Mineralogical,petrological, and geochemical studies of the Limahe mafic–ultramatic intrusion and associated Ni–Cu sulfide ores,SW China

The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ ³⁴S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ ³⁴S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher degrees of contamination with the upper crust than did the picrites. The results of this study permit us to suggest that the parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second, relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential of economic Ni–Cu sulfide deposits.     

Absolute Calibration of an Ashtech Z12-T GPS Receiver

Dual-frequency carrier phase and code measurements from geodetic type receivers are a promising tool for frequency and time transfer. In order to use them for clock comparisons, all instrumental delays should be calibrated. We have carried out the calibration of one such receiver, an Ashtech Z12-T type, by two different methods: first, by absolute calibration using a GPS simulator; second, by differential calibration with respect to a time transfer receiver that had previously been calibrated. We present the experimental set-ups and the results of the two experiments and estimate the uncertainty budget. An ultimate uncertainty of order 1 ns in the absolute calibration seems to be attainable. ? 2001 John Wiley & Sons, Inc.     

Static recovery and recrystallization microstructures in sheared octachloropropane

Octachloropropane (C₃C1₈) was sheared using a press mounted on an optical microscope and then allowed to adjust its microstructure statically, at the deformation temperature. Depending on strain rate and deformation temperature, the post-deformational changes in microstructure are strikingly different. After low temperature-high strain-rate deformation, fast growth of new strain-free grains on the boundaries of deformed grains results in the obliteration of grain-shape foliation and intracrystalline deformation features, and the development of a foam texture. After high temperature—low strain-rate deformation, on the other hand, grain-shape foliation and grains with subgrain boundaries tend to survive the adjustment. Lattice preferred orientation is maintained after the post-deformational adjustment at both deformation conditions and thus remains a good indicator of deformation.     

Enclosure experiments on survival and growth of black drum eggs and larvae in lower Chesapeake Bay

Experiments in 2.2 m³, in situ mesocosm enclosures indicate that black drum, Pogonias cromis, eggs and larvae potentially can survive in the lower Chesapeake Bay at ambient microzooplankton prey levels (≈200 prey 1^?1) in the absence of predators. In growth experiments, larva mean growth rates to 10 d posthatch were similar (0.17 mm d^?1 and 0.18 mm d^?1) when fed at prey levels of 50 prey 1^?1 and 200 prey 1^?1. Individual growth rates, however, were more variable at 50 prey 1^?1. Mortality rates also were comparable in 50 (27% d^?1) and 200 (23% d^?1) prey 1^?1 enclosures. In a second experiment, the predation potentials of the hydromedusa Nemopsis bachei and the lobate ctenophore Mnemiopsis leidyi were estimated in relation to initial black drum egg prey density, presence of alternative <1 mm zooplankton prey, and estimated daily abundance of the jellyfish on the black drum spawning grounds. Mortality rates per medusa and ctenophore were similar (0.02–0.03 d^?1), were not affected by presence of alternative prey, and were directly related to initial egg density. Results suggest that the gelatinous predators, especially the hydromedusa, could have cleared a high (≈38%) but variable fraction of the water column daily of fish eggs and yolk-sac larvae during the black drum spawning season. We hypothesize that the poor or episodic recruitment success of black drum in Chesapeake Bay results from a short spawning season that often coincides with abundance peaks of gelatinous predators and that predation on eggs and yolk-sac larvae may control recruitment.     

On predicting the response of forests in eastern North America to future climatic change

Our ability to accurately predict the response of forests in eastern North America to future climatic change is limited by our knowledge of how different tree species respond to climate. When the climatic response of eastern hemlock is modeled across its range, we find that the assumed climatic response used in simulation models is not sufficient to explain how this species is presently responding to climate. This is also the case for red spruce growing in the northern Appalachian Mountains. Consequently, simulations of future change to forests that include eastern hemlock and red spruce may need to be improved. We suspect that similar findings will be made when other tree species are studied in detail using tree-ring analysis. If so, our present understanding of how individual tree species respond to climate may not be adequate for accurately predicting future changes to these forests. Tree-ring analysis can increase our understanding of how climate affects tree growth in eastern North America and, hence, provide the knowledge necessary to produce more accurate predictions.     

Laboratory Demonstration of Hydrocarbon Migration in the Vadose Zone: Effectiveness of the U-Tube Design for Underground Storage Tank Leak Detection Monitoring

The experimental results derived from a laboratory model of gasoline migration from a simulated leaking underground storage tank (UST) demonstrate that the direction of migration through the simulated fill material is essentially straight down. Consequently, the U-tube design for leak detection monitoring of USTs has limited utility because that design relies on the assumption that the path of migration of the leaked fluids will follow the surface of the tank to the bottom and be intercepted by the U-tube below.     

Sheared shale response to deep TBM excavation

Phien-wej, N. and Cording, E.J., 1991. Sheared shale response to deep TBM excavation. Eng. Geol., 30: 371–391.

Ravelling and squeezing of sheared shale of Stillwater Tunnel caused severe problems in tunneling with a tunnel boring machine (TBM) that led to termination of the contract. The tunnel was finally holed through with two TBM's specially designed for squeezing ground. Although the shale mass in all geological conditions exhibited time-dependent response, significant squeezing was confined to sheared shale with large amounts of clay gouge infill, wherein creep of the clay gouge was the prime mechanism controlling the ground response. However, when the tunnel face was advanced at a slow rate, the observed ground squeezing in the early period was largely induced by the effect of stress change from face advance, not the creep. Ground ravelling was very significant in sheared shale due to the high degree of fissuring and fracturing of this thinly bedded shale. Failure of the first TBM resulted mainly from the incompatibility of the shield design with the sheared shale. The shield was too long and stiff and had variable diameters. Extensive observation and instrumentation programs of the project provided valuable information on rapid mechanized tunneling in heavy ground.     

Three dilemmas in the integrated assessment of climate change

Conclusions These three dilemmas embody the hardest, most important, and most enduring problems of doing assessment well. None admits simple, obvious solutions. Each can be managed better or worse for any particular assessment endeavor, but doing better requires clear understanding of the purpose of the endeavor. What ways of combining different pieces of disciplinary knowledge, of making projections, and of pursuing policy relevance are more or less appropriate will differ, depending on whether a project seeks to characterize uncertainties and gaps in knowledge; to advise a particular policy choice; to support dialog among policy actors; or to facilitate inquiry into relevant values or goals. Evaluation of the relative emphasis, the methods, and the process of an assessment can only be done relative to some such purpose.Of course, some pitfalls may be so serious as to thwart any purpose, as Risbey et al.'s discussion of the global modeling movement reminds us. The global models' most obvious pitfalls — inadequate treatment of uncertainty, neglect of economic adjustment, excessive confidence in predictions — have largely been seen and avoided by the current assessment community (though there may be more to be learned even here). But on the subtler questions of how assessment or modeling can contribute most usefully to policy, little progress has been made since the 1970s. Consequently, though assessment has advanced in many ways since then, IA remains at risk of suffering the same fate as the global models: a cycle of early enthusiasm, followed by a reaction of frustration and excessive, undeserved rejection.Current endeavors in IA have made substantial contributions to identifying and prioritizing knowledge needs, less to informing specific policy choice. Further progress cannot be guided by a single canonical view of what assessment should be and do, but will proceed incrementally down multiple paths. Several paths currently appear promising: analytic approaches to better represent multiple actors, diverse preferences, and multiple valued outcomes; better representation and application of uncertainty, including diverse expert opinion; novel methods to link assessment with policy communities; and broader participation in assessment teams and explicit focus on negotiating and elaborating pragmatic, viable critical standards. Risbey et al.'s call to develop institutions for critical reflection, mutual learning, and self-improvement will be crucial in developing and evaluating the progress made down these paths.Morgan and Dowlatabadi's checklist for desiderata of IA is a good starting point for a conversation about assessment standards, to which I would propose a few extensions and elaborations. First, there should be not just multiple assessments, but multiple assessment projects using diverse collections of methods and approaches. Second, assessment projects should explore novel methods for connecting their work with the policy community. Third, the approach should be iterative not just within each project, but across assessment projects and between them and the policy community. Fourth, assessors should not be embarrassed by, or seek to disguise, results that are merely illustrative, non-authoritative, and suggestive; these should be acknowledged as such, and the vigorous questioning and critique that will come, including partisan critique, accepted. Do not seek to avoid criticism by mumbling. An important limit to this checklist approach is suggested, though, by the way various writers have groped to define assessment standards by analogy to other domains, revealing how limited is our understanding of how to evaluate assessment. Risbey et al. refer to connoisseurship, as if assessment is like fine wine; Clark and Majone (1985) refer to artistic criticism, as if assessment is like opera singing. If these analogies are appropriate, then pursuing a single set of critical standards for assessment is at least premature, possibly erroneous. Rather, there should be a diversity of approaches, perhaps so broad that no single set of criteria for excellence could be defined. The pragmatic middle way between the too-limiting application of a single set of standards, and an anarchic refusal to evaluate, will have to be negotiated, defined, and improved incrementally.     

Time of emergence of anthropogenic warming signals in the Northeast Asia assessed from multi-regional climate models

Time of Emergence (ToE) is the time at which the signal of climate change emerges from the background noise of natural climate variability, and can provide useful information for climate change impacts and adaptations. This study examines future ToEs for daily maximum and minimum temperatures over the Northeast Asia using five Regional Climate Models (RCMs) simulations driven by single Global Climate Model (GCM) under two Representative Concentration Pathways (RCP) emission scenarios. Noise is defined based on the interannual variability during the present-day period (1981-2010) and warming signals in the future years (2021-2100) are compared against the noise in order to identify ToEs. Results show that ToEs of annual mean temperatures occur between 2030s and 2040s in RCMs, which essentially follow those of the driving GCM. This represents the dominant influence of GCM boundary forcing on RCM results in this region. ToEs of seasonal temperatures exhibit larger ranges from 2030s to 2090s. The seasonality of ToE is found to be determined majorly by noise amplitudes. The earliest ToE appears in autumn when the noise is smallest while the latest ToE occurs in winter when the noise is largest. The RCP4.5 scenario exhibits later emergence years than the RCP8.5 scenario by 5-35 years. The significant delay in ToEs by taking the lower emission scenario provides an important implication for climate change mitigation. Daily minimum temperatures tend to have earlier emergence than daily maximum temperature but with low confidence. It is also found that noise thresholds can strongly affect ToE years, i.e. larger noise threshold induces later emergence, indicating the importance of noise estimation in the ToE assessment.