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1.
The Quaternary stratigraphy of the Alpine Foreland consists of distinct terrace levels, which have been assigned to four morphostratigraphic units: Höhere (Higher) Deckenschotter, Tiefere (Lower) Deckenschotter, Hochterrasse (High Terrace) and Niederterrasse (Lower Terrace). Here, we focus on the terrace gravels at Hohle Gasse, SSE of Pratteln near Basel, which are mapped as Tiefere Deckenschotter. Petrographic and morphometric data established from clasts allowed to infer the transport mechanisms and sources of the gravels. Sedimentological analyses indicate that the gravels were transported by a braided river and deposited in a distal glaciofluvial setting. In addition, it can be shown that the majority of the clasts display multiple reworking and only a minority maintained a distinct glaciofluvial shape. Cosmogenic multi-isotope dating using 10Be and 36Cl allowed direct dating of the sediments at the study site. A depth-profile age of \(2 70_{ - 1 90}^{ + 8 30}\) ka for 10Be was achieved for the deposits at Hohle Gasse. Unfortunately, no age could be modelled from the 36Cl concentrations as the blank correction was too high. Furthermore, this age proves that the studied terrace level should be assigned to the morphostratigraphic unit Hochterrasse.  相似文献   

2.
Magnesium silicate perovskite is the predominant phase in the Earth’s lower mantle, and it is well known that incorporation of iron has a strong effect on its crystal structure and physical properties. To constrain the crystal chemistry of (Mg, Fe)SiO3 perovskite more accurately, we synthesized single crystals of Mg0.946(17)Fe0.056(12)Si0.997(16)O3 perovskite at 26 GPa and 2,073 K using a multianvil press and investigated its crystal structure, oxidation state and iron-site occupancy using single-crystal X-ray diffraction and energy-domain Synchrotron Mössbauer Source spectroscopy. Single-crystal refinements indicate that all iron (Fe2+ and Fe3+) substitutes on the A-site only, where \( {\text{Fe}}^{ 3+ } /\Upsigma {\text{Fe}}\sim 20\,\% \) based on Mössbauer spectroscopy. Charge balance likely occurs through a small number of cation vacancies on either the A- or the B-site. The octahedral tilt angle (Φ) calculated for our sample from the refined atomic coordinates is 20.3°, which is 2° higher than the value calculated from the unit-cell parameters (a = 4.7877 Å, b = 4.9480 Å, c = 6.915 Å) which assumes undistorted octahedra. A compilation of all available single-crystal data (atomic coordinates) for (Mg, Fe)(Si, Al)O3 perovskite from the literature shows a smooth increase of Φ with composition that is independent of the nature of cation substitution (e.g., \( {\text{Mg}}^{ 2+ } - {\text{Fe}}^{ 2+ } \) or \( {\text{Mg}}^{ 2+ } {\text{Si}}^{ 4+ } - {\text{Fe}}^{ 3+ } {\text{Al}}^{ 3+ } \) substitution mechanism), contrary to previous observations based on unit-cell parameter calculations.  相似文献   

3.
We investigated the dissolved major elements, $ {}^{87}{\text{Sr/}}{}^{86}{\text{Sr}},\;\delta {}^{34}{\text{S}}_{{\text{SO}}_{\text{4}} } ,\;{\text{and}}\;\delta {}^{18}{\text{O}}_{{\text{SO}}_{\text{4}} } $ composition of the Min Jiang, a headwater tributary of the Chang Jiang (Yangtze River). A forward calculation method was applied to quantify the relative contribution to the dissolved load from rain, evaporite, carbonate, and silicate reservoirs. Input from carbonate weathering dominated the major element composition (58–93%) and that from silicate weathering ranged from 2 to 18% in unperturbed Min Jiang watersheds. Most samples were supersaturated with respect to calcite, and the CO2 partial pressures were similar to or up to ～5 times higher than atmospheric levels. The Sr concentrations in our samples were low (1.3–2.5 μM) with isotopic composition ranging from 0.7108 to 0.7127, suggesting some contribution from felsic silicates. The Si/(Na* + K) ratios ranged from 0.5 to 2.5, which indicate low to moderate silicate weathering intensity. The $ \delta {}^{34}{\text{S}}_{{\text{SO}}_{\text{4}} } \;{\text{and}}\;\delta {}^{18}{\text{O}}_{{\text{SO}}_{\text{4}} } $ for five select samples showed that the source of dissolved sulfate was combustion of locally consumed coal. The silicate weathering rates were 23–181 × 103 mol/km2/year, and the CO2 consumption rates were 31–246 × 103 mol/km2/year, which are moderate on a global basis. Upon testing various climatic and geomorphic factors for correlation with the CO2 consumption rate, the best correlation coefficients found were with water temperature (r 2 = 0.284, p = 0.009), water discharge (r 2 = 0.253, p = 0.014), and relief (r 2 = 0.230, p = 0.019).  相似文献   

4.
The combined Rhone and Aare Glaciers presumably reached their last glacial maximum (LGM) extent on the Swiss Plateau prior to 24 ka. Two well-preserved, less extensive moraine stades, the Gurten and Bern Stade, document the last deglaciation of the Aare Valley, yet age constraints are very scarce. In order to establish a more robust chronology for the glacial/deglacial history of the Aare Valley, we applied 10Be surface exposure dating on eleven boulders from the Gurten and Bern Stade. Several exposure ages are of Holocene age and likely document post-depositional processes, including boulder toppling and quarrying. The remaining exposure ages, however yield oldest ages of 20.7 ± 2.2 ka for the Gurten Stade and 19.0 ± 2.0 ka for the Bern Stade. Our results are in good agreement with published chronologies from other sites in the Alps.  相似文献   

5.
Protracted pre-eruptive zircon residence is frequently detected in continental rhyolites and can conflict with thermal models, indicating briefer magma cooling durations if scaled to erupted volumes. Here, we present combined U-Th and (U-Th)/He zircon ages from the Acigöl rhyolite field (Central Anatolia, Turkey), which is part of a Quaternary bimodal volcanic complex. Unlike other geochronometers, this approach dates crystallization and eruption on the same crystals, allowing for internal consistency testing. Despite the overall longevity of Acigöl rhyolite volcanism and systematic trends of progressive depletion in compatible trace elements and decreasing zircon saturation temperatures, we find that zircon crystallized in two brief pulses corresponding to eruptions in the eastern and western part of the field during Middle and Late Pleistocene times, respectively. For Late Pleistocene zircon, resolvable differences exist between interior (average: 30.7 ± 0.9 ka; 1σ error) and rim (21.9 ± 1.3 ka) crystallization ages. These translate into radial crystal growth rates of ~10?13 to 10?14 cm/s, broadly consistent with those constrained by diffusion experiments. Rim crystallization and (U-Th)/He eruption ages (24.2 ± 0.4 ka) overlap within uncertainty. Evidence for brief zircon residence at Acigöl contrasts with many other rhyolite fields, suggesting that protracted zircon crystallization in, or recycling from, long-lived crystal mushes is not ubiquitous in continental silicic magma systems. Instead, the span of pre-eruptive zircon ages is consistent with autochthonous crystallization in individual small-volume magma batches that originated from basaltic precursors.  相似文献   

6.
The Borgulikan ore field is localized in the west of the Umlekan-Ogodzha volcanoplutonic belt made up of various igneous (upper-Amur granite-granodiorite (140–134 Ma), Burunda monzodiorite-granodiorite (130–127 Ma), and Taldan andesite (127–123 Ma)) and superposed (Early Cretaceous Gal’ka trachybasalt-rhyolite (119–115 Ma) and Late Cretaceous trachybasalt-trachyandesite (97–94 Ma)) complexes. 40Ar/39Ar dating of porphyry intrusions breaking through the Taldan volcanic complex and associated with Cu-Mo-(Au) mineralization yielded the following ages: early (dark) “pre-ore” quartz monzodiorite porphyrites — 125.8±0.7 Ma (groundmass) and 125.2±1.8 Ma (biotite phenocrysts); late (cream) “syn-ore” quartz monzodiorite porphyrites — 122.6±0.7 Ma (biotite phenocrysts). In age and many geochemical features the quartz monzodiorite porphyrites are close to the Taldan complex volcanics. Both of these rocks seem to belong to the same volcanoplutonic association.  相似文献   

7.
The crystal chemistry of a ferroaxinite from Colebrook Hill, Rosebery district, Tasmania, Australia, was investigated by electron microprobe analysis in wavelength-dispersive mode, inductively coupled plasma–atomic emission spectroscopy (ICP–AES), 57Fe Mössbauer spectroscopy and single-crystal neutron diffraction at 293 K. The chemical formula obtained on the basis of the ICP–AES data is the following: \( ^{X1,X2} {\text{Ca}}_{4.03} \,^{Y} \left( {{\text{Mn}}_{0.42} {\text{Mg}}_{0.23} {\text{Fe}}^{2 + }_{1.39} } \right)_{\varSigma 2.04} \,^{Z1,Z2} \left( {{\text{Fe}}^{3 + }_{0.15} {\text{Al}}_{3.55} {\text{Ti}}_{0.12} } \right)_{\varSigma 3.82} \,^{T1,T2,T3,T4} \left( {{\text{Ti}}_{0.03} {\text{Si}}_{7.97} } \right)_{\varSigma 8} \,^{T5} {\text{B}}_{1.96} {\text{O}}_{30} \left( {\text{OH}} \right)_{2.18} \). The 57Fe Mössbauer spectrum shows unambiguously the occurrence of Fe2+ and Fe3+ in octahedral coordination only, with Fe2+/Fe3+ = 9:1. The neutron structure refinement provides a structure model in general agreement with the previous experimental findings: the tetrahedral T1, T2, T3 and T4 sites are fully occupied by Si, whereas the T5 site is fully occupied by B, with no evidence of Si at the T5, or Al or Fe3+ at the T1–T5 sites. The structural and chemical data of this study suggest that the amount of B in ferroaxinite is that expected from the ideal stoichiometry: 2 a.p.f.u. (for 32 O). The atomic distribution among the X1, X2, Y, Z1 and Z2 sites obtained by neutron structure refinement is in good agreement with that based on the ICP–AES data. For the first time, an unambiguous localization of the H site is obtained, which forms a hydroxyl group with the oxygen atom at the O16 site as donor. The H-bonding scheme in axinite structure is now fully described: the O16–H distance (corrected for riding motion effect) is 0.991(1) Å and an asymmetric bifurcated bonding configuration occurs, with O5 and O13 as acceptors [i.e. with O16···O5 = 3.096(1) Å, H···O5 = 2.450(1) Å and O16–H···O5 = 123.9(1)°; O16···O13 = 2.777(1) Å, H···O13 = 1.914(1) Å and O16–H···O13 = 146.9(1)°].  相似文献   

8.
The Campi Flegrei volcanic district (Naples region, Italy) is a 12-km-wide, restless caldera system that has erupted at least six voluminous ignimbrites during the late Pleistocene, including the >300 km3 Campanian ignimbrite (CI) which originated from the largest known volcanic event of the Mediterranean region. The Breccia Museo (BM), a petrologically heterogeneous and stratigraphically complex volcanic deposit extending over 200 km2 in close proximity to Campi Flegrei, has long remained contentious regarding its age and stratigraphic relation to the CI. Here, we present crystallization and eruption ages for BM plutonic ejecta clasts that were determined via uranium decay series and (U–Th)/He dating of zircon, respectively. Despite mineralogical and textural heterogeneity of these syenitic clasts, their U–Th zircon rim crystallization ages are indistinguishable with an average age of 49.7 ± 2.5 ka (2σ errors; mean square of weighted deviates MSWD = 1.2; n = 34). A subset of these crystals was used to obtain disequilibrium-corrected (U–Th)/He zircon ages which average 41.7 ± 1.8 ka (probability of fit P = 0.54; n = 15). This age closely overlaps with published CI 40Ar/39Ar eruption ages (40.6 ± 0.1 ka) after recalibration to recently revised flux monitor ages. Concordant eruption ages for BM and CI agree with previous chemostratigraphic and paleomagnetic correlations, suggesting their origin from the same eruption. However, they are at variance with recalibrated 40Ar/39Ar ages which have BM postdate CI by 3 ± 1 ka. BM syenites show similar geochemical and Sr–Nd isotopical features of pre-caldera rocks erupted between 58 and 46 ka, but are distinctive from subsequent caldera-forming magmas. Energy-constrained assimilation and fractional crystallization modeling of Nd–Sr isotopic data suggests that pre-caldera magmas formed a carapace of BM-type intrusions in a mid-crust magma chamber (≥8 km depth) shielding the younger CI magma from contamination by Hercynian basement wall rocks. An ~41–50 ka hiatus in crystallization ages implies rapid solidification of these pre-CI intrusions. This argues against protracted pre-eruptive storage of a large volume of CI magma at shallow crustal levels.  相似文献   

9.
To assess the effects of river damming on dissolved inorganic carbon in the Jialing River, a total of 40 water samples, including inflow, outflow, and stratified water in four cascade reservoirs (Tingzikou, Xinzheng, Dongxiguan, Caojie) were collected in January and July, 2016. The major cations, anions, and δ13CDIC values were analyzed. It was found that the dissolved compositions are dominated by carbonate weathering, while sulfuric acids may play a relatively important role during carbonate weathering and increasing DIC concentration. Different reservoirs had variable characteristics of water physiochemical stratification. The DIC concentrations of reservoir water were lower in summer than those in winter due to the dilute effects and intensive aquatic photosynthesis, as well as imported tributaries. The δ13CDIC values in Tingzikou Reservoir were higher during summer than those in winter, which indicated that intensive photosynthesis increased the δ13CDIC values in residual water, but a similar trend was not obvious in other reservoirs. Except for in Xinzheng Reservoir, the δ13CDIC values in inflow and outflow reservoir water were lower than those in the surface water of stratified sampling in summer. For stratified sampling, it could be found that, in summer, the Tingzikou Reservoir δ13CDIC values significantly decreased with water depth due to the anaerobic breakdown of organic matter. The significant correlation (p < 0.01 or 0.05) between the DIC concentrations, the δ13CDIC values and anthropogenic species (Na++K+, Cl–, \({\text{SO}}_{4}^{2 - }\)and \({\text{NO}}_{3}^{ - }\)) showed that the isotope composition of DIC can be a useful tracer of contaminants. In total, Tingzikou Reservoir showed lacustrine features, Xinzheng Reservoir and Dongxiguan Reservoir had “transitional” features, and Caojie Reservoir had a total of “fluvial” features. Generally, cascade reservoirs in the Jialing River exhibited natural river features rather than typical lake features due to characteristics of reservoir water in physiochemical stratification, spatiotemporal variations of DIC concentrations and isotopic compositions. It is evident that the dissolved inorganic carbon dynamics of natural rivers had been partly remolded by dam building.  相似文献   

10.
The diffusion of Ni and Co was measured at atmospheric pressure in synthetic monocrystalline forsterite (Mg2SiO4) from 1,200 to 1,500 °C at the oxygen fugacity of air, along [100], with the activities of SiO2 and MgO defined by either forsterite + periclase (fo + per buffer) or forsterite + protoenstatite (fo + en buffer). Diffusion profiles were measured by three methods: laser-ablation inductively-coupled-plasma mass-spectrometry, nano-scale secondary ion mass spectrometry and electron microprobe, with good agreement between the methods. For both Ni and Co, the diffusion rates in protoenstatite-buffered experiments are an order of magnitude faster than in the periclase-buffered experiments at a given temperature. The diffusion coefficients D M (M = Ni or Co) for the combined data set can be fitted to the equation:
$$\log \,D_{\text{M}} \,\left( {{\text{in}}\,{\text{m}}^{2} \,{\text{s}}^{ - 1} } \right) = - 6.77( \pm 0.33) + \Delta E_{\text{a}} (M)/RT + 2/3\log a_{{SiO_{2} }}$$
with Ea(Ni) = ? 284.3 kJ mol?1 and Ea(Co) = ? 275.9 kJ mol?1, with an uncertainty of ±10.2 kJ mol?1. This equation fits the data (24 experiments) to ±0.1 in log D M. The dependence of diffusion on \(a_{{{\text{SiO}}_{2} }}\) is in agreement with a point-defect model in which Mg-site vacancies are charge-balanced by Si interstitials. Comparative experiments with San Carlos olivine of composition Mg1.8Fe0.2SiO4 at 1,300 °C give a slightly small dependence on \(a_{{{\text{SiO}}_{2} }}\), with D \(\propto\) (\(a_{{{\text{SiO}}_{2} }}^{0.5}\)), presumably because the Mg-site vacancies increase with incorporation of Fe3+ in the Fe-bearing olivines. However, the dependence on fO2 is small, with D \(\propto\) (fO2)0.12±0.12. These results show the necessity of constraining the chemical potentials of all the stoichiometric components of a phase when designing diffusion experiments. Similarly, the chemical potentials of the major-element components must be taken into account when applying experimental data to natural minerals to constrain the rates of geological processes. For example, the diffusion of divalent elements in olivine from low SiO2 magmas, such as kimberlites or carbonatites, will be an order of magnitude slower than in olivine from high SiO2 magmas, such as tholeiitic basalts, at equal temperatures and fO2.
  相似文献   

11.
Unlike the studies in small parcels by systematic measurements, the spatial variability of soil properties is expected to increase in those over relatively large areas or scales. Spatial variability of soil hydraulic conductivity (K h) is of significance for the environmental processes, such as soil erosion, plant growth, transport of the plant nutrients in a soil profile and ground water levels. However, its variability is not much and sufficiently known at basin scale. A study of testing the performance of cokriging of K h compared with that of kriging was conducted in the catchment area of Sarayköy II Irrigation Dam in Cank?r?, Turkey. A total of 300 soil surface samples (0–10 cm) were collected from the catchment with irregular intervals. Of the selected soil properties, because the water-stable aggregates (WSA) indicated the highest relationship with the hydraulic conductivity by the Pearson correlation analysis, it is used as an auxiliary variable to predict K h by the cokriging procedure. In addition, the sampling density was reduced randomly to n = 175, n = 150, n = 75 and n = 50 for K h to determine if the superiority of cokriging over kriging would exist. Statistically, the results showed that all reduced K h was as good as the complete K h when its auxiliary relations with WSA were used in cokriging. Particularly, the results of the “Relative Reduction in MSE” (RMSE) revealed that the reduced data set of n = 75 produced the most accurate map than the others. In this basin-scaled study, there was a clear superiority of the cokriging procedure by the reduction in data although a very undulating topography and topographically different aspects, two different land uses with non-uniform vegetation density, different parent materials and soil textures were present in the area. Hence, using the statistically significant auxiliary relationship between K h and WSA might bring about a very useful data set for watershed hydrological researches.  相似文献   

12.
An “on-line” mixing system has been developed and evaluated for continuous oxygen isotope exchange between gas-phase CO2 and liquid water. The system is composed of three basic parts: equipment and materials used to introduce water and gas into a mixing reservoir, the mixing and exchange reservoir, and a vessel used to separate gas and water phases exiting the system. A series of experiments were performed to monitor the isotope exchange process over a range of temperatures (5–40 °C) and CO2 partial pressures (202–15,200 Pa). Isotopic exchange was evaluated using CO2 having δ18O values of 30.4 and 37.8 ‰ and waters of two distinct oxygen isotope compositions (?6.5 to ?5 and 6 to 7.5 ‰). Isotope ratios were determined by isotope ratio mass spectrometry and cavity ring-down spectroscopy. CO2 did not reach oxygen isotope equilibrium under the conditions described here. However, oxygen isotope exchange rate constants were determined at different temperatures and regressed to yield the expression k (h?1) = 0.020 × T (°C) + 0.28. Using this expression, the residence time required to reach oxygen isotope equilibrium may be estimated for a given set of environmental conditions (e.g., δ18O value of water, temperature). System parameters can be modified to achieve a specific δ18O value for CO2. Consequently, the exchange system described here has the ability to deliver a constant flow of CO2 at a desired oxygen isotope composition. This ability is attractive for a variety of applications such as experiments that utilize flow-through reactors and environmental chambers or require static chemical conditions.  相似文献   

13.
In order to evaluate the effect of trace and minor elements (e.g., P, Y, and the REEs) on the high-temperature solubility of Ti in zircon (zrc), we conducted 31 experiments on a series of synthetic and natural granitic compositions [enriched in TiO2 and ZrO2; Al/(Na + K) molar ~1.2] at a pressure of 10 kbar and temperatures of ~1,400 to 1,200 °C. Thirty of the experiments produced zircon-saturated glasses, of which 22 are also saturated in rutile (rt). In seven experiments, quenched glasses coexist with quartz (qtz). SiO2 contents of the quenched liquids range from 68.5 to 82.3 wt% (volatile free), and water concentrations are 0.4–7.0 wt%. TiO2 contents of the rutile-saturated quenched melts are positively correlated with run temperature. Glass ZrO2 concentrations (0.2–1.2 wt%; volatile free) also show a broad positive correlation with run temperature and, at a given T, are strongly correlated with the parameter (Na + K + 2Ca)/(Si·Al) (all in cation fractions). Mole fraction of ZrO2 in rutile $ \left( {\mathop X\nolimits_{{{\text{ZrO}}_{ 2} }}^{\text{rt}} } \right) $ in the quartz-saturated runs coupled with other 10-kbar qtz-saturated experimental data from the literature (total temperature range of ~1,400 to 675 °C) yields the following temperature-dependent expression: $ {\text{ln}}\left( {\mathop X\nolimits_{{{\text{ZrO}}_{ 2} }}^{\text{rt}} } \right) + {\text{ln}}\left( {a_{{{\text{SiO}}_{2} }} } \right) = 2.638(149) - 9969(190)/T({\text{K}}) $ , where silica activity $ a_{{{\text{SiO}}_{2} }} $ in either the coexisting silica polymorph or a silica-undersaturated melt is referenced to α-quartz at the P and T of each experiment and the best-fit coefficients and their uncertainties (values in parentheses) reflect uncertainties in T and $ \mathop X\nolimits_{{{\text{ZrO}}_{2} }}^{\text{rt}} $ . NanoSIMS measurements of Ti in zircon overgrowths in the experiments yield values of ~100 to 800 ppm; Ti concentrations in zircon are positively correlated with temperature. Coupled with values for $ a_{{{\text{SiO}}_{2} }} $ and $ a_{{{\text{TiO}}_{2} }} $ for each experiment, zircon Ti concentrations (ppm) can be related to temperature over the range of ~1,400 to 1,200 °C by the expression: $ \ln \left( {\text{Ti ppm}} \right)^{\text{zrc}} + \ln \left( {a_{{{\text{SiO}}_{2} }} } \right) - \ln \left( {a_{{{\text{TiO}}_{2} }} } \right) = 13.84\left( {71} \right) - 12590\left( {1124} \right)/T\left( {\text{K}} \right) $ . After accounting for differences in $ a_{{{\text{SiO}}_{2} }} $ and $ a_{{{\text{TiO}}_{2} }} $ , Ti contents of zircon from experiments run with bulk compositions based on the natural granite overlap with the concentrations measured on zircon from experiments using the synthetic bulk compositions. Coupled with data from the literature, this suggests that at T ≥ 1,100 °C, natural levels of minor and trace elements in “granitic” melts do not appear to influence the solubility of Ti in zircon. Whether this is true at magmatic temperatures of crustal hydrous silica-rich liquids (e.g., 800–700 °C) remains to be demonstrated. Finally, measured $ D_{\text{Ti}}^{{{\text{zrc}}/{\text{melt}}}} $ values (calculated on a weight basis) from the experiments presented here are 0.007–0.01, relatively independent of temperature, and broadly consistent with values determined from natural zircon and silica-rich glass pairs.  相似文献   

14.
A series of natural omphacites from a wide range of P, T occurrences were investigated by electron microprobe (EMP), infrared (IR)-, Mössbauer (MS)- and optical spectroscopy in the UV/VIS spectral range (UV/VIS), secondary ion mass spectrometry (SIMS) and single crystal structure refinement by X-ray diffraction (XRD) to study the influence of hydrogen loss on valence state and site occupancies of iron. In accordance with literature data we found Fe2+ at M1 as well as at M2, and in a first approach assigned Fe3+ to M1, as indicated by MS and XRD results. Hydrogen content of three of our omphacite samples were measured by SIMS. In combination with IR spectroscopy we determined an absorption coefficient: ε i,tot = 65,000 ± 3,000 lmolH2O ?1 cm?2. Using this new ε i,tot value, we obtained water concentrations ranging from 60 to 700 ppm H2O (by weight). Hydrogen loss was simulated by stepwise heating the most water rich samples in air up to 800°C. After heat treatment the samples were analyzed again by IR, MS, UV/VIS, and XRD. Depending on the type of the OH defect, the grade of dehydration with increasing temperature is significantly different. In samples relatively poor in Fe3+ (<0.1 Fe3+ pfu), hydrogen associated with vacancies at M2 (OH bands around 3,450 cm?1) starts to leave the structure at about 550°C and is completely gone at 780°C. Hydrogen associated with Al3+ at the tetrahedral site (OH bands around 3,525 cm?1, Koch-Müller et al., Am Mineral, 89:921–931, 2004) remains completely unaffected by heat treatment up to 700°C. But all hydrogen vanished at about 775°C. However, this is different for a more Fe3+-rich sample (0.2 Fe3+ pfu). Its IR spectrum is characterized by a very intense OH band at 3,515 cm?1 plus shoulder at 3,450 cm?1. We assign this intense high-energy band to vibrations of an OH dipole associated with Fe3+ at M1 and a vacancy either at M1 or M2. OH release during heating is positively correlated with decrease in Fe2+ and combined with increase in Fe3+. That dehydration is correlated with oxidation of Fe2+ is indirectly confirmed by annealing of one sample in a gas mixing furnace at 700°C under reducing conditions keeping almost constant OH? content and giving no indication of Fe2+-oxidation. Obtained data indicate that in samples with a relatively high concentration of Fe2+ at M2 and low-water concentrations, i.e., at a ratio of Fe2+ M2/H > 10 dehydration occurs by iron oxidation of Fe2+ exclusively at the M2 site following the reaction: \( {\left[ {{\text{Fe}}^{{{\text{2 + [ M2]}}}}{\text{OH}}^{ - } } \right]} = {\left[ {{\text{Fe}}^{{{\text{3 + [ M2]}}}} {\text{O}}^{{{\text{2}} - }} } \right]} + {\text{1/2}}\;{\text{H}}_{{\text{2}}} \uparrow . \) In samples having relatively low concentration of Fe2+ at M2 but high-water concentrations, i.e., ratio of Fe2+ M2/H < 5.0 dehydration occurs through oxidation of Fe2+ at M1.  相似文献   

15.
Investigations were undertaken into the quality of surface water and groundwater bodies within the Upper Tigris Basin in Turkey to determine their suitability for potable and agricultural use. In the study area, the majority of the groundwater and surface water samples belong to the calcium–magnesium–bicarbonate type (Ca–Mg–HCO3) or magnesium–calcium–bicarbonate type (Mg–Ca–HCO3). Chemical analysis of all water samples shows that the mean cation concentrations (in mg/L) were in the order Ca2+ > Mg2+ > Na+ > K+ and that of anions are in the order \( \text{HCO}_{3}^{ - } \) > \( \text{SO}_{4}^{2 - } \) > Cl? > \( \text{CO}_{3}^{ - } \) for all groundwater and surface water samples. The Mg2+/Ca2+ ratio ranges from 0.21 to 1.30 with most of the values greater than 0.5, indicating that weathering of dolomites is dominant in groundwater. The analysis reveals that all of the samples are neutral to slightly alkaline (pH 7.0–8.7). Groundwater and surface water suitability for drinking usage was evaluated according to the World Health Organization and Turkish Standards (TSE-266) and suggests that most of the samples are suitable for drinking. Various determinants such as sodium absorption ratio, percent sodium (Na %), residual sodium carbonate and soluble sodium percentage revealed that most of the samples are suitable for irrigation. According to MH values, all of the well water samples were suitable for irrigation purposes, but 80 and 81.82% of Zillek springs and surface water samples were unsuitable. As per the PI values, the water samples from the study area are classified as Class I and Class II and are considered to be suitable for irrigation.  相似文献   

16.
We report the results of experiments designed to separate the effects of temperature and pressure from liquid composition on the partitioning of Ni between olivine and liquid, \(D_{\text{Ni}}^{\text{ol/liq}}\). Experiments were performed from 1300 to 1600 °C and 1 atm to 3.0 GPa, using mid-ocean ridge basalt (MORB) glass surrounded by powdered olivine in graphite–Pt double capsules at high pressure and powdered MORB in crucibles fabricated from single crystals of San Carlos olivine at one atmosphere. In these experiments, pressure and temperature were varied in such a way that we produced a series of liquids, each with an approximately constant composition (~12, ~15, and ~21 wt% MgO). Previously, we used a similar approach to show that \(D_{\text{Ni}}^{\text{ol/liq}}\) for a liquid with ~18 wt% MgO is a strong function of temperature. Combining the new data presented here with our previous results allows us to separate the effects of temperature from composition. We fit our data based on a Ni–Mg exchange reaction, which yields \(\ln \left( {D_{\text{Ni}}^{\text{molar}} } \right) = \frac{{ -\Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } }}{RT} + \frac{{\Delta _{r(1)} S_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } }}{R} - \ln \left( {\frac{{X_{\text{MgO}}^{\text{liq}} }}{{X_{{{\text{MgSi}}_{ 0. 5} {\text{O}}_{ 2} }}^{\text{ol}} }}} \right).\) Each subset of constant composition experiments displays roughly the same temperature dependence of \(D_{\text{Ni}}^{\text{ol/liq}}\) (i.e.,\(-\Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R\)) as previously reported for liquids with ~18 wt% MgO. Fitting new data presented here (15 experiments) in conjunction with our 13 previously published experiments (those with ~18 wt% MgO in the silicate liquid) to the above expression gives \(-\Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R\) = 3641 ± 396 (K) and \(\Delta _{r(1)} S_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R\) = ? 1.597 ± 0.229. Adding data from the literature yields \(-\Delta _{r(1)} H_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R\) = 4505 ± 196 (K) and \(\Delta _{r(1)} S_{{T_{\text{ref}} ,P_{\text{ref}} }}^{ \circ } /R\) = ? 2.075 ± 0.120, a set of coefficients that leads to a predictive equation for \(D_{\text{Ni}}^{\text{ol/liq}}\) applicable to a wide range of melt compositions. We use the results of our work to model the melting of peridotite beneath lithosphere of varying thickness and show that: (1) a positive correlation between NiO in magnesian olivine phenocrysts and lithospheric thickness is expected given a temperature-dependent \(D_{\text{Ni}}^{\text{ol/liq}} ,\) and (2) the magnitude of the slope for natural samples is consistent with our experimentally determined temperature dependence. Alternative processes to generate the positive correlation between NiO in magnesian olivines and lithospheric thickness, such as the melting of olivine-free pyroxenite, are possible, but they are not required to explain the observed correlation of NiO concentration in initially crystallizing olivine with lithospheric thickness.  相似文献   

17.
On the basis of a seven-point isochron, the RbSr whole-rock age of the Hästefjorden granite in southwestern Sweden is 1240 ± 30 Ma using a decay constant of 1.39·10?11 yr?1. The initial 87Sr/86Sr ratio is 0.712. This dating sets a lower limit for the beginning of the Dalslandian (Dal sequence) sedimentation and supports suggestions of a chronological diversity of the so-called Gothian Åmål—Kroppefjäll granite complex in western Sweden. It also invalidates correlation of the Åmål—Kroppefjäll complex as a whole with the Småland plutonics of southeastern Sweden. This proves that rocks previously considered as being formed during the “Gothian Cycle” are very different in age.  相似文献   

18.
Understanding and interpretation of ‘numbers’ produced about the depositional age of an erratic boulder by cosmogenic nuclide surface-exposure dating is important in the construction of glacial chronology. We have sampled three ‘Findlinge’ (glacially transported boulders) located on the right-lateral margin of the Aare glacier at Möschberg, Grosshöchstetten, southeast of Bern, with the aim of shedding light on this topic. The boulders have the same depositional, but different post-depositional histories: simple exposure; exhumation; and human impact. This sampling is specially selected for this study, since the boulders showing exhumation and human impact would not have been sampled in a regular surface-exposure dating application. We measured cosmogenic 10Be concentrations and calculated apparent exposure ages that are 13.6 ± 0.5, 18.1 ± 0.8, and 7.5 ± 0.4 ka, respectively. The exposure age of the first boulder reflects exhumation. The apparent exposure age of 18.1 ± 0.8 ka (erosion-corrected exposure age 19.0 ± 0.9 ka) from the second boulder correlates well with the end of the Alpine and global last glacial maximum. The third boulder shows evidence of quarrying as it is surrounded by a rim of excavation material, which is also reflected by the 7.5 ± 0.4 ka apparent exposure age. We modeled the variation of 10Be concentrations with depth down into the sediment in which the first (exhumed) boulder was once buried in, and down into the third (quarried) boulder. According to our modeling, we determined that the exhumed ‘Findling’ was buried in sediment at a depth of around 0.5 m, and around 2 m of rock was quarried from the third ‘Findling’. Our results reveal the importance of sampling for surface-exposure dating within a well defined field context, as post-depositional impacts can easily hinder exposure-dating of surfaces.  相似文献   

19.
The available experimental data on garnet-bearing-assemblages for synthetic chemical systems (MAS, FMAS, CMAS) have been used to calibrate consistent models for the Al-solubility in orthopyroxene coexisting with garnet, on the basis of equilibrium reaction Py(opx) ? Py(gt). The alternative reaction En(opx)+MgTs(opx) ? Py(gt) is discarded as it yields larger a-posteriori uncertainties. To provide a reliable equation, directly applicable to natural garnet lherzolites, each successive synthetic-system calibration is tested against Mori and Green's (1978) natural-system reequilibration data. For the MAS system, an ideal solution model with constant ΔH°, ΔV° and ΔS° based on 12-oxygen structural formulae for aluminous pyroxenes yields the best fit (GPa, K), $${\text{25,134 + 9,941 }}P - 23.177{\text{ }}T{\text{ + }}RT{\text{ ln (}}X_{{\text{Al}}}^{TB'} {\text{) = 0}}$$ . The MAS synthetic-system calibration can be directly applied to the FMAS system by adding an empirical correction term (20,835 [X Fe gt ]2) independent of either pressure and temperature. However, this correction term is not important because of the limited Fe content of mantle peridotites. When calcium is added to the MAS system, the equilibrium constant is calculated as: $$K_{{\text{CMAS}}} = {{[(1 - X_{{\text{Ca}}}^{M2} )^2 (X_{{\text{Al}}}^{TB'} )]} \mathord{\left/ {\vphantom {{[(1 - X_{{\text{Ca}}}^{M2} )^2 (X_{{\text{Al}}}^{TB'} )]} {[(1 - X_{{\text{Ca}}}^X )^3 (X_{{\text{Al}}}^Y )^2 ]}}} \right. \kern-\nulldelimiterspace} {[(1 - X_{{\text{Ca}}}^X )^3 (X_{{\text{Al}}}^Y )^2 ]}}$$ where M2 and TB′ are pyroxene sites and X and Y are garnet sites. Up to 5 GPa, X Ca X ～ and the CMAS experimental data agree well with the MAS model, but for Yamada and Takahashi's (1983) higher pressure experiments (up to 10 GPa), this no longer holds. Indeed, the garnet solid solution does not behave ideally and an asymmetric regular solution model is needed for application to the deepest natural samples available (>7GPa). Calibration based on new high pressure data yields, $$\begin{gathered} \Delta G_{{\text{CMAS}}}^{XS} = (X_{{\text{Ca}}}^X )(1 - X_{{\text{Ca}}}^X )(0.147 - X_{{\text{Ca}}}^X ) \hfill \\ {\text{ }} \cdot {\text{(6,440,535 - 1,490,654 }}P{\text{)}} \hfill \\ \end{gathered}$$ . According to tests of the inferred solution model, the CFMAS system is a good analogue of natural systems in the pressure, temperature and composition ranges covered by the natural-system reequilibration data (up to 1,500° C and 4 GPa). Simultaneous application of this thermobarometer and of the two-pyroxene mutual solubility thermometer (Bertrand and Mercier 1985) to the phases of the garnet-peridotite xenoliths from Thaba Putsoa, Lesotho, yields a refined paleogeotherm for southern Africa strongly contrasting with previous results. The “granular” nodules yield a thermal gradient of about 8 K/km characteristic of a lithospheric-type environment, whereas the “sheared” ones show a lower gradient of about 1 K/km. This is a typical geotherm expected for a steady thermal state with an inflexion point at the depth of about 160 km corresponding to the lithosphere/asthenosphere boundary.  相似文献   

20.
The phonon dispersion and thermodynamic properties of pyrope (\(\hbox {Mg}_3\hbox {Al}_2\hbox {Si}_3\hbox {O}_{12}\)) and grossular (\(\hbox {Ca}_3\hbox {Al}_2\hbox {Si}_3\hbox {O}_{12}\) ) have been computed by using an ab initio quantum mechanical approach, an all-electron variational Gaussian-type basis set and the B3LYP hybrid functional, as implemented in the Crystal program. Dispersion effects in the phonon bands have been simulated by using supercells of increasing size, containing 80, 160, 320, 640, 1280 and 2160 atoms, corresponding to 1, 2, 4, 8, 16 and 27 \(\mathbf {k}\) points in the first Brillouin zone. Phonon band structures, density of states and corresponding inelastic neutron scattering spectra are reported. Full convergence of the various thermodynamic properties, in particular entropy (S) and specific heat at constant volume (\(C_\mathrm{{V}}\)), with the number of \(\mathbf {k}\) points is achieved with 27 \(\mathbf {k}\) points. The very regular behavior of the S(T) and \(C_\mathrm{{V}}(T)\) curves as a function of the number of \(\mathbf {k}\) points, determined by high numerical stability of the code, permits extrapolation to an infinite number of \(\mathbf {k}\) points. The limiting value differs from the 27-\(\mathbf {k}\) case by only 0.40 % at 100 K for S (the difference decreasing to 0.11 % at 1000 K) and by 0.29 % (0.05 % at 1000 K) for \(C_\mathrm{{V}}\). The agreement with the experimental data is rather satisfactory. We also address the problem of the relative entropy of pyrope and grossular, a still debated question. Our lattice dynamical calculations correctly describe the larger entropy of pyrope than grossular by taking into account merely vibrational contributions and without invoking “static disorder” of the Mg ions in dodecahedral sites. However, as the computed entropy difference is found to be larger than the experimental one by a factor of 2–3, present calculations cannot exclude possible thermally induced structural changes, which could lead to further conformational contributions to the entropy.  相似文献   

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