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1.
New or “juvenile” crust forms and grows mainly through mafic to andesitic magmatism at Pacific-type or accretionary type convergent margins as well as via tectonic accretion of oceanic and island-arc terranes and translation of continental terranes. During the last decades the juvenile or recycled nature of crust has been commonly evaluated using whole-rock isotope and Hf-in-zircon isotope methods. However, evidence for the accretionary or Pacific-type nature of an orogenic belt comes from geological data, for example, from the presence of accretionary complexes (AC), intra-oceanic arcs (IOA), oceanic plate stratigraphy units (OPS), and MORB-OIB derived blueschist belts (BSB). The Central Asian Orogenic Belt (CAOB) represents the world's largest province of Phanerozoic juvenile crustal growth during ca. 800 m.y. between the East European, Siberian, North China and Tarim cratons. From geological point of view, the CAOB is a typical Pacific-type belt as it hosts numerous occurrences of accretionary complexes, intra-oceanic arcs, OPS units, and MORB-OIB derived blueschist belts. In spite of its accretionary nature, supported by positive whole rock Nd isotope characteristics in CAOB granitoids, the Hf-in-zircon isotope data reveal a big portion of recycled crust. Such a controversy can be explained by presence of accreted microcontinents, isotopically mixed igneous reservoirs and by the tectonic erosion of juvenile crust. The most probable localities of tectonic erosion in the CAOB are the middle and southern Tienshan and southern Transbaikalia because these regions comprise a predominantly recycled crust (based on isotope data), but the geological data show the presence of intra-oceanic arcs, blueschist belts and accreted OPS with oceanic island basalts (OIB) and tectonically juxtaposed coeval arc granitoids and accretionary units. This warrants combination of detailed geological studies with isotopic results, as on their own they may not reflect such processes as tectonic erosion of juvenile crust and/or arc subduction. 相似文献
2.
《Applied Geochemistry》2001,16(9-10):1003-1019
Stable isotope ratios were used as a tracer for S flow and transformations in an irrigation experiment with 5 different German forest soils. Seventy-five lysimeters constructed from soil cores, 15 from each site, were irrigated over 20 months with SO4-rich artificial canopy throughfall, simulating 3 different S input levels: 35 kg S ha−1 in treatment I, 63 kg S ha−1 in treatment II, and 131 kg S ha−1 in treatment III. The δ34S value of the irrigation SO4 was more than 22‰ higher than those of total S in the untreated soils. Mass and isotope balances for different soil S compounds were used to assess the patterns and mechanisms of S retention in individual soil horizons and their dependence on S deposition levels. Independent of the S deposition level, on average 12±5 kg ha−1 of the applied S were bound organically by the microbial biomass in all soils. Immobilization of irrigation SO4 occurred predominantly in the topsoil horizons with the formation of C-bonded S being more prevalent than the synthesis of organic sulfates. Tracer retention via formation of organic soil S compounds accounted for up to 50% of the irrigation SO4 in treatment I, from 16 to 25% in treatment II, and less than 20% in treatment III. The dominant process of inorganic S retention in the soils appeared to be adsorption of SO4, but precipitation of aluminum hydroxy sulfate minerals constituted a second potential inorganic retention process in some soils. Sulfate adsorption increased with increasing sesquioxide content of the soils and with increasing S deposition rates. In soils with high sesquioxide contents, typically more than 70% of the irrigated S was retained inorganically, whereas in the soil with the lowest sesquioxide content, generally less than 50% of the labeled irrigation S was detected in inorganic form. In the latter soil, the sesquioxide content was not high enough to fully adsorb the elevated SO4 inputs in treatments II and III. Consequently, increased tracer S export with the seepage water SO4 was observed in the experimental variants with elevated SO4 deposition rates. In soils with high sesquioxide contents, the elevated SO4 inputs in treatments II and III were fully retained in the soil horizons in inorganic form during the 20 months of the experiment and thus increased seepage water export of labeled SO4 was not observed. The ability to inorganically retain tracer S in the mineral soil horizons was identified as the major factor regulating the extent of tracer S export with the seepage water at 60 cm depth. The high retention of labeled S in all soils combined with the comparatively low recovery of irrigation SO4 with the seepage water implies that the mean transit time of S in the uppermost 60 cm of the acid forest soils varies between several years and many decades, much longer than previously thought. 相似文献
3.
Due to the uplift of Qinghai-Tibet Plateau(QTP), the cryosphere gradually developed on the higher mountain summits after the Neocene, becoming widespread during the Late Quaternary. During this time, permafrost on the QTP experienced repeated expansion and degradation. Based on the remains and cross-correlation with other proxy records such as those from glacial landforms, ice-core and paleogeography, the evolution and changes of permafrost and environmental changes on the QTP during the past 150,000 years were deduced and are presented in this paper. At least four obvious cycles of the extensive and intensive development, expansion and decay of permafrost occurred during the periods of 150–130, 80–50, 30–14 and after 10.8 ka B.P.. During the Holocene, fluctuating climatic environments affected the permafrost on the QTP, and the peripheral mountains experienced six periods of discernible permafrost changes:(1) Stable development of permafrost in the early Holocene(10.8 to 8.5–7.0 ka B.P.);(2) Intensive permafrost degradation during the Holocene Megathermal Period(HMP, from 8.5–7.0 to 4.0–3.0 ka B.P.);(3) Permafrost expansion during the early Neoglacial period(ca. 4,000–3,000 to 1,000 a B.P.);(4) Relative degradation during the Medieval Warm Period(MWP, from 1,000 to 500 a B.P.);(5) Expansion of permafrost during the Little Ice Age(LIA, from 500 to 100 a B.P.);(6) Observed and predicted degradation of permafrost during the 20 th and 21 st century. Each period differed greatly in paleoclimate, paleoenvironment, and permafrost distribution, thickness, areal extent, and ground temperatures, as well as in the development of periglacial phenomena. Statistically, closer dating of the onset permafrost formation, more identification of permafrost remains with richer proxy information about paleoenvironment, and more dating information enable higher resolution for paleo-permafrost reconstruction. Based on the scenarios of persistent climate warming of 2.2～2.6 °C in the next 50 years, and in combination of the monitored trends of climate and permafrost changes, and model predictions suggest an accelerated regional degradation of plateau permafrost. Therefore, during the first half of the 21 st century, profound changes in the stability of alpine ecosystems and hydro(geo)logical environments in the source regions of the Yangtze and Yellow rivers may occur. The foundation stability of key engineering infrastructures and sustainable economic development in cold regions on the QTP may be affected. 相似文献
4.
《Applied Geochemistry》2006,21(4):643-655
The groundwater B concentration in the alluvial aquifer of the upper Cecina River basin in Tuscany, Italy, often exceeds the limit of 1 mg L−1 set by the European Union for drinking water. On the basis of hydrogeological and geochemical observations, the main source of the B contamination of groundwater has been attributed to past releases into streams of exhausted, B-rich geothermal waters and/or mud derived from boric acid manufacturing in Larderello. The releases were discontinued 25–30 years ago.This study confirms that the B dissolved in groundwater is anthropogenic. In fact, the δ11B values of groundwater B match the range −12.2‰ to −13.3‰ of the Turkish B mineral (colemanite) processed in boric acid manufacturing, in the course of which no significant isotopic effects have been observed. This isotopic tracing of the Cecina alluvial aquifer occurs just below the confluence of the Possera Creek, which carries the B releases from Larderello. Strontium isotope ratios support this conclusion.At about 18 km from the Possera Creek confluence, the groundwater δ11B drops to much more negative values (−22‰ to −27‰), which are believed to be produced by adsorption–desorption interactions between dissolved B and the aquifer matrix. The δ11B of B fixed in well bottom sediments shows a similar variation. At present, desorption is prevailing over adsorption because the releases of B-rich water have ceased. A theoretical model is suggested to explain the isotopic trends observed.Thus, B isotopes appear to be a powerful tool for identifying the origin of B contamination in natural waters, although isotopic effects associated with adsorption–desorption processes may complicate the picture, to some extent. 相似文献
5.
《Applied Geochemistry》2006,21(5):833-838
Some hydrocarbons occluded inside asphaltene structures can be considered to be “original oil”, and are very important especially for severely post-altered crude oil in related geochemical studies such as oil/oil, oil/source correlation. The use of oxidising reagents could properly release these occluded hydrocarbons, and make possible direct study of these compounds without interference from the segments chemically bonded to the asphaltene molecule. Interference from adsorbed and/or co-precipitated compounds can be avoided by applying an asphaltene purification procedure. 相似文献
6.
The major ionic and dissolved inorganic carbon (DIC) concentrations and the stable carbon isotope composition of DIC (δ13CDIC) were measured in a freshwater aquifer contaminated by produced water brine with petroleum hydrocarbons. Our aim was to determine the effects of produced water brine contamination on the carbonate evolution of groundwater. The groundwater was characterized by three distinct anion facies: HCO3−-rich, SO42−-rich and Cl−-rich. The HCO3−-rich groundwater is undergoing closed system carbonate evolution from soil CO2(g) and weathering of aquifer carbonates. The SO42−-rich groundwater evolves from gypsum induced dedolomitization and pyrite oxidation. The Cl−-rich groundwater is contaminated by produced water brine and undergoes common ion induced carbonate precipitation. The δ13CDIC of the HCO3−-rich groundwater was controlled by nearly equal contribution of carbon from soil CO2(g) and the aquifer carbonates, such that the δ13C of carbon added to the groundwater was −11.6‰. In the SO42−-rich groundwater, gypsum induced dedolomitization increased the 13C such that the δ13C of carbon added to the groundwater was −9.4‰. In the produced water brine contaminated Cl−-rich groundwater, common ion induced precipitation of calcite depleted the 13C such that the δ13C of carbon added to the groundwater was −12.7‰. The results of this study demonstrate that produced water brine contamination of fresh groundwater in carbonate aquifers alters the carbonate and carbon isotopic evolution. 相似文献
7.
Devon M. Burr Barbara C. Bruno Peter D. Lanagan Lori S. Glaze Windy L. Jaeger Richard J. Soare Jean-Michel Wan Bun Tseung James A. Skinner Stephen M. Baloga 《Planetary and Space Science》2009,57(5-6):579-596
Fields of mesoscale raised rim depressions (MRRDs) of various origins are found on Earth and Mars. Examples include rootless cones, mud volcanoes, collapsed pingos, rimmed kettle holes, and basaltic ring structures. Correct identification of MRRDs on Mars is valuable because different MRRD types have different geologic and/or climatic implications and are often associated with volcanism and/or water, which may provide locales for biotic or prebiotic activity. In order to facilitate correct identification of fields of MRRDs on Mars and their implications, this work provides a review of common terrestrial MRRD types that occur in fields. In this review, MRRDs by formation mechanism, including hydrovolcanic (phreatomagmatic cones, basaltic ring structures), sedimentological (mud volcanoes), and ice-related (pingos, volatile ice-block forms) mechanisms. For each broad mechanism, we present a comparative synopsis of (i) morphology and observations, (ii) physical formation processes, and (iii) published hypothesized locations on Mars. Because the morphology for MRRDs may be ambiguous, an additional tool is provided for distinguishing fields of MRRDs by origin on Mars, namely, spatial distribution analyses for MRRDs within fields on Earth. We find that MRRDs have both distinguishing and similar characteristics, and observation that applies both to their mesoscale morphology and to their spatial distribution statistics. Thus, this review provides tools for distinguishing between various MRRDs, while highlighting the utility of the multiple working hypotheses approach. 相似文献
8.
In this paper the development of a large-scale gravitational deformation involving the eastern lateral moraine of the Athabasca
Glacier in Jasper National Park, Alberta, Canada, is described. Interpretation and analysis of sequential aerial photographs
indicates that a 540-m-wide segment of the eastern lateral moraine began to deform in the early 1950s; however, significant
movement only began in the late 1960s. Since then, the moraine has undergone progressive gravitational deformation leading
to a network of fractures, bulging, and the development of a large gap in the moraine crest. Geographic information system
analysis of topographic changes between 1967 and 2006 indicates that the displaced volume of the moraine is approximately
9.0 × 105 m3. In the last 39 years, the moraine crest has displaced 55 m (1.4 m yr−1) down towards the glacier. The development of slope instability is linked to a combination of debuttressing from recent glacier
recession, deformation of the moraine, as well as the movement of a large, mobile, debris-mantled slope impinging the upslope
margin of the lateral moraine. This case study illustrates the importance of glacial conditioning and local geomorphological
factors in creating conditions for large-scale moraine instability in recently deglacierized alpine basins. 相似文献
9.
Wiese FK Montevecchi WA Davoren GK Huettmann F Diamond AW Linke J 《Marine pollution bulletin》2001,42(12):1285-1290
Seabirds aggregate around oil drilling platforms and rigs in above average numbers due to night lighting, flaring, food and other visual cues. Bird mortality has been documented due to impact on the structure, oiling and incineration by the flare. The environmental circumstances for offshore hydrocarbon development in North-west Atlantic are unique because of the harsh climate, cold waters and because enormous seabird concentrations inhabit and move through the Grand Banks in autumn (storm-petrels, Oceanodroma spp), winter (dovekies, Alle alle, murres, Uria spp), spring and summer (shearwaters, Puffinus spp). Many species are planktivorous and attracted to artificial light sources. Most of the seabirds in the region are long-distance migrants, and hydrocarbon development in the North-west Atlantic could affect both regional and global breeding populations. Regulators need to take responsibility for these circumstances. It is essential to implement comprehensive, independent arm's length monitoring of potential avian impacts of offshore hydrocarbon platforms in the North-west Atlantic. This should include quantifying and determining the nature, timing and extent of bird mortality caused by these structures. Based on existing evidence of potential impacts of offshore hydrocarbon platforms on seabirds, it is difficult to understand why this has not been and is not being, systematically implemented. 相似文献
10.
《Geomorphology》2003,49(1-2):89-108
A series of spatially explicit equations are derived that form the foundation of a modeling framework that provides insight into how the interaction of the fetch effect and angle of wind approach leads to tradeoffs that govern the magnitude of aeolian sediment transport across beaches of different geometry. The spatial distribution of sediment transport rate per unit width at any point on the beach is shown to vary predictably as a function of wind angle, critical fetch, and beach geometry; and this has evident implications for the total volume and distribution of sediment transport into the dunes behind the beach as well as the proportion of sediment lost from the beach-dune system at the downwind margin. As the wind field shifts from onshore (shore perpendicular) to oblique (shore parallel) approach angle, total sediment transport rate across a dune line segment will reflect a tradeoff between transport reduction because of the cosine effect and transport enhancement because of potentially longer fetch distances traversed by the wind prior to encountering the dune line. This tradeoff is most evident on long, narrow beaches when beach width is less than the critical fetch. For such beaches and with onshore winds, the total sediment transport rate across the dune line will be less than that predicted for a wide beach because of the constraint imposed by the fetch effect. However, as the angle of wind approach becomes oblique, the available fetch becomes progressively longer, transport limitations imposed by the fetch effect are negated, and transport enhancement across the dune line is to be expected. With very large angles of wind approach, the cosine effect dominates the interaction and transport reductions across the dune line occur until the wind is shore parallel and sediment supply to the dunes ceases altogether. This sequence of adjustments and tradeoffs were only partially understood prior to this study, and yet they form the foundation of coastal dune modeling. The framework proposed in this paper serves to place future studies of process-form interaction in beach-dune systems on a robust theoretical foundation. It also facilitates the testing of various alternative hypotheses regarding the uneven spatial and temporal distribution of dune height and growth rate in coastal environments. 相似文献