Calorimetric and experimental data on AlF-bearing titanite are presented that yield thermodynamic properties of CaAlFSiO4, as well as activity-composition relations of binary titanite CaTiOSiO4-CaAlFSiO4. The heat capacity of synthetic CaAlFSiO4 was measured with differential scanning calorimetry between 170 and 850 K: CP=689.96-0.38647T+2911300T-2-8356.1T-0.5+0.00016179T2 Based on low-temperature heat capacity calculations with lattice vibrational theory (Debye model), the calorimetric entropy of CaAlFSiO4 can be expected to lie between 104.7 and 118.1 J mol-1 K-1. The temperature of the P21/a to A2/a phase change was determined calorimetrically for a titanite with XAl=0.09 (Ttransition=390 K). The decrease of the transition temperature at a rate of about 11 K per mol% CaAlFSiO4 is in good agreement with previous TEM investigations. The displacement of the reaction anorthite + fluorite = CaAlFSiO4 in the presence of CaTiOSiO4 was studied with high P-T experiments. Titanite behaves as a non-ideal, symmetrical solid-solution. The thermodynamic properties of CaAlFSiO4 consistent with a multi-site mixing model are: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBam % XvP5wqSXMqHnxAJn0BKvguHDwzZbqegm0B1jxALjhiov2Daebbnrfi % fHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr0xc9pk % 0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9 % Fve9Ff0dmeaabaqaciaacaGaaeqabaWaaeaaeaaakeaafaqaaiWaca % aabaGaeeyrauKaeeOBa4MaeeiDaqNaeeiAaGMaeeyyaeMaeeiBaWMa % eeiCaaNaeeyEaKNaeeiiaaIaee4Ba8MaeeOzayMaeeiiaaIaeeOzay % Maee4Ba8MaeeOCaiNaeeyBa0MaeeyyaeMaeeiDaqNaeeyAaKMaee4B % a8MaeeOBa4MaeeiiaaIaeeikaGIaeeyzauMaeeiBaWMaeeyzauMaee % yBa0MaeeyzauMaeeOBa4MaeeiDaqNaee4CamNaeeykaKIaeeiiaaIa % emizaq2aaSbaaSqaaiabdAgaMbqabaGccqWGibasdaahaaWcbeqaai % abicdaWaaaaOqaaiabg2da9iabgkHiTiabikdaYiabiEda3iabisda % 0iabicdaWiabc6caUiabiIda4iabgglaXkabiodaZiabc6caUiabic % daWiabbccaGiabbUgaRjabbQeakjabb2gaTjabb+gaVjabbYgaSnaa % CaaaleqabaGaeyOeI0IaeGymaedaaaGcbaGaee4uamLaeeiDaqNaee % yyaeMaeeOBa4MaeeizaqMaeeyyaeMaeeOCaiNaeeizaqMaeeiiaaIa % ee4CamNaeeiDaqNaeeyyaeMaeeiDaqNaeeyzauMaeeiiaaIaeeyzau % MaeeOBa4MaeeiDaqNaeeOCaiNaee4Ba8MaeeiCaaNaeeyEaKNaeeii % aaIaee4uam1aaWbaaSqabeaacqqGWaamaaaakeaacqqG9aqpcqqGXa % qmcqqGWaamcqqG0aancqqGUaGlcqqG5aqocqGHXcqScqqGXaqmcqqG % UaGlcqqGXaqmcqqGGaaicqqGkbGscqqGTbqBcqqGVbWBcqqGSbaBda % ahaaWcbeqaaiabgkHiTiabigdaXaaakiabbUealnaaCaaaleqabaGa % eyOeI0IaeGymaedaaaGcbaGaeeyta0KaeeyyaeMaeeOCaiNaee4zaC % MaeeyDauNaeeiBaWMaeeyzauMaee4CamNaeeiiaaIaeeiCaaNaeeyy % aeMaeeOCaiNaeeyyaeMaeeyBa0MaeeyzauMaeeiDaqNaeeyzauMaee % OCaiNaeeiiaaYaamWaaeaacqWGxbWvdaWgaaWcbaGaemisaG0aaWba % aWqabeaacqGHsislaaaaleqaaOGaeeivaqLaem4vaC1aaSbaaSqaai % abdohaZbqabaaakiaawUfacaGLDbaaaeaacqGH9aqpcqaIXaqmcqaI % ZaWmcqGGUaGlcqaI2aGncqGHXcqScqaIWaamcqGGUaGlcqaI0aanca % aMe8UaeeOsaOKaeeyBa0Maee4Ba8MaeeiBaW2aaWbaaSqabeaacqGH % sislcqaIXaqmaaaaaaaa!E403!
Enthalpy of formation (elements) dfH0
amp; = - 2740.8 ±3.0kJmol - 1
Standard state entropy S0
amp; = 104.9 ±1.1 Jmol - 1 K - 1
Margules parameter [ WH- TWs ]
WV) was determined from the excess volume of mixing based on XRD measurements (214ᆦ J mol-1 kbar-1), as well as refined from the piston-cylinder experimental results (198뀺 J mol-1 kbar-1), demonstrating consistency between crystal structure data and thermodynamic properties. The stability of AlF-bearing titanite Ca(Ti,Al)(O,F)SiO4 was investigated by thermodynamic modelling in the system Ca-Al-Si-Ti-O-F-H-C and subsystems. The petrogenetic grids are in good agreement with natural mineral assemblages, in that very Al-rich titanite (XAl>0.65ǂ.15) is generally absent because it is either unstable with respect to other phases, or its stability field lies outside the P-T conditions realised on Earth. The grids explain both the predominant occurrence of natural Al-rich titanite at high metamorphic grade such as eclogite facies conditions, as well as its scarcity in blueschist facies rocks. Wide spacing of the Al-isopleths for titanite of many high-grade assemblages prevents their use as geobarometers or thermometers. The instability of end-member CaAlFSiO4 with respect to other phases in most assemblages modelled here is consistent with the hypothesis that the presence of structural stresses in the crystal lattice of CaAlFSiO4 influences its thermodynamic stability. The titanite structure is not well suited to accommodate Al and F instead of Ti and O, causing the relatively high Gibbs free energy of CaAlFSiO4, manifested in its standard state properties. Thus, the increasing amount of CaAlFSiO4 along the binary join is the reason why titanite with XAl>0.65ǂ.15 becomes unstable in most petrogenetic grids presented here. The compositional limit of natural titanite (XAlƸ.54) probably reflects the point beyond which the less stable end member begins to dominate the solid-solution, affecting both crystal structure and thermodynamic stability. 相似文献
Neogene alkaline basaltic volcanic fields in the western Pannonian Basin, Hungary, including the Bakony–Balaton Highland and the Little Hungarian Plain volcanic fields are the erosional remnants of clusters of small-volume, possibly monogenetic volcanoes. Moderately to strongly eroded maars, tuff rings, scoria cones, and associated lava flows span an age range of ca. 6 Myr as previously determined by the K/Ar method. High resolution 40Ar/39Ar plateau ages on 18 samples have been obtained to determine the age range for the western Pannonian Basin Neogene intracontinental volcanic province. The new 40Ar/39Ar age determinations confirm the previously obtained K/Ar ages in the sense that no systematic biases were found between the two data sets. However, our study also serves to illustrate the inherent advantages of the 40Ar/39Ar technique: greater analytical precision, and internal tests for reliability of the obtained results provide more stringent constraints on reconstructions of the magmatic evolution of the volcanic field. Periods of increased activity with multiple eruptions occurred at ca. 7.95 Ma, 4.10 Ma, 3.80 Ma and 3.00 Ma. 相似文献
In the formation of zeolites by hydrothermal alteration volcanic glasses are the starting material in most cases. The experiments aimed at demonstrating in what way the chemistry of the volcanic glass influences:
the alteration rate of the volcanic glass to zeolites,
the kind of zeolites being formed and their formation conditions.
Three volcanic glasses were used, a basaltic, a phonolitic, and a rhyolitic one. The experimental conditions were as similar as possible to the natural alteration conditions. Solutions being used: H2O dist (pH ～5.5), 0.01 n NaOH (pH ～10.5), and solutions of similar chemistry to the natural ones. The temperatures were 180 °, 200 °, 250 ° C. The experiments were carried out both in closed and in open systems. The experimental results show a difference in the alteration rate and in the zeolites being formed between the basaltic and the phonolitic glasses on the one hand and the rhyolitic one on the other. In case of the closed system the SiO2-poor volcanic glasses react more rapidly than the SiO2-rich one. The zeolites being formed are chabazite, phillipsite, analcime respectively mordenite, analcime. In case of the open system the influence of the chemistry of the volcanic glass on the alteration rate and the zeolite being formed is less significant. Which zeolite is formed at a given temperature depends on: the chemistry of the starting material, the chemistry of the reacting solution and wether there is a closed or an open system. 相似文献
We present results of analyses on a sediment core from Lake Karakul, located in the eastern Pamir Mountains, Tajikistan. The core spans the last ~29 cal ka. We investigated and assessed processes internal and external to the lake to infer changes in past moisture availability. Among the variables used to infer lake-external processes, high values of grain-size end-member (EM) 3 (wide grain-size distribution that reflects fluvial input) and high Sr/Rb and Zr/Rb ratios (coinciding with coarse grain sizes), are indicative of moister conditions. High values in EM1, EM2 (peaks of small grain sizes that reflect long-distance dust transport or fine, glacially derived clastic input) and TiO2 (terrigenous input) are thought to reflect greater influence of dry air masses, most likely of Westerly origin. High input of dust from distant sources, beginning before the Last Glacial Maximum (LGM) and continuing to the late glacial, reflects the influence of dry Westerlies, whereas peaks in fluvial input suggest increased moisture availability. The early to early-middle Holocene is characterised by coarse mean grain sizes, indicating constant, high fluvial input and moister conditions in the region. A steady increase in terrigenous dust and a decrease in fluvial input from 6.6 cal ka BP onwards points to the Westerlies as the predominant atmospheric circulation through to present, and marks a return to drier and even arid conditions in the area. Proxies for productivity (TOC, TOC/TN, TOCBr), redox potential (Fe/Mn) and changes in the endogenic carbonate precipitation (TIC, δ18OCarb) indicate changes within the lake. Low productivity characterised the lake from the late Pleistocene until 6.6 cal ka BP, and increased rapidly afterwards. Lake level remained low until the LGM, but water depth increased to a maximum during the late glacial and remained high into the early Holocene. Subsequently, the water level decreased to its present stage. Today the lake system is mainly climatically controlled, but the depositional regime is also driven by internal limnogeological processes. 相似文献
Monitoring during three meteorologically different spring seasons in 2012, 2013, and 2014 revealed that temperature increase in spring, which influences spring lake mixing duration, markedly affected nutrient availability and diatom deposition in a sediment trap close to the bottom of deep Tiefer See, NE Germany. Deposition of Stephanodiscus taxa and small Cyclotella taxa was much higher after late ice out and a deep, short lake mixing period in spring 2013, compared to that after gradual warming and lengthy lake mixing periods in spring 2012 and 2014, when only brief or marginal ice cover occurred. Availability of dissolved Si and P was 33 and 20 % higher, respectively, in 2013 compared to 2014. The observed relation between high (low) diatom deposition and short (lengthy) mixing duration in spring was applied to varved sediments deposited between AD 1924 and 2008. Low detrital Si content in trapped material and a sediment core enabled use of µXRF-counts of Si as a proxy for diatom silica. The spring mixing duration for 1951–2008 was derived from FLake-model calculations. The spring warming duration related to lake mixing was approximated from air temperatures for 1924–2008 using the dates when daily mean air temperature exceeded 5 °C (start) and 10 °C (end). Diatom silica deposition showed a significant (p < 0.0001) inverse linear relationship with the modeled spring mixing duration (R2 = 0.36) and the spring warming duration (R2 = 0.28). In both cases, the relationship is strengthened when data from the period of low diatom production (1987–2005) is excluded (R2 = 0.59 and R2 = 0.35). Part of this low diatom production is related to external nutrient supply that favored growth of cyanobacteria at the expense of diatoms. This approach shows that diatom Si deposition was strongly influenced by the availability of light and nutrients, related to the duration of lake mixing and warming in spring, during most of the studied period. The remaining unexplained variability, however, indicates that additional factors influence Si deposition. Further tests in other deep, temperate lakes are necessary to verify if this relation is a common feature and consequently, if diatom Si can be used as a proxy for spring mixing duration in such lakes. 相似文献
Manganese‐ and iron‐rich materials are of major geoscientific and economic interest, many of which contain microscopic features that provide valuable information. To obtain accurate results, a homogeneous microanalytical reference material for calibration is needed. Several researchers have used the Mn‐ and Fe‐rich RMs, JMn‐1, NOD‐A‐1, NOD‐P‐1 and FeMn‐1, for this purpose; therefore, they were tested in this study to determine their suitability for microanalysis. Their homogeneity was investigated by laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) with two different types of lasers (nano‐ and femtosecond), with spot and line scan analyses and with different operating parameters, such as spot size, pulse repetition rate and fluence. As the established manganese nodule RMs revealed inhomogeneities for picogram to microgram test portions, we also investigated the new synthetic Fe‐ and Mn‐rich RM, FeMnOx‐1. FeMnOx‐1 was found to be homogeneous for large (ø 40 μm: 2% RSD repeatability) and small (ø 8–10 μm: 10% RSD repeatability) spot sizes. This homogeneity is in the range of the homogeneous NIST SRM 610 and GSE‐1G reference glasses. Furthermore, FeMnOx‐1 revealed a large‐scale homogeneity within uncertainties of a few per cent, using test portions in the ng range, when measuring four individual mounts of this material. 相似文献
Homogeneity, mass fractions of about forty trace elements and Sr isotope composition of Ca carbonate reference materials (RMs) between original and nano‐powdered pellets are compared. Our results using nanosecond and femtosecond LA‐(MC)‐ICP‐MS show that the nano‐pellets of the RMs MACS‐3NP, JCp‐1NP and JCt‐1NP are about a factor of 2–3 more homogeneous than the original samples MACS‐3, JCp‐1 and JCt‐1, and are therefore much more suitable for microanalytical purposes. With the exception of Si, the mass fractions of the synthetic RM MACS‐3 agree with its fine‐grained analogue MACS‐3NP. Very small, but significant, differences between original and nano‐pellets are observed in the RMs JCp‐1 and JCt‐1 for some trace elements with very low contents, indicating the need for re‐certification. Strontium mass fractions in the analysed RMs are high (1500–7000 mg kg?1), and their isotope compositions determined by LA‐MC‐ICP‐MS in the original and the nano‐pellets agree within uncertainty limits. 相似文献
A calibration data set of 51 surface sediment samples from Lake Donggi Cona on the northeastern Tibetan Plateau was investigated
to study the relationship between sub-fossil ostracod assemblages and water depth. Samples were collected over a depth range
from 0.6 to 80 m. A total of 16 ostracod species was identified from the lake with about half of the species restricted to
the Tibetan Plateau and its adjacent mountain ranges and poorly known in terms of ecological preferences, and the other half
displaying a mainly Holarctic distribution. Living macrophytes and macroalgae were recorded in Lake Donggi Cona down to a
depth of about 30 m, and bivalve (Pisidium cf. zugmayeri) and gastropod (Gyraulus, Radix) shells were found down to depths of 43 and 48 m, respectively. The ostracod-water-depth relationship was assessed by multivariate
statistical analysis and ostracod-based transfer functions for water depth were constructed. Weighted averaging partial least
squares (WA-PLS) regression provided the best model with a coefficient of determination r2 of 0.91 between measured and ostracod-inferred water depth, a root mean square error of prediction of 8% and a maximum bias
of 10.6% of the gradient length, as assessed by leave-one-out cross-validation. Our results show the potential of ostracods
as palaeo-depth indicators in appropriate settings. However, transfer-function applications using fossil ostracod assemblages
for palaeo-depth estimations require a thorough understanding of the palaeolimnological conditions of lakes and therefore
detailed multi-proxy analysis to avoid misinterpretation of ostracod-based inferences. 相似文献
