Alteration minerals, fluids, and gases on early Mars: Predictions from 1-D flow geochemical modeling of mineral assemblages in meteorite ALH Ellis Ave. E-mail: melwani uchicago. Abstract-Clay minerals, although ubiquitous on the ancient terrains of Mars, have not been observed in Martian meteorite Allan Hills ALH , which is an orthopyroxenite sample of the early Martian crust with a secondary carbonate assemblage. This finding requires that before encountering the unweathered orthopyroxenite host of ALH , the fluid permeated rock that became weathered during the process.
Al-MashhadanyHiba M. Therefore, we expect such a source not too far below point D. Studies Leshin et al. Lapen T. We report the saturation indices of carbonate minerals in the supporting information Fig. Changela H. Cerussi, A.
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Cancer Research66 Sanchez-Mejorada G and Rosales C Fcg receptor-mediated mitogen-activated Celebritiess nude kinase activation in monocytes is independent of Ras. Beathard GA. These recommendations may be adopted, modified, or rejected according to clinical needs and constraints, and are not intended to replace local institutional policies. For neonates, the use of transparent or sponge dressings containing chlorhexidine Bj rn schwenzer be based on clinical judgment and institutional protocol. Molecular Medicine 7 Hirano A and Wong T Functional interactions between transcriptional elements in the long terminal repeat of reticuloendotheliosis virus:cooperative DNA binding of promoter- Bj rn schwenzer enhancer-specific factors. Medical Hypotheses 52 Complications associated with different insertion techniques for Hickman catheters. Complete the infusion of lipid-containing solutions e. Herz 29
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Alteration minerals, fluids, and gases on early Mars: Predictions from 1-D flow geochemical modeling of mineral assemblages in meteorite ALH Ellis Ave. E-mail: melwani uchicago. Abstract-Clay minerals, although ubiquitous on the ancient terrains of Mars, have not been observed in Martian meteorite Allan Hills ALH , which is an orthopyroxenite sample of the early Martian crust with a secondary carbonate assemblage.
This finding requires that before encountering the unweathered orthopyroxenite host of ALH , the fluid permeated rock that became weathered during the process. We were able to predict the composition of the clay minerals formed during weathering, which included the dioctahedral smectite nontronite, kaolinite, and chlorite, all of which have been previously detected on Mars.
We also calculated host rock replacement in local equilibrium conditions by the hydrated silicate talc, which is typically considered to be a higher temperature hydrothermal phase on Earth, but may have been a common constituent in the formation of Martian soils through pervasive aqueous alteration. Finally, goethite and magnetite were also found to precipitate in the secondary alteration assemblage, the latter associated with the generation of H2. In the wake of the Curiosity rover's discovery Farley et al.
If clay minerals are ubiquitous on the ancient terrains of Mars and the secondary carbonates in the meteorite are formed by. Clay minerals were predicted to occur on the surface of Mars as a result of aqueous alteration of the basalts e. Carbonates have also been detected by orbital spectroscopy at Nili Fossae outcrops and possibly in dust see reviews by Ehlmann and Edwards  and Niles et al.
In situ, they have been detected in soil by the Phoenix lander Boynton et al. But the large, widespread outcrops of carbonates predicted by models of a warm early Martian climate e. However, a recent reanalysis of orbital data points to somewhat more extensive occurrences of carbonates on the surface of Mars, together with a spatial and possibly chemical relationship with clay minerals Wray et al. Here we aim to constrain the pH and composition of the carbonate and clay mineral-forming fluids of the ancient terrain where ALH was emplaced.
It occurs in interstices and replacing maskelynite and orthopyroxene Mittlefehldt ; Treiman ; Kring et al. A ternary diagram of representative carbonate compositions is shown in Fig. Sulfide grains pyrite, and possibly pyrrhotite and greigite occur next to primary chromite grains and within the carbonates, with some apparently in carbonate-crossing veins Mittlefehldt ; Treiman ; McKay et al.
Trace amounts of apparently preterrestrial fine-scaled phyllosilicates "phlogopitic mica" intergrown with the carbonates have been described, possibly postdating the carbonate deposition Brearley Magnetite nanocrystals, together with polycyclic aromatic hydrocarbons, sulfides, and fossil-like structures within the carbonate rosettes were interpreted as possibly biogenic e. A large range of pressure-temperature P-T conditions have been invoked to explain the abiotic formation of the alteration assemblage see supporting information, Fig.
But stable isotope analyses have shown that relatively low-temperature fluids were responsible for producing the carbonates. Specifically, the higher OSMOW in the carbonates compared to the host rock is indicative of an external source for the carbonates, particularly from a permeating fluid Romanek et al. The mechanism favored by most investigators for the low-temperature formation of the zoned carbonate is evaporation McSween and Harvey ; Warren , whereby in a short time scale, flood waters percolated through ALH and precipitated the carbonates while the water evaporated, resulting in the compositional and isotopic zonation observed in them, and accounting for the lack of other secondary.
Other authors expanded the evaporitic scenario e. The apparent paradox between the presence of carbonates but the absence of clays in the meteorite, and the presence of phyllosilicates but the rarity of carbonates on the surface of early Mars, can be addressed as a multicomponent mineral-liquid-gas system that can be simulated with thermochemical modeling.
The pressure-temperature P-T conditions related to a suite of geological contexts can be used in the software to simultaneously assess the relative stabilities of large sets of observed and predicted mineral phases that would occur in natural systems. Conversely, the presence of a particular set of alteration minerals which are computed to be stable in a modeled system is indicative of specific P-T conditions which can be extended to describe a natural system and infer geological processes where the calculated alteration minerals are present.
The program uses a modified Newton-Raphson method to solve equations of chemical equilibria for aqueous species and minerals in its database using extended Debye-Huckel theory from Tanger and Helgeson Reed , ; Spycher and Reed We disallowed the formation of dolomite and other minerals whose growth is kinetically retarded under these low-temperature conditions e. Magnesite, e. Both huntite and nesquehonite can serve as precursors to magnesite. Methane CH4 equilibration and formation with the reduction of H2O and CO2 was also prohibited in the models, given the kinetic barrier to abiogenic CH4 formation at low temperature e.
Minerals that form solid solutions and that precipitated in the models are grouped in the results for clarity, e. Carbonate compositions, on the other hand, are addressed in the results as compositional mixtures of computed discrete mineral phases, as CHIM-XPT does not calculate carbonate solid solutions, e. We allowed a continuous range of carbonate compositions to form between the carbonate mineral endmembers, but assumed that intermediate compositions form as a result of mixing between the precipitating endmembers.
We report the saturation indices of carbonate minerals in the supporting information Fig. S2 to address this. Further solid solutions and mineral endmembers are detailed in the supporting information Table S2. We did not seek to simulate the morphology of the carbonate rosettes, but aimed to understand the. We regard a model as an instructive possibility when the resulting mineral assemblage resembles the compositional range of the carbonates in ALH , while minerals other than carbonates are absent or minor.
Table 1 lists the starting conditions of each model computed here. The composition of the initial rock used in the alteration models was an "unaltered" ALH , i. All rocks and minerals are specified in our thermodynamic database as sums of elemental molar abundances, i.
Ti and Cr compounds were not included as reactants because the database does not include Ti and Cr species and minerals. Table 1. Starting parameters for the fluids used in the aqueous alteration models reported in this work. The composition of the reactant rock is shown in Table 2.
Table 2. Sulfur and chlorine were added from Lodders CO2 is the most abundant gas in the Martian atmosphere at present Owen et al. Initial CO2 fugacities fCO2 of 0. Specifically, the models were treated as closed systems to CO2, where CO2 was a limiting factor: CO2 used in carbonate formation and other reactions was not replenished. A pCO2 of 1 bar appears to be consistent with the early Martian atmospheric pressure estimated by global circulation models which allow for transient liquid water on the surface Wordsworth et al.
Other atmospheric species such as N2 and SO2 were not introduced into the initial composition of the reactant fluid in the models, as the early Martian atmosphere was most likely principally composed of CO2 Pollack et al.
We assumed that the source of cations for the minerals precipitated was the dissolved orthopyroxenite host rock. An external source for cations, such as the dissolution of an overlying carbonate-rich deposit, could potentially produce the mineralogy observed in ALH , but would ultimately not address the primary source of cations.
Subsequently, all mineral precipitates in the equilibrium assemblage were removed from the system, and another small parcel of rock was titrated. As such, at each titration step, the system achieved local equilibrium, but was out of equilibrium with the host rock and minerals precipitated in preceding steps.
An added advantage of 1-D flow models is that fCO2 below those specified by the initial conditions were also tested for their potential to precipitate phases of interest in the system, as all mineral precipitates including CO2-sequestering carbonates were removed from the system as the fluid percolated unaltered host rock, thereby decreasing the fCO2 of the fluid.
CO2 and other gas compounds were still allowed to exchange with the fluid and be incorporated into mineral precipitates. We assumed that equilibration between the minerals precipitated and evaporating fluid was kinetically slower than the formation of mineral precipitates from the evaporating fluid.
As in the percolation experiments, minerals formed were removed from the system to prevent back-reaction between the solid fraction and the remaining fluid. The resulting carbonate compositions precipitated in the flow models are summarized in carbonate ternary diagrams Figs. However, the system initially equilibrated with 1 bar fCO2 Model B resulted in a compositional migration to higher Mg content.
This composition falls in range of some carbonate compositions observed in ALH Fig. This is revealed by the elevated concentrations of H2 Fig.
Secondary mineral precipitates as a function of increased water-rock interaction i. Notice that the ordinate units are log10 moles per gram of titrated rock per kilogram of initial liquid. At this. Most of the chlorite precipitated was the "Al-free chlorite" endmember with a formula of Mg6Si4Oi0 OH 8, compositionally similar to serpentine and talc.
Table 3. Isothermal evaporation of the water brought significant changes to the carbonate compositions Fig. This resulted in. Arguably, the higher carbonate in solution in Model B Fig.
For purposes of the discussion, we concentrate on Model B. Concentrations of dissolved aqueous components and pH in the fluids of the 1-D flow models. Alternatively, the groundwater table rose to the level of the ALH host as a response to recharge from the percolating fluids. Finally, evaporation of the relatively abundant and dilute fluids that had experienced little interaction with the host rock would produce the more voluminous Mg carbonates Figs.
The Mg-rich precursor carbonate huntite is required prior to transformation to the observed magnesite, but this may also explain. Unfortunately, recognizing whether the Mg carbonate in ALH is recrystallized, postdepositionally transformed huntite is not trivial. Huntite occurs as an evaporitic near-surface weathering product and as a fine-grained diagenetic mineral in dissolution pores of ultramafic rocks e. Log10 fugacity of the dissolved gases in the alteration fluids as a function of increased water-rock interaction i.
Dashed lines divide the observed stability fields for goethite and magnetite in the system. Goethite only precipitated in the top left quadrant, and magnetite only in the bottom right quadrant. Kinsman Possibly, the shock event s that occurred after carbonate deposition and that mobilized maskelynite in the meteorite could also have transformed huntite to magnesite. Alteration phases other than carbonates were abundant even at the peak of carbonate precipitation in both 1-D flow models Fig.
In contrast, in the meteorite, carbonates form almost the entirety of the alteration assemblage observed, meaning that if the carbonates in ALH formed under the conditions tested, this would only have been possible if a mechanism had been in place to dissolve and remove or inhibit the formation of secondary phases other than carbonate. Conceivably, shock could have transformed any existing smectites back to olivine and pyroxene, although direct evidence for this transformation does not exist in the meteorite.
We note, however, that silica glasses are observed in the meteorite e. Low-temperature equilibrium conditions inhibit the precipitation of Mg carbonate e. The lack of textural and mineralogical evidence for intensive fluid interaction in ALH has been noted Treiman and Romanek , and the compositional and isotopic zonation of the carbonates in the meteorite is strongly indicative of disequilibrium conditions e.
While kaolinite, nontronite, and celadonite are not unusual phyllosilicates in low-temperature aqueous alteration systems on Earth, the precipitation of talc and chlorite in the models under these conditions Fig. Talc forms, and is stable, at ambient conditions in laboratory tests Bricker et al.
Apparently, pH exerts a strong control on the formation of talc, preferentially precipitating in alkaline conditions Tosca et al. Alternatively, thermochemical data available to us for nontronite and other smectites are as yet deficient, especially considering that they are complex solid solutions.
Low-temperature chlorite is also relatively uncommon on Earth as it tends to form in diagenetic.
Blood in press. These guidelines also identify performance indicators that can be used locally by health-care institutions or organizations to monitor their success in implementing these evidence-based recommendations. Prospective multicenter study of vascular-catheter-related complications and risk factors for positive central-catheter cultures in intensive care unit patients. Madrid, Spain, July , Category II F. The enrolled participants are to be randomly assigned to one of the three study conditions: endurance training; resistance training; active control, with assessments to be taken at three pre-specified time points. Journal of Interferon and Cytokine Research 24
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