Structure and nuclear density distribution in the cheralite—CaTh(PO4)2: studies of its behaviour under high pressure (36?GPa)     

Philippe E. Raison  Stephen Heathman  Gilles Wallez  Carmen E. Zvoriste  Denis Bykov  Ga?l Ménard  Emmanuelle Suard  Karin Popa  Nicolas Dacheux  Rudy J. M. Konings  Roberto Caciuffo 《Physics and Chemistry of Minerals》2012,39(8):685-692

The crystal structure of the cheralite—CaTh(PO₄)₂—has been revisited by neutron diffraction and its behaviour under high pressure investigated by X-ray diffraction up to 36?GPa. The neutron diffraction data at ambient pressure gave a more accurate determination of the Ca/Th cation position than previous XRD data, taking advantage that the neutron scattering lengths of calcium and thorium are of same order of magnitude. The nuclear density distribution was also determined using the maximum entropy method (MEM) confirming that the two cations are not located at the same position in the unit cell but are slightly displaced from one another along a specific direction in order to minimize the electrostatic repulsion with the surrounding phosphorus atoms. At high pressure, the compound did not show any phase transition or amorphization. From the evolution of the unit-cell volume as a function of the pressure, the zero-pressure bulk modulus B₀ and its pressure derivative B₀ ^′ have been determined by fitting the experimental compressibility curve to the Birch–Murnaghan equation of state. The results are B₀?=?140(2) GPa and B ₀ ^′ ?=?4.4(4) GPa.  相似文献   

Detection of smectites in ppm and sub-ppm concentrations using dye molecule sensors     

Marcel?Lofaj  Juraj?BujdákEmail author 《Physics and Chemistry of Minerals》2012,39(3):227-237

Methylene blue and rhodamine 6G were used as molecular sensors for the spectrophotometric titrations of the aqueous colloids of clay minerals (montmorillonite, illite and kaolinite). The dyes adsorbed on colloid particles form molecular aggregates, which exhibit spectral properties significantly different from those of dye solutions. Spectrophotometric titrations provide the most sensitive detection of smectites in aqueous colloids (sub-ppm concentrations); and the sensitivity further increases using second derivative spectroscopy. The endpoint of spectrophotometric titrations can be used for the determination of exchange capacity of the mineral in colloids and in this way to estimate its amount. The method is selective only to expandable clays, which was proven by experiments with kaolinite and illite. Spectrophotometric titrations have promising future in the analysis of clays and can be applied in many fields of geology, mineralogy, chemistry, material sciences or in industry. Its application may expand to the analysis of other nanomaterials built from charged particles and exhibiting metachromasy in the systems with organic dyes.  相似文献   

Vulnerability assessment in natural hazard and risk analysis: current approaches and future challenges   总被引：10，自引：9，他引：1  

Sven Fuchs  J?rn Birkmann  Thomas Glade 《Natural Hazards》2012,64(3):1969-1975

  相似文献   

The effect of chemical composition and oxygen fugacity on the electrical conductivity of dry and hydrous garnet at high temperatures and pressures   总被引：3，自引：0，他引：3  

Lidong?Dai  Heping?LiEmail author  Haiying?Hu  Shuangming?Shan  Jianjun?Jiang  Keshi?Hui 《Contributions to Mineralogy and Petrology》2012,163(4):689-700

The in situ electrical conductivity of hydrous garnet samples (Py₂₀Alm₇₆Grs₄–Py₇₃Alm₁₄Grs₁₃) was determined at pressures of 1.0–4.0 GPa and temperatures of 873–1273 K in the YJ-3000t apparatus using a Solartron-1260 impedance/gain-phase analyzer for various chemical compositions and oxygen fugacities. The oxygen fugacity was controlled by five solid-state oxygen buffers (Fe₂O₃ + Fe₃O₄, Ni + NiO, Fe + Fe₃O₄, Fe + FeO, and Mo + MoO₂). Experimental results indicate that within a frequency range from 10⁻² to 10⁶ Hz, electrical conductivity is strongly dependent on signal frequency. Electrical conductivity shows an Arrhenius increase with temperature. At 2.0 GPa, the electrical conductivity of anhydrous garnet single crystals with various chemical compositions (Py₂₀Alm₇₆Grs₄, Py₃₀Alm₆₇Grs₃, Py₅₆Alm₄₃Grs₁, and Py₇₃Alm₁₄Grs₁₃) decreases with increasing pyrope component (Py). With increasing oxygen fugacity, the electrical conductivity of dry Py₇₃Alm₁₄Grs₁₃ garnet single crystal shows an increase, whereas that of a hydrous sample with 465 ppm water shows a decrease, both following a power law (exponents of 0.061 and −0.071, respectively). With increasing pressure, the electrical conductivity of this hydrous garnet increases, along with the pre-exponential factors, and the activation energy and activation volume of hydrous samples are 0.7731 ± 0.0041 eV and −1.4 ± 0.15 cm³/mol, respectively. The results show that small hopping polarons ( \textFe_\textMg ^· ) \left( {{\text{Fe}}_{\text{Mg}}^{ \cdot } } \right) and protons ( \textH ^· {\text{H}}^{ \cdot } ) are the dominant conduction mechanisms for dry and wet garnet single crystals, respectively. Based on these results and the effective medium theory, we established the electrical conductivity of an eclogite model with different mineral contents at high temperatures and high pressures, thereby providing constraints on the inversion of field magnetotelluric sounding results in future studies.  相似文献   

Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions     

B?rje Dahren  Valentin R. Troll  Ulf B. Andersson  Jane P. Chadwick  Màiri F. Gardner  Kairly Jaxybulatov  Ivan Koulakov 《Contributions to Mineralogy and Petrology》2012,163(4):631-651

Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite of thermobarometric models. These include clinopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, clinopyroxene composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage in the region of 2–8 km beneath Krakatau, while existing seismic evidence points towards mid- to deep-crustal storage zone(s), at 9 and 22 km, respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7–12 km, while plagioclase records both shallow crustal (3–7 km) and sub-Moho (23–28 km) levels of crystallization. These magma storage regions coincide with well-constrained major lithological boundaries in the crust, implying that magma ascent and storage at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified a separate upper crustal (<7 km) and a lower to mid-crustal magma storage region (>7 km). Both petrological and seismic methods are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes.  相似文献   

Calcic amphiboles in calc-alkaline and alkaline magmas: thermobarometric and chemometric empirical equations valid up to 1,130°C and 2.2 GPa     

Filippo?RidolfiEmail author  Alberto?Renzulli 《Contributions to Mineralogy and Petrology》2012,163(5):877-895

The following article presents constraints of the stability of Mg-rich (Mg/(Mg + Fe²⁺) > 0.5) calcic amphibole in both calc-alkaline and alkaline magmas, testing of previous thermobarometers, and formulation of new empirical equations that take into consideration a large amount of literature data (e.g. more than one thousand amphibole compositions among experimental and natural crystals). Particular care has been taken in choosing a large number of natural amphiboles and selecting quality experimental data from literature. The final database of experimental data, composed of 61 amphiboles synthesized in the ranges of 800–1,130°C and 130–2,200 MPa, indicates that amphibole crystallization occurs in a horn-like P–T stability field limited by two increasing curves (i.e. the thermal stability and an upper limit), which should start to bend back to higher pressures. Among calcic amphiboles, magnesiohornblendes and tschermakitic pargasites are only found in equilibrium with calc-alkaline melts and crystallize at relatively shallow conditions (P up to ~1 GPa). Kaersutite and pargasite are species almost exclusively found in alkaline igneous products, while magnesiohastingsite is equally distributed in calc-alkaline and alkaline rocks. The reliability of previous amphibole applications was checked using the selected experimental database. The results of this testing indicate that none of the previous thermobarometers can be successfully used to estimate the P, T and fO₂ in a wide range of amphibole crystallization conditions. Multivariate least-square analyses of experimental amphibole compositions and physico-chemical parameters allowed us to achieve a new thermobarometric model that gives reasonably low uncertainties (T ± 23.5°C, P ± 11.5%, H₂O_melt ± 0.78wt%) for calc-alkaline and alkaline magmas in a wide range of P–T conditions (up to 1,130°C and 2,200 MPa) and ∆NNO values (±0.37 log units) up to 500 MPa. The ^AK-^[4]Al relation in amphibole can be readily used to distinguish crystals of calc-alkaline liquids from those of alkaline magmas. In addition, several chemometric equations allowing to estimate the anhydrous composition of the melts in equilibrium with amphiboles of calc-alkaline magmas were derived.  相似文献   

Phase relations of phlogopite with magnesite from 4 to 8 GPa   总被引：2，自引：2，他引：0  

Andreas?EnggistEmail author  Linglin?Chu  Robert?W.?Luth 《Contributions to Mineralogy and Petrology》2012,163(3):467-481

To evaluate the stability of phlogopite in the presence of carbonate in the Earth’s mantle, we conducted a series of experiments in the KMAS–H₂O–CO₂ system. A mixture consisting of synthetic phlogopite (phl) and natural magnesite (mag) was prepared (phl₉₀-mag₁₀; wt%) and run at pressures from 4 to 8 GPa at temperatures ranging from 1,150 to 1,550°C. We bracketed the solidus between 1,200 and 1,250°C at pressures of 4, 5 and 6 GPa and between 1,150 and 1,200°C at a pressure of 7 GPa. Below the solidus, phlogopite coexists with magnesite, pyrope and a fluid. At the solidus, magnesite is the first phase to react out, and enstatite and olivine appear. Phlogopite melts over a temperature range of ~150°C. The amount of garnet increases above solidus from ~10 to ~30 modal% to higher pressures and temperatures. A dramatic change in the composition of quench phlogopite is observed with increasing pressure from similar to primary phlogopite at 4 GPa to hypersilicic at pressures ≥5 GPa. Relative to CO₂-free systems, the solidus is lowered such, that, if carbonation reactions and phlogopite metasomatism take place above a subducting slab in a very hot (Cascadia-type) subduction environment, phlogopite will melt at a pressure of ~7.5 GPa. In a cold (40 mWm⁻²) subcontinental lithospheric mantle, phlogopite is stable to a depth of 200 km in the presence of carbonate and can coexist with a fluid that becomes Si-rich with increasing pressure. Ascending kimberlitic melts that are produced at greater depths could react with peridotite at the base of the subcontinental lithospheric mantle, crystallizing phlogopite and carbonate at a depth of 180–200 km.  相似文献   

Mafic magmas from Mount Baker in the northern Cascade arc,Washington: probes into mantle and crustal processes     

Nicole?E.?MooreEmail author  Susan?M.?DeBari 《Contributions to Mineralogy and Petrology》2012,163(3):521-546

Five mafic lava flows located on the southern flank of Mount Baker are among the most primitive in the volcanic field. A comprehensive dataset of whole rock and mineral chemistry reveals the diversity of these mafic lavas that come from distinct sources and have been variably affected by ascent through the crust. Disequilibrium textures present in all of the lavas indicate that crustal processes have affected the magmas. Despite this evidence, mantle source characteristics have been retained and three primitive endmember lava types are represented. These include (1) modified low-K tholeiitic basalt (LKOT-like), (2) typical calc-alkaline (CA) lavas, and (3) high-Mg basaltic andesite and andesite (HMBA and HMA). The Type 1 endmember, the basalt of Park Butte (49.3–50.3 wt% SiO₂, Mg# 64–65), has major element chemistry similar to LKOT found elsewhere in the Cascades. Park Butte also has the lowest overall abundances of trace elements (with the exception of the HREE), indicating it is either derived from the most depleted mantle source or has undergone the largest degree of partial melting. The Type 2 endmember is represented by the basalts of Lake Shannon (50.7–52.6 wt% SiO₂, Mg# 58–62) and Sulphur Creek (51.2–54.6 wt% SiO₂, Mg# 56–57). These two lavas are comparable to calc-alkaline rocks found in arcs worldwide and have similar trace element patterns; however, they differ from each other in abundances of REE, indicating variation in degree of partial melting or fractionation. The Type 3 endmember is represented by the HMBA of Tarn Plateau (51.8–54.0 wt% SiO₂, Mg# 68–70) and the HMA of Glacier Creek (58.3–58.7 wt% SiO₂, Mg# 63–64). The strongly depleted HREE nature of these Type 3 units and their decreasing Mg# with increasing SiO₂ suggests fractionation from a high-Mg basaltic parent derived from a source with residual garnet. Another basaltic andesite unit, Cathedral Crag (52.2–52.6 wt% SiO₂, Mg# 55–58), is an Mg-poor differentiate of the Type 3 endmember. The calc-alkaline lavas are least enriched in a subduction component (lowest H₂O, Sr/P_N, and Ba/Nb), the LKOT-like lavas are intermediate (moderate Sr/P_N and Ba/Nb), and the HMBA are most enriched (highest H₂O, Sr/P_N and Ba/Nb). The generation of the LKOT-like and calc-alkaline lavas can be successfully modeled by partial melting of a spinel lherzolite with variability in composition of slab flux and/or mantle source depletion. The HMBA lavas can be successfully modeled by partial melting of a garnet lherzolite with slab flux compositionally similar to the other lava types, or less likely by partial melting of a spinel lherzolite with a distinctly different, HREE-depleted slab flux.  相似文献   

Micro- and nano-textural evidence of Ti(–Ca–Fe) mobility during fluid–rock interactions in carbonaceous lawsonite-bearing rocks from New Zealand     

Matthieu?E.?GalvezEmail author  Olivier?Beyssac  Karim?Benzerara  Nicolas?Menguy  Sylvain?Bernard  Simon?C.?Cox 《Contributions to Mineralogy and Petrology》2012,164(5):895-914

Understanding the mobility of chemical elements during fluid–rock interactions is critical to assess the geochemical evolution of a rock undergoing burial and metamorphism and, more generally, to constrain the geochemical budget of the subduction factory. In particular, determining the behavior and mobility of Ti in aqueous fluids constitutes a great challenge that is still under scrutiny. Here, we study plant fossils preserved in blueschist metasedimentary rocks from the Marybank Formation (New Zealand). Using scanning and transmission electron microscopies (SEM and TEM), we show that the carbonaceous material (CM) composing the fossils contains abundant nano-inclusions of Ti- and Fe-oxides. These nanocrystals are mainly anatase, rutile, and Fe–Ti oxides. The mineral composition observed within the fossils is significantly different from that detected in the surrounding rock matrix. We propose that Ti and Fe might have been mobilized by the alteration of a detrital Ti–Fe-rich protolith during an early diagenetic event under acidic and reducing conditions. Aqueous fluids rich in organic ligands released by the degradation of organic matter may have been involved. Moreover, using mass balance and petrological observations, we show that the contrasted mineralogy between the rock matrix and the fossil CM might be the consequence of the chemical isolation of fossil CM during the prograde path of the rock. Such an isolation results from the early formation of quartz and Fe-rich phyllosilicate layers enclosing the fossil as characterized by SEM and TEM investigations. Overall, this study shows that investigating minerals associated with CM down to the nanometer scale in metamorphic rocks can provide a precious record of early prograde geochemical conditions.  相似文献   

Low-temperature zircon growth related to hydrothermal alteration of siderite concretions in Mississippian shales, Scotland     

Maciej J. Bojanowski  Bogus?aw Bagiński  Euan Clarkson  Ray Macdonald  Leszek Marynowski 《Contributions to Mineralogy and Petrology》2012,164(2):245-259

Zircon occurs in voids and cracks in phosphatic coprolites enclosed in siderite concretions in Mississippian shales near Edinburgh, Scotland. The zircon formed during hydrothermal alteration of early-diagenetic concretions and occurs as spherical aggregates of prismatic crystals, sometimes radiating. Vitrinite reflectance measurements indicate temperatures of ~270°C for the zircon-bearing concretions and the host shales. Molecular parameter values based on dibenzothiophene and phenanthrene distribution and occurrence of di- and tetra-hydro-products of polycyclic aromatic compounds suggest that the rocks experienced relatively high-temperature aqueous conditions related to hydrothermal fluids, perhaps associated with neighboring mafic intrusions. The zircon was dissolved from the concretions, transported in fluids, and reprecipitated in voids. This is the first record of the precipitation of authigenic zircon in sedimentary rock as a new phase, not as outgrowths.  相似文献