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1.
Wilhelm Johannes 《Contributions to Mineralogy and Petrology》1984,86(3):264-273
The beginning of melting in the system Qz-Or-Ab-An-H2 O was experimentally reversed in the pressure range
kbar using starting materials made up of mixtures of quartz and synthetic feldspars. With increasing pressure the melting
temperature decreases from 690° C at 2 kbar to 630° C at 17 kbar in the An-free alkalifeldspar granite system Qz-Or-Ab-H2O. In the granite system Qz-Or-Ab-An-H2O the increase of the solidus temperature with increasing An-content is only very small. In comparison to the alkalifeldspar
granite system the solidus temperature increases by 3° C (7° C) if albite is replaced by plagioclase An 20 (An 40). The difference
between the solidus temperatures of the alkalifeldspar granite system and of quartz — anorthite — sanidine assemblages (system
Qz-Or-An-H2O) is approximately 50° C.
With increasing water pressures plagioclase and plagioclase-alkalifeldspar assemblages become unstable and are replaced by
zoisite+kyanite+quartz and zoisite+muscovite-paragonitess +quartz, respectively. The pressure stability limits of these assemblages are found to lie between 6 and 16 kbar at 600°
C. At high water pressures (10–18 kbar) zoisite — muscovite — quartz assemblages are stable up to 700 and 720° C. The solidus
curve of this assemblage is 10–20° C above the beginning of melting of sanidine — zoisite — muscovite — quartz mixtures.
The amount of water necessary to produce sufficient amounts of melt to change a metamorphic rock into a magmatic looking one
is only small. In case of layered migmatites it is shown that 1 % of water (or even less) is sufficient to transform portions
of a gneiss into (magmatic looking) leucosomes. High grade metamorphic rocks were probably relatively dry, and anatectic magmas
of granitic or granodioritic composition are usually not saturated with water. 相似文献
2.
Grain boundary diffusion rates of oxygen, potassium and calcium in fine-grained feldspar aggregates were determined experimentally.
The starting materials were a natural albite rock from the Tanco pegmatite and aggregates hot-pressed from fragments of Amelia
albite or Ab, Or and An composition glasses. The technique employed isotopic tracers (18O, 41K, 42Ca) either evaporated onto the surface or in an aqueous solution surrounding the sample, and depth profiling using an ion
microprobe (SIMS). From the depth profiles, the product of the grain boundary diffusion coefficient (D′) and effective boundary
width (δ) was calculated using numerical solutions to the appropriate diffusion equation. The experimental reproducibility
of D′δ is a factor of 3. A separate determination of D′ independent of δ yields an effective grain boundary width of ∼3 nm,
consistent with high resolution TEM observations of a physical grain boundary width <5 nm. Oxygen (as molecular water) grain
boundary diffusion rates were determined in the Ab and Or aggregates at 450°–800° C and 100 MPa (hydrothermal), potassium
rates in Or aggregates at 450°–700° C both at 0.1 MPa (in air) and at 100 MPa (hydrothermal), and calcium rates in An aggregates
at 700°–1100° C and 0.1 MPa (in air). Oxygen grain boundary diffusion rates are similar in all three of the Ab aggregates
and in the Or aggregate. Potassium and oxygen depth profiles measured in the same samples yield different D′δ values, confirming
a diffusional transport mechanism. Potassium diffusion in the Or aggregate has a greater activation energy (216 vs 78 kJ/mol)
than oxygen, and the Arrhenius relations cross at ∼625° C. Potassium D′δ values in Or aggregates are about a factor of five
greater in hydrothermal experiments at 100 MPa than in experiments at 0.1 MPa in air. Calcium grain boundary diffusion rates
in An aggregates are 4 to 5 orders of magnitude slower than potassium in Or and have a greater (291 kJ/mol) activation energy.
This suggests that differences in formal charge and/or size of diffusing species may play an important role in their relative
grain boundary diffusion rates.
Received: 24 December 1993 / Accepted: 16 June 1994 相似文献
3.
Growth kinetics of enstatite reaction rims studied on nano-scale,Part I: Methodology,microscopic observations and the role of water 总被引:1,自引:0,他引:1
Ralf Milke Ralf Dohmen Hans-Werner Becker Richard Wirth 《Contributions to Mineralogy and Petrology》2007,154(5):519-533
The kinetics of (Mg, Fe)SiO3 pyroxene layer growth within silicate thin films with total thickness <1 μm was studied experimentally at 0.1 MPa total pressure,
controlled fO2 and temperatures from 1,000 to 1,300°C. The starting samples were produced by pulsed laser deposition. Layer thickness before
and after the experiments and layer composition as well as microstructures, grain size and shape of the interfaces were determined
by Rutherford back scattering and transmission electron microscopy assisted by focused ion beam milling. Due to the miniaturization
of the starting samples and the use of high resolution analytical methods the experimentally accessible temperature range
for rim growth experiments was extended by about 300°C towards lower temperatures. The thickness of the layers at a given
temperature increases proprotional to the square root of time, indicating a diffusion-controlled growth mechanism. The temperature
dependence of rim growth yields an apparent activation energy of 426 ± 34 kJ/mol. The small grain size in the orthopyroxene
rims implies a significant contribution of grain boundary diffusion to the bulk diffusion properties of the polycrystalline
rims. Based on microstructural observations diffusion scenarios are discussed for which the SiO2 component behaves immobile relative to the MgO component. Volume diffusion data for Mg in orthopyroxene from the literature
indicate that the measured diffusivity is probably controlled by the mobility of oxygen. The observed reaction rates are consistent
with earlier results from dry high-temperature experiments on orthopyroxene rim growth. Compared to high pressure experiments
at 1,000°C and low water fugacities, reaction rates are 3–4 orders of magnitude smaller. This observation is taken as direct
evidence for a strong effect of small amounts of water on diffusion in silicate polycrystals. In particular SiO2 changes from an immobile component at dry conditions to an extremely mobile component even at very low water fugacities. 相似文献
4.
Alfons M. van den Kerkhof Geoffrey H. Grantham 《Contributions to Mineralogy and Petrology》1999,137(1-2):115-132
In the Port Edward area of southern Kwa-Zulu Natal, South Africa, charnockitic aureoles up to 10 m in width in the normally
garnetiferous Nicholson's Point Granite, are developed adjacent to intrusive contacts with the Port Edward Enderbite and anhydrous
pegmatitic veins. Mineralogical differences between the country rock and charnockitic aureole suggest that the dehydration
reaction Bt + Qtz → Opx + Kfs + H2O and the reaction of Grt + Qtz → Opx + Pl were responsible for the charnockitization. The compositions of fluid inclusions
show systematic variation with: (1) the Port Edward Enderbite being dominated by CO2 and N2 fluid inclusions; (2) the non-charnockitized granite by saline aqueous inclusions with 18–23 EqWt% NaCl; (3) the charnockitic
aureoles by low-salinity and pure water inclusions (<7 EqWt% NaCl); (4) the pegmatites by aqueous inclusions of various salinity
with minor CO2. As a result of the thermal event the homogenization temperatures of the inclusions in charnockite show a much larger range
(up to 390 °C) compared to the fluid inclusions in granite (mostly <250 °C). Contrary to fluid-controlled charnockitization
(brines, CO2) which may have taken place along shear zones away from the intrusive body, the present “proximal” charnockitized granite
formed directly at the contact with enderbite. The inclusions indicate contact metamorphism induced by the intrusion of “dry”
enderbitic magma into “wet” granite resulting in local dehydration. This was confirmed by cathodoluminescence microscopy showing
textures indicative for the local reduction of structural water in the charnockite quartz. Two-pyroxene thermometry on the
Port Edward Enderbite suggests intrusion at temperatures of ∼1000–1050 °C into country rock with temperature of <700 °C. The
temperature of aureole formation must have been between ∼700 °C (breakdown of pyrite to form pyrrhotite) and ∼1000 °C. Charnockitization
was probably controlled largely by heat related to anhydrous intrusions causing dehydration reactions and resulting in the
release and subsequent trapping of dehydration fluids. The salinity of the metamorphic fluid in the contact zones is supposed
to have been higher at an early stage of contact metamorphism, but it has lost its salt content by K-metasomatic reactions
and/or the preferential migration of the saline fluids out of the contact zones towards the enderbite. The low water activity
inhibited the localized melting of the granite. Mineral thermobarometry suggests that after charnockite aureole genesis, an
isobaric cooling path was followed during which reequilibration of most of the aqueous inclusions occurred.
Received: 8 November 1998 / Accepted: 21 June 1999 相似文献
5.
Richard A. Yund 《Contributions to Mineralogy and Petrology》1997,126(3):224-236
The growth rates of enstatite rims produced by reaction of Fo92 and SiO2 were determined at 250–1500 MPa and 900–1100°C for a wide range of water contents. Growth rates were also determined for
forsterite rims between MgO and Mg2Si2O6 and between MgO and SiO2. Rim growth rates are parabolic indicating diffusion-controlled growth of the polycrystalline rims which are composed of ˜ 2
μm diameter grains. Rim growth rates were used to calculate the product of the grain boundary diffusion coefficient (D'A) times the effective grain boundary thickness (δ) assuming in turn that MgO, SiO2, and Mg2Si−1 are the diffusing components (coupled diffusion of a cation and oxygen or interdiffusion of Mg and Si). The values for D'MgOδ, D', and D' for enstatite at 1000°C and 700 MPa confining pressure with about 0.1 wt % water are about five times larger than the corresponding
D'Aδ values for samples initially vacuum dried at 250°C. Most of the increase in D'Aδ occurs with the first 0.1 wt % water. The activation energy for diffusion through the enstatite rims (1100–950°C) is 162 ± 30
kJ/mole. The diffusion rate through enstatite rims is essentially unchanged for confining pressures from 210–1400 MPa, but
the nucleation rate is greatly reduced at low confining pressure (for ≤ 1.0 wt % water present) and limits the conditions
at which rim growth can be measured. The corresponding values for D'Aδ through forsterite rims are essentially identical for the two forsterite-producing reactions when 0.1 wt % water is added
and similar to the D'Aδ values for enstatite at the same conditions. The D'Aδ values for forsterite are ˜ 28 times larger for samples starting with 0.1 wt % water compared to samples that were first
vacuum dried. Thus water enhances these grain boundary diffusion rates by a factor of 5–30 depending on the mineralogy, but
the total range in D'Aδ is only slightly more than an order of magnitude for as wide a range of water contents as expected for most crustal conditions.
Received: 1 July 1995 / Accepted: 1 August 1996 相似文献
6.
Samples of enstatite and forsterite were crystallized in the presence of a hydrous fluid at 15 kbar and 1100 °C. Water contents
in quenched samples were measured by 1H MAS NMR and by FTIR. If the samples were prepared in the same way, similar water concentrations were obtained by both methods.
There is no evidence that one or the other method would severely over or underestimate water contents in nominally anhydrous
minerals. However, measured water contents vary by orders of magnitude depending on sample preparation. The lowest water contents
are measured by polarized FTIR spectroscopy on clear, inclusion-free single crystals. These water contents probably reflect
the real point defect solubility in the crystals. Polycrystalline material shows much higher total water concentrations, presumably
due to hydrous species on grain boundaries, growth defects, and in submicroscopic fluid inclusions. Grinding the sample in
air further increases water concentration. This effect is even more pronounced if the sample is ground in water and subsequently
dried at 150 °C. Polarized FTIR measurements on clear single crystals of enstatite saturated at 15 kbar and 1100 °C give 199 ± 25 ppm
by weight of water. The spectra show sharp and strongly polarized bands. These bands are also present in spectra measured
through turbid, polycrystalline aggregates of enstatite. However, in these spectra, they are superimposed on much broader,
nearly isotropic bands resulting from hydrous species in grain boundaries, growth defects, and submicroscopic fluid or melt
inclusions. Total water contents for these polycrystalline aggregates are between 2000 and 4000 ppm. Water contents measured
by FTIR on enstatite powders are 5300 ppm after grinding in air and 12 600 ppm after grinding under water und subsequent drying
at 150 °C.
Received: 25 June 1999 / Revised, accepted: 4 October 1999 相似文献
7.
Rainer Thomas Paul Davidson Dieter Rhede Michael Leh 《Contributions to Mineralogy and Petrology》2009,157(4):505-523
In this paper, we show that the crystallization of miarolitic pegmatites at K?nigshain started at about 700°C, in melts containing
up to 30 mass% water. Such high water concentration at low pressures (1–3 kbar) is only possible if the melts are peralkaline.
Such peralkaline melts are highly corrosive, and reacted with the wall rock—here the granite host—forming the graphic granite
zone, in part via a magmatic–metasomatic reaction. With cooling, the water concentration in some melt fractions increased
up to 50 mass% H2O. The melt-dominated system ends below 600°C and passes into a fluid-dominated system, the beginning of which is characterized
by strong pressure fluctuations, caused by the change of OH and CO3
2− in the melt, to molecular water and CO2. We note two generations of smoky quartz, one crystallized above the β–α-transition of quartz (≈573°C), and one below, both
of which contain melt inclusions. This indicates that some melt fraction remains during at least the higher-temperature portion
of the growth of minerals into the miarolitic cavity, contradicting the view that minerals growing into a pegmatite chamber
only do so from aqueous fluids. We show that the K?nigshain miarolitic pegmatites are part of the broad spectrum of pegmatite
types, and the processes active at K?nigshain are representative of processes found in most granitic pegmatites, and are thus
instructive in the understanding of pegmatite formation in general, and constraining the composition and characteristics of
pegmatite-forming melts.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
Calcium self-diffusion in diopside at high temperature: implications for transport properties 总被引:1,自引:0,他引:1
We have investigated 44Ca self-diffusion in natural diopside single crystals (containing ∼2 atomic % Fe) at temperatures up to 1320 °C (i.e. 30 °C
below the nominal melting point). Oxygen fugacity was controlled by gaseous mixtures. Diffusion profiles ranging from ∼50
to 500 nm were analysed by Rutherford Back-Scattering Spectrometry (RBS). The present results are complementary to previous
studies, and show that in both synthetic (Fe-poor) and natural (Fe-rich) diopside, there are two different diffusion regimes
for Ca with a transition at ∼1230±15 °C. Below this temperature diffusion is characterised by an activation enthalpy of ∼284±10
kJ/mol, while at higher temperatures it increases up to ∼1006±75 kJ/mol. These regimes are proposed to be respectively extrinsic
and intrinsic. For the intrinsic regime Ca self-diffusion may involve Ca-Frenkel point defects. These are pairs of a vacancy
on a M2 site and a calcium cation on an interstitial (normally unoccupied) site. The concentration of such point defects depends
only on temperature, and it is especially important at very high temperatures. The activation enthalpy for intrinsic diffusion
may represent the half defect formation enthalpy plus the migration enthalpy for movement through interstitial sites. For
the extrinsic regime we propose Ca self-diffusion to involve extrinsic interstitial point defects with concentration proportional
to ()–0.19±0.03. We suggest that for both regimes, Ca diffusion involves the well known M3 sites in the octahedral layers, as well as sites in the tetrahedral layers, that we call M4. These sites are especially convenient to explain the observed isotropic diffusion. Increasing concentration of Ca-Frenkel
point defects may be related to the onset of premelting, which affects the thermodynamic properties of Fe-“free” diopside
above 1250 °C. In the light of the present results, premelting is also expected to occur in natural Fe-bearing diopside and
it could strongly influence its thermodynamic and transport properties. Subsequently, in deep upper mantle conditions (T≈1250 °C–1300 °C)
where premelting could occur, diffusional cation exchanges with surrounding phases and diffusion controlled creep might be
facilitated. Finally, our diffusion data support a previous suggestion that electrical conductivity may be electronic rather
than ionic.
Received: 17 December 1997 / Revised, accepted: 17 April 1998 相似文献
9.
A. M. Aksyuk A. A. Konyshev V. S. Korzhinskaya Yu. B. Shapovalov 《Doklady Earth Sciences》2016,470(1):921-923
The melting of two basic granite varieties in the Voznesenka Complex such as Yaroslavka biotite granite and Voznesenka Li–F granite was subject to experimental studies to analyze and to compare the conditions of their physicochemical formation. The experiments were conducted at 550–700°C and 50–500 MPa in pure water and in 0.1 and 1 m HF aqueous fluorine-bearing solutions. The melting temperature of Voznesenka Li–F granites was 60–70°C lower than that of Yaroslavka biotite granites. The temperature decreased by almost 100°C from the completion of biotite granite crystallization to the completion of Li–F granite crystallization. 相似文献
10.
腾冲地块高地热异常区晚白垩世-始新世钾玄质强过铝花岗岩岩石地球化学、年代学特征及构造意义 总被引:1,自引:2,他引:1
腾冲地块高地热异常区清水左所营初糜棱岩化黑云母二长花岗岩岩体、新华黑石河热田强糜棱岩化黑云母二长花岗岩岩体、热海热田硫磺塘硅化碎裂正长花岗岩岩体变形变质、岩石地球化学及锆石年代学的研究表明,晚白垩世(73Ma)初糜棱岩化黑云母二长花岗岩岩体为高温钾玄质强过铝花岗岩,形成于活动大陆边缘火山弧-后碰撞转换或过渡构造环境,并经历强烈伸展变形作用,普遍发育早期近水平-低角度(30°)韧性伸展剪切糜棱面理,局部发育晚期高角度右旋走滑挤压韧性糜棱面理;始新世(48~46Ma)强糜棱岩化黑云母二长花岗岩岩体、硅化碎裂正长花岗岩岩体为中-高温钾玄质强过铝花岗岩,并具铝质A型花岗岩特征,形成于后碰撞-板内构造环境,以发育晚期高角度(70°~87°)右旋走滑挤压韧性糜棱面理为特征,其右旋走滑韧性剪切变形时代晚于始新世(48~46Ma)。晚白垩世-始新世钾玄质强过铝花岗岩的形成与俯冲-碰撞造山隆升后的伸展垮塌、拆沉地幔物质上涌玄武质岩浆底侵和地壳部分熔融作用密切相关。始新世-第四纪岩浆活动与高地热异常区(带)空间上密切伴生,新近纪晚期-第四纪构造活动主要表现为脆性走滑-拉张正断层和构造拉分断陷盆地的形成,构造断陷边界断裂与深部岩浆活动是导致腾冲地区高地热异常区(带)中-高温地热温泉沿走滑-拉张断裂带集中分布的主要原因。 相似文献
11.
Geological and fluid inclusion studies of the Dongpo tungsten skarn ore deposit,China 总被引:1,自引:0,他引:1
The Dongpo tungsten ore deposit, the largest scheelite skarn deposit in China, is located at the contact of a 172-m. y. biotite
granite with a Devonian marble. The mineralization associated with the granite includes W, Bi-Mo, Cu-Sn and Pb-Zn ores. Several
W mineralization stages are shown by the occurrence of ore in massive skarn deposits and in later cross-cutting veins. The
high garnet/pyroxene ratio, the hedenbergite and diopside-rich pyroxene and the andradite-rich garnet show the deposit belongs
to the oxidized skarn type. Detailed fluid inclusion studies of granite, greisen, skarn and vein samples reveal three types
of fluid inclusion: (1) liquid-rich, (2) gas-rich and (3) inclusions with several daughter minerals. Type (3) is by far the
most common in both skarn and vein samples. The dominant daughter mineral in fluid inclusions is rhembic, highly birefringent,
and does not dissolve on heating even at 530°C. We assume that this mineral is calcite. The liquid phase in most of the fluid
inclusions has low to moderate salinities: 0–15 wt. %; in a few has higher salinities (30–40 wt. % NaCl equivalent). The homogenization
temperatures of inclusions in the skarn stage range from 350°C to 530°C, later tungsten mineralization-stage inclusions homogenize
between 200°C and 300°C, as do inclusions in veins. Fluid inclusions in granite and greisen resemble those of the late tungsten
mineralization stage, with low salinity and homogenization temperatures of 200°–360°C. The tungsten-forming fluids are probably
a mixture that came from biotite granite and the surrounding country rocks. 相似文献
12.
Ian Parsons John D. Fitz Gerald James K. W. Lee Tim Ivanic Ute Golla-Schindler 《Contributions to Mineralogy and Petrology》2010,160(2):155-180
Microtextural changes brought about by heating alkali feldspar crystals from the Shap granite, northern England, at atmospheric
pressure, have been studied using transmission and scanning electron microscopy. A typical unheated phenocryst from Shap is
composed of about 70 vol% of tweed orthoclase with strain-controlled coherent or semicoherent micro- and crypto-perthitic
albite lamellae, with maximum lamellar thicknesses <1 μm. Semicoherent lamellae are encircled by nanotunnel loops in two orientations
and cut by pull-apart cracks. The average bulk composition of this microtexture is Ab27.6Or71.8An0.6. The remaining 30 vol% is deuterically coarsened, microporous patch and vein perthite composed of incoherent subgrains of
oligoclase, albite and irregular microcline. The largest subgrains are ~3 μm in diameter. Heating times in the laboratory
were 12 to 6,792 h and T from 300°C into the melting interval at 1,100°C. Most samples were annealed at constant T but two were heated to simulate an 40Ar/39Ar step-heating schedule. Homogenisation of strain-controlled lamellae by Na↔K inter-diffusion was rapid, so that in all run
products at >700°C, and after >48 h at 700°C, all such regions were essentially compositionally homogeneous, as indicated
by X-ray analyses at fine scale in the transmission electron microscope. Changes in lamellar thickness with time at different
T point to an activation energy of ~350 kJmol−1. A lamella which homogenised after 6,800 h at 600°C, therefore, would have required only 0.6 s to do so in the melting interval
at 1,100°C. Subgrains in patch perthite homogenised more slowly than coherent lamellae and chemical gradients in patches persisted
for >5,000 h at 700°C. Homogenisation T is in agreement with experimentally determined solvi for coherent ordered intergrowths, when a 50–100°C increase in T for An1 is applied. Homogenisation of lamellae appears to proceed in an unexpected manner: two smooth interfaces, microstructurally
sharp, advance from the original interfaces toward the mid-line of each twinned, semicoherent lamella. In places, the homogenisation
interfaces have shapes reflecting the local arrangements of nanotunnels or pull-aparts. Analyses confirm that the change in
alkali composition is also relatively sharp at these interfaces. Si–Al disordering is far slower than alkali homogenisation
so that tweed texture in orthoclase, tartan twinning in irregular microcline, and Albite twins in albite lamellae and patches
persisted in all our experiments, including 5,478 h at 700°C, 148 h at 1,000°C and 5 h at 1,100°C, even though the ensemble
in each case was chemically homogeneous. Nanotunnels and pull-aparts were modified after only 50 min at 500°C following the
simulated 40Ar/39Ar step-heating schedule. New features called ‘slots’ developed away from albite lamellae, often with planar traces linking
slots to the closest lamella. Slot arrays were often aligned along ghost-like regions of diffraction contrast which may mark
the original edges of lamellae. We suggest that the slot arrays result from healing of pull-aparts containing fluid. At 700°C
and above, the dominant defects were subspherical ‘bubbles’, which evolved from slots or from regions of deuteric coarsening.
The small degree of partial melting observed after 5 h at 1,100°C was often in the vicinity of bubbles. Larger micropores,
which formed at subgrain boundaries in patch perthite during deuteric coarsening, retain their shape up to the melting point,
as do the subgrain boundaries themselves. It is clear that modification of defects providing potential fast pathways for diffusion
in granitic alkali feldspars begins below 500°C and that defect character progressively changes up to, and beyond, the onset
of melting. 相似文献
13.
Volume and grain boundary diffusion of calcium in natural and hot-pressed calcite aggregates 总被引:3,自引:0,他引:3
Calcium self-diffusion rates in natural calcite single crystals were experimentally determined at 700 to 900° C and 0.1 MPa
in a stream of CO2. Diffusion coefficients (D) were determined from 42Ca concentration profiles measured with an ion microprobe. The Arrhenius parameters yield an activation energy (Q)=382±37 kJ/mol
and pre-exponential factor (D0)=0.13 m2/s, and there is no measurable anisotropy. Calcium grain boundary diffusion rates were experimentally determined in natural
(Solnhofen) limestone and hot-pressed calcite aggregates at 650° to 850° C and 0.1 to 100 MPa pressure. The Solnhofen limestone
was first pre-annealed for 24 h at 700° C and 100 MPa confining pressure under anhydrous conditions to produce an equilibrium
microstructure for the diffusion experiments. Values for the product of the grain boundary diffusion coefficient (D′) and
the effective grain boundary diffusion width (δ) were determined from 42Ca concentration profiles measured with an ion microprobe. The results show that there is no measurable difference between
D′δ values obtained for pre-annealed Solnhofen samples at 0.1 and 100 MPa or between hot-pressed calcite aggregates and pre-annealed
Solnhofen samples. The temperature dependence for calcium grain boundary diffusion in Solnhofen samples annealed at 0.1 MPa
is described by the Arrhenius parameters D′
0δ=1.5×10−9 m3/s and Q=267±47 kJ/mol. Comparison of the results of this study with previously published data show that calcium is the slowest
volume diffusing species in calcite. The calcium diffusivities measured in this study place constraints on several geological
processes that involve diffusive mass transfer including diffusion-accommodated mechanisms in the deformation of calcite rocks.
Received: 19 December 1994/Accepted: 30 June 1995 相似文献
14.
Rasoul B. Sorkhabi Arvind K. Jain Tetsumaru Itaya Shiro Fukui Nand Lal Ashok Kumar 《Journal of Earth System Science》1997,106(3):169-179
The cooling and tectonic history of the Higher Himalayan Crystallines (HHC) in southwest Zanskar (along the Kishtwar-Padam
traverse) is constrained by K-Ar biotite and fission-track (FT) apatite and zircon ages. A total of nine biotite samples yields
ages in the range of 14–24 Ma, indicating the post-metamorphic cooling of these rocks through ∼ 300°C in the Miocene. Overall,
the ages become younger away from the Zanskar Shear Zone (ZSZ), which marks the basement-cover detachment fault between the
HHC and the Tethyan sedimentary zone, towards the core of the HHC. The same pattern is also observed for the FT apatite ages,
which record the cooling of the rocks through ∼ 120°C. The apatite ages range from 11 Ma in the vicinity of the ZSZ to 4 Ma
at the granitic core of the HHC. This pattern of discordant cooling ages across the HHC in southwest Zanskar reveals an inversion
of isotherms due to fast uplift-denudation (hence cooling) of the HHC core, which is, in turn, related to domal uplift within
the HHC. The Chisoti granite gneiss is the exposed domal structure along the studied traverse. Cooling history of two granite
gneisses at the core of the HHC is also quantified with the help of the biotite, zircon and apatite ages; the time-temperatures
thus obtained indicate a rapid pulse of cooling at ∼ 6 Ma, related to accelerated uplift-denudation of the HHC core at this
time. Long-term denudation rates of 0.5–0.7 mm/yr are estimated for the high-grade rocks of the Higher Himalaya in southwest
Zanskar over the past 4.0–5.5 m.yr. 相似文献
15.
The Lianhuashan tungsten deposit occurs in the volcanic terrain in the coastal area of Southeast China,where rhyolite,quartz porphyry and granite consitute a complee magmatic series.The orebodies are located in the endo-and exo-contacts between the quartz porphyry and the metasandstone of the Xiaoping coal measues.Hongenization temperatures of melt inclusions in zircon and quartz are 1100℃and 1050℃ for rhyolite,1000℃ and 860℃for quartz porphyry,and 950-1000℃and 820℃ for granite,respectively,demonstrating that the rockforming temperatures dropped successively from the eruptive to the intrusive rocks and that the homogenization temperatures of melt inclusions in zircon are 50-180℃higher than those in quartz.Homogenization temperatures of gas-liquid inclusions in quartz are 230-520℃(mostly 230-270℃)for quartz porphyry,200-450℃(mostly 200-360℃)for ore-bearing quartz veins,150-210℃for granite 170-200℃ for the vein quartz in it.Quartz from the quartz porphyry and from the ore-earing quartz veins show similar characteristics in inclusion type and homogenization temperature,indicating that intergranular solutions must have been formed upon cooling of magma and that ore-forming solutions for the tungstem mineralization were evolved mainly from ore-bearing intergranular solutions in the quartz porphyry. 相似文献
16.
The Ballachulish Igneous Complex consists of an outer quartz diorite and an inner granite, emplaced at about 300 MPa, initially
at 1000 to 1050 °C. The contact aureole (0.5–2 km wide) occurs in metapelites and metapsammites plus minor graphitic slates,
carbonate rocks and metaquartzites. A textural examination of the arkosic Appin Quartzite, which was previously believed to
have melted only within a few metres of the intrusion, demonstrates that partial melting occurred up to 500 m away from the
vertical eastern contact. Coupling petrographic observations with Qtz-Ab-Or-H2O phase relations, we determined both the amounts of actual melt and the maximum possible amounts of melt in the samples.
Melting efficiency was everywhere less than 100% and decreased with distance from the intrusion. Though perhaps not the only
possible source of fluid throughout the aureole, simple models demonstrate that H2O evolution from the pluton would have been volumetrically sufficient and persisted long enough to account for the observed
partial melting. A time-integrated fluid flux of 7000 kg/m2 from the pluton is necessary to account for the observed amounts of partial melt in the Appin Quartzite. From its inefficiency,
we infer that infiltration of the Appin Quartzite cannot have occurred along interconnected grain-edge channels. Rather, it
was controlled by hydraulic fracturing, with fracture density determining melting efficiency. Bulk-rock permeability is calculated
to be 10−20 m2, an order of magnitude lower than that necessary to permit pervasive flow of all the fluid exsolving from the pluton. There
is little difference between the calculated time-integrated fluid flux through the Appin Quartzite on the eastern flank and
an estimate of the infiltrating flux through the pelitic Leven Schist on the western flank in the time interval during which
both rock types were above their solidus temperature, despite differences in their equilibrium quartz-H2O dihedral angles at temperatures immediately below the solidus, and differences in the attitude of the contact. The rates
of H2O expulsion from the cooling pluton are consistent with highly efficient fracture-dominated flow, allowing insufficient time
for textural equilibration.
Received: 26 March 1998 / Accepted: 8 March 1999 相似文献
17.
Melt and fluid inclusions were investigated in six quartz phenocryst samples from the igneous rocks of the extrusive (ignimbrites
and rhyolites) and subvolcanic (granite porphyries) facies of the Lashkerek Depression in the Kurama mining district, Middle
Tien Shan. The method of inclusion homogenization was used, and glasses from more than 40 inclusions were analyzed on electron
and ion microprobes. The chemical characteristics of these inclusions are typical of silicic magmatic melts. The average composition
is the following (wt %): 72.4 SiO2, 0.06 TiO2, 13.3 Al2O3, 0.95 FeO, 0.03 MnO, 0.01 MgO, 0.46 CaO, 3.33 Na2O, 5.16K2O, 0.32 F, and 0.21 Cl. Potassium strongly prevails over sodium in all of the inclusions (K2O/Na2O averages 1.60). The average total of components in melt inclusions from five samples is 95.3 wt %, which indicates a possible
average water content in the melt of no less than 3–4 wt %. Water contents of 2.0 wt % and 6.6 wt % were determined in melt
inclusions from two samples using an ion microprobe. The analyses of ore elements in the melt inclusions revealed high contents
of Sn (up to 970 ppm), Th (19–62 ppm, 47 ppm on average), and U (9–26 ppm, 18 ppm on average), but very low Eu contents (0.01
ppm). Melt inclusions of two different compositions were detected in quartz from a granite porphyry sample: silicate and chloride,
the latter being more abundant. In addition to Na and K chlorides, the salt inclusions usually contain one or several anisotropic
crystals and an opaque phase. The homogenization temperatures of the salt inclusions are rather high, from 680 to 820°C. In
addition to silicate inclusions with homogenization temperatures of 820–850°C, a primary fluid inclusion of aqueous solution
with a concentration of 3.7 wt % NaCl eq. and a very high density of 0.93 g/cm3 was found in quartz from the ignimbrite. High fluid pressure values of 6.5–8.3 kbar were calculated for the temperature of
quartz formation. These estimates are comparable with values obtained by us previously for other regions of the world: 2.6–4.3
kbar for Italy, 3.7 kbar for Mongolia, 3.3–8.7 kbar for central Slovakia, and 3.3–9.6 kbar for eastern Slovakia. Unusual melt
inclusions were investigated in quartz from another ignimbrite sample. In addition to a gas phase and transparent glass, they
contain spherical Feoxide globules (81.2 wt % FeO) with high content of SiO2 (9.9 wt %). The globules were dissolved in the silicate melt within a narrow temperature range of 1050–1100°C, and the complete
homogenization of the inclusions was observed at temperatures of 1140°C or higher. The combined analysis of the results of
the investigation of these inclusions allowed us to conclude that immiscible liquids were formed in the high-temperature silicic
magma with the separation of iron oxide-dominated droplets. 相似文献
19.
The Brandberg West region of NW Namibia is dominated by poly-deformed turbidites and carbonate rocks of the Neoproterozoic Damara Supergoup, which have been regionally metamorphosed to greenschist facies and thermally metamorphosed up to mid-amphibolite facies by Neoproterozoic granite plutons. The meta-sedimentary rocks host Damaran-age hydrothermal quartz vein-hosted Sn–W mineralization at Brandberg West and numerous nearby smaller deposits. Fluid inclusion microthermometric studies of the vein quartz suggests that the ore-forming fluids at the Brandberg West mine were CO2-bearing aqueous fluids represented by the NaCl–CaCl2–H2O–CO2 system with moderate salinity (mean=8.6 wt% NaClequivalent).Temperatures determined using oxygen isotope thermometry are 415–521°C (quartz–muscovite), 392–447°C (quartz–cassiterite), and 444–490°C (quartz–hematite). At Brandberg West, the oxygen isotope ratios of quartz veins and siliciclastic host rocks in the mineralized area are lower than those in the rocks and veins of the surrounding areas suggesting that pervasive fluid–rock interaction occurred during mineralization. The O- and H-isotope data of quartz–muscovite veins and fluid inclusions indicate that the ore fluids were dominantly of magmatic origin, implying that mineralization occurred above a shallow granite pluton. Simple mass balance calculations suggest water/rock ratios of 1.88 (closed system) and 1.01 (open system). The CO2 component of the fluid inclusions had similar δ
13C to the carbonate rocks intercalated with the turbidites. It is most likely that mineralization at Brandberg West was caused by a combination of an impermeable marble barrier and interaction of the fluids with the marble. The minor deposits in the area have quartz veins with higher δ
18O values, which is consistent with these deposits being similar geological environments exposed at higher erosion levels. 相似文献
20.
Three reactions involving Mg-chlorite-muscovite and quartz werestudied between 5 and 10 kilobars water pressure over a temperaturerange of 600700 °C using mixtures of synthetic clinochlore,muscovite and quartz as starting materials. Three reactionswere reversed in this system. 3 chlorite+5 muscovite + 8 kyanite+ 5 phlogopite + 1 quartz + 12 H2O was reversed between 639.5±5.3°C and 531.8±5.1 °C at 7.24 kb and between 645.9±5.7°C and634.1±6.0°C at8.27kb. A second reaction: 1 chlorite+ 1 muscovite+2 quartz = 1 phlogopite+ 1 cordierite + 3.5 H2O was reversed between 6370±60°C and 622.8±5.2°C at 6.21 kb. A third reaction: 3 cordierite+2 muscovite = 2 phlogopite +8 alumino-silicate + 7 quartz + 1.5 H2O was reversed between660.l±5.7 °C and 650.l±5.3 °C at 6.21kb. This reaction is terminated at the beginning of melting around725 °C at 5.65 kb. These reactions determine the upper stability limits of Mg-chlorite-muscoviteand quartz assemblages between 5 and 10 kb water pressure. Theresults may be used in delimiting the upper stability of similarassemblages in natural systems. 相似文献