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1.
宁芜盆地火山-次火山岩的锆石U-Pb年龄、Hf同位素组成及其地质意义 总被引：40，自引：23，他引：17
宁芜火山盆地是长江中下游重要的火山盆地之一,在盆地内自下而上依次发育龙王山组、大王山组、姑山组和娘娘山组火山岩和若干个同源次火山岩或小侵入岩体。本文对宁芜盆地火山-次火山岩进行了详细的锆石U-Pb年龄和Hf同位素地球化学研究。研究结果表明,大王山组粗安岩锆石U-Pb年龄为130.3±0.9Ma,姑山组两个粗安岩锆石U-Pb年龄分别为128.2±1.3Ma和128.5±1.8Ma,另外三个侵入岩年龄分别为127.1±1.2Ma、128.3±0.6Ma和128.2±1.0Ma,均为早白垩纪。综合前人成果,认为长江中下游地区火山盆地内火山活动的时限在135～124Ma之间,不存在侏罗纪岩浆活动。宁芜盆地火山岩和侵入岩的锆石176Hf/177Hf值在0.282502～0.282673范围内,εHf(t)变化为-6.9～-0.7,显示岩浆源自于岩石圈富集地幔部分熔融并在上升过程中受地壳物质的混染,为岩石圈伸展环境的产物。 相似文献
2.
D. Leduc P.K. Probert K. Berkenbusch S.D. Nodder C.A. Pilditch 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(10):1363-1371
Nematodes are the most abundant metazoans of deep-sea benthic communities, but knowledge of their distribution is limited relative to larger organisms. Whilst some aspects of nematode processing techniques, such as extraction, have been extensively studied, other key elements have attracted little attention. We compared the effect of (1) mesh size (63, 45, and 32 μm) on estimates of nematode abundance, biomass, and body size, and (2) microscope magnification (50× and 100×) on estimates of nematode abundance at bathyal sites (250–3100 m water depth) on the Challenger Plateau and Chatham Rise, south-west Pacific Ocean. Variation in the effectiveness of these techniques was assessed in relation to nematode body size and environmental parameters (water depth, sediment organic matter content, %silt/clay, and chloroplastic pigments). The 63-μm mesh retained a relatively low proportion of total nematode abundance (mean±SD=55±9%), but most of nematode biomass (90±4%). The proportion of nematode abundance retained on the 45-μm mesh in surface (0–1 cm) and subsurface (1–5 cm) sediment was significantly correlated (P<0.01) with %silt/clay (R2=0.39) and chloroplastic pigments (R2=0.29), respectively. Variation in median nematode body weight showed similar trends, but relationships between mean nematode body weight and environmental parameters were either relatively weak (subsurface sediment) or not significant (surface sediment). Using a low magnification led to significantly lower (on average by 43%) nematode abundance estimates relative to high magnification (P<0.001), and the magnitude of this difference was significantly correlated (P<0.05) with total nematode abundance (R2p=0.53) and the number of small (≤250 μm length) individuals (R2p=0.05). Our results suggest that organic matter input and sediment characteristics influence the abundance of small nematodes in bathyal communities. The abundance of small individuals can, in turn, influence abundance estimates obtained using different mesh sizes and microscope magnifications. 相似文献
3.
D. Leduc P.K. Probert S.D. Nodder 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(10):1354-1362
It is essential to maximize the information that can be gathered in deep-sea studies by thoroughly assessing sample processing methods. Nematodes are commonly used for the study and monitoring of deep-sea floor habitats, but the potential effects of different methods on the quantification of community attributes remain to be quantified. Here, we consider key methodological elements by comparing the effect of sediment depth and mesh size (63, 45, and 32 μm) on: (1) estimates of nematode community attributes, and (2) the sampling effort required to detect changes in these attributes at a bathyal site on the Chatham Rise, south-west Pacific Ocean. The 63 μm mesh retained most (95%) of the nematode biomass but a lower proportion (53–71%) of the nematode abundance. Retention efficiency of common species on this mesh ranged from 12 (Hapalomus sp.) to >88% (Comesomatidae spp.). The 63 μm mesh yielded significantly lower diversity estimates than the finer meshes, and failed to detect differences in community structure observed using the 45 and 32 μm mesh sizes. Sediment depth had a substantial effect on all measured community attributes, highlighting the importance of sufficient core penetration into the sediment (≥5 cm) for adequately characterizing nematode distribution. Power analysis showed that using a 32 μm mesh and deepest core penetration led to relatively few (3–8) samples being required to detect significant changes in nematode diversity indices relative to coarser mesh sizes. Characterization of nematode diversity and community structure using appropriate and robust methods of sampling is suggested as a sensitive and efficient tool for the assessment of anthropogenic impacts on deep-sea ecosystems. 相似文献
4.
The genetic structure of populations is often shaped by the reproductive system and larval properties of the species. The waratah anemone (Actinia tenebrosa) reproduces through both asexual clones, which have very short-distance dispersal, and sexual larvae, which are believed to disperse much greater distances. The impact of this mixed strategy on the New Zealand population structure of Actinia tenebrosa was investigated using microsatellite markers. The analysis incorporated 24 sampling locations from around New Zealand and one Australian location, using four microsatellite markers, n = 420. We observed low connectivity and high genetic differentiation between all locations sampled, with a distinct pattern of isolation by distance. The most distinct grouping of locations sampled was the north-east of the North Island from Cape Reinga to East Cape, which was identified by SAMOVA and STRUCTURE analyses as being moderately diverged from the remainder of the country. A tentative correlation was observed between genetic clustering and biogeographic regionalisation, where the distribution of a number of genetic clusters matched previously defined biogeographic regions. Within each location sampled, large numbers of clones were present and a latitudinal cline was observed in the relative contribution of asexually and sexually generated recruits, with an increase in asexual recruits on the South Island's east coast. 相似文献
5.
安徽宁芜地区铁氧化物-磷灰石矿床中金云母Ar-Ar定年及其地球动力学意义 总被引：23，自引：11，他引：12
铁氧化物-磷灰石型铁矿床是长江中下游成矿带的重要组成部分,对其成岩成矿时限的精确厘定,是理解长江中下游地区中生代大规模成矿作用的动力学演化的关键。本文分别对宁芜盆地南部白象山、和睦山及中部的陶村三个大-中型铁矿床中与磁铁矿密切共生的金云母单矿物进行了Ar-Ar同位素测年,获得白象山矿床金云母Ar-Ar坪年龄为134.9±1.1Ma,对应的反等时线年龄为133±2Ma;和睦山矿床金云母Ar-Ar坪年龄为132.9±1.1Ma,对应的反等时线年龄为133.9±2.4Ma;陶村矿床金云母的反等时线年龄为128±14Ma。该区铁氧化物-磷灰石型矿床与该区火山-次火山岩具有密切的时间联系,成岩成矿时限主要集中于135～126Ma。综合研究表明,长江中下游第二期成岩成矿作用的时限为135～126Ma,对应于岩石圈的大规模快速减薄的地球动力学背景。 相似文献
6.
C.S. Law M.J. SmithC.L. Stevens E.R. Abraham M.J. Ellwood P. HillS. Nodder J. Peloquin S. PickmereK. Safi C.M. Walkington 《Deep Sea Research Part II: Topical Studies in Oceanography》2011,58(6):786-799
An in situ iron addition experiment (SAGE) was carried out in high-nitrate low-chlorophyll low-silicic acid (HNLCLSi) sub-Antarctic surface waters south-east of New Zealand. In contrast to other iron addition experiments, the phytoplankton response was minor, with a doubling of biomass relative to surrounding waters, with the temporal trends in dissolved iron and macronutrients instead dominated by physical factors such as mixing and dilution. The initial increase in patch surface area indicated a lateral dilution rate of 0.125 d−1, with a second estimate from a model of the decline in peak SF6 concentration yielding a higher lateral dilution rate of 0.16-0.25 d−1. The model was tested on the SOIREE SF6 dataset and provided a lateral dilution of 0.07 d−1, consistent with previous published estimates. MODIS ocean colour images showed elevated chlorophyll coincident with the SF6 patch on day 10 and 12, and an elevated chlorophyll filament at the SAGE experiment location 3-4 days after ship departure, which provided additional lateral dilution estimates of 0.19 and 0.128 d−1. Dissolved iron at the patch centre declined by 85% within two days of the initial infusion, of which dilution accounted for 50-65%; it also decreased rapidly after the 2nd and 3rd infusions but remained elevated after the fourth infusion. Despite decreases in nitrate and silicic acid from day 7 and 10, respectively, the final nutrient concentrations in the patch exceeded the initial concentrations due to supply from lateral intrusion and mixed-layer deepening. The low Si:N loss ratio suggested that the observed limited response to iron was primarily by non-siliceous phytoplankton. Algal growth rate exceeded the minimum dilution rate during two periods (days 3-6 and 10-14), and coincided with net chlorophyll accumulation. However, as the ratio of algal growth to dilution was the lowest reported for an iron addition experiment, dilution was clearly a significant factor in the SAGE experiment recording the lowest phytoplankton response to mesoscale iron addition. 相似文献
7.
R.V.DESYATKIN 《资源与生态学报(英文版)》2011,(3):272-276
Issues about land resources of cryolithozone and their possible transformation under global change conditions we will consider on example of the large region of the Russian Federation-the Republic of Sakha (Yakutia),which is considered as the center of the underground continental glaciation of earth in present conditions. 相似文献
8.
Deposits of Fe-Si-Mn oxyhydroxides are commonly found on the seafloor on seamounts and mid-ocean spreading centers. At Franklin Seamount located near the western extremity of Woodlark Basin, Papua New Guinea, Fe-Si-Mn oxyhydroxides are being precipitated as chimneys and mounds upon a substrate of mafic lava. Previous studies have shown that the vent fluids have a low temperature (20–30°C) and are characterized by a total dissolved iron concentration of 0.038 mM kg-1, neutral pH (6.26) and no measurable H2S. The chimneys have a yellowish appearance with mottled red–orange patches when observed in situ from a submersible, but collected samples become redder within a few hours of being removed from the sea. The amorphous iron oxyhydroxides, obtained from active and inactive vents, commonly possess filamentous textures similar in appearance to sheaths and stalks excreted by the iron-oxidizing bacteria Leptothrix and Gallionella; however, formless agglomerates are also common. Textural relationships between apparent bacterial and non-bacterial iron suggest that the filaments are coeval with and/or growing outwards from the agglomerates. The amorphous iron oxyhydroxides are suggested to precipitate hydrothermally as ferrosic hydroxide, a mixed-valence (Fe2+-Fe3+) green–yellow iron hydroxide compound. Consideration of the thermodynamics and kinetics of iron in the vent fluid, suggest that the precipitation is largely pH controlled and that large amounts of amorphous iron oxyhydroxides are capable of being precipitated by a combination of abiotic hydrothermal processes. Some biologically induced precipitation of primary ferric oxyhydroxides (two-XRD-line ferrihydrite) may have occurred directly from the fluid, but most of the filamentous iron micro-textures in the samples appear to have a diagenetic origin. They may have formed as a result of the interaction between the iron-oxidizing bacteria and the initially precipitated ferrosic hydroxide that provided a source of ferrous iron needed for their growth. The processes described at Franklin Seamount provide insight into the formation of other seafloor oxyhydroxide deposits and ancient oxide-facies iron formation. 相似文献
9.
I.V.Ashchepkov S.S.Kuligin N.V.Vladykin H.Downes M.A.Vavilov E.N.Nigmatulina S.A.Babushkina N.S.Tychkov O.S.Khmelnikova 《地学前缘(英文版)》2016,7(4):639-662
Mantle xenocrysts from early Triassic kimberlite pipes from Kharamai,Ary-Mastakh and Kuranakh fields in the Anabar shield of Siberia revealing similar compositional trends were studied to estimate the superplume influence on the subcratonic lithosphere mantle(SCLM).Pressure-temperature(PT) reconstructions using monomineral thermobarometry for 5 phases show division of the SCLM beneath the Kharamai field into 6 units:pyroxenitic Fe-rich(1-2 GPa) and Mg-rich(2-3 GPa) layers;middle with two levels of Gar-Sp pyroxenites at ~3 and 4-5 GPa;Gar-dunite-harzburgites ~4.5-6.5 GPa subjected to Ilm-Px vein metasomatism;and a Mg-rich dunite lower part.In the Anabar shield(Ary-Mastakh,Dyuken and Kuranakh fields) mantle lithosphere is composed of three large units divided into two parts:upper part with amphiboles and phlogopite;two levels of pyroxenites and eclogites at 3 and 4 GPa,and a lower part composed of refertilized dunites.Diagrams showing P-Fe~#Gar clusters for garnets and omphacites illustrate the differences between SCLM of these localities.Differences of Triassic SCLM from Devonian SCLM are in simple layering;abundance of Na-Cr-amphiboles and metasomatism in the upper SCLM part,thick pyroxenite-eclogite layer and lower part depletion,heated from SCLM base to 5.0 GPa.Kharamai mantle clinopyroxenes represent three geochemical types:(1) harzburgitic with inclined linear REE,HFSE troughs and elevated Th,U;(2) lherzolitic or pyroxenitic with round TRE patterns and decreasing incompatible elements;(3) eclogitic with Eu troughs,Pb peak and high LILE content.Calculated parental melts for garnets with humped REE patterns suggest dissolution of former Cpx and depression means Cpx and garnets extraction.Clinopyroxenes from Ary-Mastakh fields show less inclined REE patterns with HMREE troughs and an increase of incompatible elements.Clinopyroxenes from Kuranakh field show flatter spoon-like REE patterns and peaks in Ba,U,Pb and Sr,similar to those in ophiolitic harzburgites.The PT diagrams for the mantle sections show high temperature gradients in the uppermost SCLM accompanied by an increase of P-Fe~#Ol upward and slightly reduced thickness of the mantle keel of the Siberian craton,resulting from the influence of the Permian-Triassic superplume,but with no signs of delamination. 相似文献
10.
Dorothee C.E. Bakker Philip W. Boyd Edward R. Abraham Matthew A. Charette Mark P. Gall Julie A. Hall Cliff S. Law Scott D. Nodder Karl Safi Dick J. Singleton Kim Tanneberger Thomas W. Trull Anya M. Waite Andrew J. Watson John Zeldis 《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(12):1941-1960
The Lagrangian Southern Ocean Iron Release Experiment (SOIREE) allowed study of a gradually evolving iron-mediated phytoplankton bloom in water labelled with the inert tracer sulfur hexafluoride, SF6. This article describes a pelagic carbon budget for the mixed layer in SOIREE and assesses the extent to which closure of the budget is achieved. Net community production (NCP) converted 837 mmol m−2 of inorganic carbon to organic carbon in 12.0 d after the first iron addition. A large fraction (41%) of NCP remained as particulate organic carbon in the mixed layer of the iron-enriched patch, while 23% was lost by horizontal dispersion and 0–29% was exported. The closure of the carbon budget is hampered by the lack of measurements of dissolved organic carbon (DOC), by a major uncertainty in carbon export, and by use of empirical conversion factors in estimates of carbon biomass and metabolic rates. Lagrangian carbon-budget studies may be improved by direct measurement of all major carbon parameters and conversion factors. Carbon cycling in the SOIREE bloom resembled that in ‘natural’ algal blooms in the open Southern Ocean in some respects, but not in all. Daily NCP in the SOIREE bloom (70 mmol m−2 d−1) was higher than in natural blooms, partly because other studies did not account for horizontal dispersion, were for longer periods or included less productive areas. The build-up of POC stock and carbon export as a fraction of NCP in SOIREE were in the lower range of observations elsewhere. 相似文献