Sub-micron scale distributions of trace elements in zircon   总被引：2，自引：1，他引：1  

Amy E. Hofmann  John W. Valley  E. Bruce Watson  Aaron J. Cavosie  John M. Eiler 《Contributions to Mineralogy and Petrology》2009,158(3):317-335

Sub-micron scale zoning of Ti concentrations and correlations between concentrations of Ti and other trace elements (P, Ce, and Y) and cathodoluminescent (CL) banding is observed in natural zircons. Ion images were made using the Caltech Microanalysis Center’s CAMECA NanoSIMS 50L with an O⁻ primary beam focused to ~300 nm on the sample surface. The high spatial resolution of this technique allows for interrogation of chemical variations at or below the scale of CL banding in natural zircons. Images produced in this manner display two types of correlations among Ti, P, Ce, and Y (which appears to be a proxy for CL intensity): strong (correlation coefficients >0.8) and subtle (correlation coefficients ~0.15–0.4). Strongly correlated images, which display Ti variations of ca. a factor of 3 between adjacent CL bands and overall elevated trace element concentrations in CL-dark bands, were found within an oscillatory-zoned, trace element enriched sector of a CL sector-zoned zircon. Three possible causes for such correlations include: temperature-dependent equilibrium partitioning, trace element partitioning limited by diffusion in the host melt and surface-controlled, non-equilibrium growth. Comparison of our data with the expected results of these processes suggests that: (1) Ti partitioning in zircon is dependent upon non-equilibrium effects in addition to temperature and/or (2) the incorporation of elements that co-vary with Ti in zircon (e.g., Y, P and Ce) is also temperature-dependent. Sub-micron scale, high-Ti regions are also found within Proterozoic Adirondack and >4 Ga Jack Hills zircons as well as trace element enrichments (including Ti) along cracks within Jack Hills zircons.  相似文献   

Experimental calibration of oxygen isotope fractionation between quartz and zircon   总被引：3，自引：0，他引：3  

Dustin Trail  Ilya N. Bindeman  E. Bruce Watson  Axel K. Schmitt 《Geochimica et cosmochimica acta》2009,73(23):7110-7126

We report the results of an experimental calibration of oxygen isotope fractionation between quartz and zircon. Data were collected from 700 to 1000 °C, 10–20 kbar, and in some experiments the oxygen fugacity was buffered at the fayalite–magnetite–quartz equilibrium. Oxygen isotope fractionation shows no clear dependence on oxygen fugacity or pressure. Unexpectedly, some high-temperature data (900–1000 °C) show evidence for disequilibrium oxygen isotope partitioning. This is based in part on ion microprobe data from these samples that indicate some high-temperature quartz grains may be isotopically zoned. Excluding data that probably represent non-equilibrium conditions, our preferred calibration for oxygen isotope fractionation between quartz and zircon can be described by: This relationship can be used to calculate fractionation factors between zircon and other minerals. In addition, results have been used to calculate WR/melt–zircon fractionations during magma differentiation. Modeling demonstrates that silicic magmas show relatively small changes in δ¹⁸O values during differentiation, though late-stage mafic residuals capable of zircon saturation contain elevated δ¹⁸O values. However, residuals also have larger predicted melt–zircon fractionations meaning zircons will not record enriched δ¹⁸O values generally attributed to a granitic protolith. These results agree with data from natural samples if the zircon fractionation factor presented here or from natural studies is applied.  相似文献   

Finding common ground? Spaces of dialogue and the negotiation of Indigenous interests in environmental campaigns in Australia   总被引：5，自引：0，他引：5  

Jenny Pickerill 《Geoforum》2009,40(1):66-79

Critiquing the usefulness of cosmopolitanism this paper argues that we need a more nuanced and subtle understanding of how commonalities are found, created and maintained across difference. This paper uses two juxtapositions of perspective (around place and environment) to explore how such boundaries of difference can be negotiated. It uses an examination of the ways in which environmental groups in Australia have sought to negotiate Indigenous interests through creating spaces of dialogue and changing working practices. It is based on 30 interviews with both Indigenous and non-Indigenous activists across two case regions; Cape York (Queensland) and Barmah-Millewa (Victoria/New South Wales). Four issues were identified that have proved particularly contentious in negotiations to build collaborative campaigns: language; power and ownership; scale and timeframes; and economics. There are examples of both successes and ongoing problematic practices across these tensions. However there is also a growing mutual ownership of the issues. Moving beyond a colonial paternal sense of responsibility, to a dynamic and engaged mutuality of concern for both processes and outcomes has resulted in gradual, small, and progressive steps forward in Indigenous/non-Indigenous collaborative environmental campaigning.  相似文献   

On the evolutionary status of short-period cataclysmic variables     

S. P. Littlefair  V. S. Dhillon  T. R. Marsh  B. T. Gänsicke  John Southworth  I. Baraffe  C. A. Watson  C. Copperwheat 《Monthly notices of the Royal Astronomical Society》2008,388(4):1582-1594

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The effects of floods on the temperature of riparian groundwater          下载免费PDF全文

Jeffery A. Watson  M. Bayani Cardenas  Stephen B. Ferencz  Peter S.K. Knappett  Bethany T. Neilson 《水文研究》2018,32(9):1267-1281

The transition area between rivers and their adjacent riparian aquifers, which may comprise the hyporheic zone, hosts important biochemical reactions, which control water quality. The rates of these reactions and metabolic processes are temperature dependent. Yet the thermal dynamics of riparian aquifers, especially during flooding and dynamic groundwater flow conditions, has seldom been studied. Thus, we investigated heat transport in riparian aquifers during 3 flood events of different magnitudes at 2 sites along the same river. River and riparian aquifer temperature and water‐level data along the Lower Colorado River in Central Texas, USA, were monitored across 2‐dimensional vertical sections perpendicular to the bank. At the downstream site, preflood temperature penetration distance into the bank suggested that advective heat transport from lateral hyporheic exchange of river water into the riparian aquifer was occurring during relatively steady low‐flow river conditions. Although a small (20‐cm stage increase) dam‐controlled flood pulse had no observable influence on groundwater temperature, larger floods (40‐cm and >3‐m stage increases) caused lateral movement of distinct heat plumes away from the river during flood stage, which then retreated back towards the river after flood recession. These plumes result from advective heat transport caused by flood waters being forced into the riparian aquifer. These flood‐induced temperature responses were controlled by the size of the flood, river water temperature during the flood, and local factors at the study sites, such as topography and local ambient water table configuration. For the intermediate and large floods, the thermal disturbance in the riparian aquifer lasted days after flood waters receded. Large floods therefore have impacts on the temperature regime of riparian aquifers lasting long beyond the flood's timescale. These persistent thermal disturbances may have a significant impact on biochemical reaction rates, nutrient cycling, and ecological niches in the river corridor.  相似文献   

An extended finite volume method and fixed-stress approach for modeling fluid injection–induced tensile opening in fractured reservoirs     

Rajdeep Deb  Patrick Jenny 《国际地质力学数值与分析法杂志》2020,44(8):1128-1144

Fluid injection–induced tensile opening is modeled using an extended finite volume method (XFVM). An embedded fracture strategy is used for the flow problem, that is, the fractures are discretized using finite volume segments without resolving the grid around them. Further, the discontinuities across fractures are modeled using special basis functions. The fracture openings due to enhanced fluid pressure and the associated shear slip due to traction free boundary condition on the fracture segments are both modeled using these special discontinuity basis functions. Mass transfer between fractures and matrix is modeled using the pressure difference. The enhancement of fracture storativity due to tensile opening leads to stronger coupling between flow and mechanics. An iterative scheme relying on the fixed-stress approach for fractures, which conserves the stress dependent terms over each iteration of the flow problem, has been introduced. Tensile opening has been simulated for single fractures embedded in two- and three-dimensional matrices. The convergence criterion for sequentially implicit fixed-stress scheme for fractures embedded in elastic media is established and has been validated numerically. Further, for 2D simulations, the effect of the matrix permeability for fracture propagation due to tensile opening has been studied.  相似文献   

The Effect of Macrofauna on Porewater Profiles and Nutrient Fluxes in the Intertidal Zone of the Humber Estuary   总被引：3，自引：0，他引：3  

R. J. G. Mortimer  J. T. Davey  M. D. Krom  P. G. Watson  P. E. Frickers  R. J. Clifton 《Estuarine, Coastal and Shelf Science》1999,48(6):683

Macrofauna, nutrient fluxes, porewater chemistry and sediment characteristics were measured at six intertidal mudflat sites in the Humber Estuary, U.K., during the different seasons. Nereis diversicolor , Macoma balthica and Corophium volutator were found to be the dominant macrofauna. Salinity was the baseline control on macrofauna distribution but this was overprinted by periodic impoverishment due to sediment mobilization. High resolution gel probe porewater samplers provided direct evidence for the impact of burrows on porewater chemistry. The macrofauna modified nutrient fluxes during periods of mud flat stability. Nereis caused a decrease in silicate and phosphate effluxes but enhanced ammonia release and nitrate uptake. Macoma enhanced ammonia and nitrite release. The impact of Corophium was not possible to discern. The Humber is a large, highly dynamic macrotidal estuary in which sediment resuspension has a large impact on porewater profiles, nutrient fluxes and macrofaunal communities. Simple patterns and inter-relationships which are seen in small sheltered estuaries are not observed in the Humber.  相似文献   

What controls submarine channel development and the morphology of deltas entering deep-water fjords?     

Jenny A. Gales  Peter J. Talling  Matthieu J.B. Cartigny  John Hughes Clarke  Gwyn Lintern  Cooper Stacey  Michael A. Clare 《地球表面变化过程与地形》2019,44(2):535-551

River deltas and associated turbidity current systems produce some of the largest and most rapid sediment accumulations on our planet. These systems bury globally significant volumes of organic carbon and determine the runout distance of potentially hazardous sediment flows and the shape of their deposits. Here we seek to understand the main factors that determine the morphology of turbidity current systems linked to deltas in fjords, and why some locations have well developed submarine channels while others do not. Deltas and associated turbidity current systems are analysed initially in five fjord systems from British Columbia in Canada, and then more widely. This provides the basis for a general classification of delta and turbidity current system types, where rivers enter relatively deep (>200 m) water. Fjord-delta area is found to be strongly bimodal. Avalanching of coarse-grained bedload delivered by steep mountainous rivers produces small Gilbert-type fan deltas, whose steep gradient (11°–25°) approaches the sediment's angle of repose. Bigger fjord-head deltas are associated with much larger and finer-grained rivers. These deltas have much lower gradients (1.5°–10°) that decrease offshore in a near exponential fashion. The lengths of turbidity current channels are highly variable, even in settings fed by rivers with similar discharges. This may be due to resetting of channel systems by delta-top channel avulsions or major offshore landslides, as well as the amount and rate of sediment supplied to the delta front by rivers. © 2018 John Wiley & Sons, Ltd.  相似文献   

Wetland Loss Patterns and Inundation-Productivity Relationships Prognosticate Widespread Salt Marsh Loss for Southern New England     

Elizabeth Burke Watson  Cathleen Wigand  Earl W. Davey  Holly M. Andrews  Joseph Bishop  Kenneth B. Raposa 《Estuaries and Coasts》2017,40(3):662-681

Tidal salt marsh is a key defense against, yet is especially vulnerable to, the effects of accelerated sea level rise. To determine whether salt marshes in southern New England will be stable given increasing inundation over the coming decades, we examined current loss patterns, inundation-productivity feedbacks, and sustaining processes. A multi-decadal analysis of salt marsh aerial extent using historic imagery and maps revealed that salt marsh vegetation loss is both widespread and accelerating, with vegetation loss rates over the past four decades summing to 17.3 %. Landward retreat of the marsh edge, widening and headward expansion of tidal channel networks, loss of marsh islands, and the development and enlargement of interior depressions found on the marsh platform contributed to vegetation loss. Inundation due to sea level rise is strongly suggested as a primary driver: vegetation loss rates were significantly negatively correlated with marsh elevation (r ²?=?0.96; p?=?0.0038), with marshes situated below mean high water (MHW) experiencing greater declines than marshes sitting well above MHW. Growth experiments with Spartina alterniflora, the Atlantic salt marsh ecosystem dominant, across a range of elevations and inundation regimes further established that greater inundation decreases belowground biomass production of S. alterniflora and, thus, negatively impacts organic matter accumulation. These results suggest that southern New England salt marshes are already experiencing deterioration and fragmentation in response to sea level rise and may not be stable as tidal flooding increases in the future.  相似文献   

Evaluating Groundwater Interbasin Flow Using Multiple Models and Multiple Types of Data          下载免费PDF全文

Ming Ye  Liying Wang  Karl. F. Pohlmann  Jenny B. Chapman 《Ground water》2016,54(6):805-817

The groundwater interbasin flow, Q_y, from the north of Yucca Flat into Yucca Flat simulated using the Death Valley Regional Flow System (DVRFS) model greatly exceeds assessments obtained using other approaches. This study aimed to understand the reasons for the overestimation and to examine whether the Q_y estimate can be reduced. The two problems were tackled from the angle of model uncertainty by considering six models revised from the DVRFS model with different recharge components and hydrogeological frameworks. The two problems were also tackled from the angle of parametric uncertainty for each model by first conducting Morris sensitivity analysis to identify important parameters and then conducting Monte Carlo simulations for the important parameters. The uncertainty analysis is general and suitable for tackling similar problems; the Morris sensitivity analysis has been utilized to date in only a limited number of regional groundwater modeling. The simulated Q_y values were evaluated by using three kinds of calibration data (i.e., hydraulic head observations, discharge estimates, and constant‐head boundary flow estimates). The evaluation results indicate that, within the current DVRFS modeling framework, the Q_y estimate can only be reduced to about half of the original estimate without severely deteriorating the goodness‐of‐fit to the calibration data. The evaluation results also indicate that it is necessary to develop a new hydrogeological framework to produce new flow patterns in the DVRFS model. The issues of hydrogeology and boundary flow are being addressed in a new version of the DVRFS model planned for release by the U.S. Geological Survey.  相似文献