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121.
Jaye E. Cable Jonathan B. Martin Peter W. Swarzenski Mary K. Lindenberg Joel Steward 《Ground water》2004,42(7):1011-1020
122.
Serena Viti Wendy Brown Martin McCoustra Helen Fraser Nigel Mason Robert Massey 《Astronomy& Geophysics》2004,45(6):6.22-6.24
The team behind a successful project to broaden the understanding of astrochemistry – Serena Viti, Wendy Brown, Martin McCoustra, Helen Fraser, Nigel Mason and Robert Massey – recount how they went about it and what benefits resulted. 相似文献
123.
Gudrun Richter Joachim Wassermann Martin Zimmer Matthias Ohrnberger 《Journal of Volcanology and Geothermal Research》2004,135(4):331-342
In this paper we present densely sampled fumarole temperature data, recorded continuously at a high-temperature fumarole of Mt. Merapi volcano (Indonesia). These temperature time series are correlated with continuous records of rainfall and seismic waveform data collected at the Indonesian–German multi-parameter monitoring network. The correlation analysis of fumarole temperature and precipitation data shows a clear influence of tropical rain events on fumarole temperature. In addition, there is some evidence that rainfall may influence seismicity rates, indicating interaction of meteoric water with the volcanic system. Knowledge about such interactions is important, as lava dome instabilities caused by heavy-precipitation events may result in pyroclastic flows. Apart from the strong external influences on fumarole temperature and seismicity rate, which may conceal smaller signals caused by volcanic degassing processes, the analysis of fumarole temperature and seismic data indicates a statistically significant correlation between a certain type of seismic activity and an increase in fumarole temperature. This certain type of seismic activity consists of a seismic cluster of several high-frequency transients and an ultra-long-period signal (<0.002 Hz), which are best observed using a broadband seismometer deployed at a distance of 600 m from the active lava dome. The corresponding change in fumarole temperature starts a few minutes after the ultra-long-period signal and simultaneously with the high-frequency seismic cluster. The change in fumarole temperature, an increase of 5 °C on average, resembles a smoothed step. Fifty-four occurrences of simultaneous high-frequency seismic cluster, ultra-long period signal and increase of fumarole temperature have been identified in the data set from August 2000 to January 2001. The observed signals appear to correspond to degassing processes in the summit region of Mt. Merapi. 相似文献
124.
We have developed an algorithm that allows crosshole georadar amplitude data contaminated with systematic errors to be tomographically inverted. The effects of the errors, which may due to variable antenna-borehole coupling, the groundwater table, and 3-D heterogeneities in the vicinity of one or more boreholes, are included in a series of transmitter and receiver amplitude-correction factors. Tests with synthetic georadar sections demonstrate that the new approach is capable of producing reliable attenuation information, even when large systematic errors are present in the amplitude data. Standard inversions of crosshole georadar data acquired within a highly complex alpine rock glacier yield distorted tomograms. In contrast the new approach results in geologically useful images. 相似文献
125.
We study the importance of the zones of weakness and the pattern of downgoing flow in steady-state models of subducting lithosphere, which interacts mechanically and thermally with the ambient mantle. The non-linear system of governing equations consists of (i) the momentum equation in stream function formulation and (ii) the steady-state heat transfer equation including conduction and advection of heat and dissipation. A finite element method has been applied to this system. We consider the viscosity to be a non-linear function of both the temperature and the stream function. In steady-state two-dimensional (2D) flow, the stream function isolines follow material trajectories. They are used to follow the top of the subducting slab, which because of its possible increase in water content, is assumed to have a lower viscosity. The zone of weakness has been thus obtained in the self-consistent fashion since the stream function as well as the temperature are the output from our modeling and no a priori assumptions about the shape of the bending lithosphere are taken into account. It was shown that several orders decrease of viscosity in the zone of weakness is required to obtain the dip angle of about 45°. If the decrease of viscosity is not sufficient enough, the subducted slab either sinks almost vertically or does not exhibit a plate-like behavior. We have also demonstrated that shear heating can unrealistically increase at the zone of weakness for fast subductions if decrease of viscosity is underestimated. 相似文献
126.
Sulfur isotope fractionation during growth of sulfate-reducing bacteria on various carbon sources 总被引:1,自引:0,他引:1
Jutta Kleikemper Martin H. Schroth Benjamin Brunner 《Geochimica et cosmochimica acta》2004,68(23):4891-4904
Stable sulfur isotope fractionation during microbial sulfate reduction is a potential tool to estimate sulfate reduction rates at field sites. However, little is known about the influence of the utilized carbon source on the magnitude of sulfur isotope fractionation. To investigate this effect, both a pure culture (strain PRTOL1) and enrichment cultures from a petroleum hydrocarbon (PHC)-contaminated aquifer were used and grown in batch cultures on various carbon sources with an initial sulfate concentration of 1 mmol/L. As sole carbon sources the PHC components naphthalene, 1,3,5-trimethylbenzene, and heating oil (enrichment culture) and the organic acids acetate, pyruvate, benzoate, and 3-phenylpropionate (enrichment culture and PRTOL1) were used. Sulfate reduction rates of all cultures ranged from 6 ± 1 nmol cm−3 d−1 (enrichment culture grown on 1,3,5-trimethylbenzene) to 280 ± 6 nmol cm−3 d−1 (enrichment culture grown on pyruvate). Cell-specific sulfate reduction rates ranged from 1.1 × 10−14 mol cell−1 d−1 (PRTOL1 grown on pyruvate) to 1.5 × 10−13 mol cell−1 d−1 (PRTOL1 grown on acetate). Sulfur isotope enrichment factors (ε) for the enrichment culture ranged from 16.1‰ (3-phenylpropionate) to 34.5‰ (1,3,5-trimethylbenzene) and for PRTOL1 from 30.0‰ (benzoate) to 36.0‰ (pyruvate). Cultures of PRTOL1 always showed higher ε values than the enrichment culture when grown on the same carbon source due to culture-specific properties. Higher ε values were obtained when the enrichment culture was grown on PHC components than on organic acids. No relationship between ε values and cell-specific sulfate reduction rate existed when all data were combined. When comparing the magnitude of ε values determined in this laboratory study with ε values measured at contaminated and uncontaminated field sites, it becomes evident that a multitude of factors influences ε values at field sites and complicates their interpretation. The results of this study help us assess some of the general parameters that govern the magnitude of ε in sulfate-reducing environments. 相似文献
127.
After a period of considerable and sustained hegemony, many commentators have argued that contemporary processes of globalisation are acting as a challenge to nation state sovereignty. The paper argues that geographers need to focus on the ways in which the nation state continues to act, albeit in a modified manner, within the era of globalisation. This might help to position geography within globalisation debates, which--according to Dicken [Geographers and `globalization': (yet) another missed boat? forthcoming, Transactions of the Institute of British Geographers, 2004]--we have not been centrally involved in. Drawing on the work of Michael Mann, we focus on a neglected dimension of state power--namely, its ideological form--as a means of exploring how the nation state is being differentially re-engineered under globalisation. Using Mann's classification of forms of ideological organisation, we deploy three vignettes in order to demonstrate the evolving nature of ideological power within the contemporary UK State. 相似文献
128.
We have developed a significant body of new field-based evidence relating to the history of crustal extension in western Turkey. We establish that two of the NE–SW-trending basins in this region, the Gördes and Selendi Basins, whose sedimentary successions begin in the early Miocene, are unlikely to relate to late-stage Alpine compressional orogeny or to E–W extension of Tibetan-type grabens as previously suggested. We argue instead that these basins are the result of earlier (?) late Oligocene, low-angle normal faulting that created approximately N–S “scoop-shaped” depressions in which clastic to lacustine and later tuffaceous sediments accumulated during early–mid-Miocene time, separated by elongate structural highs. These basins were later cut by E–W-trending (?) Plio–Quaternary normal faults that post-date accumulation of the Neogene deposits. In addition, we interpret the Alaşehir (Gediz) Graben in terms of two phases of extension, an early phase lasting from the early Miocene to the (?) late Miocene and a young Plio–Quaternary phase that is still active. Taking into account our inferred earlier phase of regional extension, we thus propose a new three-phase “pulsed extension” model for western Turkey. We relate the first two phases to “roll-back” of the south Aegean subduction zone and the third phase to the westward “tectonic escape” of Anatolia. 相似文献
129.
130.
Balz Samuel Kamber Martin J. Whitehouse Stephen Moorbath 《Earth and Planetary Science Letters》2005,240(2):276-290
The oldest known bona fide succession of clastic metasediments occurs in the Isua Greenstone Belt, SW Greenland and consists of a variety of mica schists and rare metaconglomerates. The metasediments are in direct contact with a felsic metavolcanic lithology that has previously been dated to 3.71 Ga. Based on trace element geochemical data for > 30 metasediments, we selected the six samples with highest Zr concentrations for zircon extraction. These samples all yielded very few or no zircon. Those extracted from mica schists yielded ion probe U/Pb ages between 3.70 and 3.71 Ga. One metaconglomerate sample yielded just a single zircon of 3.74 Ga age.The mica schist hosted zircons have U/Pb ages, Th / U ratios, REE patterns and Eu anomalies indistinguishable from zircon in the adjacent 3.71 Ga felsic metavolcanic unit. Trace element modelling requires the bulk of material in the metasediments to be derived from variably weathered mafic lithologies but some metasediments contain substantial contribution from more evolved source lithologies. The paucity of zircon in the mica schists is thus explained by incorporation of material from largely zircon-free volcanic lithologies. The absence of older zircon in the mica schists and the preponderance of mafic source material imply intense, mainly basaltic resurfacing of the early Earth. The implications of this process are discussed.Thermal considerations suggest that horizontal growth of Hadean crust by addition of mafic-ultramafic lavas must have triggered self-reorganisation of the protocrust by remelting. Reworking of Hadean crust may have been aided by burial of hydrated (weathered) metabasalt due to semi-continuous addition of new voluminous basalt outpourings. This process causes a bias towards eruption of Zr-saturated partial melts at the surface with O-isotope compositions potentially different from the mantle. The oldest zircons hosted in sediments would have been buried to substantial depth or formed in plutons that crystallised at some depth, from which it took hundreds of millions of years for them to be exhumed and incorporated into much younger sediments. 相似文献