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971.
The Ordovician Kellerjochgneiss (Schwaz Augengneiss) is a polymetamorphic orthogneiss-bearing unit and is part of the Austroalpine basement nappes north of the Tauern Window. Within the Kellerjochgneiss a small, strongly deformed metapegmatite dike occurs. The pegmatite crosscuts the gneiss discordantly and contains the mineral assemblage muscovite 1,2+plagioclase+K-feldspar+chlorite+quartz+garnet 1 (Alm67–76Andr0.9–2Sps17–28Prp0.4–5)+garnet 2 (Grs36–46Alm24–32Andr8–21Sps15–17Prp0–1)±stilpnomelane±biotite±clinozoisite. The magmatic protolith assemblage is comprised of relict K-feldspar, quartz and garnet 1. Textural observations indicate that biotite and muscovite cores (muscovite 1) are either part of the magmatic- or an earlier (Variscan?) metamorphic assemblage. Geothermobarometry of the metapegmatite was done on the latest-stage (Eo-Alpine) mineral assemblage garnet 2+muscovite 2+chlorite+stilpnomelane+plagioclase+quartz. Calculations of H2O-absent intersections in the system [KCNFMAS] with the multi-equilibrium program THERMOCALC v.3.1 yielded P–T estimates of 4.4 to 6.7 kbar and 321°C to 376°C. Calculations of the P–T conditions by using the assemblage muscovite 2+chlorite+stilpnomelane+quartz yielded slightly higher pressures of 6.4 to 7.2 kbar at temperatures of 310–325°C. Correlating these P–T data with geochronological data from the neighbouring lithologies (Kellerjochgneiss, Innsbruck Quartzphyllite, Wildschönau Schists) and with structural investigations from these units indicate that the P–T estimates obtained in this investigation represent the Eo-Alpine metamorphic overprint. Hence, these unusual rocks provide important information on the Eo-Alpine P–T conditions since most samples studied from the investigated Austroalpine basement nappes north of the Tauern Window rarely contain mineral assemblages suitable for geothermobarometry. 相似文献
972.
探究CGSG系列标准物质(CGSG-1、CGSG-2、CGSG-4、CGSG-5)的元素分馏效应及均匀性问题有助于开展其质量评估和应用推广。本文采用电子探针(EMPA)和激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)研究了CGSG标准物质中的元素分馏效应、主量和微量元素单元内均匀性,并报道了主量和微量元素分析数据。结果表明,在50μm激光束斑下,CGSG系列标准物质的元素分馏效应可忽略不计。EMPA均匀性指数结果显示,CGSG标准物质主量元素的单元内均匀性满足要求;以MPI-DING标准物质为参照,LA-ICP-MS测试CGSG标准物质中的大多数微量元素的单元内均匀性良好。与已报道的数据相比,本文报道的EMPA主量元素数据偏差在2%以内;LA-ICP-MS主量元素数据偏差在5%以内,微量元素数据基本匹配,少数元素由于分析不确定度较大等原因,如Cr、Ge、Cd、As、Tl等与已报道数据偏差较大。总体上,本文报道的分析数据可为CGSG定值数据库提供进一步的补充。 相似文献
973.
Nicole A. Stroncik Andreas Klügel Thor H. Hansteen 《Contributions to Mineralogy and Petrology》2009,157(5):593-607
A thermobarometric and petrologic study of basanites erupted from young volcanic cones along the submarine portions of the
three El Hierro rift zones (NE-Rift, NW-Rift and S-Ridge) has been performed to reconstruct magma plumbing and storage beneath
the island. Mineral-melt thermobarometry applied to naturally quenched glass and clinopyroxene rims yields pressures ranging
from 350 to 1070 MPa with about 80% of the calculated pressures being in the range of 600–800 MPa. This corresponds to a depth
range of 19–26 km, implying that the main level of final crystal fractionation is within the uppermost mantle. No systematic
dependence between sample locality and fractionation pressures could be observed. Olivine and clinopyroxene crystals in the
rocks are complexly zoned and have, on an inter-sample as well as on an intra-sample scale, highly variable core and rim compositions.
This can best be explained by mixing of multiply saturated (olivine, magnetite, clinopyroxene, ilmenite), moderately evolved
magmas with more mafic magmas being either only saturated with olivine + spinel or with olivine + spinel + clinopyroxene.
The inter-sample differences indicate derivation from small, isolated magma chambers which have undergone distinct fractionation
and mixing histories. This is in contrast to oceanic intraplate volcanoes situated on plumes with high melt supply rates,
e.g. Kilauea Volcano (Hawaii), where magma is mainly transported through a central conduit system and stored in a shallow
magma chamber prior to injection into the rift zones. The plumbing system beneath El Hierro rather resembles the magma storage
systems beneath, e.g. Madeira or La Palma, indicating that small, intermittent magma chambers might be a common feature of
oceanic islands fed by plumes with relatively low fluxes, which results in only limited and periodic magma supply. 相似文献
974.
975.
Andreas J. Scheib Jonathan R. Lee Neil Breward James B. Riding 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(3):432-444
High-density regional geochemical data for surface soils in central England and East Anglia reveal that much of their geochemical character is inherited from the tills that they are developed upon. Multivariate statistical analysis highlighted three significant element associations of Al–Fe–Ga–K–La–Mg–Rb, Ca–Sr and K–Fe accounting for almost 93% of the geochemical variability of soils derived from tills. Provenancing the geochemical signatures of the latter elements enabled the construction of ice flow paths associated with two different Middle Pleistocene ‘chalky’ till sheets. A lower till sheet relating to ‘Pennine’ ice flowing from west to east across the region, and an upper till sheet deposited by North Sea ice moving into northern East Anglia, and to the west of the Fen Basin, before fanning-out across central England. Overall, geochemical signatures of different till units are largely derived from local bedrock sources, with dilution and a new geochemical signature acquired as the ice flows over and incorporates new bedrock lithologies. The results show that high resolution soil geochemical data provides a further proxy with which the flow paths of former ice sheets can be delineated. 相似文献
976.
We argue that Arctic sea ice played an important role during early stages of the last glacial inception. Two simulations of the Institut Pierre Simon Laplace coupled model 4 are analyzed, one for the time of maximum high latitude summer insolation during the last interglacial, the Eemian, and a second one for the subsequent summer insolation minimum, at the last glacial inception. During the inception, increased Arctic freshwater export by sea ice shuts down Labrador Sea convection and weakens overturning circulation and oceanic heat transport by 27 and 15%, respectively. A positive feedback of the Atlantic subpolar gyre enhances the initial freshening by sea ice. The reorganization of the subpolar surface circulation, however, makes the Atlantic inflow more saline and thereby maintains deep convection in the Nordic Seas. These results highlight the importance of an accurate representation of dynamic sea ice for the study of past and future climate changes. 相似文献
977.
Andreas Borchers Elisabeth Dietze Gerhard Kuhn Oliver Esper Ines Voigt Kai Hartmann Bernhard Diekmann 《Marine Geophysical Researches》2016,37(1):49-70
A multi-proxy study including sedimentological, mineralogical, biogeochemical and micropaleontological methods was conducted on sediment core PS69/849-2 retrieved from Burton Basin, MacRobertson Shelf, East Antarctica. The goal of this study was to depict the deglacial and Holocene environmental history of the MacRobertson Land–Prydz Bay region. A special focus was put on the timing of ice-sheet retreat and the variability of bottom-water formation due to sea ice formation through the Holocene. Results from site PS69/849-2 provide the first paleo-environmental record of Holocene variations in bottom-water production probably associated to the Cape Darnley polynya, which is the second largest polynya in the Antarctic. Methods included end-member modeling of laser-derived high-resolution grain size data to reconstruct the depositional regimes and bottom-water activity. The provenance of current-derived and ice-transported material was reconstructed using clay-mineral and heavy-mineral analysis. Conclusions on biogenic production were drawn by determination of biogenic opal and total organic carbon. It was found that the ice shelf front started to retreat from the site around 12.8 ka BP. This coincides with results from other records in Prydz Bay and suggests warming during the early Holocene optimum next to global sea level rise as the main trigger. Ice-rafted debris was then supplied to the site until 5.5 cal. ka BP, when Holocene global sea level rise stabilized and glacial isostatic rebound on MacRobertson Land commenced. Throughout the Holocene, three episodes of enhanced bottom-water activity probably due to elevated brine rejection in Cape Darnley polynya occured between 11.5 and 9 cal. ka BP, 5.6 and 4.5 cal. ka BP and since 1.5 cal. ka BP. These periods are related to shifts from warmer to cooler conditions at the end of Holocene warm periods, in particular the early Holocene optimum, the mid-Holocene warm period and at the beginning of the neoglacial. In contrast, between 7.7 and 6.7 cal. ka BP, brine rejection shut down, maybe owed to warm conditions and pronounced open-water intervals. 相似文献
978.
Ingrid KrönckeHenning Reiss Jacqueline D. EggletonJohn Aldridge Magda J.N. BergmanSabine Cochrane Johan A. CraeymeerschSteven Degraer Nicolas DesroyJean-Marie Dewarumez Gerard C.A. DuineveldKarel Essink Hans HillewaertMarc S.S. Lavaleye Andreas MollStefan Nehring Richard NewellEivind Oug Thomas PohlmannEike Rachor Mike RobertsonHeye Rumohr Michaela SchratzbergerRebecca Smith Edward Vanden Berghe Jan van DalfsenGert van Hoey Magda VincxWouter Willems Hubert L. Rees 《Estuarine, Coastal and Shelf Science》2011,94(1):1-15
The North Sea Benthos Project 2000 was initiated as a follow-up to the 1986 ICES North Sea Benthos Survey with the major aim to identify changes in the macrofauna species distribution and community structure in the North Sea and their likely causes.The results showed that the large-scale spatial distribution of macrofauna communities in the North Sea hardly changed between 1986 and 2000, with the main divisions at the 50 m and 100 m depth contours. Water temperature and salinity as well as wave exposure, tidal stress and primary production were influential environmental factors on a large (North Sea-wide) spatial scale.The increase in abundance and regional changes in distribution of various species with a southern distribution in the North Sea in 2000 were largely associated with an increase in sea surface temperature, primary production and, thus, food supply. This can be most likely related to the North Sea hydro-climate change in the late 1980s influenced by the variability in the North Atlantic Oscillation (NAO). Only one cold-temperate species decreased in abundance in 2000 at most of the stations. Indications for newly established populations of offshore non-native species were not found.Differences in macrofauna community structure on localised spatial scales were predominantly found north of the 50 m depth contour off the British coast along the Flamborough Head Front towards the Dogger Bank, off the coast of Jutland and at the Frisian Front. These changes were most likely attributed to stronger frontal systems in 2000 caused by the increased inflow of Atlantic water masses in relation to the hydro-climate change in the late 1980s. 相似文献
979.
Toxic effects of decomposing red algae on littoral organisms 总被引:2,自引:0,他引:2
Britta Eklund Andreas P. Svensson Conny Jonsson Torleif Malm 《Estuarine, Coastal and Shelf Science》2005,62(4):621-626
Large masses of filamentous red algae of the genera Polysiphonia, Rhodomela, and Ceramium are regularly washed up on beaches of the central Baltic Sea. As the algal masses start to decay, red coloured effluents leak into the water, and this tinge may be traced several hundred meters off shore. In this study, possible toxic effects of these effluents were tested on littoral organisms from different trophic levels. Effects on fertilisation, germination and juvenile survival of the brown seaweed Fucus vesiculosus were investigated, and mortality tests were performed on the crustaceans Artemia salina and Idotea baltica, as well as on larvae and adults of the fish Pomatoschistus microps. Fucus vesiculosus was the most sensitive species of the tested organisms to the red algal extract. The survival of F. vesiculosus recruits was reduced with 50% (LC50) when exposed to a concentration corresponding to 1.7 g l−1 dw red algae. The lethal concentration for I. baltica, A. salina and P. microps were approximately ten times higher. The toxicity to A. salina was reduced if the algal extract was left to decompose during two weeks but the decline in toxicity was not affected by different light or temperature conditions. This study indicates that the filamentous red algae in the central Baltic Sea may produce and release compounds with negative effects on the littoral ecosystem. The effects may be particularly serious for the key species F. vesiculosus, which reproduce in autumn when filamentous red algal blooms are most severe. 相似文献
980.