Sources of Hydrothermal Fluids Inferred from Oxygen and Carbon Isotope Composition of Calcite, Keweenaw Peninsula Native Copper District, Michigan, USA

The Mesoproterozoic North American Midcontinent Rift hosts the world’s largest accu-mulation of native copper in Michigan’s Keweenaw Peninsula. During a regional metamorpho-genic‐hydrothermal event, native copper was deposited along with spatially zoned main‐stage minerals in a thermal high. This was followed by deposition of late‐stage minerals including minor copper sulfide. Inferences from the oxygen and carbon isotopic composition of main‐stage hydrothermal fluids, as calculated from 296 new and compiled isotopic measurements on calcite, are consistent with existing models that low‐sulfur saline native copper ore‐forming fluids were domi-nantly derived by burial metamorphic processes from the very low sulfur basalt‐dominated rift fill at depth below the native copper deposits. Co‐variation of oxygen and carbon isotopic compositions are consistent with mixing of metamorphic‐derived fluids with two additional isotopically different fluids. One of these is proposed to be evolved seawater that provided an outside source of salinity. This fluid mixed at depth and participated in the formation of a well‐mixed hybrid metamorphic-dominated ore‐forming fluid. Secondary Ion Mass Spectrometry in‐situ isotopic analyses of calcite demonstrate a high degree of variability within samples that is attributed to variable degrees of shallow mixing of the hybrid ore‐forming fluid with sulfur‐poor, reduced evolved meteoric water in the zone of precipitation. The oxygen and carbon isotopic compositions of 100 new and compiled measurements on late‐stage calcite are mostly isotopically different than the main‐stage hydrothermal fluids. The late‐stage hydrothermal fluids are interpreted as various proportions of mixing of evolved meteoric water, main‐stage hybrid ore‐forming fluid, and shallow, evolved seawater in the relatively shallow zone of precipitation

Chronology of prescribing error during the hospital stay and prediction of pharmacist's alerts overriding: a prospective analysis

<p>Abstract</p> <p>Background</p> <p>Drug prescribing errors are frequent in the hospital setting and pharmacists play an important role in detection of these errors. The objectives of this study are (1) to describe the drug prescribing errors rate during the patient's stay, (2) to find which characteristics for a prescribing error are the most predictive of their reproduction the next day despite pharmacist's alert (<it>i.e</it>. override the alert).</p> <p>Methods</p> <p>We prospectively collected all medication order lines and prescribing errors during 18 days in 7 medical wards' using computerized physician order entry. We described and modelled the errors rate according to the chronology of hospital stay. We performed a classification and regression tree analysis to find which characteristics of alerts were predictive of their overriding (<it>i.e</it>. prescribing error repeated).</p> <p>Results</p> <p>12 533 order lines were reviewed, 117 errors (errors rate 0.9%) were observed and 51% of these errors occurred on the first day of the hospital stay. The risk of a prescribing error decreased over time. 52% of the alerts were overridden (<it>i.e </it>error uncorrected by prescribers on the following day. Drug omissions were the most frequently taken into account by prescribers. The classification and regression tree analysis showed that overriding pharmacist's alerts is first related to the ward of the prescriber and then to either Anatomical Therapeutic Chemical class of the drug or the type of error.</p> <p>Conclusions</p> <p>Since 51% of prescribing errors occurred on the first day of stay, pharmacist should concentrate his analysis of drug prescriptions on this day. The difference of overriding behavior between wards and according drug Anatomical Therapeutic Chemical class or type of error could also guide the validation tasks and programming of electronic alerts.</p

Magmatic volatiles: A melt inclusion study of Taupo Volcanic Zone rhyolites,New Zealand

The central segment of the Taupo Volcanic Zone (TVZ) is one of the world’s most productive areas of silicic volcanism and geothermal activity. Rhyolites largely predominate the eruptive output in the central TVZ, with only minor basalts, andesites and dacites. The rhyolites show diversity in composition, and form a compositional continuum between two end-member types (R1 and R2), as suggested in previous studies. In this thesis I present results from a quartz- (and rare plagioclase-) hosted melt inclusions study, focussing on the volatile concentration (i.e. H2O, Cl, F, CO2) and their relative distribution between R1 and R2 rhyolites. The main objective is to add further constraints on the magmatic systems with regard to their contribution to the hydrothermal systems in the central TVZ. A comparative study between R1 and R2 melt inclusions show distinct volatile, fluid-mobile, and highly incompatible element compositions. Differences in the bulk volatile concentration of the parental magmas (i.e. basalts intruding the lower crust) are suggested to be at the origin of these volatile disparities. Further analysis on the volatile exsolution of R1 and R2 melts lead to the observation that the two rhyolite types exsolve a volatile phase at different stages in their magmatic history. From Cl and H2O concentrations, it is suggested that R1 magmas exsolve a vapour phase first, whereas R2 rhyolites more likely exsolve a hydrosaline fluid phase. These results have considerable implications for the magmatic contribution into the hydrothermal systems in the central TVZ, as differences in the composition of the resulting volatile phase may be expected. The hydrothermal systems in the central TVZ are subdivided into two groups based on their gas and fluid chemistry; and the current model suggests that there are two distinct contributions: a typical ‘arc’ system, with geochemical affinity with andesitic fluids, located along the eastern margin of the TVZ, and a typical ‘rift’ system, with geochemical affinity with rhyolitic/basaltic fluids, located along the central and/or western region of the TVZ. The addition of the new data on the rhyolitic melt inclusions, leads to a re-evaluation of the magmatic contribution into the hydrothermal systems, with a particular focus on B and Cl. The results indicate a more diverse variety of contributions to the meteoric water in the hydrothermal systems, and also show that the east-west distribution of ‘arc’ and ‘rift’ fluids is not a viable model for the central TVZ. This work emphasises that melt inclusion data and their volatile degassing history cannot be underestimated when characterising and quantifying the magmatic component in hydrothermal fluids. The melt inclusion data also provide further insight into the pre-eruptive magmatic plumbing systems and are particularly important from a hazard perspective. Included in the thesis is a detailed petrological analysis of rhyolite melt inclusions across the central TVZ and an interpretation that large silicic magma systems (in the TVZ) are typically comprised of multiple batches of magma emplaced at some of the shallowest depths on Earth. Tectonic activity is suggested to play an important role in triggering large caldera-forming eruptions as the evacuation of one magma batch could cause a regional-scale readjustment that is sufficient enough to trigger and allow simultaneous eruption of an adjacent melt batch

Spatio-temporal variability of sugarcane fields and recommendations for yield forecast using NDVI

Sugarcane is a semi-perennial grass whose cultivation is characterized by an extended harvest season lasting several months leading to very high spatio-temporal variability of the crop development and radiometry. The objective of this paper is to understand this variability in order to propose appropriate spectral indicators for yield forecast. To do this, we used ground observations and Satellite Pour l'Observation de la Terre (SPOT4) and SPOT5 time series acquired monthly over a 2-year period over Reunion Island and Guadeloupe (French West Indies). We showed that variations in the Normalized Difference Vegetation Index (NDVI) of sugarcane at the field scale are the result of the interaction between the sugarcane crop calendar and plant phenology in a given climatic environment. We linked these variations to crop variables measured in the field (leaf area index and leaf colour), and derived simple, appropriate NDVI-based indicators of sugarcane yield components at the field scale (cane yield and sugar content). For biomass forecast, the best correlation (R2 = 0.78) was obtained with images acquired about 2 months before the harvest season, when all the fields are fully developed but before the maturation stage. For sugar content, a polynomial relationship (R2 = 0.75) was observed between the field NDVI acquired during the maturation stage and sugar content in the stalk. (Résumé d'auteur

Magmatic volatile distribution as recorded by rhyolitic melt inclusions in the Taupo Volcanic Zone, New Zealand

<p>The central Taupo Volcanic Zone (TVZ) is an actively rifting continental arc and is well known for its exceptionally high rate of rhyolitic magma generation and frequent caldera-forming eruptions. Two end-member types of rhyolites (R1 and R2) have been previously identified based on differences in their bulk-rock chemistry and mineral assemblage with hydrous phases crystallizing in the R1 type, which are not present or only rare in R2 rhyolites. Here we present new trace element and volatile data from rhyolitic melt inclusions measured in several representative eruptive deposits (R1 and R2 rhyolites) from the central TVZ to examine their volatile concentrations and origin. R1 and R2 show very distinct Cl concentrations, with R2 rhyolites being enriched in Cl by <em>c.</em> 1000 ppm. H₂O is slightly higher in the R1 rhyolites, whereas CO₂ concentrations are similar between the two end-member types. The origin of these volatile disparities between R1 and R2 melts is assigned to differences in the initial bulk volatile content of the parental magma, possibly associated with distinct input of fluids from the subduction zone. These disparities in bulk volatile concentrations can lead to variations in relative timing of exsolution of volatile phase(s) prior to melt inclusion entrapment. </p