Behaviour of rare-earth elements in highly evolved granitic systems: Evidence from Proterozoic molybdenite mineralized aplites and associated granites in northern Sweden   总被引：1，自引：0，他引：1  

Bj  rn   hlander  Kjell Billstr  m  Elke H  lenius 《Lithos》1989,23(4):267-280

Field relations, mineralogy, major- and trace-element contents (including REE analyses of whole-rock samples and minerals) of three Proterozoic granites and their associated molybdenite mineralized aplites have been studied at Allebuoda, Munka and Kåtaberget in northern Sweden. The granites crystallized from melts that were not saturated with water. The mineralized potassic aplites formed by quenching of residual melts caused by sudden pressure drop, H₂O saturation and vapour escape during tectonic rupturing. Leucogranites with higher Na₂O/K₂O ratios from Allebuoda and Munka crystallized during H₂O-saturated equilibrium conditions in which the exsolved vapour could continuously migrate away. The pressure was probably 3 kbar at Munka, and somewhat lower at Allebuoda.

The granites have REE patterns characterized by LREE enrichments and negative Eu anomalies. In comparison, the potassic aplites and the more sodic leucogranites are depleted in LREE, enriched in HREE and have larger negative Eu anomalies. Allanite and monazite are the most important REE carriers in the granites. These minerals are strongly enriched in LREE, whereas fluorite and xenotime, which are more abundant in the aplites, are most enriched in HREE. Due to the strong control of accessory minerals on the REE balance, REE are of limited use in petrogenetic modelling of highly evolved granitic systems.  相似文献   

The peat bog at Zinnwald-Georgenfeld revisited after 25 years: Geochemical investigation of water,Sphagnum moss and peat cores     

Elke Bozau  Sonja Lojen  Nina Zupančič 《Chemie der Erde / Geochemistry》2022,82(1):125823

From 1992 to 1994, trace metal concentrations of bog water, Sphagnum mosses and peat cores of the bog “Georgenfelder Hochmoor” at Zinnwald-Georgenfeld in the Eastern Ore Mountains (Germany) were investigated. A sampling campaign in September 2019 allows the comparison of the older measurements with today's trace metal concentrations. No changes were found in the bog waters, while the trace metal concentrations of the Sphagnum mosses have decreased significantly. Due to the low growth rate of the peat and despite certain heterogeneity between the peat cores, the investigated elemental data for the peat sampled in the 1990s and in 2019 are in the same concentration range. The maximum concentrations are measured in the upper samples of all peat cores for the analysed elements (except sulphur). Compared to upper crustal data, a different behaviour of the elements is observed: Cr, Sc, Ti, and V, rare earth elements show crustal ratios, while Al and Si are also influenced by crust-air fractionation. Cd, Cu, Ni, Pb, and Zn are additionally enriched by anthropogenic atmospheric inputs from industry and transport. These results confirm the assumption that peat cores record past atmospheric deposition.  相似文献   

If climate action becomes urgent: the importance of response times for various climate strategies     

Detlef P. van Vuuren  Elke Stehfest 《Climatic change》2013,121(3):473-486

Most deliberations on climate policy are based on a mitigation response that assumes a gradually increasing reduction over time. However, situations may occur where a more urgent response is needed. A key question for climate policy in general, but even more in the case a rapid response is needed, is: what are the characteristic response times of the response options, such as rapid mitigation or solar radiation management (SRM)? This paper explores this issue, which has not received a lot of attention yet, by looking into the role of both societal and physical response times. For mitigation, technological and economic inertia clearly limit reduction rates with considerable uncertainty corresponding to political inertia and societies’ ability to organize rapid mitigation action at what costs. The paper looks into a rapid emission reductions of 4–6 % annually. Reduction rates at the top end of this range (up to 6 %) could effectively reduce climate change, but only with a noticeable delay. Temperatures could be above those in the year of policy introduction for more than 70 years, with unknown consequences of overshoot. A strategy based on SRM is shown to have much shorter response times (up to decades), but introduces an important element of risk, such as ocean acidification and the risk of extreme temperature shifts in case action is halted. Above all, the paper highlights the role of response times in designing effective policy strategies implying that a better understanding of these crucial factors is required.  相似文献   

Reconstruction of the variability of the southwest monsoon during the past 3 ka,from the continental margin of the southeastern Arabian Sea     

Onkar S. Chauhan  Elke Vogelsang  Nathani Basavaiah  U. Syed Abdul Kader 《第四纪科学杂志》2010,25(5):798-807

From temporal variation in δ¹⁸O in Globigerinoides ruber and G. sacculifer and geochemical indices of weathering/erosion (chemical index of alteration, Al and Ti), we infer rapid southwest monsoon (SWM) deterioration with dwindling fluvial and detrital fluxes at ca. 450–650, 1000 and 1800–2200 cal. a BP during the late Holocene. We have evaluated the role of solar influx (reconstructed) and high‐latitude climate variability (archived in GRIP and GISP‐2 cores) on SWM precipitation. Broadly, our δ¹⁸O climate reconstruction is concordant with GRIP and GISP‐2, and supports a teleconnection through atmospheric connection between the SWM and the North Atlantic climate – albeit temporal extents of the Little Ice Age and Medieval Warm Period from high latitude are not entirely coeval. Moreover, there is a humid climate and enhanced precipitation during the terminal stages of the Little Ice Age. The medieval warming (ca. AD 800–1300) is not synchronous either, and is punctuated by an arid event centred at 1000 a BP. Although the delineation of the specific influence of solar influx on SWM precipitation is elusive, we surmise that SWM precipitation is a complex phenomenon and local orography along southwestern India may have a role on the entrapment of moisture from the southwest trade winds, when these hit land. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Organic carbon mobilization in a Bangladesh aquifer explained by seasonal monsoon-driven storativity changes     

Britta Planer-Friedrich  Cornelia Härtig  Heidi Lissner  Jörg Steinborn  Elke Süß  M. Qumrul Hassan  Anwar Zahid  Mahmood Alam  Broder Merkel 《Applied Geochemistry》2012

Currently, the most widely accepted hypothesis to explain high As concentrations in Bangladesh groundwaters is that dissolved organic C (DOC) reduces solid Fe (hydr)oxides and mobilizes sorbed arsenate. The nature of the DOC and its release mechanism are still controversial. Based on weekly to biweekly sampling over the course of one monsoon cycle at six monitoring wells of different depths, it is proposed that storativity changes drive natural DOC release from clay–peat layers to the adjacent aquifers. With a decrease in hydraulic heads during the dry season, total mineralization and DOC concentrations increased. With the onset of the rainy season and an increase in hydraulic heads, release of clay–peat derived components stopped and vertical water displacement due to groundwater recharge from rainwater occurred, causing aquifer flushing and a decrease in total mineralization and DOC concentrations. Total As and DOC concentrations correlated over depth. However, at the depth of maximum concentrations, the As peak was observed during the rainy season. At present, the reason for this inverse seasonal trend between As and DOC is unclear. Higher mineralization or DOC concentrations could lead to increased As sorption or the increased arsenite release is a time-lag abiotic or microbial response to the DOC peak. The vulnerability of the Pleistocene aquifer towards increased As concentrations was found to be much higher than previously assumed. Though sorption capacities were determined to be higher than in the Holocene aquifer, probably due to intact Fe (hydr)oxides, long-term continuous As input from overlying clay and peat layers by the proposed seasonal storativity changes has led to increased aqueous As concentrations of 85 μg/L, considerably higher than drinking water standards. Until now, aquifer and especially aquitard and aquiclude hydraulics have not been considered sufficiently when attempting to explain As mobilization in Bangladesh.  相似文献   

Influence of changed vegetations fields on regional climate simulations in the Barents Sea Region     

Holger Göttel  Jörn Alexander  Elke Keup-Thiel  Diana Rechid  Stefan Hagemann  Tanja Blome  Annett Wolf  Daniela Jacob 《Climatic change》2008,87(1-2):35-50

In the context of the EU-Project BALANCE () the regional climate model REMO was used for extensive calculations of the Barents Sea climate to investigate the vulnerability of this region to climate change. The regional climate model REMO simulated the climate change of the Barents Sea Region between 1961 and 2100 (Control and Climate Change run, CCC-Run). REMO on ~50 km horizontal resolution was driven by the transient ECHAM4/OPYC3 IPCC SRES B2 scenario. The output of the CCC-Run was applied to drive the dynamic vegetation model LPJ-GUESS. The results of the vegetation model were used to repeat the CCC-Run with dynamic vegetation fields. The feedback effect of the modified vegetation on the climate change signal is investigated and discussed with focus on precipitation, temperature and snow cover. The effect of the offline coupled vegetation feedback run is much lower than the greenhouse gas effect.  相似文献   

The effect of agricultural trade liberalisation on land-use related greenhouse gas emissions     

Ren Verburg  Elke Stehfest  Geert Woltjer  Bas Eickhout 《Global Environmental Change》2009,19(4):434-446

This study explores the effects of agricultural trade liberalisation and concomitant changes in agricultural areas and livestock production on greenhouse gas emissions using the coupled LEITAP–IMAGE modelling system. The results indicate that liberalisation leads to an increase in total greenhouse gas emissions by about 6% compared to the reference scenario value in 2015. The increase in CO₂ emissions are caused by vegetation clearance due to a rapid expansion of agricultural area; mainly in South America and Southeast Asia. Increased methane emissions in the case of full liberalisation are caused by less intensive cattle farming in regions such as South America and Southeast Asia. This pattern is observed up to 2050. Total global production of milk, dairy and beef do not change with full liberalisation, but production shifts were observed from North America and Europe to South America and Southeast Asia. Results are less pronounced in variants where trade liberalisation is only implemented partially. Remarkably, our study shows in the trade barrier removal scenario larger numbers of dairy cows in Australia and New Zealand (ANZ) then with full liberalisation scenario or a variant in which only milk quota are abolished. This illustrates that different types of liberalisation need to be analysed regionally and per commodity before general conclusions on the impact of trade liberalisation can be drawn. Our study contributes new information on greenhouse gas emissions to a vast number of trade liberalisation studies that focus on economic impacts. The combined economic-environmental impacts need to be assessed in detail before general conclusions on trade liberalisation can be given.  相似文献   

Women and desertification: The question of responsibility     

Elke Grawert 《GeoJournal》1993,31(1):85-88

Campaigns against desertification frequently address women, who are held responsible for rapid population growth and biomass burning. It is shown here how desertification is caused by the erosion of social coherence. This diagnosis requires a fundamental change in anti-desertification policies.  相似文献   

High resolution Th_ex stratigraphy of sediments from high-latitude areas (Norwegian Sea, Fram Strait)     

Jan C. Scholten  Reiner Botz  Augusto Mangini  Hanno Paetsch  Peter Stoffers  Elke Vogelsang 《Earth and Planetary Science Letters》1990,101(1)

We present data on the average sedimentation rates (ranging from 1.6 cm/kyr to 3 cm/kyr) for the last 300.000 years based on δ¹⁸O analyses of foraminifera in a core from the Norwegian Sea and ²³⁰Th_ex measurements in cores from the Norwegian Sea and the Fram Strait (Arctic Ocean). Furthermore, we relate ²³⁰Th_ex variations downcore to the various oxygen isotope stages. This correlation is tentatively interpreted as being a result of the paleoceanographic and paleoclimatic control of bioproductivity. It is shown that based on the average sedimentation rates and characteristic ²³⁰Th_ex variations carbonate-poor sediment cores from northern latitudes can be correlated.  相似文献   

Petrography and arrangement of Tertiary graywacke and sandstone sequences of the Northern Apennines     

Elke Deneke  Konrad Günther 《Sedimentary Geology》1981,28(3):189-230

In order to obtain new sedimentological data for a better understanding of the palaeo geological assembly of the various sedimentary and tectonic complexes of the Northern Apennines, the authors have re-examined and re-analysed the petrography of the main Tertiary graywacke and sandstone sequences of this mountain range. Several hundred thin sections and heavy-mineral preparations have been studied qualitatively and quantitatively. Generally, for all investigated graywackes and sandstones a source area with a more or less uniform petrographic organization can be assumed, since all different components, though in variable distributions, occur in all the studied sequences. Differences in the abundance of the components in the individual graywackes and sandstones are attributable to influences of the source area itself. The distribution of quartz-poor or quartz-free volcanic rocks, quartz—epidote—zoisite schists, and carbonatic cement in the samples and epidote and zoisite in the heavy-mineral preparations indicate, however, a certain palaeogeological succession of the original areas of deposition from the internal to the external parts of the mountain range.  相似文献