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181.
Christian Betzler Jörn Fürstenau Thomas Lüdmann Christian Hübscher Sebastian Lindhorst Andreas Paul John J. G. Reijmer André W. Droxler 《Basin Research》2013,25(2):172-196
Multichannel high‐resolution seismic and multibeam data were acquired from the Maldives‐isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea‐level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat‐topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east‐directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment‐drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large‐scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate‐platform growth can occur, with a coexistence of bank‐margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea‐level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo‐Pacific region. 相似文献
182.
Andreas Dietrich Ronald Gutierrez Eric P. Nelson Paul W. Layer 《Mineralium Deposita》2012,47(3):233-249
The San José district is located in the northwest part of the Deseado massif and hosts a number of epithermal Ag–Au quartz
veins of intermediate sulfidation style, including the Huevos Verdes vein system. Veins are hosted by andesitic rocks of the
Bajo Pobre Formation and locally by rhyodacitic pyroclastic rocks of the Chon Aike Formation. New 40Ar/39Ar constraints on the age of host rocks and mineralization define Late Jurassic ages of 151.3 ± 0.7 Ma to 144.7 ± 0.1 Ma for
volcanic rocks of the Bajo Pobre Formation and of 147.6 ± 1.1 Ma for the Chon Aike Formation. Illite ages of the Huevos Verdes
vein system of 140.8 ± 0.2 and 140.5 ± 0.3 Ma are 4 m.y. younger than the volcanic host rock unit. These age dates are among
the youngest reported for Jurassic volcanism in the Deseado massif and correlate well with the regional context of magmatic
and hydrothermal activity. The Huevos Verdes vein system has a strike length of 2,000 m, with several ore shoots along strike.
The vein consists of a pre-ore stage and three main ore stages. Early barren quartz and chalcedony are followed by a mottled
quartz stage of coarse saccharoidal quartz with irregular streaks and discontinuous bands of sulfide-rich material. The banded
quartz–sulfide stage consists of sulfide-rich bands alternating with bands of quartz and bands of chlorite ± illite. Late-stage
sulfide-rich veinlets are associated with kaolinite gangue. Ore minerals are argentite and electrum, together with pyrite,
sphalerite, galena, chalcopyrite, minor bornite, covellite, and ruby silver. Wall rock alteration is characterized by narrow
(< 3 m) halos of illite and illite/smectite next to veins, grading outward into propylitic alteration. Gangue minerals are
dominantly massive quartz intergrown with minor to accessory adularia. Epidote, illite, illite/smectite, and, preferentially
at deeper levels, Fe-chlorite gangue indicate near-neutral pH hydrothermal fluids at temperatures of >220°C. Kaolinite occurring
with the late sulfide-rich veinlet stage indicates pH < 4 and a temperature of <200°C. The Huevos Verdes system has an overall
strike of 325°, dipping on average 65° NE. The orientations of individual ore shoots are controlled by vein strike and intersecting
north-northwest-striking faults. We propose a structural model for the time of mineralization of the San José district, consisting
of a conjugate shear pair of sinistral north-northwest- and dextral west-northwest-striking faults that correspond to R and R′ in the Riedel shear model and that are related to master faults (M) of north-northeast-strike. Veins of 315° strike can
be interpreted as nearly pure extensional fractures (T). Variations in vein strike predict an induced sinistral shear component
for strike directions of >315°, whereas strike directions of <315° are predicted with an induced dextral strike–slip movement.
The components of the structural model appear to be present on a regional scale and are not restricted to the San José district. 相似文献
183.
A GIS-implemented, deterministic approach for the automated spatial evaluation of geometrical and kinematical properties of
rock slope terrains is presented. Based on spatially distributed directional information on planar geological fabrics and
DEM-derived topographic attribute data, the internal geometry of rock slopes can be characterized on a grid cell basis. For
such computations, different approaches for the analysis and regionalization of available structural directional information
applicable in specific tectonic settings are demonstrated and implemented in a GIS environment. Simple kinematical testing
procedures based on feasibility criteria can be conducted on a pixel basis to determine which failure mechanisms are likely
to occur at particular terrain locations. In combination with hydraulic and strength data on geological discontinuities, scenario-based
rock slope stability evaluations can be performed. For conceptual investigations on rock slope failure processes, a GIS-based
specification tool for a 2-D distinct element code (UDEC) was designed to operate with the GIS-encoded spatially distributed
rock slope data. The concepts of the proposed methodology for rock slope hazard assessments are demonstrated at three different
test sites in Germany. 相似文献
184.
Phase relations of phlogopite with magnesite from 4 to 8 GPa 总被引:2,自引:2,他引:0
Andreas?EnggistEmail author Linglin?Chu Robert?W.?Luth 《Contributions to Mineralogy and Petrology》2012,163(3):467-481
To evaluate the stability of phlogopite in the presence of carbonate in the Earth’s mantle, we conducted a series of experiments
in the KMAS–H2O–CO2 system. A mixture consisting of synthetic phlogopite (phl) and natural magnesite (mag) was prepared (phl90-mag10; wt%) and run at pressures from 4 to 8 GPa at temperatures ranging from 1,150 to 1,550°C. We bracketed the solidus between
1,200 and 1,250°C at pressures of 4, 5 and 6 GPa and between 1,150 and 1,200°C at a pressure of 7 GPa. Below the solidus,
phlogopite coexists with magnesite, pyrope and a fluid. At the solidus, magnesite is the first phase to react out, and enstatite
and olivine appear. Phlogopite melts over a temperature range of ~150°C. The amount of garnet increases above solidus from
~10 to ~30 modal% to higher pressures and temperatures. A dramatic change in the composition of quench phlogopite is observed
with increasing pressure from similar to primary phlogopite at 4 GPa to hypersilicic at pressures ≥5 GPa. Relative to CO2-free systems, the solidus is lowered such, that, if carbonation reactions and phlogopite metasomatism take place above a
subducting slab in a very hot (Cascadia-type) subduction environment, phlogopite will melt at a pressure of ~7.5 GPa. In a
cold (40 mWm−2) subcontinental lithospheric mantle, phlogopite is stable to a depth of 200 km in the presence of carbonate and can coexist
with a fluid that becomes Si-rich with increasing pressure. Ascending kimberlitic melts that are produced at greater depths
could react with peridotite at the base of the subcontinental lithospheric mantle, crystallizing phlogopite and carbonate
at a depth of 180–200 km. 相似文献
185.
Frank?DethlefsenEmail author Christoph?Haase Markus?Ebert Andreas?Dahmke 《Environmental Earth Sciences》2012,65(4):1105-1117
One of the uncertainties in the field of carbon dioxide capture and storage (CCS) is caused by the parameterization of geochemical
models. The application of geochemical models contributes significantly to calculate the fate of the CO2 after its injection. The choice of the thermodynamic database used, the selection of the secondary mineral assemblage as
well as the option to calculate pressure dependent equilibrium constants influence the CO2 trapping potential and trapping mechanism. Scenario analyses were conducted applying a geochemical batch equilibrium model
for a virtual CO2 injection into a saline Keuper aquifer. The amount of CO2 which could be trapped in the formation water and in the form of carbonates was calculated using the model code PHREEQC.
Thereby, four thermodynamic datasets were used to calculate the thermodynamic equilibria. Furthermore, the equilibrium constants
were re-calculated with the code SUPCRT92, which also applied a pressure correction to the equilibrium constants. Varying
the thermodynamic database caused a range of 61% in the amount of trapped CO2 calculated. Simultaneously, the assemblage of secondary minerals was varied, and the potential secondary minerals dawsonite
and K-mica were included in several scenarios. The selection of the secondary mineral assemblage caused a range of 74% in
the calculated amount of trapped CO2. Correcting the equilibrium constants with respect to a pressure of 125 bars had an influence of 11% on the amount of trapped
CO2. This illustrates the need for incorporating sensitivity analyses into reaction pathway modeling. 相似文献
186.
Simulation of DNAPL infiltration and spreading behaviour in the saturated zone at varying flow velocities and alternating subsurface geometries 总被引:3,自引:1,他引:2
Katharina Erning Sibylle Grandel Andreas Dahmke Dirk Schäfer 《Environmental Earth Sciences》2012,65(4):1119-1131
The influence of varying groundwater flow velocities on DNAPL infiltration and spreading behaviour was investigated by multiphase
modelling using TMVOC and PetraSim. The multiphase models were calibrated by results of previously conducted laboratory experiments
for the complete spatio-temporal range of the experiments. The small scale 2D scenario modelling was applied to qualify and
quantify changes in position, architecture, geometry and dissolution of a TCE body in a fully saturated homogeneous sandy
medium. The applied flow velocities ranging from 0.05 up to 40.00 m/day exhibited that the DNAPL TCE is affected even at the
lowest flow velocity in its position, its size and its architecture. Additionally, several impermeable lenses with simple
geometry were assumed in the model, to investigate the influence of stratified subsoil. In the experimental set-ups, the DNAPL
body reacts more sensitive to the applied groundwater flow velocities than to the geometrical set-up of the scenarios. A possible
consequence can be the transportation and displacement of a DNAPL pool due to natural or anthropogenic induced high groundwater
flow velocities, as by Pump and Treat facilities, complicating site investigation process and planning of remediation activities. 相似文献
187.
Jannis Epting Andreas Wüest Peter Huggenberger 《Central European Journal of Geosciences》2012,4(1):81-93
This article presents hydrogeophysical investigations performed in a well-developed, long-term hydrogeological gypsum karst research site where subsurface evaporite dissolution has led to the subsidence of a river dam and an adjacent highway; both constructed on gypsum-containing rock, southeast of Basel, Switzerland. An observation system was set up to improve the protection of surface and subsurface water resources during remedial construction measures of the highway and in order to understand the processes, as well as the temporal evolution, of rock water interaction (flow and dissolution). However, no detailed hydrogeological information beneath the river could be derived from the previous investigations. To supplement the basic knowledge on this area, underwater Electrical Resistivity Tomography (ERT) measurements were conducted in the river bed upstream of the dam. The ERT-data are interpreted together with drill-core information and a conceptual 3D-Model of the area behind the dam and beneath the river. Results help to delineate weathered zones, associated faults and the thickness of sediment deposits behind the dam, as well as to locate voids within the local karst system. The combination of the ERT and modeling allows the optimization of future site-specific remedial construction measures. 相似文献
188.
Acquisition and registration of terrestrial 3D laser scans is a fundamental task in mapping and modeling of cities in three dimensions. To automate this task marker-free registration methods are required. Based on the existence of skyline features, this paper proposes a novel method. The skyline features are extracted from panoramic 3D scans and encoded as strings enabling the use of string matching for merging the scans. Initial results of the proposed method in the old city center of Bremen are pre-sented. 相似文献
189.
The dynamics of the North Atlantic subpolar gyre (SPG) are assessed under present and glacial boundary conditions by investigating the SPG sensitivity to surface wind-stress changes in a coupled climate model. To this end, the gyre transport is decomposed in Ekman, thermohaline, and bottom transports. Surface wind-stress variations are found to play an important indirect role in SPG dynamics through their effect on water-mass densities. Our results suggest the existence of two dynamically distinct regimes of the SPG, depending on the absence or presence of deep water formation (DWF) in the Nordic Seas and a vigorous Greenland?CScotland ridge (GSR) overflow. In the first regime, the GSR overflow is weak and the SPG strength increases with wind-stress as a result of enhanced outcropping of isopycnals in the centre of the SPG. As soon as a vigorous GSR overflow is established, its associated positive density anomalies on the southern GSR slope reduce the SPG strength. This has implications for past glacial abrupt climate changes, insofar as these can be explained through latitudinal shifts in North Atlantic DWF sites and strengthening of the North Atlantic current. Regardless of the ultimate trigger, an abrupt shift of DWF into the Nordic Seas could result both in a drastic reduction of the SPG strength and a sudden reversal in its sensitivity to wind-stress variations. Our results could provide insight into changes in the horizontal ocean circulation during abrupt glacial climate changes, which have been largely neglected up to now in model studies. 相似文献
190.
Martin H?mmerle Tam��s G��l J��nos Unger Andreas Matzarakis 《Theoretical and Applied Climatology》2011,105(3-4):521-527
The sky view factor (SVF) describes the surface geometry and is a commonly used and important measure in urban climate investigations whose aim is the exploration of effects of a complex urban surface on climatological processes in built-up areas. A selection of methods and models for calculating the SVF was compared. For this purpose, fish eye images were taken at several locations in the city of Szeged, southern Hungary. The fish eye images equidistantly follow linear transects to cover a range of SVF values and to analyze the reaction of the methods to a continuously changing environment. The fish eye pictures were evaluated by three methods: the method according to Steyn (Atmos-Ocean 18(3):245?C258, 1980) implemented in a GIS-Script, the ??Edit free sky view factor?? tool of the RayMan model and BMSkyView. The SVF values at the coordinates of the fish eye pictures were calculated with three numerical models (SkyHelios, ArcView SVF extension, and SOLWEIG) with a 3D building data base as input. After comparing the results of the first run, a deviation occurs. The deviation disappears after implementing an option to include a weighting factor in some of the models. 相似文献