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1.
通过研究硅酸盐熔体的氧平均体积,并与硅酸盐玻璃相对比,提出硅酸盐熔体的体积可分为两部分,即硅-氧骨架部分和阳离子部分,根据氧平均体积变化规律,得出硅-氧骨架部分的体积基本不随温度变化,硅酸盐熔体的体积膨胀主要是由于“氧化物”部分的局部膨胀所致,进一步提出O~(2-)半径基本不变,而主要是阳离子半径变化,并讨论了膨胀的机制。 相似文献
2.
There is growing evidence that the budget of Pb in mantle peridotites is largely contained in sulfide, and that Pb partitions strongly into sulfide relative to silicate melt. In addition, there is evidence to suggest that diffusion rates of Pb in sulfide (solid or melt) are very fast. Given the possibility that sulfide melt “wets” sub-solidus mantle silicates, and has very low viscosity, the implications for Pb behavior during mantle melting are profound. There is only sparse experimental data relating to Pb partitioning between sulfide and silicate, and no data on Pb diffusion rates in sulfides. A full understanding of Pb behavior in sulfide may hold the key to several long-standing and important Pb paradoxes and enigmas. The classical Pb isotope paradox arises from the fact that all known mantle reservoirs lie to the right of the Geochron, with no consensus as to the identity of the “balancing” reservoir. We propose that long-term segregation of sulfide (containing Pb) to the core may resolve this paradox. Another Pb paradox arises from the fact that the Ce/Pb ratio of both OIB and MORB is greater than bulk earth, and constant at a value of 25. The constancy of this “canonical ratio” implies similar partition coefficients for Ce and Pb during magmatic processes (Hofmann et al. in Earth Planet Sci Lett 79:33–45, 1986), whereas most experimental studies show that Pb is more incompatible in silicates than Ce. Retention of Pb in residual mantle sulfide during melting has the potential to bring the bulk partitioning of Ce into equality with Pb if the sulfide melt/silicate melt partition coefficient for Pb has a value of ∼ 14. Modeling shows that the Ce/Pb (or Nd/Pb) of such melts will still accurately reflect that of the source, thus enforcing the paradox that OIB and MORB mantles have markedly higher Ce/Pb (and Nd/Pb) than the bulk silicate earth. This implies large deficiencies of Pb in the mantle sources for these basalts. Sulfide may play other important roles during magmagenesis: (1) advective/diffusive sulfide networks may form potent metasomatic agents (in both introducing and obliterating Pb isotopic heterogeneities in the mantle); (2) silicate melt networks may easily exchange Pb with ambient mantle sulfides (by diffusion or assimilation), thus “sampling” Pb in isotopically heterogeneous mantle domains differently from the silicate-controlled isotope tracer systems (Sr, Nd, Hf), with an apparent “de-coupling” of these systems. 相似文献
3.
Controls on the fractionation of isovalent trace elements in magmatic and aqueous systems: evidence from Y/Ho,Zr/Hf,and lanthanide tetrad effect 总被引:55,自引:0,他引:55
Michael Bau 《Contributions to Mineralogy and Petrology》1996,123(3):323-333
The parameters which control the behaviour of isovalent trace elements in magmatic and aqueous systems have been investigated
by studying the distribution of yttrium, rare-earth elements (REEs), zirconium, and hafnium. If a geochemical system is characterized
by CHArge-and-RAdius-Controlled (CHARAC) trace element behaviour, elements of similar charge and radius, such as the Y-Ho and Zr-Hf twin pairs, should display extremely
coherent behaviour, and retain their respective chondritic ratio. Moreover, normalized patterns of REE(III) should be smooth
functions of ionic radius and atomic number. Basic to intermediate igneous rocks show Y/Ho and Zr/Hf ratios which are close
to the chondritic ratios, indicating CHARAC behaviour of these elements in pure silicate melts. In contrast, aqueous solutions
and their precipitates show non-chondritic Y/Ho and Zr/Hf ratios. An important process that causes trace element fractionation
in aqueous media is chemical complexation. The complexation behaviour of a trace element, however, does not exclusively depend
on its ionic charge and radius, but is additionally controlled by its electron configuration and by the type of complexing
ligand, since the latter two determine the character of the chemical bonding (covalent vs electrostatic) in the various complexes. Hence, in contrast to pure melt systems, aqueous systems are characterized by non-CHARAC
trace element behaviour, and electron structure must be considered as an important additional parameter. Unlike other magmatic
rocks, highly evolved magmas rich in components such as H2O, Li, B, F, P, and/or Cl often show non-chondritic Y/Ho and Zr/Hf ratios, and “irregular” REE patterns which are sub-divided
into four concave-upward segments referred to as “tetrads”. The combination of non-chondritic Y/Ho and Zr/Hf ratios and lanthanide
tetrad effect, which cannot be adequately modelled with current mineral/melt partition coefficients which are smooth functions
of ionic radius, reveals that non-CHARAC trace element behaviour prevails in highly evolved magmatic systems. The behaviour
of high field strength elements in this environment is distinctly different from that in basic to intermediate magmas (i.e.
pure silicate melts), but closely resembles trace element behaviour in aqueous media. “Anomalous” behaviour of Y and REEs,
and of Zr and Hf, which are hosted by different minerals, and the fact that these minerals show “anomalous” trace element distributions
only if they crystallized from highly evolved magmas, indicate that non-CHARAC behaviour is a reflection of specific physicochemical
properties of the magma. This supports models which suggest that high-silica magmatic systems which are rich in H2O, Li, B, F, P, and/or Cl, are transitional between pure silicate melts and hydrothermal fluids. In such a transitional system
non-CHARAC behaviour of high field strength elements may be due to chemical complexation with a wide variety of ligands such
as non-bridging oxygen, F, B, P, etc., leading to absolute and relative mineral/melt or mineral/aqueous-fluid partition coefficients
that are extremely sensitive to the composition and structure of this magma. Hence, any petrogenetic modelling of such magmatic
rocks, which utilizes partition coefficients that have not been determined for the specific igneous suite under investigation,
may be questionable. But Y/Ho and Zr/Hf ratios provide information on whether or not the evolution of felsic igneous rocks
can be quantitatively modelled: samples showing non-chondritic Y/Ho and Zr/Hf ratios or even the lanthanide tetrad effect
should not be considered for modelling. However, the most important result of this study is that Y/Ho and Zr/Hf ratios may be used to
verify whether Y, REEs, Zr, and Hf in rocks or minerals have been deposited from or modified by silicate melts or aqueous
fluids.
Received: 4 September 1995 / Accepted: 30 October 1995 相似文献
4.
Andrea De Stefano M. G. Kopylova P. Cartigny V. Afanasiev 《Contributions to Mineralogy and Petrology》2009,158(3):295-315
We studied diamonds and barren and diamondiferous eclogite xenoliths from the Jericho kimberlite (Northern Slave craton).
The majority of the diamonds are non-resorbed octahedral crystals, with moderately aggregated N (IaB < 50%, N < 300 ppm) and δ13C = −5 to −41‰. The diamonds belong to “eclogitic” (90% of the studied samples), “websteritic” (7%) and “peridotitic” (3%)
assemblages. The Jericho diamonds differ from the majority of “eclogitic” diamonds worldwide in magnesian compositions of
associated minerals and extremely light C isotopic compositions (δ13C = −24 to −41‰). We propose that metasomatism triggered by H2O fluids may have been involved in the diamond formation. Multiple episodes of the metasomatism and associated melt extraction
of various ages are evident in Jericho eclogite xenoliths where primary garnet and clinopyroxene have been recrystallized
to more magnesian minerals with higher contents of some incompatible trace elements and to hydrous secondary phases. The model
is supported by the general similarity of mineral compositions in diamondiferous eclogites to those in diamond inclusions
and to secondary magnesian garnet and clinopyroxene in recrystallized barren eclogites. The ultimate products of the metasomatism
could be “websteritic” diamond assemblages sourced from magnesian eclogites.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
5.
A. Borisov 《Mineralogy and Petrology》2001,71(1-2):87-94
Summary I report here the experimental results on the dynamics of equilibration of silicate melts suspended from Ni loops of different
diameters at 1400 °C and at constant oxygen fugacity. It is found that saturation of silicate melt of anorthite-diopside eutectic
composition with Ni is reached during the first few hours because the nickel ions in the melt diffuse extremely rapidly. Fast
convection usually results in relatively homogeneous Ni content throughout the sample for loops with diameters 3.2–4.0 mm.
Hence, glass homogeneity with respect to an element of interest may not be sufficient evidence that metal/melt equilibrium
is reached. It is demonstrated that central parts of Ni diffusion profiles in samples with diameter as low as 2.6 mm are also
“flattened” by convection. Possible driving forces of convection in a loop sample are discussed.
Received November 8, 1999; revised version accepted July 15, 2000 相似文献
Zusammenfassung Die Loop-Technik: Dynamik der Metall/Schmelze ?quilibrierung Hier werden die experimentellen Ergebnisse zur ?quilibrierungs-Dynamik von Silikatschmelzen vorgelegt. Diese wurden bei konstanter Sauerstoff-Fugazit?t von Ni-loops verschiedener Durchmesser bei 1400 °C suspendiert. Es zeigt sich, dass Ni-S?ttigung von Silikatschmelzen von eutektischer Anorthit-Diopsid-Zusammensetzung schon w?hrend der ersten Stunden erreicht wird, da die Ni-Jonen ausserordentlich rasch in die Schmelze diffundieren. Rasche Konvektion führt zu relativ homogener Nickel-Verteilung in der Probe wenn loops mit 3.2–4.0 mm Durchmesser verwendet werden. Homogene Verteilung eines Elementes im Glas bedeutet nicht notwendigerweise, dass Gleichgewicht zwischen Metall und Schmelze erreicht wurde. Es wird gezeigt, dass zentrale Teile von Nickeldiffusions-Profilen in Proben von bis zu 2.6 mm Durchmesser auch durch Konvektion “abgeflacht” sein k?nnen. M?gliche Kr?fte die zur Konvektion in loop-Proben führen k?nnen werden diskutiert.
Received November 8, 1999; revised version accepted July 15, 2000 相似文献
6.
Russell O. Colson 《Contributions to Mineralogy and Petrology》2010,159(5):703-717
Reduction potentials (E
0) and diffusion rates (D) for divalent nickel in a variety of silicate melts and as a function of temperature have been measured in situ using voltammetric
methods. These measurements provide an indirect window into structural changes in melts at temperatures above the liquidus.
Slope of the reduction potential versus temperature (related to entropy) and slope of the diffusion rate versus 1/T (related to diffusional activation energy) remain roughly constant or change only gradually above the liquidus, with the
exception of a sharp break in slope typically observed about 60–160°C above the liquidus. This sharp break is consistent with
a structural transition in the melt rather than with a gradual change in melt structure. A correlation between the transition
temperature and the liquidus temperature, combined with the qualitative effect of prior crystallization, suggests that the
transition may be related to the melt “preparing” for crystallization roughly 100°C above the liquidus. These observations
may have implications for understanding melt activities, partitioning between melt and crystalline phases, and liquid immiscibility. 相似文献
7.
.Dr H. Taniguchi 《Mineralogy and Petrology》1993,49(1-2):13-25
Summary Density and viscosity measurements of three melts of volcanic rock composition (basalt and andesite) at low temperatures were carried out to understand the role of free volume in the viscous behavior of a magma and to estimate the flow unit in the melts. The data combined with literature data suggest the following conclusion: free-volume theory is not applicable to these silicate melts; the relation between viscosity and the inverse of free volume does not yield a straight line in a wide temperature range from the glass-transion temperature to 1550°C. However, two depolymerized melts, diopside and Oki-Dozen alkali basalt (OAB), yield almost linear relationships. Thus, the free-volume theory should hold to a fairly good approximation for these two melts. Based on this approximation, the radius of flow unit for diopside melt was calculated to be about 4.7 Å, and that for Oki-Dozen alkali basalt to be about 4.2 Å. The three-dimensional silicate anions which may correspond to the flow unit are Si14O35
14– and Si16O40
16– for diopside melt, and Si10O25
10– and Si12O30
12– for OAB melt. The temperature effect on the initial slope of the viscosity-pressure relation has also been examined in the frame of free-volume theory. It was concluded that the relative increase of the initial slope of the relation with increasing temperature might be caused by the increase of free volume.With 6 Figures 相似文献
8.
Pascal Richet Alan Whittington François Holtz Harald Behrens Susanne Ohlhorst Max Wilke 《Contributions to Mineralogy and Petrology》2000,138(4):337-347
A review of published and newly measured densities for 40 hydrous silicate glasses indicates that the room-temperature partial
molar volume of water is 12.0 ± 0.5 cm3/mol. This value holds for simple or mineral compositions as well as for complex natural glasses, from rhyolite to tephrite
compositions, prepared up to 10–20 kbar pressures and containing up to 7 wt% H2O. This volume does not vary either with the molar volume of the water-free silicate phase, with its degree of polymerization
or with water speciation. Over a wide range of compositions, this constant value implies that the volume change for the reaction
between hydroxyl ions and molecular water is zero and that, at least in glasses, speciation does not depend on pressure. Consistent
with data from Ochs and Lange (1997, 1999), systematics in volume expansion for SiO2–M2O systems (M=H, Li, Na, K) suggests that the partial molar thermal expansion coefficient of H2O is about 4 × 10−5 K−1 in silicate glasses.
Received: 30 June 1999 / Accepted: 5 November 1999 相似文献
9.
A study has been made of thermoluminescence from synthetic quartz with varying hydroxyl impurity concentrations up to approximately
300 H/106 Si which are associated with a “broad-band” IR absorption in the range 2600–3700 cm−1. These hydroxyl defects are known to be important in the hydrolytic weakening of quartz. We have found only minor differences
in the glow curves of unheated crystals but significant intensity increases when “wet” crystals are heated sufficiently to
cause bubble formation. It would seem that the electron traps are unaffected by the bubble formation, but the electron/luminescence
centre radiative recombination probability is increased. 相似文献
10.
The evolution of terrestrial planets (the Earth, Venus, Mars, Mercury, and Moon) was proved to have proceeded according to
similar scenarios. The primordial crusts of the Earth, Moon, and, perhaps, other terrestrial planets started to develop during
the solidification of their global magmatic “oceans”, a process that propagated from below upward due to the difference in
the adiabatic gradient and the melting point gradient. Consequently, the lowest melting components were “forced” toward the
surfaces of the planets in the process of crystallization differentiation. These primordial crusts are preserved within ancient
continents and have largely predetermined their inner structure and composition. Early tectono-magmatic activity at terrestrial
planets was related to the ascent of mantle plumes of the first generation, which consisted of mantle material depleted during
the development of the primordial crusts. Intermediate evolutionary stages of the Earth, Moon, and other terrestrial planets
were marked by an irreversible change related to the origin of the liquid essentially iron cores of these planets. This process
induced the ascent of mantle superplumes of the second generation (thermochemical), whose material was enriched in Fe, Ti,
incompatible elements, and fluid components. The heads of these superplumes spread laterally at shallower depths and triggered
significant transformations of the upper shells of the planets and the gradual replacement of their primordial crusts of continental
type by secondary basaltic crusts. The change in the character of the tectono-magmatic activity was associated with modifications
in the environment at the surface of the Earth, Mars, and Venus. The origin of thermochemical mantle plumes testifies that
the tectono-magmatic process involved then material of principally different type, which had been previously “conserved” at
deep portions of the planets. This was possible only if (1) the planetary bodies initially had a heterogeneous inner structure
(with an iron core and silicate mantle made up of chondritic material); and (2) the planetary bodies were heated from their
peripheral toward central portions due to the passage of a “thermal wave”, with the simultaneous cooling of the outer shells.
The examples of the Earth and Moon demonstrate that the passage of such a “wave” through the silicate mantles of the planets
was associated with the generation of mantle plumes of the first generation. When the “wave” reached the cores, whose composition
was close to the low-temperature Fe + FeS eutectic, these cores started to melt and gave rise to superplumes of the second
generation. The “waves” are thought to have been induced by the acceleration of the rotation of these newly formed planets
due to the decrease of their radii because of the compaction of their material. When this process was completed, the rotation
of the planets stabilized, and the planets entered their second evolutionary stage. It is demonstrated that terrestrial planets
are spontaneously evolving systems, whose evolution was accompanied by the irreversible changes in their tectono-magmatic
processes. The evolution of most of these planets (except the Earth) is now completed, so that they “dead” planetary bodies. 相似文献
11.
Rivalenti Giorgio Mazzucchelli Maurizio Vannucci Riccardo Hofmann Albrecht W. Ottolini Luisa Bottazzi Piero Obermiller Walter 《Contributions to Mineralogy and Petrology》1995,122(3):275-288
Field, mineralogical and petrological data are presented on a newly found carbonatite occurrence associated with “kamafugite”
lava at Cupaello, central Italy. This carbonatite occurrence is part of the Late Pleistocene Umbria-Latium ultra-alkaline
district (ULUD) which extends southwards within the Apennines to Mount Vulture, delineating an important magmatic province
along the most peripheral belt of the Tyrrhenian extensional tectonic system. This province is distinct, but probably related
genetically with the more abundant and common leucite-bearing assemblages of the Roman Comagmatic Region and represents the
first reported occurrence of carbonatite assemblages in the Mediterranean Basin. The Cupaello suite indicates that primary
or near-primary mantle silicate melts of “kamafugitic” composition are transitional with Ca-carbonatite liquid and provides
direct evidence of immiscibility of carbonatite from “kamafugite” magma. It is inferred that a primary mantle origin of Ca-carbonatites
is conditional upon a potential silicate magma that may be coupled with the carbonatite, but may not have reached the surface.
The data indicate a strong genetic link between ULUD Ca-carbonatites and some African analogues, supporting the view that
their genesis depends on similar source and associated tectonic conditions.
Received: 17 January 1995 / Accepted: 14 June 1995 相似文献
12.
H. L. Vacher Larry D. Seale Lee J. Florea Robert Brinkmann 《Environmental Geology》2008,54(5):1007-1015
We apply the logic of clinical epidemiological studies to quantify the accuracy of mapping sinkholes by ALSM in the 750 km2 Pinellas County. By such studies, a new diagnostic procedure is tested by comparing the diagnoses in a clinical trial to
diagnoses on the same patients from a more reliable, but more elaborate and expensive procedure (“gold standard” in epidemiological
context). A relatively undeveloped, 65 km2 focus area where we have aerial photographs that are effectively contemporaneous with the ALSM flights serves as the “clinical
trial”. The xy-locations in the focus area are the “patients” in the trial. The “diagnostic test” for having “sinkhole disease” is inclusion
in a database of sinkhole polygons delimited by ALSM contours (“ALSM-alone”), as detailed in Part 1. The standard of comparison
(“gold standard” would be an overstatement in the absence of geophysical testing) is inclusion in a database of sinkhole outlines
derived by best judgment of conjunctive interpretation of ALSM and aerial photography. GIS intersections that indicate the
sensitivity and specificity of the test (ALSM-alone) are 43 and 98.3%, respectively, and, in the focus area where the prevalence
of “sinkhole disease” is 4.7%, the positive and negative predictive values are 55.5 and 97.2%, respectively. Over much of
the rest of the county, where only the test can be applied, the prevalence of sinkholes is sufficiently small that it cannot
be determined to be any different from zero given the paucity of interpreted sinkholes (positive diagnoses) and the low specificity
of the test method. The conclusion, therefore, is that contemporaneous aerial photography is essential to compile an ALSM-derived
database that aims to state that the given xy-points lay inside or outside of topographic depressions in the covered karst of west-central Florida. 相似文献
13.
A series of synthetic Ca-Tschermak–diopside (CaAlAlSiO6–CaMgSi2O6) clinopyroxenes were investigated by powder infrared spectroscopy at room temperature in the wavenumber range 80–2,000 cm−1. Measurable local structural heterogeneities in the crystals are suggested by the line broadening parameter, Δcorr that are
observed for intermediate solid-solution compositions. The broadening is most pronounced in the high wavenumber region of
the IR spectra that contains stretching modes involving the TO4 polyhedra. The effective line widths for three selected wavenumber regions deviate positively from linear behavior. This
is also observed for the enthalpy of mixing of this solid solution. The relationship between “excess Δcorr”, δΔcorr, and heat
of mixing, ΔH
mix, behavior was investigated for this clinopyroxene series and for several other binary silicate solid solutions. The ΔH
mix versus δΔcorr slope values show a linear relationship with respect to the integrated excess volume of the various solid solutions. 相似文献
14.
Summary ?Many ultramafic complexes, some of which have chromitite bodies, are exposed in the Sangun zone in central Chugoku district,
Southwest Japan. Harzburgite is always dominant over dunite, but the dunite/harzburgite ratio varies from complex to complex.
Large chromitite bodies are exclusively found in relatively dunite-dominant complexes or portions.
The degree of roundness, DR#=[area/(round-length)2] (normalized by a circle’s value: 1/4π), of chromian spinel is variable, depending on lithology of the peridotites. Chromian
spinel is mostly anhedral or even vermicular (less than 0.4 in DR#) in harzburgite, and is most frequently euhedral or rounded
(within the range of 0.7 to 0.9 in DR#) in dunite.
The morphology of spinel is correlated with chemistry: the DR# is positively correlated with Ti content and Fe3+#(=Fe3+/(Cr + Al + Fe3+)), but is not related to Cr#. When chromitite is present in dunite, the spinel is relatively anhedral (vermicular) and low
in Ti and Fe3+# in the dunite whereas it is relatively euhedral and high in Ti and Fe3+# in surrounding harzburgite. We define these spinels as “extraordinary” spinels, which are commonly found in Wakamatsu mine
area in the Tari-Misaka complex, which exploits the largest chromite body in Japan. The rocks with the “extraordinary” spinels
show transitional lithologies (a gradual boundary, one meter to several tens of meters in width) between dunite and harzburgite
with “ordinary” spinels.
The formation of dunite and chromitite is interpreted as a result of the reaction of harzburgite with a relatively Ti-rich
magma (back-arc basin or MORB-like magma) and related magma mixing, as discussed by Arai and Yurimoto (1994). The dike-like occurrence of the dunite and chromitite indicates that the reaction took place along melt conduits
(=fractures) less than 200 m in width. Podiform chromitites were formed only when the reaction zone was relatively wide (several
tens of meters in width), that is, only when the degree of interaction was relatively high. The magma modified by the reaction
percolated, possibly by porous flow from the reaction zone outward, and changed the texture and chemistry of chromian spinel,
on the scale of several tens of meters. This type of melt transport, or melt flow through fractures with a melt percolation
aureole, may be prevalent in the uppermost mantle.
Received February 8, 2000;/revised version accepted December 22, 2000 相似文献
15.
Jian Wang Kéiko H. Hattori Rolf Kilian Charles R. Stern 《Contributions to Mineralogy and Petrology》2007,153(5):607-624
Quaternary basalts in the Cerro del Fraile area contain two types of mantle xenoliths; coarse-grained (2–5 mm) C-type spinel
harzburgites and lherzolites, and fine-grained (0.5–2 mm) intensely metasomatized F-type spinel lherzolites. C-type xenoliths
have high Mg in olivine (Fo = 90–91) and a range in Cr# [Cr/ (Cr + Al) = 0.17–0.34] in spinel. Two C-type samples contain
websterite veinlets and solidified patches of melt that is now composed of minute quenched grains of plagioclase + Cr-spinel + clinopyroxene + olivine.
These patches of quenched melts are formed by decompression melting of pargasitic amphibole. High Ti contents and common occurrence
of relic Cr-spinel in the quenched melts indicate that the amphibole is formed from spinel by interaction with the Ti-rich
parental magma of the websterite veinlets. The fO2 values of these two C-type xenoliths range from ΔFMQ −0.2 to −0.4, which is consistent with their metasomatism by an asthenospheric
mantle-derived melt. The rest of the C-type samples are free of “melt,” but show cryptic metasomatism by slab-derived aqueous
fluids, which produced high concentrations of fluid-mobile elements in clinopyroxenes, and higher fO2 ranging from ΔFMQ +0.1 to +0.3. F-type lherzolites are intensely metasomatized to form spinel with low Cr# (∼0.13) and silicate
minerals with low MgO, olivine (Fo = ∼84), orthpyroxene [Mg# = Mg/(Mg + ΣFe) = ∼0.86] and clinopyroxene (Mg# = ∼0.88). Patches
of “melt” are common in all F-type samples and their compositions are similar to pargasitic amphibole with low TiO2 (<0.56 wt%), Cr2O3 (<0.55 wt%) and MgO (<16.3 wt%). Low Mg# values of silicate minerals, including the amphibole, suggest that the metasomatic
agent is most likely a slab melt. This is supported by high ratios of Sr/Y and light rare earth elements (REE)/heavy REE in
clinopyroxenes. F-type xenoliths show relatively low fO2 (ΔFMQ −0.9 to −1.1) compared to C-type xenoliths and this is explained by the fusion of organic-rich sediments overlying
the slab during the slab melt. Trench-fill sediments in the area are high in organic matter. The fusion of such wet sediments
likely produced CH4-rich fluids and reduced melts that mixed with the slab melt. High U and Th in bulk rocks and clinopyroxene in F-type xenoliths
support the proposed interpretation. 相似文献
16.
Re-equilibration of melt inclusions trapped by magnesian olivine phenocrysts from subduction-related magmas: petrological implications 总被引:4,自引:1,他引:3
L. V. Danyushevsky F. N. Della-Pasqua S. Sokolov 《Contributions to Mineralogy and Petrology》2000,138(1):68-83
We describe and model a potential re-equilibration process that can affect compositions of melt inclusions in magnesian olivine
phenocrysts. This process, referred to as “Fe-loss”, can operate during natural pre-eruptive cooling of host magma and results
in lower FeOt and higher MgO contents within the initially trapped volume of inclusion. The extent of Fe-loss is enhanced by large temperature
intervals of magma cooling before eruption. The compositions of homogenised melt inclusions in olivine phenocrysts from several
subduction-related suites demonstrate that (1) Fe-loss is a common process, (2) the maximum observed degree of re-equilibration
varies between suites, and (3) within a single sample, variable degrees of re-equilibration can be recorded by melt inclusions
trapped in olivine phenocrysts of identical composition. Our modelling also demonstrates that the re-equilibration process
is fast going to completion, in the largest inclusions in the most magnesian phenocrysts it is completed within 2 years. The
results we obtained indicate that the possibility of Fe-loss must be considered when estimating compositions of parental subduction-related
magmas from naturally quenched glassy melt inclusions in magnesian olivine phenocrysts. Compositions calculated from glassy
inclusions affected by Fe-loss will inherit not only erroneously low FeOt contents, but also low MgO due to the inherited higher Mg##of the residual melt in re-equilibrated inclusions. We also demonstrate
that due to the higher MgO contents of homogenised melt inclusions affected by Fe-loss, homogenisation temperatures achieved
in heating experiments will be higher than original trapping temperatures. The extent of overheating will increase depending
on the degree of re-equilibration, and can reach up to 50 °C in cases where complete re-equilibration occurs over a cooling
interval of 200 °C.
Received: 2 November 1998 / Accepted: 27 September 1999 相似文献
17.
The tectono-magmatic evolution of the Earth and Moon started after the solidification of their magmatic “oceans”, whose in-situ
crystallization produced the primordial crusts of the planets, with the composition of these crusts depending on the depths
of the “oceans”. A principally important feature of the irreversible evolution of the planetary bodies, regardless of their
sizes and proportions of their metallic cores and silicate shells, was a fundamental change in the course of their tectono-magmatic
processes during intermediate evolutionary stages. Early in the geological evolution of the Earth and Moon, their magmatic
melts were highly magnesian and were derived from mantle sources depleted during the solidification of the magmatic “oceans”;
this situation can be described in terms of plume tectonics. Later, geochemically enriched basalts with high concentrations
of Fe, Ti, and incompatible elements became widespread. These rocks were typical of Phanerozoic within-plate magmatism. The
style of tectonic activity has also changed: plate tectonics became widespread at the Earth, and large depressions (maria)
started to develop at the Moon. The latter were characterized by a significantly thinned crust and basaltic magmatism. These
events are thought to have been related to mantle superplumes of the second generation (thermochemical), which are produced
(Dobretsov et al., 2001) at the boundary between the liquid core and silicate mantle owing to the accumulation of fluid at
this interface. Because of their lower density, these superplumes ascended higher than their precursors did, and the spreading
of their head parts resulted in active interaction with the superjacent thinned lithosphere and a change in the tectonic regime,
with the replacement of the primordial crust by the secondary basaltic one. This change took place at 2.3–2.0 Ga on the Earth
and at 4.2–3.9 Ga on the Moon. Analogous scenarios (with small differences) were also likely typical of Mars and Venus, whose
vast basaltic plains developed during their second evolutionary stages. The change in the style of tectonic-magmatic activity
was associated with important environmental changes on the surfaces of the planets, which gave rise to their secondary atmospheres.
The occurrence of a fundamental change in the tectono-magmatic evolution of the planetary bodies with the transition from
depleted to geochemically enriched melts implies that these planets were originally heterogeneous and had metal cores and
silicate shells enriched in the material of carbonaceous chondrites. The involvement of principally different material (that
had never before participated in these processes) in tectono-magmatic processes was possible only if these bodies were heated
from their outer to inner levels via the passage of a heating wave (zone) with the associated cooling of the outermost shells.
The early evolutionary stages of the planets, when the waves passed through their silicate mantles, were characterized by
the of development of super-plumes of the first generation. The metallic cores were the last to melt, and this processes brought
about the development of thermochemical super-plumes. 相似文献
18.
H. A. Gilg A. Lima R. Somma H. E. Belkin B. De Vivo R. A. Ayuso 《Mineralogy and Petrology》2001,73(1-3):145-176
Summary We present new mineral chemistry, fluid inclusion, stable carbon and oxygen, as well as Pb, Sr, and Nd isotope data of Ca-Mg-silicate-rich
ejecta (skarns) and associated cognate and xenolithic nodules from the Mt. Somma-Vesuvius volcanic complex, Italy. The typically
zoned skarn ejecta consist mainly of diopsidic and hedenbergitic, sometimes “fassaitic” clinopyroxene, Mg-rich and Ti-poor
phlogopite, F-bearing vesuvianite, wollastonite, gehlenite, meionite, forsterite, clinohumite, anorthite and Mg-poor calcite
with accessory apatite, spinell, magnetite, perovskite, baddeleyite, and various REE-, U-, Th-, Zr- and Ti-rich minerals.
Four major types of fluid inclusions were observed in wollastonite, vesuvianite, gehlenite, clinopyroxene and calcite: a)
primary silicate melt inclusions (THOM = 1000–1050 °C), b) CO2 ± H2S-rich fluid inclusions (THOM = 20–31.3 °C into the vapor phase), c) multiphase aqueous brine inclusions (THOM = 720–820 °C) with mainly sylvite and halite daughter minerals, and d) complex chloride-carbonate-sulfate-fluoride-silicate-bearing
saline-melt inclusions (THOM = 870–890 °C). The last inclusion type shows evidence for immiscibility between several fluids (silicate melt – aqueous chloride-rich
liquid – carbonate/sulfate melt?) during heating and cooling below 870 °C. There is no evidence for fluid circulation below
700 °C and participation of externally derived meteoric fluids in skarn formation. Skarns have considerably variable 206Pb/204Pb (19.047–19.202), 207Pb/204Pb (15.655–15.670), and 208Pb/204Pb (38.915–39.069) and relatively low 143Nd/144Nd (0.51211–0.51244) ratios. The carbon and oxygen isotope compositions of skarn calcites (δ13CV-PDB = −5.4 to −1.1‰; δ18OV-SMOW = 11.7 to 16.4‰) indicate formation from a 18O- and 13C-enriched fluid. The isotope composition of skarns and the presence of silicate melt inclusion-bearing wollastonite nodules
suggests assimilation of carbonate wall rocks by the alkaline magma at moderate depths (< 5 km) and consequent exsolution
of CO2-rich vapor and complex saline melts from the contaminated magma that reacted with the carbonate rocks to form skarns.
Received March 1, 2000; revised version accepted November 2, 2000 相似文献
19.
C. Carbonin A. Dal Negro S. Ganeo E. M. Piccirillo 《Contributions to Mineralogy and Petrology》1991,108(1-2):34-42
The crystallochemical variations of clinopyroxene in response to changes in fO
2 and melt composition have been determined for a basalt-pantellerite suite (Boseti Complex, Main Ethiopian Rift) by crystal
structure refinement and microprobe analysis. The pyroxene evolutionary trend has both a “Ca-minimum” and late iron enrichment.
During crystallization from basalts to trachytes, clinopyroxene geometry depends mainly on the relationships between T and
M2 sites; for example, high SiO2 activity in the magma causes high Si occupancy in T site, which in turn requires low Ca occupancy in M2 site in order to
fulfill the local charge balance requirements. In contrast, clinopyroxene crystallized from acid melts is characterized by
high Fe2+ (M1) content and therefore by a very large M1 site. Longer 〈M1-O1〉 and M1-O2 bond lengths require shorter T-O1 and T-O2 bond
lengths and high Si occupancy in T site. It is concluded that the “Ca-minimum” in the clinopyroxene structure is regarded
as the lowest value at which the charge balance requirements are satisfied in a C2/c clinopyroxene structure. 相似文献
20.
S. I. Mayr H. Burkhardt Yu. Popov A. Wittmann 《International Journal of Earth Sciences》2008,97(2):385-399
Internal surface, formation factor, Nuclear Magnetic Resonance (NMR)-T2 relaxation times and pore radius distributions were
measured on representative core samples for the estimation of hydraulic permeability. Permeability is estimated using various
versions of the classic Kozeny–Carman-equation (K–C) and a further development of K–C, the fractal PaRiS-model, taking into
account the internal surface. In addition to grain and pore size distribution, directly connected to permeability, internal
surface reflects the internal structure (“micro morphology”). Lithologies could be grouped with respect to differences in
internal surface. Most melt rich impact breccia lithologies exhibit large internal surfaces, while Tertiary post-impact sediments
and Cretaceous lithologies in displaced megablocks display smaller internal surfaces. Investigations with scanning electron
microscopy confirm the correlation between internal surface and micro morphology. In addition to different versions of K–C,
estimations by means of NMR, pore radius distributions and some gas permeability measurements serve for cross-checking and
calibration. In general, the different estimations from the independent methods and the measurements are in satisfactory accordance.
For Tertiary limestones and Suevites bulk with very high porosities (up to 35%) permeabilites between 10−14 and 10−16 m2 are found, whereas in lower Suevite, Cretaceous anhydrites and dolomites, bulk permeabilites are between 10−15 and 10−23 m2. 相似文献