Comparison of Major and Trace Element Analyses by ICP, XRF, INAA and ID Methods

Element concentration data for a set of silicate igneous rocks have been determined by four independent analytical methods: inductivelycoupled plasma emission spectroscopy (ICP), instrumental neutron activation analysis (INAA), x-ray fluorescence (XRF), and isotope dilution mass spectrometry (ID). The results show excellent agreement among elements determined by more than one technique, and demonstrate the suitability of commercially available ICP instrumentation for the routine analysis of geologic material compared to other standard methods.     

贵州锦丰(烂泥沟)金矿床含砷黄铁矿和脉石英及其包裹体的稀土元素特征

贵州锦丰(烂泥沟)金矿是滇黔桂"金三角"目前已探明的最大的卡林型金矿床.含砷黄铁矿是该矿床最主要的载金矿物,脉石英是最显著的热液蚀变作用产物.含砷黄铁矿、脉石英及其包裹体具有相同的稀土元素特征,表现为轻重稀土分馏明显(LREE/HREE7.95～31.77,(La/Yb)N8.97～40.49);轻稀土有一定的分异((La/Sm)n3.20～5.29),曲线右倾程度大;重稀土分异不明显((Gd/Yb)n1.41～3.35),曲线平坦;负铕异常明显(δEu 0.59～0.71);微弱的铈负异常(δCe 0.97～0.98).代表成矿流体特征的脉石英包裹体稀土配分型式及特征值与区域上不同时代的幔源基性-超基性岩差别较大,而与矿床围岩、矿石、含砷黄铁矿及其包裹体稀土配分型式及特征值十分相似,具上部地壳普通沉积岩的特点,反映成矿流体主要不是来源于地幔,而是以壳源为主.Eu负异常反映了偏酸性(富CO2)、还原性的成矿环境;微弱的Ce负异常表明成矿流体来源于以沉积水和热脱水为主的盆地流体.     

Climate Change Impacts for the Conterminous USA: An Integrated Assessment

During this century global warming will lead to changes in global weather and climate, affecting many aspects of our environment. Agriculture is the sector of the United States economy most likely to be directly impacted by climatic changes. We have examined potential changes in dryland agriculture (Part 3) and in water resources necessary for crop production (Part 4) in response to a set of climate change scenarios. In this paper we assess to what extent, under these same scenarios, water supplies will be sufficient to meet the irrigation requirement of major grain crops in the US. In addition, we assess the overall impacts of changes in water supply on national grain production. We apply the 12 climate change scenarios described in Part 1 to the water resources and crop growth simulation models described in Part 2 for the conterminous United States. Drawing on data from Parts 3 and 4 we calculate what the aggregate national production would be in those regions in which grain crops are currently produced by applying irrigation where needed and water supplies allow. The total amount of irrigation water applied to crops declines under all climate change scenarios employed in this study. Under certain of the scenarios and in particular regions, precipitation decreases so much that water supplies are too limited; in other regions precipitation becomes so plentiful that little value is derived from irrigation. Nationwide grain crop production is greater when irrigation is applied as needed. Under irrigation, less corn and soybeans are produced under most of the climate change scenarios than is produced under baseline climate conditions. Winter wheat production under irrigation responds significantly to elevated atmospheric carbon dioxide concentrations [CO₂] and appears likely to increase under climate change.     

The art of the science: climate forecasts for wildfire management in the southeastern United States

This article illustrates how a wildfire risk forecast evolved iteratively based on stakeholder consultations. An assessment based on phone interviews indicates that such forecasts can assist fire management decisions, such as deployment of human, financial, and material resources and management of forest, timber, and habitats, and public safety. But careful attention to communication, collaboration, and capacity building is key to realizing this potential.     

Climate Change Impacts for the Conterminous USA: An Integrated Assessment

As carbon dioxide and other greenhouse gasses accumulate in the atmosphere and contribute to rising global temperatures, it is important to examine how a changing climate may affect natural and managed ecosystems. In this series of papers, we study the impacts of climate change on agriculture, water resources and natural ecosystems in the General Circulation Model (GCM)-derived climate change projections, described in Part 1, to drive the crop production and water resource models EPIC (Erosion Productivity Impact Calculator) and HUMUS (Hydrologic Unit Model of the United States). These models are described and validated in this paper using historical crop yields and streamflow data in the conterminous United States in order to establish their ability to accurately simulate historical crop and water conditions and their capability to simulate crop and water response to the extreme climate conditions predicted by GCMs. EPIC simulated grain and forage crop yields are compared with historical crop yields from the US Department of Agriculture (USDA) and with yields from agricultural experiments. EPIC crop yields correspond more closely with USDA historical county yields than with the higher yields from intensively managed agricultural experiments. The HUMUS model was validated by comparing the simulated water yield from each hydrologic basin with estimates of natural streamflow made by the US Geological Survey. This comparison shows that the model is able to reproduce significant observed relationships and capture major trends in water resources timing and distribution across the country.     

Reaction between slab-derived melts and peridotite in the mantle wedge: experimental constraints at 3.8 GPa

Laboratory experiments on natural, hydrous basalts at 1–4 GPa constrain the composition of “unadulterated” partial melts of eclogitized oceanic crust within downgoing lithospheric slabs in subduction zones. We complement the “slab melting” experiments with another set of experiments in which these same “adakite” melts are allowed to infiltrate and react with an overlying layer of peridotite, simulating melt:rock reaction at the slab–mantle wedge interface. In subduction zones, the effects of reaction between slab-derived, adakite melts and peridotitic mantle conceivably range from hybridization of the melt, to modal or cryptic metasomatism of the sub-arc mantle, depending upon the “effective” melt:rock ratio. In experiments at 3.8 GPa, assimilation of either fertile or depleted peridotite by slab melts at a melt:rock ratio 2:1 produces Mg-rich, high-silica liquids in reactions which form pyrope-rich garnet and low-Mg# orthopyroxene, and fully consume olivine. Analysis of both the pristine and hybridized slab melts for a range of trace elements indicates that, although abundances of most trace elements in the melt increase during assimilation (because melt is consumed), trace element ratios remain relatively constant. In their compositional range, the experimental liquids closely resemble adakite lavas in island-arc and continental margin settings, and adakite veins and melt inclusions in metasomatized peridotite xenoliths from the sub-arc mantle. At slightly lower melt:rock ratios (1:1), slab melts are fully consumed, along with peridotitic olivine, in modal metasomatic reactions that form sodic amphibole and high-Mg# orthopyroxene.     

Constraints from eclogite and MARID xenoliths on origins of mantle Zr/Hf–Nb/Ta variability

New trace-element data of rutile in kimberlite-borne ~1.85 Ga eclogite and pyroxenite xenoliths from the central Slave craton, as well as ~110 Ma MARID xenoliths from the Kaapvaal craton, provide constraints on the origins of lithospheric and sublithospheric mantle variability in high field strength element ratios. Rutiles in eclogites and pyroxenites have Zr/Hf ranging from 20 to 62 and Nb/Ta ranging from 10 to 40. Rutiles in MARID xenoliths have Zr/Hf from 24 to 33 and Nb/Ta from 10 to 41. Calculated whole-rock Zr/Hf is suprachondritic for eclogites with suggested gabbroic protoliths and subchondritic for boninite-like eclogites; the latter is consistent with cpx-controlled depletion in the protolith source. Within each eclogite type, positive correlations of Zr/Hf with La/Lu and negative correlations with Lu/Hf likely reflect fractionation of cpx and/or plagioclase during crystallisation of the protoliths. Zr/Hf–Nb/Ta relationships of some MARID-type rocks, which are products of lithospheric mantle metasomatism, and eclogite xenoliths plot on a silicate differentiation trend, whereas other samples have higher Nb/Ta at a given Zr/Hf. Fractionation of a few percent rutile from an HFSE-rich mafic melt can generate a trend towards strongly increased Nb/Ta at minimally changed Zr/Hf in the residual melt. Superposition of rutile fractionation on the effects of silicate differentiation, which fractionates Zr/Hf more strongly than Nb/Ta, can explain the Zr/Hf–Nb/Ta relationships of most eclogites from the central Slave craton as well as those of MARID rocks, metasomatised peridotites and group II kimberlites. By contrast, Zr/Hf–Nb/Ta relationships suggest that Group I kimberlites are mixtures between depleted peridotite and carbonatite. Thus, high Nb/Ta is a signature of lithospheric processes and may not be important in deeply subducted eclogites that bypass extended residence in the lithosphere. Conversely, considerable primary Zr/Hf variability was inherited by the eclogites, which is indicative of the compositional diversity of ancient subducted oceanic crust, which is expected to have generated substantial heterogeneity in sublithospheric basalt sources.     

Diapirism synchronous with regional deformation and gold mineralisation,a new concept for granitoid emplacement in the Southern Cross Province,Western Australia

The Southern Cross Province in the Archean Yilgarn Block of Western Australia comprises large dome-shaped granitoid bodies surrounded by narrow greenstone belts. Determination of the emplacement mechanism of these domes is fundamental for understanding the tectonic history of this region. Many structures in the greenstone belts show trends which reflect their tectonic relationships with the granitoid domes. Some of these structures host large gold occurrences. The domes have concentric foliation patterns, both within the granitoids themselves, and in the neighbouring greenstone belts. The smaller domes only have radial mineral lineation patterns in their wall rocks, but the largest dome, the Ghooli Dome, has also a tangential pattern. The prevailing gentle dip of the foliation in the centre of this dome and the abundance of greenstone xenoliths suggest that the present exposures are close to its roof. Geothermometry and geobarometry on mineral assemblages in the Ghooli granitoid and its xenoliths show that its crystallisation temperature was just above 700 °C at a relatively high pressure of 4.3 to 6.2 kbar. These P-T conditions are higher than those inferred for peak metamorphism in the greenstones. Therefore, this granitoid must have been emplaced initially at crustal levels deeper than the maximum burial of the greenstones which flank the dome. The Ghooli Dome has a SHRIMP U-Pb zircon age of 2691 ± 7 Ma. Diapiric rise of the granitoid plutons taking place in a regional compressive tectonic regime is considered to be the most likely mechanism for the final emplacement of these bodies into their host rock at about 2636–2620 Ma. This concept is preferred over the alternatives because it best reconciles the calculated P-T data, the observed structural patterns, the presence of pegmatites and aplites in the host rock, and the orientation of the mineral-bearing structures.     

南极Amanda湾帝企鹅卵的生态生物学及与其它南极海鸟卵的比较

对南极Amanda湾帝企鹅的卵进行了生态生物学观测与相应的统计分析。结果显示,帝企鹅卵为典型的卵形卵,平均长、短径分别为121.3mm和83.8mm;平均卵容量409.3ml(322.6-506.4ml),卵的平均壳厚为1.11mm(0.94-1.23mm)。帝企鹅和南方巨鹱、白眉企鹅以及灰贼鸥等南极海鸟的卵相比较,卵的形态大小与容量成正比,同时,容量较大的卵具有较厚的卵壳,以增强对卵的保护。这些海鸟卵的生态生物学特征,包括保护色的有无、卵容量的大小,以及卵壳厚度等特征参数,是这些海鸟种的明显特征,并与亲鸟在繁殖期的窝卵数以及孵化习性相协调,以达到对南极环境的适应与生存。