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1.
Stress-induced proton disorder in hydrous ringwoodite 总被引:1,自引:1,他引:0
Monika Koch-Müller Sergio Speziale Fiorenza Deon Maria Mrosko Ulrich Schade 《Physics and Chemistry of Minerals》2011,38(1):65-73
We have measured in situ high-pressure IR absorption of synthetic hydrous (MgxFe1−x)2SiO4 ringwoodites (x = 0.00 to 0.61) up to a maximum pressure of 30 GPa. In our study, we combined the megabar-type diamond-anvil cell (DAC) with
conventional and synchrotron FTIR spectroscopy. The high-pressure measurements were performed in three different pressure-transmitting
environments: (1) CsI powder, (2) cryogenically loaded liquid argon, and (3) cryogenically loaded liquid argon annealed at
8.6 GPa at temperature of 120°C before further pressure increase. Between 10 and 12 GPa, all the samples loaded with methods
(1) and (2), independent on composition, showed a sudden disappearance of the prominent OH-stretching feature and simultaneous
discontinuities and/or changes in the pressure dependence of lattice vibrations compared with spectra of samples loaded with
method (3). In experiments performed with method (3) the OH-stretching vibrations as well as lattice vibrations could be observed
up to 30 GPa and their pressure behavior (dν/dP) can well be described by linear fits. Molecular vibrations, such as the OH stretching, are sensitive to non-hydrostatic
conditions, especially in minerals with highly symmetric structures. We interpret the disappearance of the OH bands using
methods (1) and (2) as a stress-induced proton disordering in hydrous ringwoodite. Our results confirm that argon pressure
medium produces strongly non-hydrostatic conditions comparable to CsI or KBr, if it is not thermally annealed at pressures
above 8 GPa. Our results suggest that the transition observed in hydrous Mg-ringwoodite end member is not present in compositions
containing Fe. By comparing the behavior of samples compressed in different environments, we suggest that sudden disappearance
of the OH-stretching band in hydrous ringwoodite could be driven by deterioration of the quasi-hydrostatic stress condition
instead of a pressure-induced effect. 相似文献
2.
H. Fukui O. Ohtaka T. Nagai T. Katsura K. Funakoshi W. Utsumi 《Physics and Chemistry of Minerals》2000,27(6):367-370
Using the high-pressure differential thermal analysis (HP-DTA) system in a cubic multianvil high-pressure apparatus, we measured
the melting points of portlandite, Ca(OH)2, up to 6 GPa and 1000 °C. We detected endothermic behavior at the temperature and pressure conditions of 800 °C and 2.5 GPa,
769 °C and 3.5 GPa, 752 °C and 4.0 GPa, 686 °C and 5.0 GPa, and 596 °C and 6.0 GPa, respectively, due to melting of portlandite.
By in situ X-ray studies under pressure, the melting of portlandite was observed at 730 °C and 4.32 GPa and at 640 °C and 5.81 GPa,
respectively. Results of both HP-DTA and X-ray studies were consistent within experimental error. The melting is congruent
and has a negative Clapeyron slope, indicating that liquid Ca(OH)2 has higher densities than crystalline portlandite in this pressure range.
Received: 19 June 1999 / Revised, accepted: 11 September 1999 相似文献
3.
D. W. Fan M. N. Ma W. G. Zhou S. Y. Wei Z. Q. Chen H. S. Xie 《Physics and Chemistry of Minerals》2011,38(2):95-99
The high-pressure X-ray diffraction study of a natural arsenopyrite was investigated up to 28.2 GPa using in situ angle-dispersive
X-ray diffraction and a diamond anvil cell at National Synchrotron Light Source, Brookhaven National Laboratory. The 16:3:1
methanol–ethanol–water mixture was used as a pressure-transmitting medium. Pressures were measured using the ruby-fluorescence
method. No phase change has been observed up to 28.2 GPa. The isothermal equation of state (EOS) was determined. The values
of K
0, and K′
0 refined with a third-order Birch–Murnaghan EOS are K
0 = 123(9) GPa, and K′
0 = 5.2(8). Furthermore, we confirm that the linear compressibilities (β) along a, b and c directions of arsenopyrite is elastically isotropic (β
a
= 6.82 × 10−4, β
b
= 6.17 × 10−4 and β
c
= 6.57 × 10−4 GPa−1). 相似文献
4.
An experimental investigation of antigorite dehydration in natural silica-enriched serpentinite 总被引:1,自引:0,他引:1
José Alberto Padrón-Navarta Jörg Hermann Carlos J. Garrido Vicente López Sánchez-Vizcaíno María Teresa Gómez-Pugnaire 《Contributions to Mineralogy and Petrology》2010,159(1):25-42
Piston cylinder experiments were performed to constrain the pressure and temperature conditions for two high-pressure antigorite
dehydration reactions found in silica-enriched serpentinites from Cerro del Almirez (Nevado–Filábride Complex, Betic Cordillera,
southern Spain). At 630–660°C and pressures greater than 1.6 GPa, antigorite first reacts with talc to form orthopyroxene ± chlorite + fluid.
We show that orthopyroxene + antigorite is restricted to high-pressure metamorphism of silica-enriched serpentinite. This
uncommon assemblage is helpful in constraining metamorphic conditions in cold subduction environments, where antigorite serpentinites
have no diagnostic assemblages over a large pressure and temperature range. The second dehydration reaction leads to the breakdown
of antigorite to olivine + orthopyroxene + chlorite + fluid. The maximum stability of antigorite is found at 680°C at 1.9 GPa,
which also corresponds to the maximum pressure limit for tremolite coexisting with olivine + orthopyroxene. The high aluminium
(3.70 wt% Al2O3) and chromium contents (0.59 wt% Cr2O3) of antigorite in the investigated starting material is responsible for the expansion of the serpentinite stability to 60–70°C
higher temperatures at 1.8 GPa than the antigorite stability calculated in the Al-free system. The antigorite from our study
has the highest Al–Cr contents among all experimental studies and therefore likely constraints the maximum stability of antigorite
in natural systems. Comparison of experimental results with olivine–orthopyroxene–chlorite–tremolite assemblages outcropping
in Cerro del Almirez indicates that peak metamorphic conditions were 680–710°C and 1.6–1.9 GPa. 相似文献
5.
T. Okada W. Utsumi H. Kaneko M. Yamakata O. Shimomura 《Physics and Chemistry of Minerals》2002,29(7):439-445
An experimental technique to make real-time observations at high pressure and temperature of the diamond-forming process
in candidate material of mantle fluids as a catalyst has been established for the first time. In situ X-ray diffraction experiments
using synchrotron radiation have been performed upon a mixture of brucite [Mg(OH)2] and graphite as starting material. Brucite decomposes into periclase (MgO) and H2O at 3.6 GPa and 1050 °C while no periclase is formed after the decomposition of brucite at 6.2 GPa and 1150 °C, indicating
that the solubility of the MgO component in H2O greatly increases with increasing pressure. The conversion of graphite to diamond in aqueous fluid has been observed at
7.7 GPa and 1835 °C. Time-dependent X-ray diffraction profiles for this transformation have been successfully obtained.
Received: 17 July 2001 / Accepted: 18 February 2002 相似文献
6.
Kirill K. Zhuravlev J. M. Jackson A. S. Wolf J. K. Wicks J. Yan S. M. Clark 《Physics and Chemistry of Minerals》2010,37(7):465-474
We present isothermal volume compression behavior of two polycrystalline (Mg,Fe)O samples with FeO = 39 and 78 mol% up to
~90 GPa at 300 K using synchrotron X-ray diffraction and neon as a pressure-transmitting medium. For the iron-rich (Mg0.22Fe0.78)O sample, a structural transition from the B1 structure to a rhombohedral structure was observed at 41.6 GPa, with no further
indication of changes in structural or compression behavior changes up to 93 GPa. In contrast, a change in the compression
behavior of (Mg0.61Fe0.39)O was observed during compression at P ≥ 71 GPa and is indicative of a spin crossover occurring in the Fe2+ component of (Mg0.61Fe0.39)O. The low-spin state exhibited a volume collapse of ~3.5%, which is a larger value than what was observed for a similar
composition in a laser-heated NaCl medium. Upon decompression, the volume of the high-spin state was recovered at approximately
65 GPa. We therefore bracket the spin crossover at 65 ≤ P (GPa) ≤ 77 at 300 K (Mg0.61Fe0.39)O. We observed no deviation from the B1 structure in (Mg0.61Fe0.39)O throughout the pressure range investigated. 相似文献
7.
Akio Suzuki Eiji Ohtani Hidenori Terasaki Keisuke Nishida Hiromi Hayashi Tatsuya Sakamaki Yuki Shibazaki Takumi Kikegawa 《Physics and Chemistry of Minerals》2011,38(1):59-64
The viscosity of a silicate melt of composition NaAlSi2O6 was measured at pressures from 1.6 to 5.5 GPa and at temperatures from 1,350 to 1,880°C. We employed in situ falling sphere
viscometry using X-ray radiography. We found that the viscosity of the NaAlSi2O6 melt decreased with increasing pressure up to 2 GPa. The pressure dependence of viscosity is diminished above 2 GPa. By using
the relationship between the logarithm of viscosity and the reciprocal temperature, the activation energies for viscous flow
were calculated to be 3.7 ± 0.4 × 102 and 3.7 ± 0.5 × 102 kJ/mol at 2.2 and 2.9 GPa, respectively. 相似文献
8.
Riko Iizuka Hiroyuki Kagi Kazuki Komatsu Daichi Ushijima Satoshi Nakano Asami Sano-Furukawa Takaya Nagai Takehiko Yagi 《Physics and Chemistry of Minerals》2011,38(10):777-785
The pressure responses of portlandite and the isotope effect on the phase transition were investigated at room temperature
from single-crystal Raman and IR spectra and from powder X-ray diffraction using diamond anvil cells under quasi-hydrostatic
conditions in a helium pressure-transmitting medium. Phase transformation and subsequent peak broadening (partial amorphization)
observed from the Raman and IR spectra of Ca(OH)2 occurred at lower pressures than those of Ca(OD)2. In contrast, no isotope effect was found on the volume and axial compressions observed from powder X-ray diffraction patterns.
X-ray diffraction lines attributable to the high-pressure phase remained up to 28.5 GPa, suggesting no total amorphization
in a helium pressure medium within the examined pressure region. These results suggest that the H–D isotope effect is engendered
in the local environment surrounding H(D) atoms. Moreover, the ratio of sample-to-methanol–ethanol pressure medium (i.e.,
packing density) in the sample chamber had a significant effect on the increase in the half widths of the diffraction lines,
even at pressures below the hydrostatic limit of the pressure medium. 相似文献
9.
《Gondwana Research》2008,13(4):438-453
This paper presents a regional scale observation of metamorphic geology and mineral assemblage variations of Kontum Massif, central Vietnam, supplemented by pressure–temperature estimates and reconnaissance geochronological results. The mineral assemblage variations and thermobarometric results classify the massif into a low- to medium-temperature and relatively high-pressure northern part characterised by kyanite-bearing rocks (570–700 °C at 0.79–0.86 GPa) and a more complex southern part. The southern part can be subdivided into western and eastern regions. The western region shows very high-temperature (> 900 °C) and -pressure conditions characterised by the presence of garnet and orthopyroxene in both mafic and pelitic granulites (900–980 °C at 1.0–1.5 GPa). The eastern region contains widespread medium- to high-temperature and low-pressure rocks, with metamorphic grade increasing from north to south; epidote- or muscovite-bearing gneisses in the north (< 700–740 °C at < 0.50 GPa) to garnet-free mafic and orthopyroxene-free pelitic granulites in the south (790–920 °C at 0.63–0.84 GPa). The Permo-Triassic Sm–Nd ages (247–240 Ma) from high-temperature and -pressure granulites and recent geochronological studies suggest that the south-eastern part of Kontum Massif is composed of a Siluro-Ordovician continental fragment probably showing a low-pressure/temperature continental geothermal gradient derived from the Gondwana era with subsequent Permo-Triassic collision-related high-pressure reactivation zones. 相似文献
10.
Klaus Schollenbruch Alan B. Woodland Daniel J. Frost 《Physics and Chemistry of Minerals》2010,37(3):137-143
The stability of hercynite (FeAl2O4) has been investigated experimentally between 7 and 24 GPa and 900 and 1,700°C. Hercynite breaks down to its constituent
oxides at 7–8.5 GPa and temperatures >1,000°C. The incorporation of a small magnetite component in the hercynite necessitated
a small correction to fix the location of the endmember reaction: FeAl2O4 = Al2O3 + FeO in P–T space. After making this correction, the position of the phase boundary was used to evaluate thermodynamic data for hercynite.
Our results support a relatively large S
298° for hercynite, on the order of 115 J mol−1 K−1. Experiments up to 24 GPa and 1,400°C failed to detect any high-pressure polymorph of FeAl2O4; only corundum + wüstite were detected. This behaviour contrasts with that observed for the analogous MgAl2O4 system where the constituent oxides recombine at high pressure to produce “post-spinel” phases with CaFe2O4-type and CaTi2O4-type structures. 相似文献
11.
We used an in situ measurement method to investigate the phase transition of CaGeO3 polymorphs under high pressures and temperatures. A multi-anvil high-pressure apparatus combined with intense synchrotron
X-ray radiation was used. The transition boundary between a garnet and a perovskite phase at T = 900–1,650 K and P = 3–8 GPa was determined as occurring at P (GPa) = 9.0−0.0023 × T (K). The transition pressure determined in our study is in general agreement with that observed in previous high-pressure
experiments. The slope, dP/dT, of the transition determined in our study is consistent with that calculated from calorimetry data. 相似文献
12.
Xiaozhi Yang Leonid Dubrovinsky M. A. G. M. Manthilake Qingguo Wei 《Physics and Chemistry of Minerals》2012,39(1):57-64
In situ Raman spectra of hydrous wadsleyite (β-Mg2SiO4) with ~1.5 wt% H2O, synthesized at 18 GPa and 1,400°C, have been measured in an externally heated diamond anvil cell up to 15.5 GPa and 673 K.
With increasing pressure (at room temperature), the three most intense bands at ~549, 720 and 917 cm−1 shift continuously to higher frequencies, while with increasing temperature at 14.5 GPa, these bands generally shift to lower
frequencies. The temperature-induced frequency shifts at 14.5 GPa are significantly different from those at ambient pressure.
Moreover, two new bands at ~714 and ~550 cm−1 become progressively significant above 333 and 553 K, respectively, and disappear upon cooling to room temperature. No corresponding
Raman modes of these two new bands were reported for wadsleyite at ambient conditions, and they are thus probably related
to thermally activated processes (vibration modes) at high-pressure and temperature conditions. 相似文献
13.
The melting behaviour of three carbonated pelites containing 0–1 wt% water was studied at 8 and 13 GPa, 900–1,850°C to define
conditions of melting, melt compositions and melting reactions. At 8 GPa, the fluid-absent and dry carbonated pelite solidi
locate at 950 and 1,075°C, respectively; >100°C lower than in carbonated basalts and 150–300°C lower than the mantle adiabat.
From 8 to 13 GPa, the fluid-present and dry solidi temperatures then increase to 1,150 and 1,325°C for the 1.1 wt% H2O and the dry composition, respectively. The melting behaviour in the 1.1 wt% H2O composition changes from fluid-absent at 8 GPa to fluid-present at 13 GPa with the pressure breakdown of phengite and the
absence of other hydrous minerals. Melting reactions are controlled by carbonates, and the potassium and hydrous phases present
in the subsolidus. The first melts, which composition has been determined by reverse sandwich experiments, are potassium-rich
Ca–Fe–Mg-carbonatites, with extreme K2O/Na2O wt ratios of up to 42 at 8 GPa. Na is compatible in clinopyroxene with
D\textNa\textcpx/\textcarbonatite = 10-18 D_{\text{Na}}^{{{\text{cpx}}/{\text{carbonatite}}}} = 10{-}18 at the solidus at 8 GPa. The melt K2O/Na2O slightly decreases with increasing temperature and degree of melting but strongly decreases from 8 to 13 GPa when K-hollandite
extends its stability field to 200°C above the solidus. The compositional array of the sediment-derived carbonatites is congruent
with alkali- and CO2-rich melt or fluid inclusions found in diamonds. The fluid-absent melting of carbonated pelites at 8 GPa contrasts that at
≤5 GPa where silicate melts form at lower temperatures than carbonatites. Comparison of our melting temperatures with typical
subduction and mantle geotherms shows that melting of carbonated pelites to 400-km depth is only feasible for extremely hot
subduction. Nevertheless, melting may occur when subduction slows down or stops and thermal relaxation sets in. Our experiments
show that CO2-metasomatism originating from subducted crust is intimately linked with K-metasomatism at depth of >200 km. As long as the
mantle remains adiabatic, low-viscosity carbonatites will rise into the mantle and percolate upwards. In cold subcontinental
lithospheric mantle keels, the potassic Ca–Fe–Mg-carbonatites may freeze when reacting with the surrounding mantle leading
to potassium-, carbonate/diamond- and incompatible element enriched metasomatized zones, which are most likely at the origin
of ultrapotassic magmas such as group II kimberlites. 相似文献
14.
Arne P. Willner Axel Gerdes Hans-Joachim Massonne Alexander Schmidt Masafumi Sudo Stuart N. Thomson Graciela Vujovich 《Contributions to Mineralogy and Petrology》2011,162(2):303-327
The Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is
composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde
garnet growth in metapelite and metabasite occurred between 1.2 GPa, 470°C and 1.4 GPa, 530°C, when the penetrative s2-foliation was formed. The average age of garnet crystallization of 390 ± 2 Ma (2σ) was determined from three four-point Lu–Hf
mineral isochrones from metapelite and metabasite samples and represents the time of collision. Peak pressure conditions are
followed by a decompression path with slight heating at 0.5 GPa, 560°C. Fluid release during decompression caused equilibration
of mineral compositions at the rims and also aided Ar diffusion. An 40Ar/39Ar plateau age of white mica at 353 ± 1 Ma (1σ) indicates the time of cooling below 350–400°C. These temperatures were attained
at pressures of 0.2–0.3 GPa, indicative of an average exhumation rate of ≥1 mm/a for the period 390–353 Ma. Late hydrous influx
at 0.1–0.3 GPa caused pervasive growth of sericite and chlorite and reset the Ar/Ar ages of earlier coarse-grained white mica.
At 284–295 Ma, the entire basement cooled below 280°C (fission track ages of zircon) after abundant post-collisional granitoid
intrusion. The deeply buried epicontinental sedimentary rocks, the high peak pressure referring to a low metamorphic geotherm
of 10–12°C/km, and the decompression/heating path are characteristics of material buried and exhumed within a (micro) continent–continent
collisional setting. 相似文献
15.
In order to elucidate high-pressure transformations of high-P clinopyroxene (C2/c) at kinetically low temperature where atoms are not thermally activated, the transformation processes of FeGeO3 clinopyroxene (C2/c) have been investigated at pressures up to 20 GPa and 365 °C by powder X-ray diffraction using a synchrotron radiation source
and TEM observation. With increasing pressure up to 20 GPa at room temperature, FeGeO3 high-P clinopyroxene (C2/c) reversibly transforms into a new high-pressure phase, FeGeO3(II). On increasing the temperature up to 365 °C, this phase rapidly transforms into FeGeO3 ilmenite within about 2 h. Intensity analysis of the X-ray diffraction pattern reveals that the high-pressure phase of FeGeO3(II) has an intermediate structure between clinopyroxene and ilmenite: the cation arrangement is similar to that of clinopyroxene
and the oxygen arrangement is similar to that of ilmenite. The comparison of the crystal structures of these polymorphs suggests
that clinopyroxene to FeGeO3(II) and FeGeO3(II) to ilmenite transformations are performed by the slight deformation of the oxygen packing and the short-range movement
of cations, respectively. It is shown that this high-P clinopyroxene transforms into ilmenite through a low-activation energy
path under the low-temperature condition.
Received: 30 August 2000 / Accepted: 10 February 2001 相似文献
16.
Zucchini A. Comodi P. Katerinopoulou A. Balic-Zunic T. McCammon C. Frondini F. 《Physics and Chemistry of Minerals》2012,39(4):319-328
A combined powder and single-crystal X-ray diffraction analysis of dolomite [CaMg(CO3)2] heated to 1,200°C at 3 GPa was made to study the order–disorder–reorder process. The order/disorder transition is inferred
to start below 1,100°C, and complete disorder is attained at approximately 1,200°C. Twinned crystals characterized by high
internal order were found in samples annealed over 1,100°C, and their fraction was found to increase with temperature. Evidences
of twinning domains combined with probable remaining disordered portions of the structure imply that reordering processes
occur during the quench. Twin domains are hereby proposed as a witness to thermally induced intra-layer-type cation disordering. 相似文献
17.
Jinyuan Yan Bin Chen Selva Vennila Raju Budhiram K. Godwal Alastair A. MacDowell Jason Knight Hongwei Ma Quentin Williams 《Physics and Chemistry of Minerals》2012,39(4):269-275
The high-pressure behavior of HgO-montroydite was investigated up to 36.5 GPa using angle-dispersive X-ray diffraction. The
tetragonal phase of this material (HgO-II), a distortion of the NaCl structure, transforms into the cubic NaCl structure (HgO-III)
above ~31.5 GPa. The transformation of mercury oxide from the orthorhombic Pnma (HgO-I) structure to a tetragonal I4/mmm structure
(HgO-II) is confirmed to occur at 13.5 ± 1.5 GPa. Neither of the high-pressure phases, HgO-II nor HgO-III, is quenchable in
pressure. The derived isothermal bulk modulus of HgO-II and its pressure derivative strongly depend on the assumed zero-pressure
volume of this phase, but our elasticity results on HgO-II nevertheless lie significantly closer to theoretical calculations
than prior experimental results, and the measured pressure of the phase transformation to the NaCl structure is also in agreement
with recent theoretical results. The general accord with theory supports the existence of significant relativistic effects
on the high-pressure phase transitions of HgO. 相似文献
18.
Margaret Hanrahan Gerhard Brey Alan Woodland Rainer Altherr Hans-Micheal Seitz 《Contributions to Mineralogy and Petrology》2009,158(2):169-183
An eclogite barometer has profound importance in the study of upper mantle processes and potential application to diamond
prospecting. Studies on the partitioning of Li between clinopyroxene (cpx) and garnet (grt) in natural samples have shown
that this particular element is very sensitive to changes in pressure and could be calibrated as the barometer demanded for
bimineralic eclogites. Experiments were performed from 4 to 13 GPa and 1,100–1,400°C in the CMAS (CaO, MgO, Al2O3, SiO2) system with Li added as Li3PO4 to quantify this pressure dependence into a barometer expressed in the following equation: P = (0.00255T – ln K
d)/0.2351 where P is in GPa, T is in °C and K
d is defined as the partition coefficient of Li (in ppm) between clinopyroxene and garnet. The experimental pressures are reproduced
to ±0.38 GPa (1σ) by this equation. This barometer is strictly applicable only to CMAS. Experiments at 1,300°C, 8–12 GPa showed
that Henry’s Law is fulfilled for Li partitioning between cpx and grt in the concentration range of approximately 0.01–1 wt%
Li. Direct application of the equation to experiments in natural systems performed at 1,300°C from 4 to 13 GPa consistently
overestimates pressures by approximately 2 GPa.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
19.
B. Coldwell J. Adam T. Rushmer C. G. Macpherson 《Contributions to Mineralogy and Petrology》2011,162(4):835-848
Piston-cylinder experiments on a Pleistocene adakite from Mindanao in the Philippines have been used to establish near-liquidus
and sub-liquidus phase relationships relevant to conditions in the East Philippines subduction zone. The experimental starting
material belongs to a consanguineous suite of adakitic andesites. Experiments were conducted at pressures from 0.5 to 2 GPa
and temperatures from 950 to 1,150°C. With 5 wt. % of dissolved H2O in the starting mix, garnet, clinopyroxene and orthopyroxene are liquidus phases at pressures above 1.5 GPa, whereas clinopyroxene
and orthopyroxene are liquidus (or near-liquidus) phases at pressures <1.5 GPa. Although amphibole is not a liquidus phase
under any of the conditions examined, it is stable under sub-liquidus conditions at temperature ≤1,050°C and pressures up
to 1.5 GPa. When combined with petrographic observations and bulk rock chemical data for the Mindanao adakites, these findings
are consistent with polybaric fractionation that initially involved garnet (at pressures >1.5 GPa) and subsequently involved
the lower pressure fractionation of amphibole, plagioclase and subordinate clinopyroxene. Thus, the distinctive Y and HREE
depletions of the andesitic adakites (which distinguish them from associated non-adakitic andesites) must be established relatively
early in the fractionation process. Our experiments show that this early fractionation must have occurred at pressures >1.5 GPa
and, thus, deeper than the Mindanao Moho. Published thermal models of the Philippine Sea Plate preclude a direct origin by
melting of the subducting ocean crust. Thus, our results favour a model whereby basaltic arc melt underwent high-pressure
crystal fractionation while stalled beneath immature arc lithosphere. This produced residual magma of adakitic character which
underwent further fractionation at relatively low (i.e. crustal) pressures before being erupted. 相似文献
20.
Carl Spandler Greg Yaxley David H. Green Dean Scott 《Contributions to Mineralogy and Petrology》2010,160(4):569-589
We performed a series of piston-cylinder experiments on a synthetic pelite starting material over a pressure and temperature
range of 3.0–5.0 GPa and 1,100–1,600°C, respectively, to examine the melting behaviour and phase relations of sedimentary
rocks at upper mantle conditions. The anhydrous pelite solidus is between 1,150 and 1,200°C at 3.0 GPa and close to 1,250°C
at 5.0 GPa, whereas the liquidus is likely to be at 1,600°C or higher at all investigated pressures, giving a large melting
interval of over 400°C. The subsolidus paragenesis consists of quartz/coesite, feldspar, garnet, kyanite, rutile, ±clinopyroxene
±apatite. Feldspar, rutile and apatite are rapidly melted out above the solidus, whereas garnet and kyanite are stable to
high melt fractions (>70%). Clinopyroxene stability increases with increasing pressure, and quartz/coesite is the sole liquidus
phase at all pressures. Feldspars are relatively Na-rich [K/(K + Na) = 0.4–0.5] at 3.0 GPa, but are nearly pure K-feldspar
at 5.0 GPa. Clinopyroxenes are jadeite and Ca-eskolaite rich, with jadeite contents increasing with pressure. All supersolidus
experiments produced alkaline dacitic melts with relatively constant SiO2 and Al2O3 contents. At 3.0 GPa, initial melting is controlled almost exclusively by feldspar and quartz, giving melts with K2O/Na2O ~1. At 4.0 and 5.0 GPa, low-fraction melting is controlled by jadeite-rich clinopyroxene and K-rich feldspar, which leads
to compatible behaviour of Na and melts with K2O/Na2O ≫ 1. Our results indicate that sedimentary protoliths entrained in upwelling heterogeneous mantle domains may undergo melting
at greater depths than mafic lithologies to produce ultrapotassic dacitic melts. Such melts are expected to react with and
metasomatise the surrounding peridotite, which may subsequently undergo melting at shallower levels to produce compositionally
distinct magma types. This scenario may account for many of the distinctive geochemical characteristics of EM-type ocean island
magma suites. Moreover, unmelted or partially melted sedimentary rocks in the mantle may contribute to some seismic discontinuities
that have been observed beneath intraplate and island-arc volcanic regions. 相似文献