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1.
Amanda Albright Olsen 《Geochimica et cosmochimica acta》2008,72(7):1758-1766
We ran a series of 124 semi-batch reactor experiments to measure the dissolution rate of forsterite in solutions of nitric and oxalic acid solutions over a pH range of 0-7 and total oxalate concentrations between 0 and 0.35 m at 25 °C. We found that the empirical rate law for the dissolution of forsterite in these solutions is
2.
The discharge of radioactive waste, from nuclear fuel reprocessing facilities, into the coastal waters of north-west Europe has resulted in a significant increase in the inventories of a number of artificial radionuclides in the North Atlantic. Radiocaesium, 90Sr and 99Tc, which behave conservatively in seawater, have been used widely as tracers of water movement through the North Sea, Norwegian Coastal Current, Barents Sea, Greenland Sea, Fram Strait, Eurasian Basin, East Greenland Current and Denmark Strait overflow. These studies are summarised in the present paper. It has been estimated that 22% of the 137Cs Sellafield discharge has passed into the Barents Sea, en route to the Nansen Basin, via the Bjomoya-Fugloya Section, with another 13% passing through the Fram Strait. This amounts to 14 PBq 137Cs. Quantifying the influx of other radionuclides has been more problematic. The inflowing Atlantic water now appears to be diluting waters in the Arctic Basin, which were contaminated in the late 1970s and early 1980s as a result of the substantial decrease in the discharge of reprocessing wastes. Sellafield (U.K.) has dominated the supply of 134Cs, 137Cs, 90Sr, 99Tc and Pu, whereas La Hague (France) has contributed a larger proportion of 129I and 125Sb. 相似文献
3.
To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea (ECS) shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector (BSR) occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural "anomalies" are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation:to help gather enough methane into a small area and to modulate the thermal regime. 相似文献
4.
Tony T. Gregg Amanda Dewees Drema Gross Bill Hoffman Dan Strub Matt Watson 《中国海洋大学学报(英文版)》2006,5(4):375-380
1Water LossInitiativesUnaccounted-for water(or unbilled water)has beenreceiving newscrutiny at both the state and nationallevels.For years,water conservationeffortsin Europehave emphasized reduction in water loss to a muchgreater extent thaninthe United S… 相似文献
5.
Reforestation Programs in Southwest China: Reported Success, Observed Failure, and the Reasons Why 总被引:4,自引:2,他引:2
Ever since the disastrous floods of 1998, the Chinese government has used the Natural Forest Protection and Sloping Land Conversion Programs to promote afforestation and reforestation as means to reduce runoff, control erosion, and stabilize local livelihoods. These two ambitious programs have been reported as large-scale successes, contributing to an overall increase in China’s forest cover and to the stated goals of environmental stabilization. A small-scale field study at the project level of the implementation of these two programs in Baiwu Township, Yanyuan County, Sichuan, casts doubt upon the accuracy and reliability of these claims of success; ground observations revealed utter failure in some sites and only marginal success in others. Reasons for this discrepancy are posited as involving ecological, economic, and bureaucratic factors. Further research is suggested to determine whether these discrepancies are merely local aberrations or represent larger-scale failures in reforestation programs. 相似文献
6.
Gold mineralization at Hutti is confined to a series of nine parallel, N–S to NNW–SSE trending, steeply dipping shear zones.
The host rocks are amphibolites and meta-rhyolites metamorphosed at peak conditions of 660±40°C and 4±1 kbar. They are weakly
foliated (S1) and contain barren quartz extension veins. The auriferous shear zones (reefs) are typically characterized by four alteration
assemblages and laminated quartz veins, which, in places, occupy the entire reef width of 2–10 m, and contain the bulk of
gold mineralization. A <1.5 m wide distal chlorite-sericite (+biotite, calcite, plagioclase) alteration zone can be distinguished
from a 3–5 m wide proximal biotite-plagioclase (+quartz, muscovite, calcite) alteration zone. Gold is both spatially and temporally
associated with disseminated arsenopyrite and pyrite mineralization. An inner chlorite-K-feldspar (+quartz, calcite, scheelite,
tourmaline, sphene, epidote, sericite) alteration halo, which rims the laminated quartz veins, is characterized by a pyrrhotite,
chalcopyrite, sphalerite, ilmenite, rutile, and gold paragenesis. The distal chlorite-sericite and proximal biotite-plagioclase
alteration assemblages are developed in microlithons of the S2–S3 crenulation cleavage and are replaced along S3 by the inner chlorite-K-feldspar alteration, indicating a two-stage evolution for gold mineralization. Ductile D2 shearing, alteration, and gold mineralization formed the reefs during retrograde evolution and fluid infiltration under upper
greenschist to lower amphibolite facies conditions (560±60°C, 2±1 kbar). The reefs were reactivated in the D3 dextral strike-slip to oblique-slip environment by fault-valve behavior at lower greenschist facies conditions (ca. 300–350°C),
which formed the auriferous laminated quartz veins. Later D4 crosscutting veins and D5 faults overprint the gold mineralization. The alteration mineralogy and the structural control of the deposit clearly points
to an orogenic style of gold mineralization, which took place either during isobaric cooling or at different levels of the
Archean crust. From overlaps in the tectono-metamorphic history, it is concluded that gold mineralization occurred during
two tectonic events, affecting the eastern Dharwar craton in south India between ca. 2550 – 2530 Ma: (1) The assemblage of
various terranes of the eastern block, and (2) a tectono-magmatic event, which caused late- to posttectonic plutonism and
a thermal perturbation. It differs, however, from the pre-peak metamorphic gold mineralization at Kolar and the single-stage
mineralization at Ramagiri. Notably, greenschist facies gold mineralization occurred at Hutti 35–90 million years later than
in the western Dharwar craton.
Editorial handling: G. Beaudoin 相似文献
7.
Characterising youthful strike-slip fault systems within transtensional regimes is often complicated by the presence of tectonic geomorphic features produced by normal faulting associated with oblique extension. The Petersen Mountain fault in the northern Walker Lane tectonic province exhibits evidence of both normal and strike-slip faulting. We present the results of geologic and geomorphic mapping, and palaeoseismic trenching that characterise the fault's style and sense of deformation. The fault consists of two major traces. The western trace displaces colluvial, landslide, and middle to late Pleistocene alluvial fans and is associated with aligned range front saddles, linear drainages, and oversteepened range front slopes. The eastern trace is associated with a low linear bedrock ridge, a narrow graben, right deflected stream channels, and scarps in late Pleistocene alluvial fan deposits. A trench on the eastern trace of the fault exposed a clear juxtaposition of disintegrated granodiorite bedrock against sand and boulder alluvial fan deposits across a steeply east-dipping fault. The stratigraphic evidence supports the occurrence of at least one late Pleistocene earthquake with a component of lateral displacement. As such, the Petersen Mountain fault accommodates part of the ~7 mm/yr of dextral shear distributed across the northern Walker Lane. 相似文献
8.
9.
Systematic marine conservation planning in data-poor regions: Socioeconomic data is essential 总被引:1,自引:0,他引:1
Natalie C. Ban Gretchen J.A. Hansen Michael Jones Amanda C.J. Vincent 《Marine Policy》2009,33(5):794-800
Systematic planning for conservation is highly regarded but relies on spatially explicit data that are lacking in many areas of conservation concern. The decision support tool Marxan is applied to a reef system in the central Philippines where 30 marine protected areas (MPAs) have been established in communities without much use of biophysical data. The intent was to explore how Marxan might assist with the legally required expansion to protect 15% of marine waters, and how existing MPAs might affect that process. Results show that biophysical information alone did not provide much guidance in identifying patterns of conservation importance in areas where the data are poor. Socioeconomic data were needed to distinguish among possible areas for protection; but here, as elsewhere in marine environments, the availability of such data was very limited. In the final analysis, local knowledge and integrated understanding of socioeconomic realities may offer the best spatially explicit information. The 30 existing MPAs, which encompassed a small proportion of the reef system, did not limit future options in developing a suite of MPAs on a broader scale. Rather, they appeared to generate the support for MPAs that is obligatory for any larger zoning effort. In summary, establishing MPAs based on community-driven criteria has biological and social value, but efforts should be made to collect ecological and socioeconomic data to guide the continued creation of MPAs. 相似文献
10.