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Katie A. Smart Thomas Chacko Thomas Stachel Karlis Muehlenbachs Richard A. Stern Larry M. Heaman 《Geochimica et cosmochimica acta》2011,75(20):6027-6047
Diamonds from high- and low-MgO groups of eclogite xenoliths from the Jericho kimberlite, Slave Craton, Canada were analyzed for carbon isotope compositions and nitrogen contents. Diamonds extracted from the two groups show remarkably different nitrogen abundances and δ13C values. While diamonds from high-MgO eclogites have low nitrogen contents (5-82 ppm) and extremely low δ13C values clustering at ∼−40‰, diamonds from the low-MgO eclogites have high nitrogen contents (>1200 ppm) and δ13C values from −3.5‰ to −5.3‰.Coupled cathodoluminescence (CL) imaging and SIMS analysis of the Jericho diamonds provides insight into diamond growth processes. Diamonds from the high-MgO eclogites display little CL structure and generally have constant δ13C values and nitrogen contents. Some of these diamonds have secondary rims with increasing δ13C values from −40‰ to ∼−34‰, which suggests secondary diamond growth occurred from an oxidized growth medium. The extreme negative δ13C values of the high-MgO eclogite diamonds cannot be produced by Rayleigh isotopic fractionation of average mantle-derived carbon (−5‰) or carbon derived from typical organic matter (∼−25‰). However, excursions in δ13C values to −60‰ are known in the organic sedimentary record at ca. 2.7 and 2.0 Ga, such that diamonds from the high-MgO eclogites could have formed from similar organic matter brought into the Slave lithospheric mantle by subduction.SIMS analyses of a diamond from a low-MgO eclogite show an outer core with systematic rimwards increases in δ13C values coupled with decreases in nitrogen contents, and a rim with pronounced alternating growth zones. The coupled δ13C-nitrogen data suggest that the diamond precipitated during fractional crystallization from an oxidized fluid/melt from which nitrogen was progressively depleted during growth. Model calculations of the co-variation of δ13C-N yielded a partition coefficient (KN) value of 5, indicating that nitrogen is strongly compatible in diamond relative to the growth medium. δ13C values of diamond cores (−4‰) dictate the growth medium had higher δ13C values than primary mantle-derived carbon. Therefore, possible carbon sources for the low-MgO eclogite diamonds include oxidized mantle-derived (e.g. protokimberlite or carbonatite) fluids/melts that underwent some fractionation during migration or, devolatilized subducted carbonates. 相似文献
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Katie Head Chris S. M. Turney Jon R. Pilcher J. G. Palmer M. G. L. Baillie 《第四纪科学杂志》2007,22(1):65-75
The Northern Hemisphere cooling event 8200 years ago is believed to represent the last known major freshwater pulse into the North Atlantic as a result of the final collapse of the North American Laurentide ice sheet. This pulse of water is generally believed to have occurred independently of orbital variations and provides an analogue for predicted increases in high‐latitude precipitation and ice melt as a result of anthropogenically driven future climate change. The precise timing, duration and magnitude of this event, however, are uncertain, with suggestions that the 100‐yr meltwater cooling formed part of a longer‐term cold period in the early Holocene. Here we undertook a multiproxy, high‐resolution investigation of a peat sequence at Dooagh, Achill Island, on the west coast of Ireland, to determine whether the 8200‐year cold event impacted upon the terrestrial vegetation immediately ‘downwind’ of the proposed changes in the North Atlantic. We find clear evidence for an oscillation in the early Holocene using various measures of pollen, indicating a disruption in the vegetation leading to a grassland‐dominated landscape, most probably driven by changes in precipitation rather than temperature. Radiocarbon dating was extremely problematic, however, with bulk peat samples systematically too young for the North Atlantic event, suggesting significant contamination from downward root penetration. The sustained disruption to vegetation over hundreds of years at Dooagh indicates the landscape was impacted by a long‐term cooling event in the early Holocene, and not the single century length 8200‐year meltwater event proposed in many other records in the North Atlantic region. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Abstract— We have surveyed Martian impact craters greater than 5 km in diameter using Viking and thermal emission imaging system (THEMIS) imagery to evaluate how the planform of the rim and ejecta changes with decreasing impact angle. We infer the impact angles at which the changes occur by assuming a sin2θ dependence for the cumulative fraction of craters forming below angle θ. At impact angles less than ?40° from horizontal, the ejecta become offset downrange relative to the crater rim. As the impact angle decreases to less than ?20°, the ejecta begin to concentrate in the cross‐range direction and a “forbidden zone” that is void of ejecta develops in the uprange direction. At angles less than ?10°, a “butterfly” ejecta pattern is generated by the presence of downrange and uprange forbidden zones, and the rim planform becomes elliptical with the major axis oriented along the projectile's direction of travel. The uprange forbidden zone appears as a “V” curving outward from the rim, but the downrange forbidden zone is a straight‐edged wedge. Although fresh Martian craters greater than 5 km in diameter have ramparts indicative of surface ejecta flow, the ejecta planforms and the angles at which they occur are very similar to those for lunar craters and laboratory impacts conducted in a dry vacuum. The planforms are different from those for Venusian craters and experimental impacts in a dense atmosphere. We interpret our results to indicate that Martian ejecta are first emplaced predominantly ballistically and then experience modest surface flow. 相似文献
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Elliot?J.?SwallowEmail authorView author&#;s OrcID profile Colin?J.?N.?Wilson Madison?L.?Myers Paul?J.?Wallace Katie?S.?Collins Euan?G.?C.?Smith 《Contributions to Mineralogy and Petrology》2018,173(4):33
Complexities in the nature of large-scale silicic eruptions and their magmatic systems can be discerned through micro-analytical geochemical studies. We present high-resolution, stratigraphically constrained compositional data on glassy matrix material and feldspar crystals from the initial fall deposits and earliest ignimbrite (base of member A) of the 2.08 Ma, ~?2500 km3 Huckleberry Ridge Tuff (HRT), Yellowstone. We use these data to document the nature of the magmatic system and compositional changes related to the transition from fall to widespread ignimbrite deposition, inferred to mark the onset of caldera collapse. Although major element glass compositions are relatively uniform, trace elements span a large range (e.g. Ba 10–900 ppm, Sr/Rb?=?0.005–0.09), with highly evolved glasses dominating in the fall deposits. Several trace elements (e.g. Ba and light rare earth elements) in the glass samples serve to define statistically significant compositional clustering in the fall deposits and basal ignimbrite. These clusters are inferred to reflect melt compositions controlled by fractional crystallisation processes and are interpreted to represent multiple, discrete melt-dominant domains that were tapped by multiple vents. The onset of widespread ignimbrite deposition is marked by an increase in the number of erupted melt compositional clusters from four in the fall deposits to eight, representing nine melt-dominant domains. There is an absence of geographical variation of glass compositions within the basal ignimbrite, with samples from proximal to distal localities north, west and south of the HRT caldera exhibiting similar variability. Pairing of glass analyses with sanidine major and minor element compositional data suggests that the nine melt compositional domains converged at depth into two compositionally distinct upper-crustal magmatic lineages that were both active during these early stages of the eruption. Our data collectively indicate the evacuation of an exceptionally complex and heterogeneous magma system. The onset of widespread ignimbrite deposition, inferred to relate to caldera collapse, occurred after ~ 50 km3 of magma had been discharged. Although external controls were important as an eruption trigger, depressurisation of the system led to caldera collapse with the eruption of numerous discrete melt-dominant domains. 相似文献
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Albanese Katie A. Chakraborty Mrinal Hadad Christopher M. Chin Yu-Ping 《Aquatic Geochemistry》2021,27(3):159-171
Triclosan (TCS) is an antimicrobial compound found in many household products used across the world. TCS is not completely removed in wastewater systems, resulting in trace-level concentrations present ubiquitously in surface waters. The direct photodegradation of TCS has been widely studied, with results indicating that TCS breaks down to chlorophenols and dioxins. To date, no studies have specifically investigated the effects of alkalinity on the photolysis of the acidic form of TCS. This study assessed the effect of carbonate/bicarbonate alkalinity, which is ubiquitous in natural waters, on the photolysis rate of TCS. Results indicate that bicarbonate enhances the photodegradation of TCS at pH values well below the pKa of TCS (7.9), with direct photolysis reaction kinetics that are very slow in the absence of buffers, but significant in the presence of bicarbonate (0.711 h?1 at pH 6.55). At pH values well above its pKa, both unbuffered- and buffered-mediated photolysis increased dramatically (1.92 h?1 for direct photolysis and 2.86 h?1 in buffered water) and is attributable to the increased photoreactivity of TCS by its conjugate base. Photolysis of methyl triclosan (MeTCS), a non-acidic analog of TCS, demonstrated the importance of TCS’s acidic functionality as MeTCS did not degrade at any pH. The observed influence of alkalinity on the acidic form of TCS photolysis was attributed to both a decrease in its excited state pKa, coupled with TCS deprotonation through an excited state proton transfer to a base (bicarbonate and to a lesser degree hydrogen phosphate) resulting in the more photo-labile conjugate base form of TCS.
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Katie Ayers Lesley L. Rhodes John Tyrrell Melissa Gladstone Chris Scholin 《新西兰海洋与淡水研究杂志》2013,47(6):1225-1231
The sandwich hybridisation assay (SHA) is a DNA probe‐based method for rapid identification and enumeration of toxic micro‐algae which uses species specific oligonucleotide probes targeted at ribosomal RNA. It is suited to fragile micro‐algal cells which commonly collapse during the fixation stage of sample collection, compromising identification by traditional microscopy. The assay has been available for research for several years, but was validated and accepted for international accreditation for commercial laboratory use in New Zealand in May 2004 (International Accreditation New Zealand: ISO 17025). During the validation of the raphidophyte assay, some discrepancies were noted between SHA cell concentration estimates and traditional light microscope cell counts. Higher SHA estimates were recorded when blooms had collapsed but rRNA was still present in sea water. Conversely, higher traditional cell counts occurred when sample delivery was delayed more than 48 h, presumably owing to degradation of rRNA in the live cultures used for the SHA. SHA cell concentration estimates of the toxic diatom bloom‐former Pseudo‐nitzschia australis were also compared with whole cell format DNA probe counts and traditional microscope counts; SHA counts were comparable for the three methods tested. 相似文献
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