A newly defined Late Ordovician magmatic‐thermal event in the Mt Painter Province,northern Flinders Ranges,South Australia     

M. A. Elburg  P. D. Bons  J. Foden  J. Brugger 《Australian Journal of Earth Sciences》2013,60(4):611-631

Magmatism,metamorphism and metasomatism in the Palaeoproterozoic‐Mesoproterozoic Mt Painter Inlier and overlying Neoproterozoic Adelaidean rocks in the northern Flinders Ranges (South Australia) have previously been interpreted as resulting from the ca 500 Ma Delamerian Orogeny. New Rb–Sr, Sm–Nd and U–Pb data, as well as structural analysis,indicate that the area also experienced a second thermal event in the Late Ordovician (ca 440 Ma). The Delamerian Orogeny resulted in large‐scale folding, prograde metamorphism and minor magmatic activity in the form of a small volume of pegmatites and leucogranites. The Late Ordovician event produced larger volumes of granite (the British Empire Granite in the core of the inlier) and these show Nd isotopic evidence for a mantle component. The high‐temperature stage of this magmatic‐hydrothermal event also gave rise to unusual diopside‐titanite veins and the primary uranium mineralisation in the basement, of which the remobilisation was younger than 3.5 Ma. It is possible that parts of the Mt Gee quartz‐hematite epithermal system developed during the waning stages of the Late Ordovician event. We suggest that the Ordovician hydrothermal system was also the cause of the commonly observed retrogression of Delamerian metamorphic minerals (cordierite, andalusite) and the widespread development of actinolite, scapolite, tremolite and magnetite in the cover sequences. Deformation during the Late Ordovician was brittle. The recognition of the Late Ordovician magmatic‐hydrothermal event in the Mt Painter Province might help to link the tectonic evolution of central Australia and the southeast Australian Lachlan Fold Belt.  相似文献   

Gradients in coral reef communities exposed to muddy river discharge in Pohnpei,Micronesia     

Yimnang Golbuu  Katharina Fabricius  Steven Victor  Robert H. Richmond 《Estuarine, Coastal and Shelf Science》2008

This study analyzed how coral communities change along a gradient of increasing exposure to a mud-discharging river in the Enipein Catchment, Pohnpei, Micronesia. Using video transects, we quantified benthic communities at five sites along a gradient moving away from the river mouth towards the barrier reef. The most river-impacted site was characterized by a high accumulation of mud, low coral cover and low coral diversity. Although coral cover leveled off at ∼400 m from the river mouth to values found at the outer-most sites, coral diversity continued to increase with increasing distance, suggesting that the most distant site was still impacted by the river discharges. Fungiidae, Pavona, Acropora, Pachyseris and Porites rus all significantly increased in cover with distance from the river, while Turbinaria decreased. The combined presence and abundance of these six species groups, together with coral species richness, may help to indicate the effects of terrestrial runoff in similar runoff-exposed settings around Micronesia, whereas coral cover is not a sensitive indicator for river impact. Coral reefs are important resources for the people of Pohnpei. To prevent further degradation of this important resource, an integrated watershed approach is needed to control terrestrial activities.  相似文献   

Using multispectral landsat and sentinel-2 satellite data to investigate vegetation change at Mount St. Helens since the great volcanic eruption in 1980     

Katharina Teltscher  Fabian Ewald Fassnacht 《山地科学学报》2018,15(9):1851-1867

Long-term analyses of vegetation succession after catastrophic events are of high interest for an improved understanding of succession dynamics. However, in many studies such analyses were restricted to plot-based measurements. Contrarily, spatially continuous observations of succession dynamics over extended areas and time-periods are sparse. Here, we applied a change vector analysis (CVA) to investigate vegetation succession dynamics at Mount St. Helens after the great volcanic eruption in 1980 using Landsat. We additionally applied a supervised random forest classification using Sentinel-2 data to map the currently prevailing vegetation types. Change vector analysis was performed with the normalized difference vegetation index (NDVI) and the urban index (UI) for three subsequent decades after the eruption as well as for the whole observation time between 1984 and 2016. The influence of topography on the current vegetation distribution was examined by comparing altitude, slope angles and aspect values of vegetation classes derived by the random forest classification. Wilcox- Rank-Sum test was applied to test for significant differences between topographic properties of the vegetation classes inside and outside of the areas affected by the eruption. For the full time period, a total area of 516 km² was identified as re-vegetated, whereas the area and magnitude of re-growing vegetation decreased during the three decades and migrated closer to the volcanic crater. Vegetation losses were mainly observed in regions unaffected by the eruption and related mostly to timber harvesting. The vegetation type classification reached a high overall accuracy of approximately 90%. 36 years after the eruption, coniferous and deciduous trees have established at formerly devastated areas dominating with a proportion of 66%, whereas shrubs are more abundant in riparian zones. Sparse vegetation dominates at regions very close to the crater. Elevation was found to have a great influence on the reestablishment and distribution of the vegetation classes within the devastated areas showing in almost all cases significant differences in altitude distribution. Slope was less important for the different classes - only representing significantly higher values for meadows, whereas aspect seems to have no notable influence on the reestablishment of vegetation at Mount St. Helens. We conclude that major vegetation succession dynamics after catastrophic events can be assessed and characterized over large areas from freely available remote sensing data and hence contribute to an improved understanding of succession dynamics.  相似文献   

Regional policy in Costa Rica: The problems of implementation     

Ernst A. Brugger 《Geoforum》1982,13(2):177-192

In most Third World countries regional planning and regional policy is formally well-developed, but in practice is not implemented. In spite of increasing regional disparities, narrow sectoral and centrally decided programmes and projects dominate over territorial and decentralized ones. This article examines theoretically and empirically why, in the case of Costa Rica, the implementation problem is so difficult and which strategic approaches would best suit an effective regional policy.  相似文献   

Stress Sensitivity of Seismic and Electric Rock Properties of the Upper Continental Crust at the KTB     

Axel Kaselow  Katharina Becker  Serge A. Shapiro 《Pure and Applied Geophysics》2006,163(5-6):1021-1029

We test the hypothesis that the general trend of P-wave and S-wave sonic log velocities and resistivity with depth in the pilot hole of the KTB site Germany, can be explained by the progressive closure of the compliant porosity with increasingly effective pressure. We introduce a quantity θ_c characterizing the stress sensitivity of the mentioned properties. An analysis of the downhole measurements showed that estimates of the quantitiy θ_c for seismic velocities and electrical formation factor of the in situ formation coincide. Moreover, this quantity is 3.5 to 4.5 times larger than the averaged stress sensitivity obtained from core samples. We conclude that the hypothesis mentioned above is consistent with both data sets. Moreover, since θ_c corresponds approximately to the inverse of the effective crack aspect ratio, larger in situ estimates of θ_c might reflect the influence of fractures and faults on the stress sensitivity of the crystalline formation in contrast to the stress sensitivity of the nearly intact core samples. Finally, because the stress sensitivity is directly related to the elastic nonlinearity we conclude that the elastic nonlinearity (i.e., deviation from linear stress-strain relationship i.e., Hooke's law) of the KTB rocks is significantly larger in situ than in the laboratory.  相似文献   

An in situ XAS study of copper(I) transport as hydrosulfide complexes in hydrothermal solutions (25-592 °C, 180-600 bar): Speciation and solubility in vapor and liquid phases     

B.E. Etschmann  W. Liu  H. Müller  O. Proux  J. Brugger 《Geochimica et cosmochimica acta》2010,74(16):4723-2827

Chloride and hydrosulfide are the principal ligands assumed to govern transport of copper in hydrothermal fluids. Existing solubility experiments suggest that Cu(I)-hydrosulfide complexes are dominant compared to chloride complexes at low salinities in alkaline solutions (H₂S_(aq)/HS⁻ pH buffer), and may be important in transporting Cu in low density magmatic vapors, potentially controlling the liquid-vapor partitioning of Cu. This study provides the first in situ evidence of the solubility of copper sulfides and the nature and structure of the predominant Cu species in sulfur-containing fluids at temperatures up to 592 °C and pressures of 180-600 bar. XANES and EXAFS data show that at elevated T (?200 °C), Cu solubility occurs via a linear Cu complex. At 428 °C in alkaline solutions, Cu is coordinated by two sulfur atoms in a distorted linear coordination (angle ∼150-160°). This geometry is consistent with the species predicted by earlier solubility studies. In addition, in situ measurements of the solubility of chalcocite in 2 m NaHS solutions performed in this study are in remarkably good agreement with the solubilities calculated using available thermodynamic data for Cu(I)-hydrosulfide complexes, also supporting the interpretation of speciation in these studies and validating the extrapolation of low-T thermodynamic properties for to high P-T. Data on phase separation for the 2 m NaHS solution show that while significant amounts of copper can be partitioned into the vapor phase, there is no indication for preferential partitioning of Cu into the vapor. This is consistent with recent partitioning experiments conducted in autoclaves by Pokrovski et al. (2008a) and Simon et al. (2006). XANES data suggest that the species present in the low density phase is very similar to that present in the high density liquid, i.e., , although Cu(HS)(H₂S)⁰ cannot be excluded on the basis of XAS data.  相似文献   

Volume diffusion of Ytterbium in YAG: thin-film experiments and combined TEM–RBS analysis     

Katharina Marquardt  Elena Petrishcheva  Rainer Abart  Emmanuel Gardés  Richard Wirth  Ralf Dohmen  Hans-Werner Becker  Wilhelm Heinrich 《Physics and Chemistry of Minerals》2010,37(10):751-760

In this study, we address volume diffusion of ytterbium in yttrium aluminum garnet (YAG) using thin-film single crystal diffusion couples. We employ analytical transmission electron microscopy (ATEM) as a tool for combined microstructural and microchemical analysis and compare the results to Rutherford backscattering (RBS) analysis. Given the high spatial resolution of the method, we focus on microstructural changes of the thin-film diffusant source during the diffusion anneal. We evaluate the potential influence of the associated changes in its transport properties on the evolution of concentration profiles in the single crystal substrate. This approach allows us to test the reliability of determination of volume diffusion coefficients from thin-film diffusion experiments. We found that for the chosen experimental setting, the influence of thin-film re-crystallization is small when compared with the experimental uncertainty and good estimates for the volume diffusion coefficients of Yb in YAG can be obtained using standard assumptions. Both Yb-concentration profiles analyzed with ATEM and with RBS give similar results. At 1,450°C and 1 bar, we infer log D _Yb (m²/s) values of −19.37 ± 0.07 (TEM) and −19.84 ± 0.02 (RBS). Although the change in thin-film transport properties associated with successive crystallization during the diffusion anneal does not play a major role for our experimental setup, this effect cannot generally be ignored.  相似文献   

The art of adaptation: Living with climate change in the rural American Southwest     

Julie Brugger  Michael Crimmins 《Global Environmental Change》2013,23(6):1830-1840

As adaptation has come to the forefront in climate change discourse, research, and policy, it is crucial to consider the effects of how we interpret the concept. This paper draws attention to the need for interpretations that foster policies and institutions with the breadth and flexibility to recognize and support a wide range of locally relevant adaptation strategies. Social scientists have argued that, in practice, the standard definition of adaptation tends to prioritize economic over other values and technical over social responses, draw attention away from underlying causes of vulnerability and from the broader context in which adaptive responses take place, and exclude discussions of inequality, justice, and transformation. In this paper, we discuss an alternate understanding of adaptation, which we label “living with climate change,” that emerged from an ethnographic study of how rural residents of the U.S. Southwest understand, respond to, and plan for weather and climate in their daily lives, and we consider how it might inform efforts to develop a more comprehensive definition. The discussion brings into focus several underlying features of this lay conception of adaptation, which are crucial for understanding how adaptation actually unfolds on the ground: an ontology based on nature–society mutuality; an epistemology based on situated knowledge; practice based on performatively adjusting human activities to a dynamic biophysical and social environment; and a placed-based system of values. We suggest that these features help point the way toward a more comprehensive understanding of climate change adaptation, and one more fully informed by the understanding that we are living in the Anthropocene.  相似文献   

Changes in the Geometry and Volume of Rabots glaciär,Sweden, 2003–2011: Recent Accelerated Volume Loss Linked to More Negative Summer Balances          下载免费PDF全文

Keith A. Brugger  Latysha Pankratz 《Geografiska Annaler: Series A, Physical Geography》2015,97(2):265-278

Terminus geometry, ice margins, and surface elevations on Rabots glaciär were measured using differential GPS during summer 2011 and compared with those similarly measured in 2003. Glacier length over the eight years decreased by ～105 m corresponding to 13 m a^?1, a rate consistent with ice recession over the last several decades. Measured changes in surface elevations show that between 2003 and 2011 the glacier's volume decreased by ～27.6 ± 2.6 × 10⁶ m³, or 3.5 ± 0.3 × 10⁶ m³ a^?1. This compares favorably with an estimate of ?28.1 ± 2.6 × 10⁶ m³ based on a mass‐balance approach. The rate of volume loss appears, however, to have significantly increased after 2003, being substantially greater than rates determined for the intervals 1959–80, 1980–89, and 1989–2003. This increase corresponds to a sustained interval of more negative summer balances. Previous work suggests that as of 2003 Rabots glaciär had not yet completed its response to a ～1°C warming that occurred c. 1900, and thus the current marked increase rate of ice loss might reflect the effect of recent, or accelerated regional warming that occurred during the last decade superimposed on its continued response to that earlier warming.  相似文献   

The most frequent interfaces in olivine aggregates: the GBCD and its importance for grain boundary related processes     

Katharina?MarquardtEmail author  Gregory?S.?Rohrer  Luiz?Morales  Erik?Rybacki  Hauke?Marquardt  Brian?Lin 《Contributions to Mineralogy and Petrology》2015,170(4):40

Rocks consist of crystal grains separated by grain boundaries that impact the bulk rock properties. Recent studies on metals and ceramics showed that the grain boundary plane orientation is more significant for grain boundary properties than other characteristics such as the sigma value or disorientation (in the Earth’s science community more frequently termed misorientation). We determined the grain boundary character distribution (GBCD) of synthetic and natural polycrystalline olivine, the most abundant mineral of Earth’s upper mantle. We show that grain boundaries of olivine preferentially contain low index planes, in agreement with recent findings on other oxides (e.g. MgO, TiO₂, Al₂O₃ etc.). Furthermore, we find evidence for a preferred orientation relationship of 90° disorientations about the [001] direction forming tilt and twist grain boundaries, as well as a preference for the 60° disorientation about the [100] axis. Our data indicate that the GBCD, which is an intrinsic property of any mineral aggregate, is fundamental for understanding and predicting grain boundary related processes.  相似文献