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1.
Vadim S. Kamenetsky Andrey A. Gurenko 《Contributions to Mineralogy and Petrology》2007,153(4):465-481
The origin of compositional heterogeneities among the magmas parental to mid-ocean ridge basalts (MORB) was investigated using
a single rock piece of the olivine-phyric basalt from 43°N, Mid-Atlantic Ridge (AII D11-177). The exceptional feature of this
sample is presence of very primitive olivine crystals (90–91 mol% Fo) that are significantly variable in terms of CaO (0.15–0.35 wt%).
A population of low-Ca olivine (0.15–0.25 wt% CaO) is also notably distinct from high-Ca olivine population in AII D11-177,
and primitive MORB olivine in general, in having unusual assemblage of trapped mineral and glass inclusions. Mineral inclusions
are represented by high-magnesian (Mg# 90.7–91.1 mol%) orthopyroxene and Cr-spinel, distinctly enriched in TiO2 (up to 5 wt%, c.f. <1 wt% in common MORB spinel). Glass inclusions associated with orthopyroxene and high-Ti Cr-spinel have
andesitic compositions (53–58 wt% SiO2). Compared to the pillow-rim glass and “normal” MORB inclusions, the Si-rich glass inclusions in low-Ca olivine have strongly
reduced Ca and elevated concentrations of Ti, Na, K, P, Cl, and highly incompatible trace elements. Strong variability is
recorded among glass inclusions within a single olivine phenocrysts. We argue that the observed compositional anomalies are
mineralogically controlled, and thus may arise from the interaction between hot MORB magmas and crystal cumulates in the oceanic
crust or magma chamber. 相似文献
2.
K. R. Rao S. L. Chaplot Narayani Choudhury Subrata Ghose J. M. Hastings L. M. Corliss D. L. Price 《Physics and Chemistry of Minerals》1988,16(1):83-97
Magnesium-rich olivine (Mg0.9Fe0.1)2SiO4 is considered to be a major constituent of the Earth's upper mantle. Because of its major geophysical importance, the temperature and pressure dependence of its crystal structure, elastic and dielectric constants, long-wavelength phonon modes and specific heat have been measured using a variety of experimental techniques. Theoretical study of lattice dynamics provides a means of analyzing and understanding a host of such experimental data in a unified manner. A detailed study of the lattice dynamics of forsterite, Mg2SiO4, has been made using a crystal potential function consisting of Coulombic and short-range terms. Quasiharmonic lattice dynamical calculations based on a rigid molecular-ion model have provided theoretical estimates of elastic constants, long-wavelength modes, phonon dispersion relation for external modes along the three high symmetry directions in the Brillouin zone, total and partial density of states and inelastic neutron scattering cross-sections. The neutron cross-sections were used as guides for the coherent inelastic neutron scattering experiment on a large single crystal using a triple axis spectrometer in the constant Q mode. The observed and predicted phonon dispersion relation show excellent agreement. The inelastically scattered neutron spectra from a powder sample have been analyzed on the basis of a phonon density of states calculated from a rigid-ion model, which includes both external and internal modes. The experimental data from a powder sample show good agreement with the calculated spectra, which include a multiphonon contribution in the incoherent approximation. The computed phonon densities of states are used to calculate the specific heat as a function of temperature using both the rigid molecular-ion and rigid ion models. These results are in very good agreement with the calorimetric measurement of the specific heat. The interatomic potential developed here can be used with some confidence to study physical properties of forsterite as a function of pressure and temperature. 相似文献
3.
Olivine-hosted melt inclusions have been analyzed from the young (4,150 ± 300 ybp) Dotsero basaltic (48.2 wt% SiO2) lava flow in Northwest Colorado, USA. Silicate melt-inclusion compositions have a bimodal distribution (41–46 wt% SiO2 and 47–50 wt% SiO2). Low-Si melt inclusions record high pre-eruptive sulfur concentrations (>1,000 ppm S) and variations in their major- and
trace-element compositions appears to be related to shallow assimilation of local basement sandstone. Whole-rock compositions
are modeled as a contamination of low-Si inclusion compositions with ~10 wt% sandstone. Host olivine crystallization may have
accompanied magma injection into a shallow storage chamber. In contrast to the low-Si melt inclusions, the high-Si population
is relatively degassed and records late-stage rapid crystallization either during or post-eruption. Hopper or skeletal olivine
grains in conjunction with the bimodal inclusion compositions suggest relatively rapid cooling rates at the time of eruption
and inclusion entrapment. Inclusion compositions, in conjunction with mineral textures, therefore provide a more complete
picture of shallow magma processes, coupling the relative timing of undercooling and crystallization, assimilation and melt
compositional evolution. Most of the inclusion and host textural and compositional data indicates late and very shallow petrogenetic
processes and does not appear to record deeper (mid-, lower-crustal) processes. 相似文献
4.
Cliff S. J. Shaw 《Contributions to Mineralogy and Petrology》1999,135(2-3):114-132
A large body of recent work has linked the origin of Si-Al-rich alkaline glass inclusions to metasomatic processes in the
upper mantle. This study examines one possible origin for these glass inclusions, i.e., the dissolution of orthopyroxene in
Si-poor alkaline (basanitic) melt. Equilibrium dissolution experiments between 0.4 and 2 GPa show that secondary glass compositions
are only slightly Si enriched and are alkali poor relative to natural glass inclusions. However, disequilibrium experiments
designed to examine dissolution of orthopyroxene by a basanitic melt under anhydrous, hydrous and CO2-bearing conditions show complex reaction zones consisting of olivine, ± clinopyroxene and Si-rich alkaline glass similar
in composition to that seen in mantle xenoliths. Dissolution rates are rapid and dependent on volatile content. Experiments
using an anhydrous solvent show time dependent dissolution rates that are related to variable diffusion rates caused by the
saturation of clinopyroxene in experiments longer than 10 minutes. The reaction zone glass shows a close compositional correspondence
with natural Si-rich alkaline glass in mantle-derived xenoliths. The most Si-and alkali-rich melts are restricted to pressures
of 1 GPa and below under anhydrous and CO2-bearing conditions. At 2 GPa glass in hydrous experiments is still Si-␣and alkali-rich whereas glass in the anhydrous and
CO2-bearing experiments is only slightly enriched in SiO2 and alkalis compared with the original solvent. In the low pressure region, anhydrous and hydrous solvent melts yield glass
of similar composition whereas the glass from CO2-bearing experiments is less SiO2 rich. The mechanism of dissolution of orthopyroxene is complex involving rapid incongruent breakdown of the orthopyroxene,
combined with olivine saturation in the reaction zone forming up to 60% olivine. Inward diffusion of CaO causes clinopyroxene
saturation and uphill diffusion of Na and K give the glasses their strongly alkaline characteristics. Addition of Na and K
also causes minor SiO2 enrichment of the reaction glass by increasing the phase volume of olivine. Olivine and clinopyroxene are transiently stable
phases within the reaction zone. Clinopyroxene is precipitated from the reaction zone melt near the orthopyroxene crystal
and redissolved in the outer part of the reaction zone. Olivine defines the thickness of the reaction zone and is progressively
dissolved in the solvent as the orthopyroxene continues to dissolve. Although there are compelling reasons for supporting
the hypothesis that Si-rich alkaline melts are produced in the mantle by orthopyroxene – melt reaction in the mantle, there
are several complications particularly regarding quenching in of disequilibrium reaction zone compositions and the mobility
of highly polymerized melts in the upper mantle. It is considered likely that formation of veins and pools of Si-rich alkaline
glass by orthopyroxene – melt reaction is a common process during the ascent of xenoliths. However, reaction in situ within
the mantle will lead to equilibration and therefore secondary melts will be only moderately siliceous and alkali poor.
Received: 24 August 1998 / Accepted: 2 December 1998 相似文献
5.
François Faure Pierre Schiano Gilles Trolliard Christian Nicollet Bernard Soulestin 《Contributions to Mineralogy and Petrology》2007,153(4):405-416
Dynamic crystallization experiments in the CaO–MgO–Al2O3–SiO2 (CMAS) system have been used to investigate the change in crystal shape when pre-existing polyhedral olivine crystals are
cooled rapidly (1,639–2,182°C/h). Polyhedral olivines are crystallized initially in a first step using a slow cooling rate
(2°C/h), then skeletal and dendritic overgrowths develop on the polyhedral crystals during a subsequent fast cooling event.
During this second episode small dendritic olivines also nucleate within the liquid phase. Observation of the experimental
sample by optical microscopy shows that the polyhedral olivine shape progressively changes to a skeletal and then to a dendritic
morphology in the following sequence: polyhedral ⇒ hopper polyhedral ⇒ dendritic polyhedral. This evolutional sequence is
discussed in terms of changes in the crystal growth conditions during cooling and a general relation between these olivine
dynamic crystallization experiments and the integrated model of crystal growth by Sunagawa (Bull Minér 104:81–87, 1981, Morphology of crystals, Terra Scientific Publishing Company, 1987) is proposed. 相似文献
6.
End-member synthetic fayalite and forsterite and a natural solid-solution crystal of composition (Mg1.80,Fe0.20)SiO4 were investigated using Raman spectroscopy. Polarized single-crystal spectra were measured as a function of temperature. In addition, polycrystalline forsterite and fayalite, isotopically enriched in 26Mg and 57Fe, respectively, were synthesized and their powder spectra measured. The high-wavenumber modes in olivine consist of internal SiO4 vibrations that show little variation upon isotopic substitution. This confirms conclusions from previous spectroscopic studies that showed that the internal SiO4 vibrations have minimal coupling with the lower-wavenumber lattice modes. The lowest wavenumber modes in both forsterite and fayalite shift in energy following isotopic substitution, but with energies less than that which would be associated with pure Mg and Fe translations. The low-wavenumber Raman modes in olivine are best described as lattice modes consisting to a large degree of mixed vibrations of M(2) cation translations and external vibrations of the SiO4 tetrahedra. The single-crystal spectra of forsterite and Fo90Fa10 were recorded at a number of temperatures from room temperature to about 1200 °C. From these data the microscopic Grüneisen parameters for three different Ag modes for both compositions were calculated, and also the structural state of the solid solution crystal was investigated. Small discontinuities observed in the wavenumber behavior of a low-energy mixed Mg/T(SiO4) mode between 700 and 1000 °C may be related to minor variations in the Fe–Mg intracrystalline partitioning state in the Fo90Fa10 crystal, but further spectroscopic work is needed to clarify and quantify this issue. The mode wavenumber and intensity behavior of internal SiO4 vibrations as a function of temperature are discussed in terms of crystal field and dynamic splitting and also 1 and 3 coupling. Crystal-field splitting increases only very slightly with temperature, whereas dynamical-field splitting is temperature dependent. The degree of 1–3 coupling decreases with increasing temperature. 相似文献
7.
Quantum-thermodynamic treatment of intrinsic anharmonicity; Wallace’s theorem revisited 总被引:1,自引:0,他引:1
Wallace (in Thermodynamics of crystals, 1972) developed a theorem, rooted in rigid lattice dynamics, which incorporates intrinsic anharmonic effects in solids. The practical
application of this theorem in mineral physics is computationally involved and this is the main reason for the theorem not
getting the attention it deserves. Because intrinsic anharmonicity is an important issue at the extreme conditions in planetary
mantles, we derived a method which removes the computational obstacles in applying this theorem. We extended the theorem to
incorporate details of the phonon spectrum and tested our algorithm on forsterite (Mg2SiO4). Using a least squares inversion technique applied to all available experimental data, we show that it results in an accurate
representation of thermodynamic properties and sound wave velocities of Mg2SiO4 in its complete pressure–temperature stability range. We also show that the accuracy of our results is not significantly
affected by the use of a different equation of state. 相似文献
8.
An olivine grain from a peridotite nodule 9206 (Udachnaya kimberlite, Siberia) was investigated by TEM methods including
AEM, HRTEM, SAED and EELS techniques. A previous study of the 9206 olivine sample revealed OH absorption bands in the IR spectrum
and abundant nanometer-sized OH-bearing inclusions, of hexagonal-like or lamellar shape. Inclusions, which are several hundred
nm in size, consist of 10 ? phase, talc and serpentine (chrysotile and lizardite). The lamellar (LI) and hexagon-like small
inclusions of several ten nm in size (SI) are the topic of the present paper. AEM investigations of the inclusions reveal
Mg, Fe and Si as cations only. The Mg/Si and Fe/Si atomic ratios are lower in the inclusions than in the host olivine. The
Si concentration in the olivine host and both lamellar inclusions and small inclusions is the same. A pre-peak at 528eV was
observed in EEL spectra of LI and SI, which is attributed to OH− or Fe3+. From these data it is concluded that there is a OH−- or Fe3+-bearing cation-deficient olivine-like phase present.
HRTEM lattice fringe images of LI and SI exhibit modulated band-like contrasts, which are superimposed onto the olivine lattice.
Diffraction patterns (Fourier-transforms) of the HREM images as well as SAED patterns show that the band-like contrasts in
HRTEM images of the inclusions are caused by periodic modulations of the olivine lattice. Three kinds of superperiodicity
in the olivine structure such as 2a, 3a and 3c, were observed in SAED patterns. The corresponding olivine supercells labelled
here as Hy-2a, Hy-3a and Hy-3c were derived. The M1-vacancies located in the (100) and (001) octahedral layers of the olivine
lattice are suggested to form ordered arrays of planar defects (PD), which cause the band-like contrasts in HRTEM patterns
as well as the superperiodicity in the SAED patterns.
The vacancy concentrations as well as the chemical composition of Hy-2a, Hy-3a and Hy-3c olivine supercells were calculated
using crystal chemical approaches, assuming either {(OH)<
O−V"
Me−(OH)<
O}↔, or {F
e
<
Fe
−H
Me
′}↔ or {2F
e
<
Fe
−V
Me
"}↔ point defect associates. The calculated theoretical compositions Mg1.615Fe+2
0.135v0.25SiO4H0.5 (Hy-2a) and Mg1.54Fe2+
0.12v0.33SiO4H0.66 (Hy-3a and Hy-3c) are in a good agreement with the AEM data on inclusions. Hy-2a, Hy-3a and Hy-3c are considered to be a
hydrous olivine with the extended chemical formula (Mg1-yFe2+
y)2−xvxSiO4H2x. The crystal structure of hydrous olivine is proposed to be a modular olivine structure with Mg-vacant modules. The crystal
chemical formula of hydrous olivines in terms of a modular structure can be written as [MgSiO4H2] · 3[Mg1.82Fe0.18SiO4] for Hy-2a, [MgSiO4H2] · 2[Mg1.82Fe0.18SiO4] for Hy-3a and Hy-3c.
Hydrous olivine is suggested to be exsolved from the olivine 9206, which has been initially saturated by OH-bearing point
defects. The olivine 9206 hydration as well as the following exsolution of hydrous olivine inclusions is suggested to occur
at high pressure-high temperature conditions of the upper mantle.
Received: 15 January 2001 / Accepted: 2 July 2001 相似文献
9.
The paper presents data on naturally quenched melt inclusions in olivine (Fo 69–84) from Late Pleistocene pyroclastic rocks
of Zhupanovsky volcano in the frontal zone of the Eastern Volcanic Belt of Kamchatka. The composition of the melt inclusions
provides insight into the latest crystallization stages (∼70% crystallization) of the parental melt (∼46.4 wt % SiO2, ∼2.5 wt % H2O, ∼0.3 wt % S), which proceeded at decompression and started at a depth of approximately 10 km from the surface. The crystallization
temperature was estimated at 1100 ± 20°C at an oxygen fugacity of ΔFMQ = 0.9–1.7. The melts evolved due to the simultaneous
crystallization of olivine, plagioclase, pyroxene, chromite, and magnetite (Ol: Pl: Cpx: (Crt-Mt) ∼ 13: 54: 24: 4) along the tholeiite evolutionary trend and became progressively enriched in FeO, SiO2, Na2O, and K2O and depleted in MgO, CaO, and Al2O3. Melt crystallization was associated with the segregation of fluid rich in S-bearing compounds and, to a lesser extent, in
H2O and Cl. The primary melt of Zhupanovsky volcano (whose composition was estimated from data on the most primitive melt inclusions)
had a composition of low-Si (∼45 wt % SiO2) picrobasalt (∼14 wt % MgO), as is typical of parental melts in Kamchatka and other island arcs, and was different from MORB.
This primary melt could be derived by ∼8% melting of mantle peridotite of composition close to the MORB source, under pressures
of 1.5 ± 0.2 GPa and temperatures 20–30°C lower than the solidus temperature of “dry” peridotite (1230–1240°C). Melting was
induced by the interaction of the hot peridotite with a hydrous component that was brought to the mantle from the subducted
slab and was also responsible for the enrichment of the Zhupanovsky magmas in LREE, LILE, B, Cl, Th, U, and Pb. The hydrous
component in the magma source of Zhupanovsky volcano was produced by the partial slab melting under water-saturated conditions
at temperatures of 760–810°C and pressures of ∼3.5 GPa. As the depth of the subducted slab beneath Kamchatkan volcanoes varies
from 100 to 125 km, the composition of the hydrous component drastically changes from relatively low-temperature H2O-rich fluid to higher temperature H2O-bearing melt. The geothermal gradient at the surface of the slab within the depth range of 100–125 km beneath Kamchatka
was estimated at 4°C/km. 相似文献
10.
Segregation veins are common in lava sheets and result from internal differentiation during lava emplacement and degassing.
They consist of evolved liquid, most likely replaced by gas-filter pressing from a ∼50% crystallised host lava. Pairs of samples,
host lavas and associated segregation veins from the Reykjanes Peninsula (Iceland), Lanzarote (Canary Islands) and the Masaya
volcano (Nicaragua) show extreme mineralogical and compositional variations (MgO in host lava, segregation veins and interstitial
glass ranges from 8–10 wt%, 3–6 wt%, and to less than 0.01 wt%, respectively). These samples allow the assessment of the internal
lava flow differentiation mechanism, since both the parental and derived liquid are known in addition to the last magma drops
in the form of late interstitial glasses. The mineralogical variation, mass-balance calculated from major- and trace element
composition, and transitional metal partition between crystals and melts are all consistent with fractional crystallisation
as the dominant differentiation mechanism. The interstitial glasses are highly silicic (SiO2 = 70–80 wt%) and represent a final product of high-degree (75–97%) fractional crystallisation of olivine tholeiite at a pressure
close to one atmosphere. The tholeiitic liquid-line-of-decent and the composition of the residual melts are governed by the
K2O/Na2O of the initial basaltic magma. The granitic minimum is reached if the initial liquid has a high K2O/Na2O whereas trondhjemitic composition is the final product of magma with low initial K2O/Na2O.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
11.
Dawnika L. Blatter Ian S. E. Carmichael 《Contributions to Mineralogy and Petrology》1998,132(2):121-138
Approximately 150 km west of Mexico City in the central part of the Mexican Volcanic Belt (MVB) near Zitácuaro, Mexico, young
volcanism has produced shield volcanoes, large volume silicic deposits, and fault-related basalt and andesite lava flows and
cinder cones. This paper concerns a small cluster of Pleistocene andesite cones and flows which can be separated into two
distinct groups: high-magnesium andesites (>6% MgO, 57–59% SiO2), conveniently called basaltic andesites, with phenocrysts of orthopyroxene and augite, or augite and olivine; and andesites
(60–62% SiO2, <4.6% MgO), which have phenocrysts of orthopyroxene and augite, and ghosts of relict hornblende. Remarkably, plagioclase
phenocrysts are absent, and evenly distributed but sparse (0.5–3.5%) quartz xenocrysts are present in all the lavas. In order
to establish the conditions under which early crystallizing plagioclase is suppressed in these lavas, water saturated experiments
up to 3 kbars were performed on one of the basaltic andesites. The conditions required to reproduce the phenocryst assemblages
(either olivine + augite or opx + augite) are temperatures in excess of 1000 °C, with water saturated liquids (>3 wt%) at
pressures of about 1 kbar. Compared to basaltic andesites of western Mexico, the Zitácuaro basaltic andesites have ∼2 wt%
lower Al2O3 concentrations, which causes plagioclase to precipitate at significantly lower temperatures, and it therefore follows the
crystallization sequence: olivine, augite, and orthopyroxene. Based on ubiquitous quartz xenocrysts, with glassy rhyolitic
inclusions, a reasonable conclusion is that substantial mixing of a quartz-bearing rhyolitic magma with a parental basaltic
andesite has occurred at low pressure (shallow depth), and this would account for the low Al2O3 concentrations in the Zitácuaro basaltic andesites. Whatever the mechanism of incorporation, the quartz xenocrysts are evidence
of contamination of basaltic magma with more siliceous material, thus making it difficult to use these magmas as indicators
of mantle melting processes.
Received: 29 July 1997 / Accepted: 29 January 1998 相似文献
12.
Experimental insights into the formation of high-Mg basaltic andesites in the trans-Mexican volcanic belt 总被引:1,自引:1,他引:0
High-Mg basaltic andesites and andesites occur in the central trans-Mexican volcanic belt, and their primitive geochemical
characteristics suggest equilibration with mantle peridotite. These lavas may represent slab melts that reequilibrated with
overlying peridotite or hydrous partial melts of a peridotite source. Here, we experimentally map the liquidus mineralogy
for a high-Mg basaltic andesite (9.6 wt% MgO, 54.4 wt% SiO2, Mg# = 75.3) as a function of temperature and H2O content over a range of mantle wedge pressures. Our results permit equilibration of this composition with a harzburgite
residue at relatively high water contents (>7 wt%) and low temperatures (1,080–1,150°C) at 11–14 kbar. However, in contrast
to the high Ni contents characteristic of olivine phenocrysts in many such samples from central Mexico, those of olivine phenocrysts
in our sample are more typical of mantle melts that have fractionated a small amount of olivine. To account for this and the
possibility that the refractory mantle source may have had olivine more Fo-rich than Fo90, we numerically evaluated alternative equilibration conditions, using our starting bulk composition adjusted to be in equilibrium
with Fo92 olivine. This shifts equilibration conditions to higher temperatures (1,180–1,250°C) at mantle wedge pressures (11–15 kbar)
for H2O contents (>3 wt%) comparable to those analyzed in olivine-hosted melt inclusions from this region. Comparison with geodynamic
models shows that final equilibration occurred shallower than the peak temperature of the mantle wedge, suggesting that basaltic
melts from the hottest part of the wedge reequilibrated with shallower mantle as they approached the Moho. 相似文献
13.
In this paper we describe the mineralogy and geochemistry of basanites and melt inclusions in minerals from the Tergesh pipe,
northern Minusinsk Depression. The rocks are composed of olivine and clinopyroxene phenocrysts and a groundmass of olivine,
clinopyroxene, titanomagnetite, plagioclase, apatite, ilmenite, and glass. Melt inclusions were found only in the olivine
and clinopyroxene phenocrysts. Primary melt inclusions in olivine contain glass, rh?nite, clinopyroxene, a sulfide globule,
and low-density fluid. The phase composition of melt inclusions in clinopyroxene is glass + low-density fluid ± xenogenous
magnetite. According to thermometric investigations, the olivine phenocrysts began crystallizing at T = 1280–1320°C and P > 3.5 kbar, whereas groundmass minerals were formed under near-surface conditions at T ≤ 1200°C. The oxygen fugacity gradually changed during basanite crystallization from oxidizing (NNO) to more reducing conditions
(QFM). The investigation of glass compositions (heated and unheated inclusions in phenocrysts and groundmass) showed that
the evolution of a basanite melt during its crystallization included mainly an increase in SiO2, Al2O3, and alkalis, while a decrease in femic components, and the melt composition moved gradually toward tephriphonolite and trachyandesite.
Geochemical evidence suggests that the primary basanite melt was derived from a mantle source affected by differentiation.
Original Russian Text ? T.Yu. Timina, V.V. Sharygin, A.V. Golovin, 2006, published in Geokhimiya, 2006, No. 8, pp. 814–833. 相似文献
14.
Victoria E. Hamilton 《Chemie der Erde / Geochemistry》2010,70(1):7-33
The reststrahlen features in thermal infrared, or vibrational, spectra of Mg-Fe olivines ((Mg,Fe)2SiO4) exhibit trends in position, strength, and number of features that are diagnostic of the relative proportions of the Mg and Fe cations in the minerals. Although band positions move to lower wavenumbers (longer wavelengths) across the forsterite–fayalite compositional binary in a generally linear manner, specific feature shifts in transmittance data are described best by two linear fits with a break in slope near Fo70. The break in slope may be accompanied by an offset as well; both traits are attributed to structural changes in olivine brought about by distortion of the crystal lattice by Fe. Reflectance and emissivity spectra exhibit similar trends in band position with composition, and all three types of data demonstrate that some olivine band strengths change across the Mg–Fe solid solution series and also are diagnostic of composition. Olivines have been identified in a wide array of thermal infrared spectra of planetary materials and have been interpreted as being present on the surfaces of Mercury, the Moon, Mars, and a number of asteroids based on the analysis of thermal infrared spectra. New linear least squares models of the emissivity spectra of olivine-bearing Martian meteorites enable a preliminary estimation of the accuracy with which quantitative estimates of olivine abundance and solid solution composition can be derived from the spectra of mixtures. 相似文献
15.
Dexter Perkins Elizabeth Y. Anthony 《Contributions to Mineralogy and Petrology》2011,162(6):1139-1157
In peridotites, olivine, clinopyroxene, and orthopyroxene are complex solid solutions with wide stability fields. Depending
mostly on bulk composition and pressure, these minerals may be accompanied by plagioclase (low pressure), spinel (moderate
pressure), or garnet (high pressure), resulting in 4-phase and rarer 5-phase assemblages. Although a particular mineral assemblage
is stable over a range of P–T, the compositions of the individual minerals vary with changing P–T conditions. Application
of standard geothermobarometers to olivine–clinopyroxene–orthopyroxene–spinel peridotites is problematic. An alternative approach
is to use a bulk rock composition to calculate equilibrium phase diagrams to determine the conditions under which a particular
assemblage is stable. This requires consideration of the 7-component system SiO2–Al2O3–Cr2O3–FeO–MgO–CaO–Na2O, internally consistent thermodynamic data for end members, and reliable mixing models for all mineral solutions. Experimental
studies in simpler systems, and solution models from the literature, permit derivation of multicomponent thermodynamic mixing
models for the key minerals. The models, when applied to xenoliths from Kilbourne Hole, constrain P and T of equilibration
and are less sensitive to mineral compositional variations, or uncertainty in activity models, than standard thermobarometry.
Our modeling provides the first tightly constrained pressure estimates for Kilbourne Hole, placing the xenoliths in the spinel
stability field at depths (30–45 km) that correspond to the uppermost mantle beneath the Rio Grande Rift. The fine-grained
equigranular lherzolite, porphyroclastic lherzolite, and some harzburgite-dunite specimens equilibrated at average conditions
of 11.5 Kbar-930°C, 12 Kbar-990°C, and 13 Kbar-1,080°C, respectively. The mantle beneath the Rio Grande Rift is layered; the
fine-grained equigranular lherzolite derives from relatively shallow depth (35 km average), and the porphyroclastic lherzolite
from slightly deeper levels. Lying 5–10 km beneath both lherzolites, the harzburgite-dunite represents a depth where melt
extraction has significantly altered mantle chemistry and where local thermodynamic equilibrium has not been maintained. 相似文献
16.
We have conducted high pressure (to 3 kbar), water saturated melting experiments on an andesite (62 wt% SiO2) and a basaltic andesite (55 wt% SiO2) from western Mexico. A close comparison between the experimental phase assemblages and their compositions, and the phenocryst
assemblages of the lavas, is found in water saturated liquids, suggesting that the CO2 content was minimal in the fluid phase. Thus the historic lavas from Volcan Colima (with phenocrysts of orthopyroxene, augite,
plagioclase, and hornblende) were stored at a temperature between 950–975 °C, at a pressure between 700–1500 bars, and with
a water content of 3.0–5.0 wt%. A hornblende andesite (spessartite) from Mascota, of nearly identical composition but with
only amphibole phenocrysts, had a similar temperature but equilibrated at a minimum of 2000 bars pressure with a dissolved
water content of at least 5.5 wt% in the liquid. Experiments on the basaltic andesite show that the most common natural phenocryst
assemblages (olivine, ±augite, ±plagioclase) could have precipitated at temperatures from 1000–1150 °C, in liquids with a
wide range of dissolved water content (∼2.0–6.0 wt%) and a corresponding pressure range. A lava of the same bulk composition
with phenocrysts of hornblende, olivine, plagioclase, and augite is restricted to temperatures below 1000 °C and pressures
below 2500 bars, corresponding to <5.5 wt% water in the residual liquid. Although there is some evidence for mixing in the
andesites (sporadic olivine phenocrysts), the broad theme of the history of both lava types is that the phenocryst assemblages
for both the andesitic magmas and basaltic andesitic magmas are generated from degassing and reequilibration on ascent of
initially hydrous parents containing greater than 6 wt% water. Indeed andesitic magmas could be related to a basaltic andesite
parent by hornblende-plagioclase fractionation under the same hydrous conditions.
Received: 10 December 1996 / Accepted: 21 August 1997 相似文献
17.
D. M. Ruscitto P. J. Wallace A. J. R. Kent 《Contributions to Mineralogy and Petrology》2011,162(1):109-132
Primitive chemical characteristics of high-Mg andesites (HMA) suggest equilibration with mantle wedge peridotite, and they
may form through either shallow, wet partial melting of the mantle or re-equilibration of slab melts migrating through the
wedge. We have re-examined a well-studied example of HMA from near Mt. Shasta, CA, because petrographic evidence for magma
mixing has stimulated a recent debate over whether HMA magmas have a mantle origin. We examined naturally quenched, glassy,
olivine-hosted (Fo87–94) melt inclusions from this locality and analyzed the samples by FTIR, LA-ICPMS, and electron probe. Compositions (uncorrected
for post-entrapment modification) are highly variable and can be divided into high-CaO (>10 wt%) melts only found in Fo > 91
olivines and low-CaO (<10 wt%) melts in Fo 87–94 olivine hosts. There is evidence for extensive post-entrapment modification
in many inclusions. High-CaO inclusions experienced 1.4–3.5 wt% FeOT loss through diffusive re-equilibration with the host olivine and 13–28 wt% post-entrapment olivine crystallization. Low-CaO
inclusions experienced 1–16 wt% olivine crystallization with <2 wt% FeOT loss experienced by inclusions in Fo > 90 olivines. Restored low-CaO melt inclusions are HMAs (57–61 wt% SiO2; 4.9–10.9 wt% MgO), whereas high-CaO inclusions are primitive basaltic andesites (PBA) (51–56 wt% SiO2; 9.8–15.1 wt% MgO). HMA and PBA inclusions have distinct trace element characteristics. Importantly, both types of inclusions
are volatile-rich, with maximum values in HMA and PBA melt inclusions of 3.5 and 5.6 wt% H2O, 830 and 2,900 ppm S, 1,590 and 2,580 ppm Cl, and 500 and 820 ppm CO2, respectively. PBA melts are comparable to experimental hydrous melts in equilibrium with harzburgite. Two-component mixing
between PBA and dacitic magma (59:41) is able to produce a primitive HMA composition, but the predicted mixture shows some
small but significant major and trace element discrepancies from published whole-rock analyses from the Shasta locality. An
alternative model that involves incorporation of xenocrysts (high-Mg olivine from PBA and pyroxenes from dacite) into a primary
(mantle-derived) HMA magma can explain the phenocryst and melt inclusion compositions but is difficult to evaluate quantitatively
because of the complex crystal populations. Our results suggest that a spectrum of mantle-derived melts, including both PBA
and HMA, may be produced beneath the Shasta region. Compositional similarities between Shasta parental melts and boninites
imply similar magma generation processes related to the presence of refractory harzburgite in the shallow mantle. 相似文献
18.
A. A. Gurenko Thor H. Hansteen Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》1996,124(3-4):422-435
Picritic units of the Miocene shield volcanics on Gran Canaria, Canary Islands, contain olivine and clinopyroxene phenocrysts
with abundant primary melt, crystal and fluid inclusions. Composition and crystallization conditions of primary magmas in
equilibrium with olivine Fo90-92 were inferred from high-temperature microthermometric quench experiments, low-temperature microthermometry of fluid inclusions
and simulation of the reverse path of olivine fractional crystallization based on major element composition of melt inclusions.
Primary magmas parental for the Miocene shield basalts range from transitional to alkaline picrites (14.7–19.3 wt% MgO, 43.2–45.7
wt% SiO2). Crystallization of these primary magmas is believed to have occurred over the temperature range 1490–1150° C at pressures
≈5 kbar producing olivine of Fo80.6-90.2, high-Ti chrome spinel [Mg/ (Mg+Fe2+)=0.32–0.56, Cr/(Cr+Al)=0.50–0.78, 2.52–8.58 wt% TiO2], and clinopyroxene [Mg/(Mg+Fe)=0.79–0.88, Wo44.1-45.3, En43.9-48.0, Fs6.8-11.0] which appeared on the liquidus together with olivine≈Fo86. Redox conditions evolved from intermediate between the QFM and WM buffers to late-stage conditions of NNO+1 to NNO+2. The
primary magmas crystallized in the presence of an essentially pure CO2 fluid. The primary magmas originated at pressures >30 kbar and temperatures of 1500–1600° C, assuming equilibrium with mantle
peridotite. This implies melting of the mantle source at a depth of ≈100 km within the garnet stability field followed by
migration of melts into magma reservoirs located at the boundary between the upper mantle and lower crust. The temperatures
and pressures of primary magma generation suggest that the Canarian plume originated in the lower mantle at depth ≈900 km
that supports the plume concept of origin of the Canary Islands.
Received: 23 October 1995/Accepted: 21 February 1996 相似文献
19.
Mt. Baker is a dominantly andesitic stratovolcano in the northern Cascade arc. In this study, we show that the andesites are
not all derived from similar sources, and that open-system processes were dominant during their petrogenesis. To this end,
we discuss petrographic observations, mineral chemistry, and whole rock major and trace element chemistry for three of Mt.
Baker’s late Pleistocene to Holocene lava flow units. These include the basalt and basaltic andesite of Sulphur Creek (SC)
(51.4–55.8 wt% SiO2, Mg# 57–58), the Mg-rich andesite of Glacier Creek (GC) (58.3–58.7 wt% SiO2, Mg# 63–64), and the andesite and dacite of Boulder Glacier (BG) (60.2–64.2 wt% SiO2, Mg# 50–57). Phenocryst populations in all units display varying degrees of reaction and disequilibrium textures along with
complicated zoning patterns indicative of open-system processes. All lavas are medium-K and calc-alkaline, but each unit displays
distinctive trace element and REE characteristics that do not correlate with the average SiO2 content of the unit. The mafic lavas of SC have relatively elevated REE abundances with the lowest (La/Yb)N (~4.5). The intermediate GC andesites (Mg- and Ni-rich) have the lowest REE abundances and the highest (La/Yb)N (~6.7) with strongly depleted HREE. The more felsic BG lavas have intermediate REE abundances and (La/Yb)N (~6.4). The high-Mg character of the GC andesites can be explained by addition of 4% of a xenocrystic olivine component.
However, their depleted REE patterns are similar to other high-Mg andesites reported from Mt. Baker and require a distinct
mantle source. The two dominantly andesitic units (GC and BG) are different enough from each other that they could not have
been derived from the same parent basalt. Nor could either of them have been derived from the SC basalt by crystal fractionation
processes. Crystal fractionation also cannot explain the compositional diversity within each unit. Compositional diversity
within the SC unit (basalt to basaltic andesite) can, however, be successfully modeled by mixing of basalt with compositions
similar to the dacites in the BG unit. Given that the BG dacites erupted at ~80–90 ka, and a similar composition was mixed
with the SC lavas at 9.8 ka, the process that produced this felsic end-member must have been repeatedly active for at least
70 ka. 相似文献
20.
Mineral chemistry of submarine lavas from Hilo Ridge, Hawaii: implications for magmatic processes within Hawaiian rift zones 总被引:10,自引:0,他引:10
Huai-Jen Yang Frederick A. Frey David A. Clague Michael O. Garcia 《Contributions to Mineralogy and Petrology》1999,135(4):355-372
The crustal history of volcanic rocks can be inferred from the mineralogy and compositions of their phenocrysts which record
episodes of magma mixing as well as the pressures and temperatures when magmas cooled. Submarine lavas erupted on the Hilo
Ridge, a rift zone directly east of Mauna Kea volcano, contain olivine, plagioclase, augite ±orthopyroxene phenocrysts. The
compositions of these phenocryst phases provide constraints on the magmatic processes beneath Hawaiian rift zones. In these
samples, olivine phenocrysts are normally zoned with homogeneous cores ranging from ∼ Fo81 to Fo91. In contrast, plagioclase, augite and orthopyroxene phenocrysts display more than one episode of reverse zoning. Within each
sample, plagioclase, augite and orthopyroxene phenocrysts have similar zoning profiles. However, there are significant differences
between samples. In three samples these phases exhibit large compositional contrasts, e.g., Mg# [100 × Mg/(Mg+Fe+2)] of augite varies from 71 in cores to 82 in rims. Some submarine lavas from the Puna Ridge (Kilauea volcano) contain phenocrysts
with similar reverse zonation.
The compositional variations of these phenocrysts can be explained by mixing of a multiphase (plagioclase, augite and orthopyroxene)
saturated, evolved magma with more mafic magma saturated only with olivine. The differences in the compositional ranges of
plagioclase, augite and orthopyroxene crystals between samples indicate that these samples were derived from isolated magma
chambers which had undergone distinct fractionation and mixing histories. The samples containing plagioclase and pyroxene
with small compositional variations reflect magmas that were buffered near the olivine + melt ⇒Low-Ca pyroxene + augite +
plagioclase reaction point by frequent intrusions of mafic olivine-bearing magmas. Samples containing plagioclase and pyroxene
phenocrysts with large compositional ranges reflect magmas that evolved beyond this reaction point when there was no replenishment
with olivine-saturated magma. Two of these samples contain augite cores with Mg# of ∼71, corresponding to Mg# of 36–40 in
equilibrium melts, and augite in another sample has Mg# of 63–65 which is in equilibrium with a very evolved melt with a Mg#
of ∼30. Such highly evolved magmas also exist beneath the Puna Ridge of Kilauea volcano. They are rarely erupted during the
shield building stage, but may commonly form in ephemeral magma pockets in the rift zones.
The compositions of clinopyroxene phenocryst rims and associated glass rinds indicate that most of the samples were last equilibrated
at 2–3 kbar and 1130–1160 °C. However, in one sample, augite and glass rind compositions reflect crystallization at higher
pressures (4–5 kbar). This sample provides evidence for magma mixing at relatively high pressures and perhaps transport of
magma from the summit conduits to the rift zone along the oceanic crust-mantle boundary.
Received: 8 July 1998 / Accepted: 2 January 1999 相似文献