查看更多>>摘要：Zabuyelite (Li2CO3) was discovered in sedimentary environments, but it can form in igneous environments (e.g., rare-element pegmatites). This experiment extends the solubility and crystallization behaviors of Li2CO3 in an aqueous solution to igneous conditions (up to 783 degrees C and 8.24 kbar) from sedimentary conditions using a Bassett-type hydrothermal diamond-anvil cell. The solubility of Li2CO3 in an aqueous solution increases with temperature and pressure above the vapor-liquid critical pressure-temperature (P-T) condition. This is in contrast to its negative temperature coefficient in vapor-saturated water. The solubility data are fitted with the eq. R x T x lnx(Li2CO3) = -3.0328 x 10(4)-16.6486 x T + 3.3252 x 10(3) x P (r(2) = 0.9643), where X-Li(2)CO(3) is the mole fraction (mol/mol) of Li2CO3, 714 <= T (K) <= 1056, 3.28 <= P (kbar) <= 8.24, and R is the gas constant. Zabuyelite grows quickly when nucleated from complete Li2CO3-dissolved aqueous solutions during cooling (at average rates of 0.2-3.0 mu m(2)/s), especially in the initial exponential growth stage with approximately 18.7-34.2 mu m(2)/s. This is orders of magnitude faster than other pegmatite minerals (e.g., spodumene), forming tabular crystals with the pseudo-hexagonal outlines of monoclinic systems in an aqueous solution. Nevertheless, zabuyelite forms microcrystals in Li2CO3 melt. In addition, zabuyelite crystallization (exhibiting significant temperature dependence) dominantly occurs at similar to 450-600 degrees C. The aforementioned crystallization features are identical with the features of zabuyelite contained in crystal-rich fluid inclusions from pegmatite, proving the zabuyelite's daughter-mineral nature in the fluid inclusions, hence indicating the primary origin of the crystal-rich inclusions in pegmatite. In the future, the solubility model of Li2CO3 in an aqueous solution can infer pegmatite formation conditions based on the analysis of the Li2CO3 content dissolved in the pegmatite crystallization media.
查看更多>>摘要：To better understand the behaviors of calcium (Ca) isotopes during igneous and metamorphic processes that differentiate the Earth and other rocky planets, we investigated the effects of pressure and Ca/Fe concentration on the average Ca-O bond length and the reduced partition function ratio of Ca-44/Ca-40 (10(3)ln(44/40Ca)beta) in garnet using first-principles calculations. Our calculations show that (1) the average Ca-O bond length increases and 10(3)ln(44/40Ca)beta decreasing (approximately 0.41 parts per thousand at 1000 K from a Ca/(Fe + Ca + Mg) of 1/24 to 12/12) with increasing Ca concentrations. In contrast to orthopyroxene and forsterite, whose Ca-O bond lengths and 10(3)ln(44/40Ca)beta are sensitive to Ca concentrations only in narrow range, the garnet Ca-O bond length and 10(3)ln(44/40Ca)beta vary with Ca concentrations in wide ranges. (2) The average Ca-O bond length increases and 10(3)ln(44/40Ca)beta decreases with increasing Fe concentrations (by 0.12 parts per thousand at 1000 K, FeO content of 12.4 wt%). (3) The average Ca-O bond length decreases by similar to 0.014 angstrom, and 10(3)ln(44/40Ca)beta increases by 0.1 parts per thousand-0.2 parts per thousand at 1000 K when the pressure increases from 0 to 3 GPa. (4) However, the pressure effect on 10(3)ln(44/40Ca)alpha(garnet-clinopyroxene) is insignificant. Using our new results of the effects of pressure and Ca/Fe concentration on 10(3)ln(44/40Ca)alpha(garnet-clinopyroxene), we evaluated the observed difference in Ca isotope compositions between garnet and clinopyroxene in natural samples. Most have reached equilibrium, whereas some samples exceed our prediction, which might reflect the majorite effect or kinetic fractionation.
查看更多>>摘要：Iron (Fe) (hydr)oxides are effective antimony (Sb) adsorbents with limited individual Sb(III) oxidation capacity in natural waters. The coexistence of Mn(II) and Fe (hydr)oxides may significantly promote the oxidation of Sb (III). However, the mechanism of Sb(III) oxidation and adsorption in the presence of Mn(II) and Fe (hydr)oxides remains unclear. Therefore, in the present study, the effect of dissolved Mn(II) on the oxidation and adsorption of Sb(III) in the ferrihydrite/hematite-Mn(II) system under aerobic conditions and the mechanism were comprehensively investigated. The results of kinetic experiments showed that Sb(III) was efficiently removed in the presence of ferrihydrite/hematite and Mn(II). Further characterization confirmed the formation of Mn(III/IV) oxides on the surface of ferrihydrite and hematite, which were the main oxidants for Sb(III) oxidation. However, removal mechanisms were different between the ferrihydrite-Mn(II) system and the hematite-Mn(II) system. The adsorption of Sb was the main cause of Sb(III) removal in the ferrihydrite-Mn(II) system. For the hematite-Mn(II) system, Sb(III) oxidation played a more important role in Sb(III) removal; however, Sb adsorption was inhibited as a result of Mn oxide formation on the hematite surface and the limited adsorption capacity of hematite. Therefore, the present study revealed that Mn(II) and ferrihydrite/hematite were both critical to Sb(III) oxidation and adsorption under aerobic conditions, which may be helpful for a better understanding of Sb migration and transformation in natural waters.
查看更多>>摘要：The development of high-resolution gas source mass spectrometry has permitted entirely new types of measurements of multiply-substituted isotopologues in gas species of geochemical significance. Here, we present recent advances afforded by measurements of (NN)-N-15-N-15 in natural samples, together with (NN)-N-14-N-14 and (NN)-N-15-N-14. We show that the abundance of the doubly-substituted (NN)-N-15-N-15 isotopologue in hydrothermal gases, often mixtures of volatiles of widely different origins, allows tracing the provenance of nitrogen. The approach is based on the recent finding that atmospheric N-2 has a substantial enrichment in (NN)-N-15-N-15 of nearly 20 parts per thousand relative to any other source of N-2. This is particularly useful for the study of hydrothermal gases, where characterizing the isotopic composition and provenance of volcanic N-2 is important for a wide range of applications in high-temperature geochemistry, but where air-derived N-2 is unavoidable. In this review, we summarize the evidence that (NN)-N-15-N-15 is an unambiguous tracer of air contamination. We compare two sets of published (NN)-N-15-N-15 data acquired on gases from plume and arc volcanoes. We show how different sources of volcanic N-2 may be in plume versus arc environments, and discuss the first-order constraints on the deep N cycle that are provided by the new (NN)-N-15-N-15 data. Important findings include that the delta N-15 tracer, used alone or in conjunction with N-2/Ar and N-2/He ratios, can be surprisingly deceiving. Isotope fractionation of atmospheric nitrogen occurs within hydrothermal systems, resulting in negative delta N-15 values similar to estimates for mantle values, yet with (NN)-N-15-N-15 values that preclude a mantle origin. The (NN)-N-15-N-15 data show that the true delta N-15 of volcanic components is positive in arcs but near-zero at the Yellowstone plume. In other words, atmospheric N-2 can mimic mantle delta N-15, and mantle delta N-15 can look like the value of air. Without (NN)-N-15-N-15, the apportioning of mantle and atmospheric N-2 in mixed gases can easily be wrong. With (NN)-N-15-N-15, we also determine the true N-2/He-3 and N-2/Ar-36 ratios of volcanic components in hydrothermal systems. Results inform our understanding of the deep nitrogen cycle. Plume and arc volcanic end-members show distinct isotope and elemental ratios, consistent with sub-arc sources being overwhelmed by near-quantitative slab devolatilization, while the Yellowstone plume source is not reflecting volatile subduction.
Holden, Courtney, VKyser, T. KurtisLongstaffe, Fred J.Wang, Yuxiang...
12页
查看更多>>摘要：Stable isotope compositions of otoliths can be used to provide thermal histories of fish. This tool, however, is currently unrefined for catadromous species, such as the American eel Anguilla rostrata, where the otolith is formed in both marine and freshwater environments. We reared 2000 elvers in fresh water for 32 weeks in 10 temperature treatments ranging from 10 to 34 degrees C, and then measured delta O-18 and delta C-13 of otoliths to 1) determine how somatic and otolith growth responded to temperature; 2) evaluate the relationship between water temperature and delta O-18 and delta C-13 of otoliths; and 3) develop a species-specific isotopic fractionation equation that isolates the freshwater portion of the otolith. Our results show that eel elvers have a high optimum temperature for somatic growth (27-28 degrees C). Optimum temperature for otolith growth was slightly higher, suggesting that otolith growth can be decoupled from body growth. The expression for carbonate-water isotopic fractionation of American eel otoliths over the temperature range examined was 1000ln alpha(aragonite-water) = 14.30(10(3) T-1) - 18.651. This equation accurately predicted water temperature (predictive error 0.49 degrees C) for 180 American eel otoliths obtained from a different controlled rearing study (conducted at 22 and 28 degrees C). This experiment validated the use of the oxygen and carbon isotope compositions of otoliths to determine the thermal history of American eels in fresh water, thus providing a method that can be applied to wild eels.
查看更多>>摘要：Hydrothermal fluids enriched in halogens (e.g., F and Cl) are essential for ore formation as well as associated alteration processes. Chloride-bearing solutions facilitate mineral re-equilibration and metal mass transfer by forming soluble complexes with Cl-. Fluorine is enriched in a variety of hydrothermal ore deposits and their alteration halos, but the significance of this enrichment remains controversial. Fluorine may simply reflect the source of the fluids, but may also play an active role in controlling the metal budget, with four main hypotheses having been proposed: (i) fluoride increases the mobility of some metals by forming stable coordination complexes; (ii) fluoride acts as a precipitating agent, due to the low solubility of many fluoride minerals; and fluorine improves fluid flow either (iii) by promoting silicate dissolution and creating fluid pathways under acidic conditions (HF(aq)), or (iv) by affecting the kinetics of interface coupled dissolution-reprecipitation reactions by modifying the dissolution and nucleation processes. Here, we tested the least studied mechanism (iv) by performing experiments to examine the effects of fluoride and chloride ions on the fluid-mediated albitisation of perthite (intergrowth of albite and microcline) at 600 degrees C and 2 kbar. We found that the albitisation rate depends on the Cl/(Cl + F) ratio, but not in a linear manner: reaction rates reach a maximum in solutions featuring 'Goldilocks' Cl/(Cl + F) ratios between 0.5- 0.99 (i.e., Cl/F is between 1 and 100). Based on recent advances in halogen chemistry, we propose that the observed Goldilocks effect was caused by non-covalent interactions between the dihalogen ClF(aq) and Si(OH)(4)(aq). To test this hypothesis, we calculated the bonding energy between the Si(OH)(4)(g) and ClF(g) molecules via Car-Parrinello first principle calculations. The positive values obtained indicate that ClF(g) can form a stable halogen bond with Si(OH)(4)(g). If confirmed experimentally in hydrothermal fluids, such complexes could make process (iv) a powerful and widely applicable mechanism for increasing silicate reaction kinetics, thereby promoting efficient coupling between fluid flow and fluid-rock interaction, a key factor in the development of mineral systems.
查看更多>>摘要：Recent results from laboratory and field studies support that dissimilatory metal reducing (DMR) bacteria influence the fate and transport of uranium in anaerobic subsurface environments. To date, most research efforts have focused on the reduction of soluble U(VI) by DMR bacteria to form insoluble uraninite (UO2). Subsurface environments harbor, however, large reservoirs of U(VI) in solid or mineral form. Uranium that is structure-bound in minerals is expected to be more refractory to microbial reduction than soluble U, based on analogy with Fe respiration. The reducibility of U(VI) could impact the fate of U(IV) by controlling mineral precipitation reactions, which has implications for the long-term immobilization of U in subsurface environments. We studied anoxic cultures of Shewanella putrefaciens CN32 incubated with natural carnotite-group minerals by X-ray diffraction, electron microscopy, scanning transmission X-ray microscopy (STXM). Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements at U-N-4,N-5, V-L-2,L-3, and O-K edges on cultures incubated up to 10 months show that V(V) was reduced to V(IV), whereas U was not reduced. In contrast, V(V) and U(VI) in solution were both completely reduced to lower oxidation states by CN32, as precipitates within the exopolymer surrounding the bacteria. Assays for the toxicity of U and V to CN32 showed that biofilm formation was stimulated at 0.001 M U(VI), and growth was inhibited at concentrations of U(VI) greater than 0.001 M. Vanadium did not inhibit growth or stimulate biofilm formation at any concentration tested. Investigations of the bacteriamineral and bacteria-metal interface at the nanometer and molecular scales provide new insights into the corespiration of V and U that help explain their biogeochemical cycling and have implications for subsurface bioremediation of these elements.
查看更多>>摘要：The processes initiating the first cooling step of the last greenhouse-to-icehouse transition, from 90 million years ago (Ma) onward still remain enigmatic. While the combination of mountain uplift and continental weathering has been proposed as a major sink for atmospheric CO2 and a climate driver over geological timescales, this hypothesis is much debated and its potential importance in triggering the late Cretaceous global cooling is yet to be explored. In this work, we combined clay mineralogy, trace and major element concentrations, and a new proxy of silicate weathering intensity based on Nd and Hf isotopes (Delta epsilon(HR(t)clay)) to explore the potential links between the uplift of the brazilian margin, silicate weathering and climate evolution during the late Cretaceous. Our new Delta epsilon(HR(t)clay) proxy data suggest - for the first time - that marked increase of silicate weathering intensity occurred in southeast Brazil during the late Cretaceous, from similar to 85 to 70 Ma, related to the tectonic uplift affecting the eastern South American margin at that time. Combined with clay mineralogical analyses, our Hf-Nd isotope data further suggests the existence of a relatively arid local climate during the Turonian-Santonian interval, during which physical disaggregation of rocks most likely prevailed, accompanying the uplift of the Brazilian margin. From the Santonian, we propose that the exposure of new high-elevation regions favored instead locally enhanced precipitations and more hydrolysing conditions, thereby promoting chemical weathering and atmospheric CO2 drawdown. Altogether, our multi-proxy investigation suggests that the uplift of the Brazilian margin could have contributed to the late Cretaceous cooling, potentially playing a key role in the onset of the last greenhouse-to-icehouse transition.
Konhauser, Kurt O.Flynn, Shannon L.Alessi, Daniel S.Gingras, Murray K....
12页
查看更多>>摘要：The combination of hydraulic fracturing with horizontal drilling has revolutionized oil and gas production. However, most of our understanding of the subsurface mechanisms and chemical interactions that occur during the process come from analyses of flowback and produced water (FPW). While the chemical composition of FPW can provide some information to understand water-rock interactions in the subsurface, the mechanisms by which dissolved species, including potentially toxic heavy metals (PTHM), are mobilized remain poorly constrained. In this study, we used stirred benchtop reactors to simulate the geochemical processes that occur when injected hydraulic fracturing fluid (HFF) interacts with reservoir rock formations of the Upper Devonian Duvernay Formation, a mudstone formation that is an important hydraulic fracturing target in west-central Alberta, Canada. Our aims were to: (1) assess whether our laboratory methods can be used to predict the inorganic chemistry of FPW, including concentrations of PTHM, and (2) to ascertain the reaction kinetics and mechanisms of the release of inorganic components from reservoir rocks. Our results indicate that elemental concentration data from reactor experiments coupled with saturation indices modelling can be used to predict the assemblage of solid phases that precipitates downhole, such as barite + celestine + gypsum. High salinity experiments (0.5 M NaCl), simulating FPW reuse, showed increased concentrations of many dissolved species with increasing salinity. Our findings were corroborated with geochemical modelling of FPW samples collected from operating unconventional wells in the Duvernay Formation. FPW from wells using a mixture of recycled produced water (RPW) and fresh source water to make up the injected HFF had higher concentrations of many elements, including the PTHM, Ba, Sr, and As. Our work illustrates the potential environmental risks of using RPW in hydraulic fracturing operations in the event of a spill and it provides a robust benchtop approach to predict the leaching of elements from the host rock during hydraulic fracturing.
查看更多>>摘要：We present zircon (U-Th)/He(ZHe) data for 17 Proterozoic basement samples from elevation profiles on the three peaks in the Front Range of Colorado that are at elevations over 14,000 ft. (4267 m, locally known as "fourteeners"), with complementary Raman data for a sample subset. ZHe dates from Longs Peak in the northern Front Range are uniformly Late Cretaceous to Eocene (37 +/- 1 Ma to 137 +/- 2 Ma), while those from Mt. Evans (34 +/- 1 to 606 +/- 18 Ma) and Pikes Peak (111 +/- 5 Ma to 773 +/- 17 Ma) in the central and southern Front Range are as old as Cryogenian. The results suggest hotter Late Cretaceous to Eocene burial temperatures to the north, attributable to northward thickening Cretaceous burial as proposed previously. Neoproterozoic sandstone injectites in the central range and kimberlite-hosted Cambrian sedimentary xenoliths in the northern range document that Precambrian basement was at the surface in the Cryogenian and/or in the Cambrian, as inferred previously for basement below the Great Unconformity in the southern range. Thermal history modeling demonstrates that ZHe data from the three fourteeners are compatible with the hypothesis of initial basement exhumation throughout the range by the Cryogenian. The study outcomes highlight important considerations for resolving deep-time thermal histories, including younger burial magnitude, detailed sampling position in structural blocks, availability of paleosurface markers, and construction of inverse thermal history models that integrate geologic knowledge and are designed to test geologically realistic thermal history scenarios.
NSTL
Elsevier