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1.
Andrey A. Gurenko Ilya N. Bindeman Marc Chaussidon 《Contributions to Mineralogy and Petrology》2012,164(1):185-189
The comment by Day et al. (Contrib Mineral Petrol, 2012) (1) discusses the validity of the previously obtained oxygen isotope data for El Hierro and La Palma (Canary Island) olivines,
(2) questions the approach by Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) of using weakly correlated variations of δ18Oolivine values with X
px
(proportion of pyroxenite-derived melt in the parental magma), and (3) provides reasons why oxygen isotope data by secondary
ion mass spectrometry (SIMS) “offer sensitive means for detecting melt-crust interactions.” We respond these comments and
report a new set of oxygen isotope measurements performed by SIMS and single-grain laser fluorination methods. These measurements
confirm our previous data and conclusions and demonstrate the ability of the SIMS technique to analyze O isotopes in terrestrial
samples with 2-sigma uncertainty better than ±0.25 ‰. 相似文献
2.
Victor Kress 《Contributions to Mineralogy and Petrology》2007,154(2):191-204
Experiments were performed in the system O–S–Fe–Ni designed to extend our understanding of the chemistry of sulfide liquids.
Results indicate that adding nickel to Fe-rich sulfide liquids in equilibrium with silicate liquids extends their stability
field to much higher oxygen fugacities and lower sulfur fugacities. Increasing Ni/Fe at a given temperature and sulfur and
oxygen fugacity is accompanied by a significant decrease in the oxygen content of the sulfide liquid. Results of these experiments
are combined with data from the literature to calibrate an associated regular solution model for O–S–Fe–Ni liquids. This model
represents a complete refit of the associated regular solution model of Kress (Contrib Mineral Petrol 139:316–325, 2000). The resulting model is combined with the olivine solution model of Hirschmann (Am Mineral 76:1232–1248, 1991) to explore the effect of variations in oxygen and sulfur fugacities on the distribution of Fe and Ni between olivine and
sulfide liquid. Predicted olivine–sulfide distribution trends parallel those observed by Gaetani and Grove (Geochim Cosmochim
Acta 61:1829–1846, 1997), Gaetani and Grove (Earth Planet Sci Lett 169:147–163, 1999), Brenan and Caciagli (Geochim Cosmochim Acta 64:307–320, 2000) and Brenan (Geochim Cosmochim Acta 67:2663–2681, 2003), but are systematically offset toward lower predicted Ni in the sulfide. Nevertheless our results are consistent with the
assertion that low K
D
os
values in magmatic ore deposits such as the J-M Reef reflect high iron contents in the sulfides combined with relatively
high oxygen fugacities.
相似文献
Victor KressEmail: |
3.
T. W. Sisson J.-I. Kimura M. L. Coombs 《Contributions to Mineralogy and Petrology》2009,158(6):803-829
A basanite–nephelinite glass suite from early submarine Kilauea defines a continuous compositional array marked by increasing
concentrations of incompatible components with decreasing SiO2, MgO, and Al2O3. Like peripheral and post-shield strongly alkalic Hawaiian localities (Clague et al. in J Volcanol Geotherm Res 151:279–307,
2006; Dixon et al. in J Pet 38:911–939, 1997), the early Kilauea basanite–nephelinite glasses are interpreted as olivine fractionation products from primary magnesian
alkalic liquids. For early Kilauea, these were saturated with a garnet–phlogopite–sulfide peridotite assemblage, with elevated
dissolved CO2 contents responsible for the liquids’ distinctly low-SiO2 concentrations. Reconstructed primitive liquids for early Kilauea and other Hawaiian strongly alkalic localities are similar
to experimental 3 GPa low-degree melts of moderately carbonated garnet lherzolite, and estimated parent magma temperatures
of 1,350–1,400°C (olivine–liquid geothermometry) match the ambient upper mantle geotherm shortly beneath the base of the lithosphere.
The ~3 GPa source regions were too hot for stable crystalline carbonate and may have consisted of ambient upper mantle peridotite
containing interstitial carbonate–silicate or carbonatitic liquid, possibly (Dixon et al. in Geochem Geophys Geosyst 9(9):Q09005,
2008), although not necessarily, from the Hawaiian mantle plume. Carbonate-enriched domains were particularly susceptible to further
melting upon modest decompression during upward lithospheric flexure beneath the advancing Hawaiian Arch, or by conductive
heating or upward drag by the Hawaiian mantle plume. The early Kilauea basanite–nephelinite suite has a HIMU-influenced isotopic
character unlike other Hawaiian magmas (Shimizu et al. in EOS Tran Amer Geophys Union 82(47): abstr V12B-0962, 2001; Shimizu et al. in Geochim Cosmochim Acta 66(15A):710, 2002) but consistent with oceanic carbonatite involvement (Hoernle et al. in Contrib Mineral Petrol 142:520–542, 2002). It may represent the melting products of a fertile domain in the ambient upper mantle impinged upon and perturbed by the
sustained plume source that feeds later shield-stage magmatism. 相似文献
4.
Zr-in-rutile thermometry in HP/UHP eclogites from Western China 总被引:5,自引:0,他引:5
Guibin Zhang David J. Ellis Andrew G. Christy Lifei Zhang Shuguang Song 《Contributions to Mineralogy and Petrology》2010,160(3):427-439
Four Zr-in-rutile thermometry calibrations are applied to eclogites from Western China. Here, we show that if rutile grows
in equilibrium with Qtz and Zrn, and is isolated inside garnet, it preserves its Zr composition and does not undergo compositional
change due to cation exchange with the host garnet. It thus preserves the composition for the P–T conditions of its formation and the growth zoning of the host garnet. For the HP/UHP metamorphic temperature, the Tomkins
et al. (J Metamorph Geol 25:703–713, 2007) calibration yields temperatures that agree well with previous studies, whereas the other three calibrations (Zack et al.
in Contrib Mineral Petrol 148:471–488, 2004; Watson et al. in Contrib Mineral Petrol 151:413–433, 2006; Ferry and Watson in Contrib Mineral Petrol in 154:429–437, 2007), which do not include a pressure correction, give systematically lower temperatures. Zr contents of rutile inclusions within
garnet show systematic decrease from garnet core to rim. The rutile inclusions in garnet rims contain the lowest Zr content,
similar to that in the matrix. Analyses confirm that the pressure plays a significant role in modifying the primary temperature
dependence of the Zr content of rutile. Rutiles trapped in garnets are unable to re-equilibrate easily during retrogression,
but those in the matrix can do so, providing retrograde P–T path information. 相似文献
5.
The standard thermodynamic properties at 25°C, 1 bar (ΔG
fo, ΔH
fo, S
o, C
Po, V
o, ω) and the coefficients of the revised Helgeson–Kirkham–Flowers equations of state were evaluated for several aqueous complexes
formed by dissolved metals and either arsenate or arsenite ions. The guidelines of Shock and Helgeson (Geochim Cosmochim Acta
52:2009–2036, 1988) and Sverjensky et al. (Geochim Cosmochim Acta 61:1359–1412, 1997) were followed and corroborated with alternative approaches, whenever possible. The SUPCRT92 computer code was used to generate
the log K of the destruction reactions of these metal–arsenate and metal–arsenite aqueous complexes at pressures and temperatures required
by the EQ3/6 software package, version 7.2b. Apart from the AlAsO4o and FeAsO4o complexes, our log K at 25°C, 1 bar are in fair agreement with those of Whiting (MS Thesis, Colorado School of Mines, Golden, CO, 1992). Moreover, the equilibrium constants evaluated in this study are in good to fair agreement with those determined experimentally
for the Ca–dihydroarsenate and Ca–hydroarsenate complexes at 40°C (Mironov et al., Russ J Inorg Chem 40:1690, 1995) and for Fe(III)–hydroarsenate complex at 25°C (Raposo et al., J Sol Chem 35:79–94, 2006), whereas the disagreement with the log K measured for the Ca–arsenate complex at 40°C (Mironov et al., Russ J Inorg Chem 40:1690, 1995) might be due to uncertainties in this measured value. The implications of aqueous complexing between dissolved metals and
arsenate/arsenite ions were investigated for seawater, high-temperature geothermal liquids and acid mine drainage and aqueous
solutions deriving from mixing of acid mine waters and surface waters.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
6.
Zr diffusion in titanite 总被引:2,自引:0,他引:2
D. J. Cherniak 《Contributions to Mineralogy and Petrology》2006,152(5):639-647
Chemical diffusion of Zr under anhydrous, pO2-buffered conditions has been measured in natural titanite. The source of diffusant was either zircon powder or a ZrO2–Al2O3–titanite mixture. Experiments were run in sealed silica glass capsules with solid buffers (to buffer at NNO or QFM). Rutherford Backscattering Spectrometry (RBS) was used to measure diffusion profiles. The following Arrhenius parameters were obtained for Zr diffusion parallel to c over the temperature range 753–1,100°C under NNO-buffered conditions: D
Zr = 5.33 × 10−7 exp(−325 ± 30 kJ mol−1/RT) m2 s−1 Diffusivities are similar for experiments buffered at QFM. These data suggest that titanite should be moderately retentive of Zr chemical signatures, with diffusivities slower than those for O and Pb in titanite, but faster than those for Sr and the REE. When applied in evaluation of the relative robustness of the recently developed Zr-in-titanite geothermometer (Hayden and Watson, Abstract, 16th V.M. Goldschmidt Conference 2006), these findings suggest that Zr concentrations in titanite will be less likely to be affected by later thermal disturbance than the geothermometer based on Zr concentrations in rutile (Zack et al. in Contrib Mineral Petrol 148:471–488, 2004; Watson et al. in Contrib Mineral. Petrol, 2006), but much less resistant to diffusional alteration subsequent to crystallization than the Ti-in-Zircon geothermometer (Watson and Harrison in Science 308:841–844, 2005). 相似文献
7.
The low-temperature heat capacity (C
P) of stishovite (SiO2) synthesized with a multi-anvil device was measured over the range of 5–303 K using the heat capacity option of a physical
properties measurement system (PPMS) and around ambient temperature using a differential scanning calorimeter (DSC). The entropy
of stishovite at standard temperature and pressure calculated from DSC-corrected PPMS data is 24.94 J mol−1 K−1, which is considerably smaller (by 2.86 J mol−1 K−1) than that determined from adiabatic calorimetry (Holm et al. in Geochimica et Cosmochimica Acta 31:2289–2307, 1967) and about 4% larger than the recently reported value (Akaogi et al. in Am Mineral 96:1325–1330, 2011). The coesite–stishovite phase transition boundary calculated using the newly determined entropy value of stishovite agrees
reasonably well with the previous experimental results by Zhang et al. (Phys Chem Miner 23:1–10, 1996). The calculated phase boundary of kyanite decomposition reaction is most comparable with the experimental study by Irifune
et al. (Earth Planet Sci Lett 77:245–256, 1995) at low temperatures around 1,400 K, and the calculated slope in this temperature range is mostly consistent with that determined
by in situ X-ray diffraction experiments (Ono et al. in Am Mineral 92:1624–1629, 2007). 相似文献
8.
Mingbin Huang D. G. Fredlund M. D. Fredlund 《Geotechnical and Geological Engineering》2010,28(2):105-117
There are significant advantages in using indirect pedo-transfer functions, (PTFs) for the estimation of unsaturated soil
properties. The pedo-transfer functions can be used for the estimation of the soil–water characteristic curve (SWCC) which
in turn is used for the estimation of other unsaturated soil properties. The accuracy of the indirect pedo-transfer function
method for the estimation of the SWCC depends on the PTF and the equation used to best-fit the particle-size distribution
(PSD) data. The objectives of this study are to: (1) evaluate the performance of the Fredlund et al. (Can Geotech J 37:817–827,
2000) equation for best-fitting the particle-size distribution, (PSD) data, and, (2) compare the predictions made by two of the
commonly used PTFs; namely, Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) and Fredlund et al. (Can Geotech J 39:1103–1117, 2002), for estimating the SWCC from the PSD. The authors used 258 measured PSDs and SWCC datasets from the Loess Plateau, China,
for this study. The dataset consisted of 187 silt–loam soils, 41 loam soils, 11 silt–clay–loam soils, 10 sand–loam soils,
6 silt–clay soils, and 3 loam–sand soils. The SWCC and PSD datasets were measured using a Pressure Plate apparatus and the
pipette method, respectively. The comparison between the estimated and measured particle-size distribution curves showed that
the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation closely prepresented the PSD for all soils in the Loess Plateau, with a lower root mean square error (RMSE) of
0.869%. The comparison between the estimated and measured water contents at the same suction showed that the Fredlund et al.
(Can Geotech J 39:1103–1117, 2002) PTF performed somewhat better than the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) function. The Fredlund et al. method had RMSE value of 0.039 cm3 cm−3 as opposed to 0.046 cm3 cm−3 for the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) method. The Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF produced the closest predictions for sand–loam, loam–sand, and loam soils, with a lower RMSE for gravimetric water content
ranging from 0.006 to 0.036 cm3 cm−3. There were consistent over-estimations observed for silt–loam, silt–clay–loam, and slit–clay soils with RMSE values for
gravimetric water content ranging from 0.037 to 0.043 cm3 cm−3. The measured and estimated air-entry values were closest when using the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF. The measured and estimated maximum slopes on the SWCC were closest when using the Arya and Paris (Soil Sci Soc Am J
45:1023–1030, 1981) PTF. 相似文献
9.
Viktor A. Kurepin 《Contributions to Mineralogy and Petrology》2010,160(3):391-406
A refined thermodynamic model of H2O and CO2 bearing cordierite based on recent data on volatile incorporation into cordierite (Thompson et al. in Contrib Mineral Petrol
142:107–118, 2001; Harley and Carrington in J Petrol 42:1595–1620, 2001) reflects non-ideality of channel H2O and CO2 mixing. The dependence of cordierite H2O and CO2 contents on P, T and equilibrium fluid composition has been calculated for the range 600–800°C and 200–800 MPa. It has been used for establishing
thermodynamic conditions of cordierite formation and the following retrograde P–T paths of cordierite rocks from many localities. Estimates of the H2O and CO2 activities have shown that cordierites in granites, pegmatites and high-pressure granulites were formed in fluid-saturated
conditions and wide range of H2O/CO2 relations. Very low cordierite H2O contents in many migmatites may be caused not only by fluid-undersaturated conditions at rock formation and H2O leakage on retrograde P–T paths but also by the presence of additional volatile components like CH4 and N2. The pressure dependence of cordierite-bearing mineral equilibria on fluid H2O/CO2 relations has been evaluated. 相似文献
10.
Andrey A. Gurenko Kaj A. Hoernle Alexander V. Sobolev Folkmar Hauff Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2010,159(5):689-702
The Canary Island primitive basaltic magmas are thought to be derived from an HIMU-type upwelling mantle containing isotopically
depleted (NMORB)-type component having interacted with an enriched (EM)-type component, the origin of which is still a subject
of debate. We studied the relationships between Ni, Mn and Ca concentrations in olivine phenocrysts (85.6–90.0 mol.% Fo, 1,722–3,915 ppm
Ni, 1,085–1,552 ppm Mn, 1,222–3,002 ppm Ca) from the most primitive subaerial and ODP Leg 157 high-silica (picritic to olivine
basaltic) lavas with their bulk rock Sr–Nd–Pb isotope compositions (87Sr/86Sr = 0.70315–0.70331, 143Nd/144Nd = 0.51288–0.51292, 206Pb/204Pb = 19.55–19.93, 207Pb/204Pb = 15.60–15.63, 208Pb/204Pb = 39.31–39.69). Our data point toward the presence of both a peridotitic and a pyroxenitic component in the magma source.
Using the model (Sobolev et al. in: Science 316:412–417, 2007) in which the reaction of Si-rich melts originated during partial
melting of eclogite (a high pressure product of subducted oceanic crust) with ambient peridotitic mantle forms olivine-free
reaction pyroxenite, we obtain an end member composition for peridotite with 87Sr/86Sr = 0.70337, 143Nd/144Nd = 0.51291, 206Pb/204Pb = 19.36, 207Pb/204Pb = 15.61 and 208Pb/204Pb = 39.07 (EM-type end member), and pyroxenite with 87Sr/86Sr = 0.70309, 143Nd/144Nd = 0.51289, 206Pb/204Pb = 20.03, 207Pb/204Pb = 15.62 and 208Pb/204Pb = 39.84 (HIMU-type end member). Mixing of melts from these end members in proportions ranging from 70% peridotite and 30%
pyroxenite to 28% peridotite and 72% pyroxenite derived melt fractions can generate the compositions of the most primitive
Gran Canaria shield stage lavas. Combining our results with those from the low-silica rocks from the western Canary Islands
(Gurenko et al. EPSL 277:514–524, 2009), at least four distinct components are required. We propose that they are (1) HIMU-type
pyroxenitic component (representing recycled ocean crust of intermediate age) from the plume center, (2) HIMU-type peridotitic
component (ancient recycled ocean crust stirred into the ambient mantle) from the plume margin, (3) depleted, MORB-type pyroxenitic
component (young recycled oceanic crust) in the upper mantle entrained by the plume, and (4) EM-type peridotitic component
from the asthenosphere or lithosphere above the plume center. 相似文献
11.
Laurent Chauvaud Julien Thébault Jacques Clavier Anne Lorrain Øivind Strand 《Estuaries and Coasts》2011,34(2):211-220
Mollusk shells contain geochemical information about environmental conditions that prevailed at the time of formation. We
investigated ontogenetic and seasonal variations of δ13C in calcitic shells of Pecten maximus. Ontogenetic variations of δ13Cshell in three large specimens collected in Norway, France, and Spain exhibited a similar linear decrease with increasing shell
height. We removed this linear drift (detrending). These three residual time series displayed variations that could be linked
to environmental fluctuations. To check it, we reanalyzed the isotopic datasets of Lorrain et al. (Journal of Experimental
Marine Biology and Ecology 275:47–61, 2002, Geochimica et Cosmochimica Acta 68:3509–3519, 2004), who worked on three scallops harvested in 2000 in the bay of Brest (France), a well-monitored ecosystem. Lowest values
of δ13Cshell detrended were recorded in all shells in late spring–early summer, most likely reflecting corresponding variations in food availability.
Our results indicate that ontogenetic and seasonal variations of δ13Cshell cannot be used as a proxy for past δ13CDIC variations but should be considered as promising tools for ecophysiological studies. 相似文献
12.
The premise of the Wilson et al. comment is that the Ti-in-quartz solubility calibration (Thomas et al. in Contrib Mineral
Petrol 160:743–759, 2010) is fundamentally flawed. They reach this conclusion because P–T estimates using the Ti-in-quartz calibration differ from their previous interpretations for crystallization conditions of
the Bishop and Oruanui rhyolites. If correct, this assertion has far-reaching implications, so a careful assessment of the
Wilson et al. reasoning is warranted. Application of the Ti-in-quartz calibration as a thermobarometer in rutile-free rocks
requires an estimation of TiO2 activity in the liquid ( (liquid–rutile); referenced to rutile saturation) and an independent constraint on either P or T to obtain the crystallization temperature or pressure, respectively. The foundation of Wilson et al.’s argument is that temperature
estimates obtained from Fe–Ti oxide thermometry accurately reflect crystallization conditions of quartz in the two rhyolites
discussed. We maintain that our experimental approach is sound, the thermodynamic basis of the Ti-in-quartz calibration is
fundamentally correct, and our experimental results are robust and reproducible. We suggest that the reason Wilson et al.
obtain implausible pressure estimates is because estimates for T and they used as input values for the Ti-in-quartz calibration are demonstrably too high. Numerous studies show that Fe–Ti oxide
temperature estimates of some rhyolites are substantially higher than those predicted by well-constrained phase equilibria.
In this reply, we show that when reasonable input values for T and (liquid–rutile) are used, pressure estimates obtained from the Ti-in-quartz calibration are well aligned with phase equilibria
and essentially identical to melt inclusion volatile saturation pressures. 相似文献
13.
Yasumasa Ogawa Naotatsu Shikazono Daizo Ishiyama Hinako Sato Toshio Mizuta Takanori Nakano 《Mineralium Deposita》2007,42(3):219-233
The Sr, Ba, and rare earth elements (REEs) concentrations and Sr isotopic composition of anhydrite and gypsum have been determined
for samples from the Matsumine, Shakanai, and Hanaoka Kuroko-type massive sulfide–sulfate deposits of northern Japan to evaluate
the mechanisms of sekko (anhydrite and gypsum) ore formation. The Sr isotopic compositions of the samples fall in the range
of 0.7077–0.7087, intermediate between that for middle Miocene (13–15 Ma) seawater (0.7088) (Peterman et al., Geochim Cosmochim
Acta, 34:105–120, 1970) and that for country rocks (e.g., 0.7030–0.7050) (Shuto, Assn Geol Collab Japan Monograph 18:91–105, 1974). The Kuroko anhydrite samples exhibit two types of chondrite-normalized REE patterns: one with a decrease from light REEs
(LREEs) to heavy REEs (HREEs) (type I), and another with a LREE-depleted pattern (type II).
Based on the Sr content and isotopic ratio (assuming an Sr/Ca (mM/M) of 8.7 for seawater), anhydrite is considered to have
formed by mixing of preheated seawater with a hydrothermal solution of Sr/Ca (mM/M) = ca. 0.59–1.36 under the condition in
which the partition coefficient (Kd) ranges between ca. 0.5 and 0.7. This results in the formation of anhydrite with higher
Sr content with an Sr isotopic value close to that of seawater under seawater-dominant conditions.
Larger crystals of type II anhydrite are partly replaced by smaller ones, indicating that anhydrite dissolution and recrystallization
occurred after or during the formation of sekko ore. Gypsum, which partially replaces anhydrite in the Kuroko deposits, also
exhibits two distinct chondrite-normalized REE patterns. Because LREEs are likely to be more readily mobilized during dissolution
and recrystallization, it is hypothesized that LREEs are leached from type I anhydrite, resulting in the formation of type
II anhydrite with LREE-depleted profiles. 相似文献
14.
Swastika Chatterjee Sirshendu Bhattacharyya Surajit Sengupta Tanusri Saha-Dasgupta 《Physics and Chemistry of Minerals》2011,38(4):259-265
We report studies based on a combination of ab initio electronic structure and Monte Carlo (MC) technique on the problem of
cation partitioning among inequivalent octahedral sites, M1 and M2 in mixed olivines containing Mg2+ and Fe2+ ions. Our MC scheme uses interactions derived out of ab initio, density functional calculations carried out on measured crystal
structure data. Our results show that there is no reversal of the preference of Fe for M1 over M2 as a function of temperature.
Our findings do not agree with the experimental findings of Redfern et al. (Phys Chem Miner 27:630–637, 2000), but are in agreement with those of Heinemann et al. (Eur J Mineral 18:673–689, 2006) and Morozov et al. (Eur J Mineral 17:495–500, 2005). 相似文献
15.
The comment of Martin Oczlon contains some significant contributions to the topics discussed in the article of Huckriede et
al. (Int J Earth Sci 93:414–431, 2004). Contrary to Oczlon’s comment, the central results of Huckriede et al. (Int J Earth Sci 93:414–431, 2004) are clearly different from the tectonic model of Oczlon (Geol Rundsch 83:20–31, 1994). Additionally, there is no reason for a new interpretation of the 40K/40Ar muscovite cooling-ages from allochthonous units. 相似文献
16.
We report the oxygen isotope composition of olivine and orthopyroxene phenocrysts in lavas from the main magma types at Mt
Shasta and Medicine Lake Volcanoes: primitive high-alumina olivine tholeiite (HAOT), basaltic andesites (BA), primitive magnesian
andesites (PMA), and dacites. The most primitive HAOT (MgO > 9 wt%) from Mt. Shasta has olivine δ18O (δ18OOl) values of 5.9–6.1‰, which are about 1‰ higher than those observed in olivine from normal mantle-derived magmas. In contrast,
HAOT lavas from Medicine Lake have δ18OOl values ranging from 4.7 to 5.5‰, which are similar to or lower than values for olivine in equilibrium with mantle-derived
magmas. Other magma types from both volcanoes show intermediate δ18OOl values. The oxygen isotope composition of the most magnesian lavas cannot be explained by crustal contamination and the trace
element composition of olivine phenocrysts precludes a pyroxenitic mantle source. Therefore, the high and variable δ18OOl signature of the most magnesian samples studied (HAOT and BA) comes from the peridotitic mantle wedge itself. As HAOT magma
is generated by anhydrous adiabatic partial melting of the shallow mantle, its 1.4‰ range in δ18OOl reflects a heterogeneous composition of the shallow mantle source that has been influenced by subduction fluids and/or melts
sometime in the past. Magmas generated in the mantle wedge by flux melting due to modern subduction fluids, as exemplified
by BA and probably PMA, display more homogeneous composition with only 0.5‰ variation. The high-δ18O values observed in magnesian lavas, and principally in the HAOT, are difficult to explain by a single-stage flux-melting
process in the mantle wedge above the modern subduction zone and require a mantle source enriched in 18O. It is here explained by flow of older, pre-enriched portions of the mantle through the slab window beneath the South Cascades. 相似文献
17.
Cliff S. J. Shaw 《Contributions to Mineralogy and Petrology》2006,151(6):665-680
The dissolution rate of quartz in melts of the CMAS and CAS systems at 1,600°C and 1.5 GPa is a function of both the silica activity of the melt and its viscosity. In melts with low silica activity quartz dissolves more quickly than in higher aSiO2 melts regardless of viscosity. For melts with equal aSiO2, dissolution is faster in the low viscosity melt. Quartz dissolution is controlled by interface kinetics in three of the four melts used in this study for times much greater than predicted by the model of Zhang et al. (in Contrib Mineral Petrol 102:492–513 1989). One melt which was previously shown to adhere to the predicted behaviour at lower temperature shows a significant activation time at higher temperature. All the dissolution data indicate that there are likely to be three distinct domains of dissolution behaviour, although the details of why a particular melt falls in any one domain require further study. Although the current database is small, the relationship between quartz solubility and the dissolution constant indicate that solubility may be a useful parameter for predicting dissolution rates, particularly if silica activity and melt viscosity are also known. 相似文献
18.
Colin J. N. Wilson Terry M. Seward Aidan S. R. Allan Bruce L. A. Charlier Léa Bello 《Contributions to Mineralogy and Petrology》2012,164(2):359-368
Trace concentrations of Ti in quartz are used to indicate the pressure and temperature conditions of crystallization in the ‘TitaniQ’ geothermobarometer of Thomas et al. (Contrib Miner Petrol 160:743–759, 2010). It utilises the partitioning of Ti into quartz as an indicator of the pressures and/or temperatures of crystal growth. For a given value of TiO2 activity in the system, if temperatures are inferred to ±20 °C, pressure is constrained to ±1 kbar and vice versa. There are significant contrasts, however, between the conclusions from TitaniQ and those for natural quartz (as well as other mineral phases) in volcanic rocks. Application of the TitaniQ model to quartz from the 27 ka Oruanui and 760 ka Bishop high-silica rhyolites, where the values of T, P and TiO2 activity are constrained by other means (Fe–Ti oxide equilibria, melt inclusion entrapment pressures in gas-saturated melts, melt and amphibole compositions), yields inconsistent results. If realistic values are given to any two of these three parameters, then the value of the third is wholly unrealistic. The model yields growth temperatures at or below the granite solidus, pressures in the lower crust or upper mantle, or TiO2 activities inconsistent with the mineralogical and chemical compositions of the magmas. CL imagery and measurements of Ti (and other elements) in quartz are of great value in showing the growth histories and changes in conditions experienced by crystals, but direct linkages to P, T conditions during crystal growth cannot be achieved. 相似文献
19.
Sebastiano Imposa 《Environmental Geology》2008,55(5):1061-1073
In this study 50 seismic events, preceding and accompanying the eruptions occurring in 1981 and 1983, have been considered.
Seismic moments, fault radii, stress drops and seismic energies have been calculated using Brune’s model (J Geophys Res 75:4997–5009,
1970; J Geophys Res 76:5002, 1971); site, anelastic attenuation along the propagation path, geometrical spreading and interaction with the free surface effects
are taken into account. For each event we have also estimated the equivalent Wood–Anderson magnitude (MWAeq) (Scherbaum and
Stoll in Bull Seism Soc Am 73:1321–1343, 1983); relations among all these source parameters have been determined. Furthermore, the hypothesis of self-similarity (Aki in
J Geophys Res 72:1217–1231, 1967) is not verified for events with seismic moments <1012 N-m: in fact the relationship between log-stress drop and log-moment is linear up to a moment of 1012 N-m (events of 1981 eruption), while for higher moments (events of 1983 eruption) the slope of the regression line is not
significantly different from zero. We suppose that such a behaviour is related to a heterogeneous medium with barriers on
the faults. Finally, the main conclusion is that eruptions of 1981 and 1983 differ from one another both in eruptive and seismic
aspects; analysis of seismic energies indicates an increase in Mt. Etna’s activity, confirmed by studies performed on the
following lateral eruption of 1991–1993 (Patanè et al. in Bull Volcanol 47:941–952, 1995), occurring on the same structural trend. 相似文献
20.
A new profile mass balance procedure is presented to calculate the chemical composition of solid precipitated during cooling and crystallization of many tholeiitic and alkaline magmas. It is a variant of the earlier interval method (MacLean 2000, Contrib Mineral Petrol 139:85–100), and is also based on chemical variation diagrams of lava sequences (liquid profiles) constructed with a quantitative monitor of fractionation derived from the residual enrichment of an incompatible trace high field-strength element (HFSE). In this new profile method, the concentration of a component in solid is shown by mass transfer considerations to be a function of its mass on a liquid fractionation path (profile) and on a path (profile) of perfect incompatible enrichment. The latter hypothetically contains all of the component, hence subtraction of the amount contained in liquid will yield its mass in the solid. The calculations are straightforward and adaptable to both equilibrium and fractional crystallization processes. Corrections to the fractionation monitor for measured
(solid/liquid distribution coefficient), estimates of "trapped liquid" in solid, and other variables, can be applied. The method is illustrated with chemical data for a suite of alkaline volcanic rocks from Mt. Erebus, Antarctica (Kyle et al. 1992, J Petrol 33:849–875). The lavas are silica-undersaturated, and range from nepheline-bearing basanite to phonolite. The solids correspond to those of ultrabasic rocks through most of fractionation, and are more SiO2-undersaturated than the lavas.Editorial responsibility: I. Parsons 相似文献