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1.
The diffusivity of water has been investigated for a haplogranitic melt of anhydrous composition Qz28Ab38Or34 (in wt %) at temperatures of 800–1200°C and at pressures of 0.5–5.0 kbar using the diffusion couple technique. Water contents
of the starting glass pairs varied between 0 and 9 wt %. Concentration-distance profiles for the different water species (molecular
water and hydroxyl groups) were determined by near-infrared microspectroscopy. Because the water speciation of the melt is
not quenchable (Nowak 1995; Nowak and Behrens 1995; Shen and Keppler 1995), the diffusivities of the individual species can
not be evaluated directly from these profiles. Therefore, apparent chemical diffusion coefficients of water (D
water) were determined from the total water profiles using a modified Boltzmann-Matano analysis. The diffusivity of water increases
linearly with water content <3 wt % but exponentially at higher water contents. The activation energy decreases from 64 ± 10 kJ/mole
for 0.5 wt % water to 46 ± 5 kJ/mole for 4 wt % water but remains constant at higher water contents. A small but systematic
decrease of D
water with pressure indicates an average activation volume of about 9 cm3/mole. The diffusivity (in cm2/s) can be calculated for given water content (in wt %), T (in K) and P (in kbar) by
in the ranges 1073 K ≤ T ≤ 1473 K; 0.5 kbar ≤ P≤ 5␣kbar; 0.5 wt % ≤ C
water ≤ 6 wt %. The absence of alkali concentration gradients in the glasses after the experiments shows that interdiffusion of
alkali and H+ or H3O+ gives no contribution to the transport of water in aluminosilicate melts. The H/D interdiffusion coefficients obtained at
800°C and 5 kbar using glass pieces with almost the same molar content of either water or deuterium oxide are almost identical
to the chemical diffusivities of water. This indicates that protons are transported by the neutral component H2O under these conditions.
Received: 26 March 1996 / Accepted: 23 August 1996 相似文献
2.
Stichtite, a rare (14 known localities worldwide) hydrated carbonate-hydroxide of Mg and Cr with ideal formula Mg6Cr2 (OH)16 CO3 · 4H2O, occurs exclusively in Cr-rich serpentinites of ophiolites or greenstone belts. Physical properties (hardness = 1.5–2, specific
gravity = 2.16–2.2, perfect basal [0001] cleavage, grain size commonly < 100 μm) resemble talc, but the mineral has an attractive
purple to lilac color; chemical analyses demonstrate it to be a non-silicate. Stichtite generally occurs as irregular to rounded
masses (< 1 cm – 30 cm across) and as veinlets (< 1 mm – > 2 cm wide) within serpentinite. Macroscopic and microscopic textures,
such as crosscutting veinlets and stringers, demonstrate that stichtite formation invariably post-dated serpentinization.
In some specimens stichtite surrounds relict grains of Cr-rich spinel; in others stichtite has completely replaced euhedral
or subhedral chromites. Chemical analyses of stichtites reveal substantial substitution of Al and Fe3+ for Cr in specimens from many localities, reflecting a possible compositional continuum between stichtite and rhombohedral
polymorphs hydrotalcite (Mg6Al2 (OH)16 CO3 · 4H2O) and pyroaurite (Mg6Fe2 (OH)16 CO3 · 4H2O). We report the first electron microprobe analyses of stichtites from seven localities, and summarize all available published
chemical data. Stichtites very likely inherited part of their trivalent cation chemistry from precursor Cr-rich spinels, but
stichtite growth apparently post-dated characteristic “ferritchromit” alteration, as demonstrated by the depletion of Al and
enrichment in Fe3+ in stichtite relative to primary chromite core compositions. Stichtite appears to form by reaction between serpentine and
altered chromite, during addition of substantial fluid, either as separate H2O and CO2 phases, or as a mixed volatile phase. Such reactions must involve removal of substantial SiO2, possibly by transport and remote deposition of silica by throughgoing aqueous and carbonic fluid.
Received: 4 April 1996 / Accepted: 16 September 1996 相似文献
3.
Iron tracer diffusion experiments in diopside have been performed using natural and synthetic single crystals of diopside,
and stable iron tracers enriched in 54Fe, at temperatures in the range 950–1100 °C, total pressure 1 atm, for times up to 29 days. Iron isotope diffusion profiles
were determined with an ion microprobe. For experiments performed at log pO2 = −13, in directions parallel to the c axis and the b axis of two natural, low iron (Fe ∼ 1.8 at %) diopsides, the data obey
a single Arrhenius relationship of the form D = 6.22−5.9
+49.6×10−15 exp(−161.5 ± 35.0 kJ mol−1/RT) m2 s−1. A single datum for iron diffusion in iron-free, single-crystal diopside at 1050 °C, is approximately 1 order of magnitude
slower than in the natural crystals. The pO2 dependence of iron diffusion in natural crystals at 1050 °C (power exponent = 0.229 ± 0.036) indicates a vacancy mechanism;
this is consistent with the results of unpublished atomistic simulation studies. There is no evidence of anisotropy for iron
diffusion in diopside.
Received: 16 March 1999 / Accepted: 10 April 2000 相似文献
4.
N. S. Bagdassarov 《Physics and Chemistry of Minerals》1999,26(6):513-520
The present study deals with the small strain torsion deformation of MACOR glass-ceramic samples at high temperatures (450–850 °C)
and over a range of low frequencies (20 Hz–5 mHz). The samples of MACOR ceramic consist of 55 vol% randomly oriented, sheet-like
fluorophlogopite mica crystals (∼100–20 μm in planar size, 1–2 μm in thickness) and 45 vol% of isotropic alumino-borosilicate
glass matrix. Measurements of the complex shear modulus show that the sample does not possess the relaxed shear viscosity
even at temperatures above the glass transition temperature of the glass matrix. The maximum of the imaginary component G
′′() of the shear modulus is ∼0.15 of the unrelaxed value G
∞, the relaxation strength Δ≈0.9. The activation energy of the peak of G
′′() is ∼245 kJ mol−1. Using this value of E
a
, the data obtained at various frequencies and temperatures have been reduced to a master curve using the dimensionless variable
ωτ, where ∼0 exp(−E
a
/RT). The internal friction Q−1(ωτ) is ∝1/()0.35−0.4 in the low-temperature high-frequency range (1); passes through a maximum at ∼1 and trends asymptotically to a value Q−1∼0.25–0.30 at ≪1. The behaviour of Q
−1(ωτ) differs from that of a Caputo body by the presence of the resolved peak which may be attributed to the slow mechanical
relaxation of mica crystals due to rotation as well as flexing and bending modes of crystal deformation.
Received: 26 June 1998 / Revised, accepted: 13 January 1999 相似文献
5.
Petrographic, electron microprobe, and bulk-rock geochemical analyses indicate that the distribution and composition of ferromagnesian
silicates (biotite, garnet, and staurolite) in and adjacent to the metamorphosed Bleikvassli Zn–Pb–(Cu) volcanogenic massive
sulfide deposit, Norway, are dependent upon the competing effects of f O2–f S2 and host-rock composition. The enrichment in magnesium content of these silicates within the orebody and at distances of
as much as 5–10 m away is due to the increased f O2 and f S2 conditions imposed on the silicates in zones subject to minor hydrothermal alteration during regional metamorphism. Alternatively,
within pelitic country rocks at distances >5–10 m from ore, the host-rock chemistry controls the composition of metamorphic
silicate minerals. Also, country rocks within a few meters of ore are distinguished by the common presence of zinc-bearing
staurolite (up to 9 wt% ZnO) coexisting with biotite ± garnet. Rocks in the Bleikvassli deposit were hydrothermally enriched
in zinc and fluorine prior to metamorphism. The fluorine resides mainly in biotite, which is an additional contributing factor
to the magnesium enrichment of that mineral due to Fe2+–F avoidance. Our inference that the sulfidation–oxidation halo around the Bleikvassli ore deposit is only meters in width
contrasts with the view of Maiga (1983), who proposed the effects of sulfidation could be identified at distances >159 m from
ore. It is evident that the delineation of a sulfidation–oxidation halo bordering a metamorphosed massive sulfide deposit
must be done carefully in order to discriminate between the effects due to variations in primary rock composition versus those
resulting from a sulfur and oxygen fugacity gradient between the massive sulfides and the sulfur-poor country rocks.
Received: 1 March 1998 / Accepted: 3 May 2000 相似文献
6.
Water-saturated and water-undersaturated experiments (a
H2
O = 1.0 and 0.5) were performed in the temperature range 780–1040°C at 2 and 5 kbar in order to determine the upper thermal
stability of phlogopite in granitic melts. Starting compositions were: (A) subaluminous mixtures of 20 wt % synthetic phlogopite
and 80 wt % synthetic anhydrous haplogranitic glass; (B) peraluminous mixtures (normative corundum = 4 %) of 20 wt % synthetic
phlogopite and 80 wt % synthetic anhydrous peraluminous haplogranitic glass. The molar quartz: albite: orthoclase ratio of
the glasses of the 2␣kbar runs was 35:39:26 and that of the 5 kbar runs 30:42:28. In the subaluminous system, phlogopite is
stable up to 820°C at a
H2
O = 1.0 and up to 780°C at a
H2
O = 0.5. At higher temperatures, it is replaced by enstatite. In the peraluminous system phlogopite has a remarkably higher
thermal stability (up to 1000°C at 5 kbar and a
H2
O = 1.0) and there is a temperature interval of 80°C at a
H2
O = 1.0, and 90–100°C at a
H2
O = 0.5 between the first appearance of enstatite and the disappearance of phlogopite. In the peraluminous system, phlogopite
is a solid solution (ss) of phlogopite, muscovite, talc and eastonite components. The crystalline product of the phlogopitess breakdown reaction is an aluminous enstatite. The MgO-content of the melt depends on the normative corundum content of the
starting material and the run temperature. It is independent of pressure. In the subaluminous system, the MgO-content ranges
between 0.05 and 0.3 wt % in the temperature interval 780–880°C at both investigated water activities. The MgO-content of
the peraluminous melts at a
H2
O = 1.0 ranges between 0.4 and 1.7 wt % and at a
H2
O = 0.5 between 0.2 and 1.4 wt % in the temperature range 780–980°C.
Received: 28 August 1995 / Accepted: 6 August 1996 相似文献
7.
The infrared spectrum of CaAl2Si2O7 · H2O-lawsonite, has been characterized to pressures of 20 GPa at 300 K. Our results constrain the response to compression of
the silicate tetrahedra, hydroxyl units, and water molecules in this material. The asymmetric and symmetric stretching and
bending vibrations of the Si2O7 groups (at zero pressure frequencies between 600 and 1000 cm−1) increase in frequency with pressure at rates between 3.6 and 5.9 cm−1/GPa. All silicate modes appear to shift continuously with pressure to 20 GPa, although the lowest frequency stretching vibration
becomes unresolvable above 18 GPa, and a splitting of the main bending vibration is observed near this pressure. The O-H stretches
of the hydroxyl units exhibit a discontinuity in their mode shifts at ∼8–9 GPa, which we interpret to be produced by a pressure-induced
change in hydrogen bonding. The stretching and bending vibrations of the water molecule are relatively unaffected by compression
to 20 GPa, thus demonstrating that the structural cavities in which water molecules reside are relatively rigid. Significant
changes in the amplitude of the O-H stretches of the hydroxyl and water units are observed at this pressure as well; nevertheless,
our results demonstrate that the dominant structural units in lawsonite persist metastably at 300 K with only modest structural
modifications well beyond the known stability field of this phase.
Received: 10 July 1998 / Revised, accepted: 23 October 1998 相似文献
8.
Slovakia has many areas rich in thermal waters one of which is the Hornonitrianska kotlina depression. At four localities
three types of waters are found. The first belongs to the Ca–Mg–HCO3 type with T.D.S. 0.7 g/l, the second to the Ca–Mg–SO4 type with T.D.S. 1.37–2.01 g/l and the third to the Ca–Mg–SO4–HCO3 type with T.D.S. 0.97 g/l. Discharge at individual localities varies up to 30 l/s and temperatures of water reach 32.5–66.6 °C.
The waters are predominantly used for healing, rehabilitation purposes, recreation and heating.
Received: 8 March 1999 · Accepted: 7 June 1999 相似文献
9.
K. Kuroda T. Irifune T. Inoue N. Nishiyama M. Miyashita K. Funakoshi W. Utsumi 《Physics and Chemistry of Minerals》2000,27(8):523-532
Determination of the phase boundary between ilmenite and perovskite structures in MgSiO3 has been made at pressures between 18 and 24 GPa and temperatures up to 2000 °C by in situ X-ray diffraction measurements
using synchrotron radiation and quench experiments. It was difficult to precisely define the phase boundary by the present
in situ X-ray observations, because the grain growth of ilmenite hindered the estimation of relative abundances of these phases.
Moreover, the slow reaction kinetics between these two phases made it difficult to determine the phase boundary by changing
pressure and temperature conditions during in situ X-ray diffraction measurements. Nevertheless, the phase boundary was well
constrained by quench method with a pressure calibration based on the spinel-postspinel boundary of Mg2SiO4 determined by in situ X-ray experiments. This yielded the ilmenite-perovskite phase boundary of P (GPa) = 25.0 (±0.2) – 0.003
T (°C) for a temperature range of 1200–1800 °C, which is generally consistent with the results of the present in situ X-ray
diffraction measurements within the uncertainty of ∼±0.5 GPa. The phase boundary thus determined between ilmenite and perovskite
phases in MgSiO3 is slightly (∼0.5 GPa) lower than that of the spinel-postspinel transformation in Mg2SiO4.
Received: 19 May 1999 / Accepted: 21 March 2000 相似文献
10.
The melting reaction: albite(solid)+ H2O(fluid) =albite-H2O(melt) has been determined in the presence of H2O–NaCl fluids at 5 and 9.2 kbar, and results compared with those obtained in presence of H2O–CO2 fluids. To a good approximation, albite melts congruently at 9 kbar, indicating that the melting temperature at constant
pressure is principally determined by water activity. At 5 kbar, the temperature (T)- mole fraction (X
(H2O) ) melting relations in the two systems are almost coincident. By contrast, H2O–NaCl mixing at 9 kbar is quite non-ideal; albite melts ∼70 °C higher in H2O–NaCl brines than in H2O–CO2 fluids for X
(H2O) =0.8 and ∼100 °C higher for X
(H2O) =0.5. The melting temperature of albite in H2O–NaCl fluids of X
(H2O)=0.8 is ∼100 °C higher than in pure water. The P–T curves for albite melting at constant H2O–NaCl show a temperature minimum at about 5 kbar. Water activities in H2O–NaCl fluids calculated from these results, from new experimental data on the dehydration of brucite in presence of H2O–NaCl fluid at 9 kbar, and from previously published experimental data, indicate a large decrease with increasing fluid pressure
at pressures up to 10 kbar. Aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids
provide a mechanism for reducing water activities, buffering and limiting crustal melting, and generating anhydrous mineral
assemblages during deep crustal metamorphism in the granulite facies and in subduction-related metamorphism. Low water activity
in high pressure-temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting, but
may be due to the presence of low a
(H2O) brines.
Received: 17 March 1995/Accepted: 9 April 1996 相似文献
11.
Implications from inclusions in topaz for greisenisation and mineralisation in the Hensbarrow topaz granite, Cornwall, England 总被引：3，自引：0，他引：3
B. J. Williamson C. J. Stanley J. J. Wilkinson 《Contributions to Mineralogy and Petrology》1997,127(1-2):119-128
Textural and geochemical studies of inclusions in topaz from greisens in the Hensbarrow topaz granite stock (St. Austell,
Cornwall) are used to constrain the composition of fluids responsible for late stage greisening and mineralisation. The topaz
contains an abundant and varied suite of inclusions including aqueous liquid + vapour (L + V), quartz, zinnwaldite, albite,
K-feldspar, muscovite, ilmenorutile, apatite, columbite, zircon, varlamoffite [(Sn, Fe)(O, OH)2] and qitianlingite [(Fe+2,Mn+2)2(Nb,Ta)2W+6O10]. Primary L + V inclusions in topaz show relatively high T
h (mainly 300 to >500 °C) and a narrow range of salinities (23–30 wt % NaCl equivalent) compared with those in greisen quartz
(150–450 °C, 0–50 wt % NaCl equivalent). Textures indicate that topaz formed earlier than quartz and the fluid inclusion data
are interpreted as indicating a cooling of the hydrothermal fluids during greisenisation, mixing with meteoric waters and
a decrease in pressure causing intermittent boiling. The presence of early-formed albite and K-feldspar as inclusions in the
topaz is likely to indicate that the greisen-forming fluid became progressively more acid during greisenisation. The most
distinctive inclusions in the topaz are wisp- and bleb-shaped quartz, < 50 μm in size, which show textural characteristics
indicating former high degrees of plasticity. They often have multiple shrinkage bubbles at their margins rich in Sn, Fe,
Mn, S and Cl and, more rarely, contain euhedral albite, K-feldspar, stannite or pyrrhotite crystals up to 40 μm in size. The
quartz inclusions show similar morphologies to inclusions in topaz from quartz-topaz rocks elsewhere which have been interpreted
as trapped “silicate melt”. Their compositions are, however, very different to those expected for late stage topaz-normative
granitic melts. From their textural and chemical characteristics they are interpreted as representing crystallised silica
colloid, probably trapped as a hydro gel during greisenisation. There is also evidence for the colloidal origin of inclusions
of varlamoffite in the topaz. These occurrences offer the first reported evidence in natural systems for the formation of
colloids in high temperature hydrothermal fluids. Their high ore carrying potential is suggested by the presence of varlamoffite
and the occurrence of stannite, pyrrhotite and SnCl within the quartz inclusions.
Received: 9 April 1996 / Accepted: 12 November 1996 相似文献
12.
The environmental conditions prevailing in the Chicam-Toctina drainage system (approx. 138 km2 in Córdoba, Argentina) are considered representative of a number of catchments in Argentina's Sierras Pampeanas Range. Two
groups of ions reflect the sources of dissolved species in the catchment: a) a group (Cl–, SO2–
4, and Na+) which recognizes natural and anthropogenic sources, and which exhibits significant correlations with N–
3 and NO–
2, and b) another group of components (Ca2+, Mg2+, and HCO–
3) which is clearly controlled by carbonate rocks and their waste rock products. In the headwaters, stockpiled marble quarry
mining wastes provide a more open system to CO2 gaseous exchange than the outcropping rocks, thus promoting the increase of carbonate dissolution (up to 4.88 g km–2 s–1 during the rainy season). This specific yield was 20% higher than the amount estimated for an area with fewer extended mining
activities. The dissolved load delivered by the upper reaches is subjected in the lower drainage area to various processes,
mainly controlled by the presence of the city of Alta Gracia (approx. 40,000 inhabitants). In the dry season, due to nutrient
inputs supplied by the city, photosynthetic activity plays a major role controlling stream pH. Hence, the high values of calcite
saturation indexes and the increase of CaCO3 concentration in bed sediments can be explained by calcite precipitation. Such a process could be accompanied by the coprecipitation
on calcium carbonate of low solubility heavy metal carbonates.
Received : 17 January 1997 · Accepted : 31 March 1997 相似文献
13.
Andrea Orlando Yves Thibault Alan D. Edgar 《Contributions to Mineralogy and Petrology》2000,139(2):136-145
Experiments ranging from 2 to 3 GPa and 800 to 1300 °C and at 0.15 GPa and 770 °C were performed to investigate the stability
and mutual solubility of the K2ZrSi3O9 (wadeite) and K2TiSi3O9 cyclosilicates under upper mantle conditions. The K2ZrSi3O9–K2TiSi3O9 join exhibits complete miscibility in the P–T interval investigated. With increasing degree of melting the solid solution becomes progressively enriched in Zr, indicating
that K2ZrSi3O9 is the more refractory end member. At 2 GPa, in the more complex K2ZrSi3O9–K2TiSi3O9–K2Mg6Al2Si6O20(OH)4 system, the presence of phlogopite clearly limits the extent of solid solution of the cyclosilicate to more Zr-rich compositions
[Zr/(Zr + Ti) > 0.85], comparable to wadeite found in nature, with TiO2 partitioning strongly into the coexisting mica and/or liquid. However, at 1200 °C, with increasing pressure from 2 to 3 GPa,
the partitioning behaviour of TiO2 changes in favour of the cyclosilicate, with Zr/(Zr + Ti) of the K2(Zr,Ti)Si3O9 phase decreasing from ∼0.9 to ∼0.6. The variation in the Ti content of the coexisting phlogopite is related to its degree
of melting to forsterite and liquid, following the major substitution VITi+VI□=2VIMg.
Received: 26 January 1999 / Accepted: 10 January 2000 相似文献
14.
Mobility of components in metasomatic transformation and partial melting of gneisses: an example from Sri Lanka 总被引：2，自引：1，他引：1
L. L. Perchuk O. G. Safonov T. V. Gerya B. Fu D. E. Harlov 《Contributions to Mineralogy and Petrology》2000,140(2):212-232
Reaction textures, fluid inclusions, and metasomatic zoning coupled with thermodynamic calculations have allowed us to estimate
the conditions under which a biotite–hornblende gneiss from the Kurunegala district, Sri Lanka [hornblende (NMg=38–42) + biotite (NMg=42–44) + plagioclase + quartz + K-feldspar + ilmenite + magnetite] was transformed into patches of charnockite along shear
zones and foliation planes. Primary fluid inclusion data suggest that two immiscible fluids, an alkalic supercritical brine
and almost pure CO2, coexisted during the charnockitisation event and subsequent post-peak metamorphic evolution of the charnockite. These metasomatic
fluids migrated through the amphibolite gneiss along shear zones and into the wallrock under peak metamorphic conditions of
700–750 °C, 5–6 kbar, and afl
H2O=0.52–0.59. This resulted in the formation of charnockite patches containing the assemblage orthopyroxene (NMg=45–48) + K-feldspar (Or70–80) + quartz + plagioclase (An28) in addition to K-feldspar microveins along quartz and plagioclase grain boundaries. Remnants of the CO2-rich fluid were trapped as separate fluid inclusions. The charnockite patches show the following metasomatic zonation patterns:
– a transition zone with the assemblage biotite (NMg= 49–51) + hornblende (NMg = 47–50) + plagioclase + quartz + K-feldspar + ilmenite + magnetite;
– a KPQ (K-feldspar–plagioclase–quartz) zone with the assemblage K-feldspar + plagioclase + orthopyroxene (NMg=45–48) + quartz + ilmenite + magnetite;
– a charnockite core with the assemblage K-feldspar + plagioclase + orthopyroxene (NMg = 39–41) + biotite (NMg=48–52) + quartz + ilmenite + magnetite.
Systematic changes in the bulk chemistry and mineralogy across the four zones suggest that along with metasomatic transformation,
this process may have been complicated by partial melting in the charnockite core. This melting would have been coeval with
metasomatic processes on the periphery of the charnockite patch. There is also good evidence in the charnockitic core that
a second mineral assemblage, consisting of orthopyroxene (NMg= 36–42) + biotite (NMg=50–51) + K-feldspar (Or70–80) + quartz + plagioclase (An28–26), could have crystallised from a partial melt during cooling from 720 to 660 °C at decreasing afl
H2O from 0.67 to 0.5. Post-magmatic evolution of charnockite at T < 700 °C resulted in fluids being released during the crystallisation
of the charnockitic core. These gave rise to the formation of late stage rim myrmekites along K-feldspar grain boundaries
as well as late stage biotite, cummingtonite, and carbonates.
Received: 15 September 1999 / Accepted: 8 June 2000 相似文献
15.
Summary Fe-Ti-P-rich rocks (FTP) are unusual with respect to their mineralogy and bulk composition. Varieties of these rocks are mostly
related to Proterozoic massif-type anorthosites and to a lesser extent to the upper parts of mafic-ultramafic intracratonic
layered complexes and other igneous rock suites. We present results on the geology, mineralogy and geochemistry of a new occurrence
of FTP, associated with mafic rocks in the northwestern part of Iran. The Qareaghaj mafic-ultramafic intrusion (QMUI) is a
small igneous body situated between Palaeozoic sedimentary rocks and a Precambrian low grade metamorphic complex. The QMUI
is composed mainly of non-mineralized mafic and apatite- and Fe-Ti oxide-rich ultramafic rocks. The mafic rocks, mainly coarse-grained
gabbro, microgabbro and amphibolite, have a simple mineral assemblage (plagioclase + clinopyroxene + ilmenite) and based on
field observations, mineralogy and chemical composition are comagmatic. The ultramafic rocks with high proportion of olivine
(∼40–66 vol.%), apatite (∼0.1–16 vol.%), ilmenite (∼11–19 vol.%) and magnetite (∼2–13 vol.%), have unusual bulk compositions
(e.g., SiO2 ∼ 21–30 wt.%, total iron expressed as Fe2O3
tot ∼ 26–42 wt.%, TiO2 ∼ 5–11 wt.%, MgO ∼ 9–20 wt.%, P2O5 up to 5.1 wt.%, Cr ∼ 40–160 ppm, Ni ∼ 7–73 ppm). The FTP forms numerous sill-like layers, ranging in thickness from ∼5 cm
to few meters. These rocks, totally enclosed in mafic rocks with sharp and concordant contacts, show a magmatic lamination
and follow the general NW–SE trend of QMUI. The apatite-rich ultramafic rocks makes up 90–95% of the total ultramafic outcrops
and contain Mg-poor olivine (Mg# ∼ 40–58) and low-Mg spinel (Mg# ∼ 30–44) in contrast to apatite-poor ones (∼60–63 and ∼43–46,
respectively). Field relationships, mineral compositions and geochemical data suggested that the FTP are not related to the
mafic host rocks. On the contrary, they intruded latter into the gabbros during plastic, high temperature deformation in local
shear zones. Fractional crystallization of P-rich ferrobasaltic parental magma at depth, probably in an open magmatic system,
not far from the QMUI magma chamber, is considered as responsible for the formation of the evolved FTP in QMUI. 相似文献
16.
Pb diffusion in rutile 总被引：16，自引：0，他引：16
D. J. Cherniak 《Contributions to Mineralogy and Petrology》2000,139(2):198-207
Diffusion of Pb was measured in natural and synthetic rutile under dry, 1 atmosphere conditions, using mixtures of Pb titanate
or Pb sulfide and TiO2 as the sources of diffusant. Pb depth profiles were then measured with Rutherford Backscattering Spectrometry (RBS). Over
the temperature range 700–1100 °C, the following Arrhenius relation was obtained for the synthetic rutile: D=3.9 × 10−10exp(−250 ± 12 kJ mol−1/RT) m2s−1. Results for diffusion in natural and synthetic rutile were quite similar, despite significant differences in trace element
compositions. Mean closure temperatures calculated from the diffusion parameters are around 600 °C for rutile grains of ∼100 μm
size. This is about 100 °C higher than rutile closure temperature determinations from past field-based studies, suggesting
that rutile is more resistant to Pb loss through volume diffusion than previously thought.
Received: 28 June 1999 / Accepted: 29 December 1999 相似文献
17.
Bernd Wunder 《Contributions to Mineralogy and Petrology》1998,132(2):111-120
The water-pressure and temperature stability fields of clinohumite-OH, chondrodite-OH and phase A were determined in reversed
equilibrium experiments up to 100 kbar within the system MgO–SiO2–H2O. Their PT-fields differ from results from former synthesis experiments. Bracketing experiments on the reaction phase A + low P-clinoenstatite ⇆ forsterite + water resulted in a slightly steeper dP/dT-slope compared to earlier experiments for this equilibrium. Clinohumite-OH and chondrodite-OH both have large stability fields
which extend over pressure ranges of more than 80 kbar. However, they are hardly relevant as hydrous minerals within the subducted
oceanic lithosphere. Both are too Mg-rich for a typical mantle bulk composition. In addition, the dehydration of subducted
oceanic lithosphere – due to (forsterite + water)-forming reactions – will occur before the two humite-group phases even become
stable. Restricted to the cool region of cold subducting slabs, phase A, however, might be formed via the reactions phase
A + low P-/high P-clinoenstatite ⇆ forsterite + water or antigorite + brucite ⇆ phase A + water, before dehydration of the oceanic lithosphere
occurs.
Received: 22 July 1997 / Accepted: 12 March 1998 相似文献
18.
Twenty nine samples of silica sinter, ranging in age from modern to Miocene, record temporal changes in both mineralogy and
texture. When first deposited, sinters consist largely of noncrystalline spheres (<1–8 μm diameter) of opal-A exhibiting varying
degrees of close-packing. Particle densities range from 1.5 to 2.1 g cm−3, total water 4–10 wt%, and porosities 35–60%. Changes over ∼10,000 years following deposition are slight although the spheres
may be invested by an additional film of secondary silica. For the next 10,000 to ∼50,000 years, the silica incrementally
crystallises to become poorly crystalline opal-CT and/or opal-C; spherical particles of thin-bladed crystals (lepispheres)
replace opal-A particles and coalesce in microbotryoidal aggregates (∼10–30 μm diameter). Amygdaloidal fibrous clusters occur
with lepispheres. As silica lattice ordering becomes enhanced, total water content drops to <7 wt%, particle density increases
to ∼2.3 g cm−3, and porosity reduces to <30%. The change from opal-A to opal-C takes place over a briefer periods (∼50 years) in silica
sinters that contain other materials (e.g. calcite, sulfur, alunite, plant remains). Sinters older than ∼50,000 years have
recrystallised to microcrystalline quartz. With the onset of quartz crystallisation at ∼20,000 years, total water is <0.2 wt%,
particle density approximates quartz (2.65 g cm−3), and porosity is <4%. The progressive changes in silica species and texture yield ageing profiles for sinters that may serve
as guides to the paleohydrology of geothermal systems and/or epithermal ore deposits in areas where surface thermal activity
has declined or ceased.
Received: 18 November 1998 / Accepted: 6 July 1999 相似文献
19.
Near-infrared (NIR) absorption bands related to total water (4000 and 7050 cm−1), OH groups (4500 cm−1) and molecular H2O (5200 cm−1) were studied in two polymerised glasses, a synthetic albitic composition and a natural obsidian. The water contents of the
glasses were determined using Karl Fischer titration. Molar absorption coefficients were calculated for each of the bands
using albitic glasses containing between 0.54 and 9.16 wt.% H2O and rhyolitic glasses containing between 0.97 and 9.20 wt.% H2O. Different combinations of baseline type and intensity measure (peak height/area) for the combination bands at 4500 and
5200 cm−1 were used to investigate the effect of evaluation procedure on calculated hydrous species concentrations. Total water contents
calculated using each of the baseline/molar absorption coefficient combinations agree to within 5.8% relative for rhyolitic
and 6.5% relative for albitic glasses (maximum absolute differences of 0.08 and 0.15 wt.% H2O, respectively). In glasses with water contents >1 wt.%, calculated hydrous species concentrations vary by up to 17% relative
for OH and 11% relative for H2O (maximum absolute differences of 0.33 and 0.43 wt.% H2O, respectively). This variation in calculated species concentrations is typically greater in rhyolitic glasses than albitic.
In situ, micro-FTIR analysis at 300 and 100 K was used to investigate the effect of varying temperature on the NIR spectra of the
glasses. The linear and integral molar absorption coefficients for each of the bands were recalculated from the 100 K spectra,
and were found to vary systematically from the 300 K values. Linear molar absorption coefficients for the 4000 and 7050 cm−1 bands decrease by 16–20% and integral molar absorption coefficients by up to 30%. Depending on glass composition and baseline
type, the integral molar absorption coefficients for the absorption bands related to OH groups and molecular H2O change by up to −5.8 and +7.4%, respectively, while linear molar absorption coefficients show less variation, with a maximum
change of ∼4%. Using the new molar absorption coefficients for the combination bands to calculate species concentrations at
100 K, the maximum change in species concentration is 0.08 wt.% H2O, compared with 0.39 wt.% which would be calculated if constant values were assumed for the combination band molar absorption
coefficients. Almost all the changes in the spectra can therefore be interpreted in terms of changing molar absorption coefficient,
rather than interconversion between hydrous species.
Received: 17 December 1998 / Revised, accepted 8 July 1999 相似文献
20.
Friedrich Lucassen Sven Lewerenz Gerhard Franz José Viramonte Klaus Mezger 《Contributions to Mineralogy and Petrology》1999,134(4):325-341
Crustal xenoliths from basanitic dikes and necks that intruded into continental sediments of the Cretaceous Salta Rift at
Quebrada de Las Conchas, Provincia Salta, Argentina were investigated to get information about the age and the chemical composition
of the lower crust. Most of the xenoliths have a granitoid composition with quartz-plagioclase-garnet-rutile ± K-feldspar
as major minerals. The exceedingly rare mafic xenoliths consist of plagioclase-clinopyroxene-garnet ± hornblende. All xenoliths
show a well equilibrated granoblastic fabric and the minerals are compositionally unzoned. Thermobarometric calculations indicate
equilibration of the mafic xenoliths in the granulite facies at temperatures of ca. 900 °C and pressures of ca. 10 kbar. The
Sm-Nd mineral isochron ages are 95.1 ± 10.4 Ma, 91.5 ± 13.0 Ma, 89.0 ± 4.2 Ma (granitoid xenoliths), and 110.7 ± 23.6 Ma (mafic
xenolith). These ages are in agreement with the age of basanitic volcanism (ca. 130–100 and 80–75 Ma) and are interpreted
as minimum ages of metamorphism. Lower crustal temperature at the time given by the isochrons was above the closure temperature
of the Sm-Nd system (>600–700 °C). The Sm-Nd and Rb-Sr isotopic signatures (147Sm/144Nd = 0.1225–0.1608; 143Nd/144Ndt
0 = 0.512000–0.512324; 87Rb/86Sr = 0.099–0.172; 87Sr/86Srt
0 = 0.708188–0.7143161) and common lead isotopic signatures (206Pb/204Pb = 18.43–18.48; 207Pb/204Pb = 15.62–15.70; 208Pb/204Pb = 38.22 –38.97) of the granitoid xenoliths are indistinguishable from the isotopic composition of the Early Paleozoic metamorphic
basement from NW Argentina, apart from the lower 208Pb/204Pb ratio of the basement. The Sm-Nd depleted mantle model ages of ca. 1.8 Ga from granitoid xenoliths and Early Paleozoic
basement point to a similar Proterozoic protolith. Time constraints, the well equilibrated granulite fabric, P-T conditions and lack of chemical zoning of minerals point to a high temperature in a crust of nearly normal thickness at ca.
90 Ma and to a prominent thermal anomaly in the lithosphere. The composition of the xenoliths is similar to the composition
of the Early Paleozoic basement in the Andes of NW Argentina and northern Chile. A thick mafic lower crust seems unlikely
considering low abundance of mafic xenoliths and the predominance of granitoid xenoliths.
Received: 21 July 1998 / Accepted: 27 October 1998 相似文献