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101.
Two kinds of mylonite series rocks, felsic and mafic, have been recognized in the NW-striking shear zone of the Jiapigou gold
belt. During ductile deformation, a large amount of fluid interacted intensively with the mylonite series rocks: plagioclases
were sericitized and theAn values declined rapidly, finally all of them were transformed to albites; dark minerals were gradually replaced by chlorites
(mostly ripidolite). Meanwhile, large-scale and extensive carbonation also took place, and the carbonatization minerals varied
from calcite to dolomite and ankerite with the development of deformation. The δ13C values of the carbonates are −3.0‰ – −5.6‰ suggesting a deep source of carbon. The ductile deformation is nearly an iso-volume
one (f
v≈1). With the enhancement of shear deformation, SiO2 in the two mylonite series rocks was depleted, while volatile components suchs as CO2 and H2O, and some ore-forming elements such as Au and S were obviously enriched. But it is noted that the enrichment of Au in both
the mylonite series rocks did not reach the paygrade of gold. The released SiO2 from water-rock interactions occurred in the form of colloids and absorbed gold in the fluid. When brittle structures were
formed locally in the ductile shear zone, the ore-forming fluids migrated to the structures along microfractures, and preciptated
auriferous quartz because of reduction of pressure and temperature. Fluid inclusion study shows that the temperature and pressure
of the ore-forming fluids are 245–292°C and 95.4–131.7 MPa respectively; the salinity is 12.88–16.33wt% NaCl; the fluid-phase
is rich in Ca2+, K+, Na+, Mg2+, F− and Cl−, while the gaseous phases are rich in CO2 and CH4. The δD and δ18O, values of the ore-forming fluid are −84.48‰ – −91.73‰ and −0.247‰ – +2.715‰ respectively, suggesting that the fluid is
composed predominantly of meteoric water.
This project is financially supported by the National Natural Science Foundation of China (No. 9488010). 相似文献
102.
George C. Reid 《Climatic change》1997,37(2):391-405
Spacecraft measurements of the sun's total irradiance since 1980 have revealed a long-term variation that is roughly in phase with the 11-year solar cycle. Its origin is uncertain, but may be related to the overall level of solar magnetic activity as well as to the concurrent activity on the visible disk. A low-pass Gaussian filtered time series of the annual sunspot number has been developed as a suitable proxy for solar magnetic activity that contains a long-term component related to the average level of activity as well as a short-term component related to the current phase of the 11-year cycle. This time series is also assumed to be a proxy for solar total irradiance, and the irradiance is reconstructed for the period since 1617 based on the estimate from climatic evidence that global temperatures during the Maunder Minimum of solar activity, which coincided with one of the coldest periods of the Little Ice Age, were about 1 °C colder than modern temperatures. This irradiance variation is used as the variable radiative forcing function in a one-dimensional ocean–climate model, leading to a reconstruction of global temperatures over the same period, and to a suggestion that solar forcing and anthropogenic greenhouse-gas forcing made roughly equal contributions to the rise in global temperature that took place between 1900 and 1955. The importance of solar variability as a factor in climate change over the last few decades may have been underestimated in recent studies. 相似文献
103.
John B. Reid Jr. Eric Steig Wilfred B. Bryan 《Contributions to Mineralogy and Petrology》1989,101(3):318-325
Basalt petrologists disagree as to whether the commonly used projection, forsterite-diopside-silica, in the system CMAS (CaO-MgO-Al2O3-SiO2), can adequately resolve differences in basaltic glass compositions for purposes of petrogenetic modelling. Here, we suggest than an analogous plot, the aluminium-factor diagram (ALFE) of Nesbitt and Cramer (1981), has greater diagnostic value than Fo-Di-Sil. A plot of molar (Al2O2-CaO-Na2O-K2O)/(FeO + MgO) vs FeO/(FeO + MgO), it produces more coherent patterns both for experimental basalt glasses, and for natural lavas. It is, like Fo-Di-Sil, a projection through plagioclase, but has the advantage that it monitors changes in Fe/(Fe + Mg) in melts and associated crystalline phases, and is particularly useful in assessing the timing of clinopyroxene crystallization in a suite of lavas. The diagram owes its greater resolving power to the fact that the computation of its coordinates is less sensitive to analytical uncertainty than for Fo-Di-Sil. In the latter diagram, normative quartz is calculated as a residual and thus manifests the uncertainties in all the major elements. 相似文献
104.
L. H. Bowen E. DeGrave D. A. Reid R. C. Graham S. B. Edinger 《Physics and Chemistry of Minerals》1989,16(7):697-703
Celadonite from the northwestern Mojave Desert area of California was examined by detailed Mössbauer spectroscopy at temperatures from 10 K to 400 K. In addition to the predominant Fe3+ doublet with isomer shift 0.4 mm s–1 and quadrupole splitting 0.4 mm s–1, another Fe3+ doublet with 0.4, 1.2 mm/s and two Fe2+ doublets with 1.1, 1.7, 2.7 mm s–1 at 300 K were distinguished. The minor Fe3+ component is ascribed to dehydroxylated surface sites. Most of the remaining Fe(90%) is M2 cis-OH octahedral in an ordered M+–M2+ array. However, about 10% is M1 trans-OH Fe2+. Isomer shift vs. T gives Debye temperatures of 570 K for Fe3+ in M2 and 380 K for both Fe2+ sites, indicating greater vibrational freedom for Fe2+. Quadrupole splitting vs. T for Fe2+ gives a valence electronic energy splitting of 760 cm–1 between the ground and first excited state for M2. The M1 sites have a more drastic variation in vs. T which indicates not only a lower first excited state but a rhombic distortion at these sites. A proposed explanation is a neighboring M2 site vacancy. The soil clay formed from this celadonite, which is mostly Fe-rich smectite, was also studied by Mössbauer spectroscopy. About half the Fe2+ has been oxidized in the clay, but the isomer shifts and quadrupole splittings are essentially the same as in the original celadonite. A texture orientation in the clay absorber was detected by measuring the absorber at 55° to the source radiation. This texture effect produces asymmetric doublets in the usual 90° measurement. 相似文献
105.
Several studies have provided evidence for the enrichment of trace elements in coastal waters, particularly for copper. These enrichments have been attributed to diffusion from continental shelf sediments and to an influx of river water. We attempted to resolve between these sources by undertaking an extensive suite of measurements of trace metals (Cu, Ni, Cd), 226Ra and 228Ra in the surface waters of the Gulf of Mexico, along with trace metal profiles at 6 stations (April 1981 and December 1982). These data establish that enrichments of copper, nickel and cadmium occur in the shallow waters of the Gulf of Mexico. On the Mississippi continental shelf, high trace element concentrations (Cu, Ni: ~ 9 nmol/kg; Cd: ~ 200 pmol/kg) in lower-salinity waters (26‰) are similar to those observed in the Mississippi plume at the same salinity. This evidence suggests a river water source. On the other hand, trace element enrichments are also observed in the northern Gulf (Cu: +0.4 nmol/kg; Ni: +0.5 nmol/kg; Cd: +20 pmol/kg) which coincide with an increase in 228Ra but are not accompanied by decreased salinity. The excess of evaporation over precipitation in this region makes it possible that this water could be evaporated estuarine water; therefore, hydrographic observations cannot distinguish readily between river and shelf sources. A regional flux balance shows that most of the excess copper in the surface waters of the Florida Current can be supplied by the river-borne dissolved copper flux. Within the uncertainties of such calculations, the continental shelf copper flux must be less than or equal to the river flux. 相似文献
106.
The behaviour of platinum-group elements in basalts from the East Greenland rifted margin 总被引:5,自引:0,他引:5
Peter Momme Christian Tegner Kent C. Brooks Reid R. Keays 《Contributions to Mineralogy and Petrology》2002,143(2):133-153
. The continental flood basalts of the East Greenland volcanic rifted margin were extruded during continental breakup above the ancestral Iceland mantle plume at 55 Ma. Three distinct magma types, the low-Ti, high-Ti and very high-Ti series (LTS, HTS and VHTS respectively), are found intercalated in the ~6-km-thick Plateau Lava sequence. Incompatible trace elements indicate that the LTS are derived from a more depleted mantle source compared to HTS and VHTS. The LTS is characterised by increasing Cu (105 to 248 ppm) and Pd (7 to 24 ppb), constant Cu/Pd ratio (~10,000), and decreasing Ir (1.1 to <0.05 ppb) and Ru (1.8 to <0.3 ppb) concentrations during magmatic differentiation (16 to 7 wt% MgO). The constant Cu/Pd ratio reflects silicate- and chromite-dominated fractionation without concurrent segregation of sulphide. S-undersaturated differentiation is also indicated in the HTS, which also displays increasing Pd (6-16 ppb) and decreasing Ir concentrations (1 to <0.05 ppb) during differentiation, and the Cu/Pd ratios for the entire series average 21,000. However, some HTS samples have elevated Cu/Pd ratios (up to 33,000). Cu/Pd ratios in the HTS do not correlate with MgO, and this is interpreted to reflect varying Cu/Pd ratios of HTS parental magmas rather than S-saturated differentiation. During S-undersaturated differentiation of the LTS and HTS, Pt/Pd ratios decrease from 1.3 to 0.11 and 1.1 to 0.2 respectively, which indicates that Pd is much more incompatible than Pt during S-undersaturated differentiation. The VHTS consists exclusively of highly evolved samples with low MgO (6.6-6.1 wt%) and Pd/Ir ratios 98-228. Here, Cu/Pd ratios increase from 17,500 to 35,000 with decreasing Cr concentrations which indicate that these magmas experienced silicate fractionation with concurrent segregation of sulphide. The LTS represent melting of a depleted source and show high PGE concentrations and constant Cu/Pd ratios during S-undersaturated differentiation. Melting of a normal depleted upper mantle source generates S-saturated melts (MORB), and the depleted LTS source is therefore considered an extraordinary S-poor component within the ancestral Iceland plume. Of the three series, the VHTS contain the largest contribution from enriched mantle portions. The VHTS have similar PGE but much higher Nb concentrations for instance compared to the most evolved LTS and HTS samples, indicating that the enriched source contributes Nb but not PGE. 相似文献
107.
Thomas A. Davidson Helen Bennion Michael Reid Carl D. Sayer Thomas J. Whitmore 《Journal of Paleolimnology》2018,60(2):109-116
The special issue titled “Putting the Ecology into Palaeoecology” stems from a session with that name that was held at the 2015 International Paleolimnological Association meeting (International Paleolimnology Symposium) in Lanzhou, China. We briefly describe the motivation for the session, and summarise the contributions to this special issue. Additionally, we discuss our perceptions and concerns about the progress, challenges and future directions of palaeolimnology, stressing the importance of meaningful integration of ecological principles and thinking into palaeoapproaches. 相似文献
108.
The movement of sediment through mountain river networks remains difficult to predict, as processes beyond streamflow and particle size are responsible for the entrainment and transport of bedload sediment. In deglaciated catchments, additional complexity arises from glacial impacts on landscape organization. Research to date indicates that the quantity of sediment stored in the channel is an important component of sediment transport in systems which alternate between supply and transport limited states, but limited long-term field data exist which can capture storage-transfer dynamics over a timescale encompassing episodic supply typical of mountain streams. We use a 45-year dataset with annual and decadal-scale data on sediment storage, channel morphology, and wood loading to investigate the spatial and temporal organization of storage in Carnation Creek, a previously glaciated 11 km2 catchment on Vancouver Island, British Columbia. Sediment is supplied episodically to the channel, including additions from debris flows in the early 1980s just upstream of the studied channel region. Analyzing the spatial and temporal organization of sediment storage along 3.0 km of channel mainstem reveals a characteristic storage wavelength similar to the annual bedload particle travel distance. Over time, two scales of variation in storage are observed: small-scale fluctuation of 3–10 years corresponding to local erosional and depositional processes, and larger scale response over 25–35 years related to supply of sediment from hillslopes. Complex relationships between storage and sediment transfer (i.e., annual change in storage) are identified, with decadal-scale hysteresis present in storage-transfer relations in sites influenced by hillslope sediment and logjams. We propose a conceptual model linking landscape organization to temporal variability in storage and to storage–export cycles. Collectively, our results reaffirm the importance of storage to sediment transport and channel morphology, and highlight the complexity of storage–transport interactions. © 2019 John Wiley & Sons, Ltd. 相似文献
109.
Acta Geotechnica - The small-strain elastic shear wave velocity ($$V_S$$) is a basic mechanical property of soils and is an important parameter in geotechnical engineering. Recently, $$V_S$$ has... 相似文献
110.
Andrew J. Kenny Hein Rune Skjoldal Georg H. Engelhard Peter J. Kershaw James B. Reid 《Progress in Oceanography》2009,81(1-4):132
An ecosystem approach to the management of the marine environment has received considerable attention over recent years. However, there are few examples which demonstrate its practical implementation. Much of this relates to the history of existing marine monitoring and assessment programmes which (for many countries) are sectoral, making it difficult to integrate monitoring data and knowledge across programmes at the operational level.To address this, a scientific expert group, under the auspices of the International Council for the Exploration of the Sea (ICES), prepared a plan for how ICES could contribute to the development of an Integrated Ecosystem Assessment (IEA) for the North Sea by undertaking a pilot study utilising marine monitoring data. This paper presents the main findings arising from the expert group and in particular it sets out one possible integrated approach for assessing the relative significance of environmental forcing and fishing pressure on the ecological status of the North Sea, it then compares the findings with assessments made of other Large Marine Ecosystems (LMEs).We define the North Sea ecosystem on the basis of 114 state and pressure variables resolved as annual averages between 1983 and 2003 and at the spatial scale of ICES rectangles. The paper presents results of integrated time-series and spatial analysis which identifies and explains significant spatial and temporal gradients in the data. For example, a significant shift in the status of the North Sea ecosystem (based upon 114 state-pressure variables) is identified to have occurred around 1993. This corresponds to previously documented shifts in the environmental conditions (particularly sea surface temperature) and changes in the distribution of key species of plankton (Calanus sp.), both reported to have occurred in 1989. The difference in specific timing between reported regime shifts for the North Sea may be explained, in part, by time-lag dependencies in the trophic structure of the ecosystem with shifts in higher trophic levels occurring later than 1989.By examining the connection (or relatedness) between ecosystem components (e.g. environment, plankton, fish, fishery and seabirds) for the identified regime states (1983–1993; 1993–2003) we conclude that both the North Sea pelagic and benthic parts of the ecosystem were predominantly top-down (fishery) controlled between 1983 and 1993, whereas between 1993 and 2003 the pelagic stocks shifted to a state responding mainly to bottom-up (environment) influences. However, for the demersal fish stocks between 1993 and 2003 top-down (fishery) pressure dominated even though over this period significant reductions in fishing pressure occurred. The present analysis, therefore, provides further evidence in support of the need for precautionary management measures taken in relation to setting fishery quotas. 相似文献