Modeling hot spring chemistries with applications to martian silica formation     

G.M. Marion  D.C. Catling  J.S. Kargel 《Icarus》2011,212(2):629-642

Many recent studies have implicated hydrothermal systems as the origin of martian minerals across a wide range of martian sites. Particular support for hydrothermal systems include silica (SiO₂) deposits, in some cases >90% silica, in the Gusev Crater region, especially in the Columbia Hills and at Home Plate. We have developed a model called CHEMCHAU that can be used up to 100 °C to simulate hot springs associated with hydrothermal systems. The model was partially derived from FREZCHEM, which is a colder temperature model parameterized for broad ranges of temperature (<−70 to 25 °C), pressure (1-1000 bars), and chemical composition. We demonstrate the validity of Pitzer parameters, volumetric parameters, and equilibrium constants in the CHEMCHAU model for the Na-K-Mg-Ca-H-Cl-ClO₄-SO₄-OH-HCO₃-CO₃-CO₂-O₂-CH₄-Si-H₂O system up to 100 °C and apply the model to hot springs and silica deposits.A theoretical simulation of silica and calcite equilibrium shows how calcite is least soluble with high pH and high temperatures, while silica behaves oppositely. Such influences imply that differences in temperature and pH on Mars could lead to very distinct mineral assemblages. Using measured solution chemistries of Yellowstone hot springs and Icelandic hot springs, we simulate salts formed during the evaporation of two low pH cases (high and low temperatures) and a high temperature, alkaline (high pH) sodic water. Simulation of an acid-sulfate case leads to precipitation of Fe and Al minerals along with silica. Consistency with martian mineral assemblages suggests that hot, acidic sulfate solutions are plausibility progenitors of minerals in the past on Mars. In the alkaline pH (8.45) simulation, formation of silica at high temperatures (355 K) led to precipitation of anhydrous minerals (CaSO₄, Na₂SO₄) that was also the case for the high temperature (353 K) low pH case where anhydrous minerals (NaCl, CaSO₄) also precipitated. Thus we predict that secondary minerals associated with massive silica deposits are plausible indicators on Mars of precipitation environments and aqueous chemistry. Theoretical model calculations are in reasonable agreement with independent experimental silica concentrations, which strengthens the validity of the new CHEMCHAU model.  相似文献   

Low signal-to-noise event detection based on waveform stacking and cross-correlation: application to a stimulation experiment   总被引：1，自引：1，他引：0  

Katrin Plenkers  Joachim R. R. Ritter  Marion Schindler 《Journal of Seismology》2013,17(1):27-49

We study the microseismicity (M _L ?<?2) in the region of Landau, SW Germany. Here, due to thick sediments (~3?km) and high cultural seismic noise, the signal-to-noise ratio is in general very low for microearthquakes. To gain new insights into the occurrence of very small seismic events, we apply a three-step detection approach and are able to identify 207 microseismic events (?1?<?M _L ?<?~1) with signal-to-noise ratios smaller than 3. Recordings from a temporary broadband network are used with station distances of approximately 10?km. First, we apply a short-term to long-term average detection algorithm for data reduction. The detection algorithm is affected severely by transient noise signals. Therefore, the most promising detections, selected by coinciding triggers and high-amplitude measures, are reviewed manually. Thirteen seismic events are identified in this way. Finally, we conduct a cross-correlation analysis. As master template, we use the stacked waveforms of five manually detected seismic events with a repeating waveform. This search reveals additional 194 events with a cross-correlation coefficient exceeding 0.65 which ensures a stable identification. Our analysis shows that the repeating events occurred during the stimulation of a geothermal reservoir within a source region of only about 0.5?km³. Natural background seismicity exceeding our detection level of M _L ?~?0.7 is not found in the region of Landau by our analysis.  相似文献   

Resolution of impact‐related microstructures in lunar zircon: A shock‐deformation mechanism map     

Nicholas E. TIMMS  Steven M. REDDY  David HEALY  Alexander A. NEMCHIN  Marion L. GRANGE  Robert T. PIDGEON  Robert HART 《Meteoritics & planetary science》2012,47(1):120-141

Abstract– The microstructures of lunar zircon grains from breccia samples 72215, 73215, 73235, and 76295 collected during the Apollo 17 mission have been characterized via optical microscopy, cathodoluminescence imaging, and electron backscatter diffraction mapping. These zircon grains preserve deformation microstructures that show a wide range in style and complexity. Planar deformation features (PDFs) are documented in lunar zircon for the first time, and occur along {001}, {110}, and {112}, typically with 0.1–25 μm spacing. The widest PDFs associated with {112} contain microtwin lamellae with 65°/<110> misorientation relationships. Deformation bands parallel to {100} planes and irregular low‐angle (<10°) boundaries most commonly have <001> misorientation axes. This geometry is consistent with a dislocation glide system with <100>{010} during dislocation creep. Nonplanar fractures, recrystallized domains with sharp, irregular interfaces, and localized annealing textures along fractures are also observed. No occurrences of reidite were detected. Shock‐deformation microstructures in zircon are explained in terms of elastic anisotropy of zircon. PDFs form along a limited number of specific {hkl} planes that are perpendicular to directions of high Young’s modulus, suggesting that PDFs are likely to be planes of longitudinal lattice damage. Twinned {112} PDFs also contain directions of high shear modulus. A conceptual model is proposed for the development of different deformation microstructures during an impact event. This “shock‐deformation mechanism map” is used to explain the relative timing, conditions, and complexity relationships between impact‐related deformation microstructures in zircon.  相似文献   

New igneous zircon Pb/Pb and metamorphic Rb/Sr ages in the Yaounde Group (Cameroon, Central Africa): implications for the Central African fold belt evolution close to the Congo Craton     

Sébastien Owona  Marion Tichomirowa  Lothar Ratschbacher  Joseph Mvondo Ondoa  Dieudonné Youmen  J?rg Pf?nder  Félix M. Tchoua  Pascal Affaton  Georges Emmanuel Ekodeck 《International Journal of Earth Sciences》2012,101(7):1689-1703

Three meta-igneous bodies from the Yaounde Group have been analyzed for their petrography, geochemistry, and ²⁰⁷Pb/²⁰⁶Pb zircon ages. According to their geochemical patterns, they represent meta-diorites. The meta-plutonites yielded identical zircon ages with a mean of 624?±?2?Ma interpreted as their intrusion age. This age is in agreement with previously published zircon ages of meta-diorites from the Yaounde Group. The meta-diorites derived mainly from crustal rocks with minor contribution from mantle material. The ⁸⁷Rb/⁸⁶Sr isochron ages of one meta-diorite sample and three meta-sedimentary host rocks are significantly younger than the obtained intrusion age. Therefore, they are not related to igneous processes. ⁸⁷Rb/⁸⁶Sr isochron ages differ from sample to sample (599?±?3, 572?±?4, 554?±?5, 540?±?5?Ma) yielding the oldest Neoproterozoic age (~600?Ma) for a paragneiss sample at a more northern location. The youngest Rb/Sr isochron age (~540?Ma) was obtained for a mica schist sample at a more southern location closer to the border of the Congo Craton. The ⁸⁷Rb/⁸⁶Sr whole rock-biotite ages are interpreted as cooling ages related to transpressional processes during exhumation. Therefore, several discrete metamorphic events related to the exhumation of the Yaounde Group were dated. It could be shown by Rb/Sr dating for the first time that these late tectonic processes occurred earlier at more distant northern locations of the Yaounde Group and lasted at least until early Cambrian (~540?Ma) more closely to the border of the Congo Craton.  相似文献   

Coral skeletal delta(15)N reveals isotopic traces of an agricultural revolution     

Marion GS  Dunbar RB  Mucciarone DA  Kremer JN  Lansing JS  Arthawiguna A 《Marine pollution bulletin》2005,50(9):931-944

This study introduces a new method of tracing the history of nutrient loading in coastal oceans via delta(15)N analysis of organic nitrogen preserved in the skeleton of the massive Porites coral. Four coral cores were collected in Bali, Indonesia, from reefs exposed to high levels of fertilizers in agricultural run-off, from lagoonal corals impacted by sewage, and from a reef located 30 km offshore. Skeletal delta(15)N in the agriculturally exposed coral declined from 10.7+/-0.4 per thousand in 1970-1971, when synthetic fertilizers (-0.8 per thousand+/-0.2 per thousand) were introduced to Bali, to a depleted "anthropogenic" baseline of 3.5 per thousand+/-0.4% in the mid-1990s. delta(15)N values were negatively correlated with rainfall, suggesting that marine delta(15)N lowers during flood-bourn influxes of waste fertilizers. Reef cores exposed to untreated sewage in terrestrial discharge were enriched (7.8 and 7.3+/-0.4 per thousand), while the offshore core reflected background oceanic signals (6.2+/-0.4 per thousand). delta(15)N, N concentration, and C:N systematics indicate that the N isotopic composition of skeletal organic matter was generally well preserved over 30 years. We suggest that skeletal organic delta(15)N can serve as a recorder of past nitrogen sources. In Bali, this tracer suggests that the intensification of Western style agricultural practices since 1970 are contributing to the degradation of coastal coral reefs.  相似文献   

Tomographic radiotracer studies of the spatial distribution of heterogeneous geochemical transport processes     

Marion Gründig  Michael Richter  Anita Seese  Osama Sabri 《Applied Geochemistry》2007

Within the scope of the further development of geochemical transport models the consideration of the influence of the heterogeneous structures of the geological layers plays an important role. For the verification and parameter estimation of such models it is necessary to measure the heterogeneous transport and sorption processes inside the samples. Tomographic radiotracer methods (positron emission tomography (PET)) enable nondestructive spatially resolved observations of the transport processes in these layers. A special quantitative evaluation system for geoscientific PET studies was developed. Investigations of the water flow distribution in a drill core of a lignite mining dump and of the migration of Cu ions in a horizontal soil column illustrate the potential of this method. Spatial distribution functions of the flow velocity, the specific mass flow and the longitudinal dispersivity were determined on the basis of PET investigations.  相似文献   

Equal-mobility bed load transport in a small, step-pool channel in the Ouachita Mountains     

Daniel A. Marion  Frank Weirich 《Geomorphology》2003,55(1-4):139

Equal-mobility transport (EMT) of bed load is more evident than size-selective transport during near-bankfull flow events in a small, step-pool channel in the Ouachita Mountains of central Arkansas. Bed load transport modes were studied by simulating five separate runoff events with peak discharges between 0.25 and 1.34 m³/s (1.0- to 1.6-year recurrence intervals) in a natural channel using controlled releases from a storage tank. EMT occurrence was investigated using four different bed load relationships suggested by previous research. With each of these approaches, the relationship of a given bed load characteristic (D_max, distribution percentile, displacement distance and skewness) to some independent factor (τ_c*, τ and grain size) was assessed to determine which transport mode was evident. Regression models derived using combinations of these four relationships with different datasets provide seven separate tests. Five of the seven tests indicate that EMT occurred or was predominant. Several reasons may explain the apparent contradictory results, but the confounding effects of changes in the structural arrangements of bed material prior to or during the events seem particularly important.  相似文献   

Simultaneous and Sensitive HPLC Determination of Mono‐ and Disaccharides,Uronic Acids,and Amino Sugars after Derivatization by Reductive Amination     

Klaus Fischer  Marion Wacht  Axel Meyer 《洁净——土壤、空气、水》2003,31(2):134-144

The reductive amination of low‐molecular‐weight saccharides, uronic acids, and amino sugars, followed by a separation of the derivates by means of ion‐pair chromatography or RP‐HPLC, offers an interesting alternative to HPAEC‐PAD for the environmental analysis of these compounds. Under this aspect various potential amination reagents, i.e., p‐amino‐benzoic acid (p‐AMBA), p‐AMBA propyl ester, 1‐aminopyrene, 2‐(2‐aminophenyl)indole, and 4‐aminoazobenzene, were tested with regard to the formation of derivates and to the chromatographic properties of the formed derivates. p‐AMBA, p‐AMBA propyl ester and 4‐aminoazobenzene proved to be especially suited, because they facilitate the amination of all carbohydrate reference components together with a complete separation and sensible detection (detection limits < 0.5 mg/L) of the derivates. Mainly the following elution sequence was ascertained: amino sugars (hexosamines) / disaccharide(s) / monosaccharides (hexoses) / hexuronic acid(s) / N‐acetyl‐D‐glucosamine. Detection limits down to 0.1 μmol/L were realized using p‐AMBA as reagent, facilitating the determination of the target compounds in landfill leachates and lysimeter percolates. Applying the p‐AMBA propyl ester for derivatization, chromatographic interferences with weakly retained derivates and the coelution of the reagent with its galactosamine derivate can be avoided, since the ester elutes after its derivates unlike p‐AMBA itself.  相似文献   

Interference processes on scouring at bed sills     

Mario A. Lenzi  Andrea Marion  Francesco Comiti 《地球表面变化过程与地形》2003,28(1):99-110

The local scouring downstream of bed sills forming a sequence for bed stabilization in steep channels has been investigated in a laboratory flume. The initial bed slopes ranged from 0·078 to 0·148. The bed alluvium was characterised by a non‐uniform grain size distribution. The results show that when the ratio between the critical water depth h_c and the sill spacing L rises above a characteristic value the scouring dynamics become heavily affected by the presence of the downstream sill, associated with the onset of a form of “interference” which renders the scouring process less effective. The difference with an “undisturbed” case is demonstrated. Self‐affinity of scour holes is confirmed and the scour length appears to be the reference parameter from which the scour depth might be evaluated. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Modeling ferrous-ferric iron chemistry with application to martian surface geochemistry     

Giles M. Marion  Jeffrey S. Kargel 《Geochimica et cosmochimica acta》2008,72(1):242-266

The Mars Global Surveyor, Mars Exploration Rover, and Mars Express missions have stimulated considerable thinking about the surficial geochemical evolution of Mars. Among the major recent mission findings are the presence of jarosite (a ferric sulfate salt), which requires formation from an acid-sulfate brine, and the occurrence of hematite and goethite on Mars. Recent ferric iron models have largely focused on 25 °C, which is a major limitation for models exploring the geochemical history of cold bodies such as Mars. Until recently, our work on low-temperature iron-bearing brines involved ferrous but not ferric iron, also obviously a limitation. The objectives of this work were to (1) add ferric iron chemistry to an existing ferrous iron model (FREZCHEM), (2) extend this ferrous/ferric iron geochemical model to lower temperatures (<0 °C), and (3) use the reformulated model to explore ferrous/ferric iron chemistries on Mars.The FREZCHEM model is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. Ferric chloride and sulfate mineral parameterizations were based, in part, on experimental data. Ferric oxide/hydroxide mineral parameterizations were based exclusively on Gibbs free energy and enthalpy data. New iron parameterizations added 23 new ferrous/ferric minerals to the model for this Na-K-Mg-Ca-Fe(II)-Fe(III)-H-Cl-SO₄-NO₃-OH-HCO₃-CO₃-CO₂-O₂-CH₄-H₂O system.The model was used to develop paragenetic sequences for Rio Tinto waters on Earth and a hypothetical Martian brine derived from acid weathering of basaltic minerals. In general, model simulations were in agreement with field evidence on Earth and Mars in predicting precipitation of stable iron minerals such as jarosites, goethite, and hematite. In addition, paragenetic simulations for Mars suggest that other iron minerals such as lepidocrocite, schwertmannite, ferricopiapite, copiapite, and bilinite may also be present on the surface of Mars. Evaporation or freezing of the Martian brine led to similar mineral precipitates. However, in freezing, compared to evaporation, the following key differences were found: (1) magnesium sulfates had higher hydration states; (2) there was greater total aqueous sulfate (SO_4T = SO₄ + HSO₄) removal; and (3) there was a significantly higher aqueous Cl/SO_4T ratio in the residual Na-Mg-Cl brine. Given the similarities of model results to observations, alternating dry/wet and freeze/thaw cycles and brine migration could have played major roles in vug formation, Cl stratification, and hematite concretion formation on Mars.  相似文献