Gauss filter) and of two alternative procedures (wavelets and Slepian) is studied.  相似文献   

Reconstructing past eutrophication trends from diatoms and biogenic silica in the sediment and the pelagic zone of Lake Constance, Germany     

Martin Wessels  Kirsten Mohaupt  Reiner Kümmerlin  Angela Lenhard 《Journal of Paleolimnology》1999,21(2):171-192

In Lake Constance, phosphorus concentrations and the seasonal development of phytoplankton communities in water samples from the pelagic zone were regularly recorded since the 1950's. Before the 1950's, there were occasional investigations of plankton communities since 1896. We compared these data with the sedimentary record in two sediment cores. Then, the eutrophication history of Lake Constance was inferred from diatoms. The record of biogenic silica in the cores is discussed with respect to diatom biomass increase.Diatom assemblages in the sediment cores precisely reflected the pelagic diatom development for the period 1971--1992. Both sediment cores and the water samples have a high interannual variability of diatom assemblages. Below a sediment depth of 27 cm (AD 1920), more than 50% of the diatoms were partly corroded, and we limited the reconstruction of trophic state changes to the interval of 1920--1993. Oligotrophic conditions of Lake Constance were indicated by the dominance of various Cyclotella taxa from 1920 to 1940. Since 1939/1940, increasing abundance of it Tabellaria fenestrata showed oligotrophic to mesotrophic conditions. Between 1953 and 1956, increasing Stephanodiscus hantzschii and disappearing Cyclotella indicated advanced eutrophication and total phosphorus values ranged between 8--10 mg m-3 during turnover in late winter. Further eutrophication was shown by disappearing T. fenestrata and increasing S. minutulus in 1963. Maximum TP concentrations of 87 mg m-3 occurred in 1979/80 and was accompanied by increasing abundances of Aulacoseira granulata. From 1986 to 1992, reoccurrence of Tabellaria fenestrata and Cyclotella indicate some recovery of Lake Constance.Biogenic silica and diatom abundances were similar among cores but indicate a 3--4 fold increase of diatom biomass only. This was far below the estimate of biomass increase from sedimentary pigment data (25 fold) and the estimate of phytoplankton data from the literature (70 fold).  相似文献   

On the geoid–quasigeoid separation in mountain areas     

Jakob Flury  Reiner Rummel 《Journal of Geodesy》2009,83(9):829-847

The separation between the reference surfaces for orthometric heights and normal heights—the geoid and the quasigeoid—is typically in the order of a few decimeters but can reach nearly 3 m in extreme cases. The knowledge of the geoid–quasigeoid separation with centimeter accuracy or better, is essential for the realization of national and international height reference frames, and for precision height determination in geodetic engineering. The largest contribution to the geoid–quasigeoid separation is due to the distribution of topographic masses. We develop a compact formulation for the rigorous treatment of topographic masses and apply it to determine the geoid–quasigeoid separation for two test areas in the Alps with very rough topography, using a very fine grid resolution of 100 m. The magnitude of the geoid–quasigeoid separation and its accuracy, its slopes, roughness, and correlation with height are analyzed. Results show that rigorous treatment of topographic masses leads to a rather small geoid–quasigeoid separation—only 30 cm at the highest summit—while results based on approximations are often larger by several decimeters. The accuracy of the topographic contribution to the geoid–quasigeoid separation is estimated to be 2–3 cm for areas with extreme topography. Analysis of roughness of the geoid–quasigeoid separation shows that a resolution of the modeling grid of 200 m or less is required to achieve these accuracies. Gravity and the vertical gravity gradient inside of topographic masses and the mean gravity along the plumbline are modeled which are important intermediate quantities for the determination of the geoid–quasigeoid separation. We conclude that a consistent determination of the geoid and quasigeoid height reference surfaces within an accuracy of few centimeters is feasible even for areas with extreme topography, and that the concepts of orthometric height and normal height can be consistently realized and used within this level of accuracy.  相似文献