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101.
Louise Hansen 《Geografiska Annaler: Series A, Physical Geography》2001,83(3):131-144
The landscapes of western Jameson Land bordering Hall Bredning fjord comprise upper river basins, glacial landscapes, lower river basins and a near‐shore zone. The upper river basins are incised into bedrock and display no cover of young sediments whilst the glacial landscapes, located closer to the coast, are dominated by Pleistocene deposits and an irregular topography with hills and ridges. The lower river basins, dissecting the glacial landscapes, are connected to the upper river basins and contain well‐defined Holocene delta terraces. The near‐shore zone, which includes the present coast, displays a few raised shorelines. Geomorphological observations combined with stratigraphic work and 14C dates provide a chronological framework for the development of landscape and shoreline, as presented by a four‐stage reconstruction. The first stage covers the deglaciation of western Jameson Land at the Weichselian‐Holocene transition after a collapse of the main fjord glacier in Hall Bredning. The sea inundated the low‐lying areas on Jameson Land forming small side‐entry fjord basins that possibly follow the track of older valleys. This was followed by a second stage, the paraglacial period, when large meltwater production and sediment transport resulted in a fast infilling of the side‐entry fjord basins by deltas. These are now exposed in terraces in the lower river basins at 70–80 m a.s.l. During a third stage, the relaxation period, fluvial activity decreased and the land surface was increasingly occupied by a cover of tundra vegetation. A glacio‐isostatic rebound resulted in a relative sea level fall and fluvial incision. During stages two and three the coast was exposed to shallow marine processes that aided the alignment of the coast. Stages one to three presumably lasted for less than 2000 years. During stage four, the stable period, lasting for several thousand years till the present, there were minor adjustments of shoreline and landscape. The four‐step reconstruction describes the sedimentary response of a lowland fjord margin to dramatic changes in climate and sea level. The distribution of erosion and sedimentation during this development was mainly controlled by topography. The reconstruction of the latest environmental development of Jameson Land puts new light on Jameson Land's long and complex Quaternary stratigraphic record. The reconstruction may also be used as a model for the interpretation of deposits in similar areas elsewhere. 相似文献
102.
Coupled substitutions in the tourmaline group 总被引:2,自引:0,他引:2
Franklin F. Foit Jr. Philip E. Rosenberg 《Contributions to Mineralogy and Petrology》1977,62(2):109-127
Statistical analysis of 136 natural tourmaline compositions from the literature reveals the presence and extent of coupled substitutions involving several cations and structural sites. In schorls and dravites these are a dehydroxylation type substitution (1) (OH)–+R2+ = R3++O2– and an alkali-defect type substitution (2) R++R2+ = R3++, Al3+ being the predominant R3+ action. Substitution (1) which represents solid solution towards a proton-deficient end-member, R+ R
3
3+
R
6
3+
(BO3)3 Si6O18O3(OH), accounts for three times as much of the observed compositional variability as does (2) which represents substitution toward a hypothetical alkali-free end-member, (R
2
2+
R3+) R
6
3+
(BO3)3Si6O18(OH)4. The occurrence of both of these substituions produces intermediates between end-member schorl/ dravite, R+ R
3
2+
R
6
3+
(BO3)3Si6O18(OH)4, and a new series within the tourmaline group, R
1–x
+
R
3
3+
R
6
3+
(BO3)3Si6O18O3–x (OH)1+x.In addition to dehydroxylation type, 2(OH)–+Li+ = R3++202–, and possibly alkali-defect type, 2R++Li+ = R3++2, substitutions, a third type Li++O2– = (OH)–+, occurs in the elbaites giving rise to Li-poor, proton-rich species. All three substitutions serve to reduce the Li-content of natural elbaite which, as a result, does not attain the composition of the ideal end-member, Na(Li1.5Al1.5)Al6(BO3)3Si6O18(OH)4. Substitution from elbaite and schorl/dravite toward R
1–x
+
R
3
3+
R
6
3+
(BO3)3Si6O18O3–x(OH)1+x is very extensive and may be complete.Substitution toward R
1–x
+
R
3
3+
R
6
3+
(BO3)3Si6O18O3–x(OH)1+x results in improved local charge balance. The mean deviation
from oxygen charge saturation
is at a maximum in end-member schorl, dravite and elbaite. Substitutions (1) and (2) progressively decrease
but substitution (1) does so more effectively, which may explain its predominance in nature. However, alkali-defective end-members appear to be unstable regardless of
. Substitution (3) in the elbaites cannot be discussed on the basis of charge balance considerations at present due to the lack of structural information on proton-rich species. 相似文献
103.
Fe2+-F avoidance, reported in the literature in micas and amphiboles, can be accounted for by crystal field theory. The crystal field splitting parameter, ΔO, of Fe2+ octahedrally coordinated to F? is significantly smaller than its value when (OH)? is the coordinating anion. Thus, the presence of Fe2+ is not favored at sites where F? substitutes for (OH)? due to smaller crystal field stabilization energy. 相似文献
104.
Louise Levien Donald J. Weidner Charles T. Prewitt 《Physics and Chemistry of Minerals》1979,4(2):105-113
The thirteen single-crystal elastic moduli for diopside as determined by the acoustic technique based on Brillouin scattering are: c11=2.23, c22=1.71, c33=2.35, c44=0.74, c55=0.67, c66=0.66, c12=0.77, c13=0.81, c15=0.17, c23=0.57, c25=0.07, c35=0.43, c46=0.073. The Reuss bound of the adiabatic bulk and shear moduli calculated from these data are K s=1.08 Mbar and G=0.651 Mbar. The room-pressure isothermal bulk modulus, K T , and the pressure derivative of the bulk modulus, K′ T have also been determined on a four-circle diffractometer, from a single crystal mounted in a gasketed opposed-anvil diamond cell, giving values of K T =1.13 Mbar and K′ T =4.8. The principal axes of the strain ellipsoid, calculated from the elastic moduli and observed in the static compression data, are identical, and the linear compressibilities are in reasonable agreement. The single-crystal elastic moduli can be correlated with the structural features of diopside. 相似文献
105.
The younger granites in Finland contain more REE than the older ones. In the youngest, postorogenic rapakivi granites, the total REE concentration is highest, the light REE are more enriched, and the negative Eu anomaly is more pronounced than in the older granites. The enrichment of the light REE, the anomalous behavior of the extreme elements (La, Ce, and Lu) in normalized graphs, and the depletion of Eu indicate the degree of differentiation the rock has undergone. These features are usually more pronounced in large, homogeneous granites than in metamorphic or volcanogenic rocks. Silicic vein rocks usually contain less REE than the granites proper; the distribution pattern in many is as in granites, but in some the heavy elements are more enriched. The positive Eu anomaly in Precambrian metamorphic rocks is tentatively attributed to metamorphic differentiation and to the secretion of silicic material from the host rock. 相似文献
106.
Louise Crabtree 《The Australian geographer》2005,36(3):333-350
Basic aspects of sustainable housing design such as increasing density, mixed use and proximity to public transport are being adopted increasingly in Australian cities. Sustainable building codes such as NSW's BASIX and Victoria's Green Star rating systems are also being implemented and advanced. More substantial improvements and endeavours such as onsite food production, energy generation and waste treatment, are being seen increasingly as necessary for urban sustainability, yet little is being done to institutionalise or normalise these through Australia's housing system. Similarly, concerns about the social sustainability of housing identify the need for mixed, flexible tenure and dwelling types, with again little uptake despite evidence of demand. Given that we seem to know what needs doing to move towards sustainability, this paper investigates two ecologically and socially sound community-based housing developments in Australia, with a view to finding what helped or hindered these efforts and what may further the uptake of sustainable design. Assessment of the uptake of sustainable planning initiatives reveals the prevalence of a decidedly neoliberal agenda which shies away from the more substantial challenges ecocity design and community-based enterprise may represent. Such community-based initiatives must, however, be supported at a broader scale, to avoid possible outsourcing of governmental responsibility or the relegation of sustainable design to the sole realm of the wealthy. 相似文献
107.
Fieldwork in geography has come under close scrutiny from feminist and postcolonial scholars in recent years. In relation to physical geography, commentators have pointed to a range of practices and images (notably the 'heroic', masculinist 'ideal') that have acted to deter and exclude women, from undergraduates to senior academics. For some, fieldwork is one of the key sites of gender discrimination for women in physical geography. This paper starts from a position of agreement with many of these critiques, but also seeks to 'reclaim' some more positive accounts and perspectives on the subject. In doing so, it aims to critique and disrupt the dominant image of physical geography fieldwork as essentially a masculinist endeavour, and encourage a wider view of the challenges and pleasures of fieldwork for women in physical geography. 相似文献
108.
Margaret T. Glasscoe Andrea Donnellan Louise H. Kellogg Gregory A. Lyzenga 《Pure and Applied Geophysics》2004,161(11-12):2343-2357
— Geodetic data indicate that the northern Metropolitan Los Angeles region is shortening at a rate of 4.5–6.0 mm/yr between downtown Los Angeles and the San Gabriel Mountains. If we assume that all of the uplift of the San Gabriel Mountains is due to the major frontal fault system (the Sierra Madre fault) and use reported values for bedrock uplift, slip per event and recurrence intervals to determine the slip rate on the Sierra Madre fault, we obtain slip rates between 0.6–1.27 mm/yr. Using these slip rates, the horizontal shortening attributable to the Sierra Madre fault accounts for only ~33% of the observed shortening across the basin, leaving ~67% of the shortening to be accounted for elsewhere. Herein we present a suite of models that test possible shortening mechanisms to account for this strain deficit. The models incorporate a range of fault geometries and have a layered structure with variable vertical and horizontal rheologies. The models demonstrate how lower-crust rheology and the presence of a low rigidity, anelastically deforming sedimentary basin affects the dissipation of stress imposed on the viscous layers by elastic failure of the faults. We found that viscoelastic models with a single fault, vertically strong crust and a compliant sedimentary basin yield a horizontal velocity profile that best matches the geodetically observed velocity profile across the Los Angeles Basin. Our models also indicate that we are still not accounting for all of the observed deformation. Therefore, more complex models that include both laterally varying rheologies and frictional properties on faults must be considered. 相似文献
109.
110.