共查询到20条相似文献,搜索用时 703 毫秒
1.
The interdependence of the Fe(Mg)–1 (e.g., FeO-MgO in silicate melt; CaFeSi2O6-CaMgSi2O6 in pyroxene) and TiAl2(MgSi2)–1 exchange reactions between silicate melts and coexisting Ca-pyroxene has been examined. High-calcium clinopyroxenes were grown in 1 atmosphere melting and crystallization experiments on rock powders spanning the composition range tholeiite to melilitite (1,0922+Mg2+ exchange and
suggest that at given values of
extent of Fe(Mg)–1 substitution is strongly coupled with the TiAl2(MgSi2)–1 substitution in pyroxenes near the five-component space CaMg(Si2O6-CaFe(Si)2O6-CaTi(Al)2O6-CaFe(Al,Si)2O6-CaAl(Al,Si)2O6. The inferred stabilization of Ti in iron-rich relative to magnesium pyroxene is consistent with the operation of Fe2+Ti4+ intervalence charge transfer interactions (e.g., Rossman 1980) and observations on zoning in natural titanaugites (e.g., Tracy and Robinson 1977). Although the rims of some pyroxenes grown in some melting experiments exhibit prominent zoning in TiAl2(MgSi2)–1, the average values of
inferred from the compositions of these pyroxenes, together with those of the relatively homogeneous pyroxenes produced in crystallization experiments, exhibit a 11 correlation with values of
derived from the solution model of Ghiorso et al. (1983) with a standard error of 750 calories. The Ti contents of Ca-rich pyroxenes crystallizing from a wide range of natural silicate liquids can therefore be predicted. 相似文献
2.
Allan F. Wilson 《Contributions to Mineralogy and Petrology》1976,55(2):131-138
Data from analyses of three coexisting pairs of pyroxenes with a wide range of Fe content from each of two localities are used to show the large systematic variation and predictable correlation of Fe (or Mg) of a pyroxene with its content of Al, Mn and Na in mafic granulites. Comparisons of pyroxenes can then be made more meaningful by normalizing Al, or other elements, to an appropriate Mg value. As both P and T may affect the element distribution of the two pyroxenes differently (especially Al and Na) the factor used in normalizing is found to vary from region to region. 相似文献
3.
Aenigmatite, sodic pyroxene and arfvedsonite occur as interstitial minerals in metaluminous to weakly peralkaline syenite patches in alkali dolerite, Morotu, Sakhalin. Aenigmatite is zoned from Ca, Al, Fe3+-rich cores to Ti, Na, Mn, Si-rich rims reflecting the main substitutions Fe2+Ti4+Fe3+, NaSiCaAl and Mn2+Fe2+. Aenigmatite replaces aegirine and ilmenite supporting the existence of a no-oxide field in
— T space. In one case aenigmatite has apparently formed by reaction between ilmenite and arfvedsonite. Titanian aegirine (up to 3.0 wt% TiO2) and Fe-chlorite may replace aenigmatite. Sodic pyroxene occurs as zoned crystals with cores of aegirine-augite rimmed by aegirine and in turn by pale green aegirine containing 93 mol% NaFe3+Si2O6. Additional substitution of the type NaAlCaFe2+ is indicated by significant amounts (up to 6 mol%) of NaAlSi2O6. Arfvedsonite is zoned with rims enriched in Na, Fe and depleted in Ca which parallels the variation of these elements in the sodic pyroxenes.The high peralkalinity of the residual liquid from which the mafic phases formed resulted from the early crystallization of microperthite (which makes up the bulk of the syenites) leading to an increase in the Na2O/(Na2O+K2O) and (Na2O+K2O)/Al2O3 ratios of the remaining interstitial liquid which is also enriched in Ti, Fe, and Mn. Bulk composition of the melt,
, temperature and volatile content were all important variables in determining the composition and stability of the peralkaline silicates.
in the residual liquid appears to have been buffered by arfvedsonite-aegirine and later by the arfvedsonite-aenigmatite and aenigmatite-aegirine equilibria under
conditions of a no-oxide field. An increase in
, above that of the alkali buffer reactions, is inferred by an increase of Ti and Mn in aenigmatite rims. The latest postmagmatic vapour crystallization stage of the syenites is marked by extremely low
which may have been facilitated by exsolution of a gas phase. Low
is supported by the replacement of aenigmatite by titanian aegirine, and the formation of rare Ti-rich garnet with a very low (Ti4++Fe3+)/(Ti+Fe) ratio of 0.51, associated with leucoxene alteration of ilmenite. 相似文献
4.
Tj. Peters V. Trommsdorff J. Sommerauer 《Contributions to Mineralogy and Petrology》1978,66(4):383-388
The compositions of coexisting pyroxmangites, rhodonites, rhodochrosites and manganese calcites in regional metamorphosed manganese cale-silicate marbles from Val Scerscen and Alagna were analysed by microprobe and permit definition of critical tie lines at metamorphic grades appropriate to temperatures between 400 and 450 °C.Variations in composition of coexisting mineral pairs in one and the same locality are attributed to variations in
and not to metamorphic temperatures. From the analysed assemblages isothermal
plots (with SiO2 as excess component) were constructed for the system CaO-MnO-SiO2-CO2. 相似文献
5.
Trace element analyses of 1-atm and high-pressure experiments show that in komatiite and peridotite, the olivine (OL)/liquid (L) distribution coefficient for Al2O3 (
) increases with pressure and temperature. Olivine in equilibrium with liquid accepts as much as 0.2 wt% Al2O3 in solution at 6 GPa. Convergence to equilibrium compositions at this high level is shown by cation diffusion of Al into synthetic forsterite crystals of low-Al contents in the presence of melt. Convergence to low-Al equilibrium compositions at lower P and T is shown by diffusion of Al out of synthetic forsterite with high initial Al content. Isobaric and isothermal experimental data subsets reveal that temperature and pressure variations both have real effects on
. Variation in silicate melt composition has no detectable effect on
within the limited range of experimentally investigated mixtures. Least-squares regression for 24 experiments, using komatiite and peridotite, performed at 1 atm to 6 GPa and 1300 to 1960°C, gives the best fit equation:
Increase in
with increasingly higher-pressure melting is consistent with incorporation of a spinel-like component of low molar volume into olivine, although other substitutions possibly involving more complex coupling cannot be ruled out. High P-T ultrabasic melting residues, if pristine, may be recognized by the high
calculated from microprobe analyses of Al2O3 concentrations in residual olivines and estimated Al2O3 concentration in the last liquid removed. In general the low levels of Al in natural olivine from mantle xenoliths suggest that pristine residues are rarely recovered. 相似文献
6.
Clinopyroxenes from various lithologic units in a single tholeiitic dolerite intrusion 50 m thick were analysed with the electron microprobe. Microphenocrysts of augite in the chilled marginal rock have the least scattered CaMgFe ratios, around Ca38Mg50Fe12, and lowest Ti/Al ratios, less than 1/4, of the augites examined; they crystallized prior to emplacement. The augites which crystallized in situ are more Fe-rich and have higher Ti/Al ratios, close to 1/2. Pigeonite started crystallizing later than augite and formed rims to augite crystals. Continuous zoning from augite to subcalcic augite as was previously reported by Benson (1944) for the same dolerite is not observed. Subcaloic ferroaugites, however, link augite and ferropigeonite in the outermost margins of pyroxenes in the later segregations. The small scale differentiation in situ gave rise to globules, veins, and pegmatoids, in which sector-zoning of augite is well developed. The {100} sectors are enriched in MgSiO3, FeSiO3, and MnSiO3 components relative to the {010} and the {110} sectors, and are accordingly depleted in other components. The protosite theory of sector-zoning formation proposed by Nakamura (1973) is further developed and the environment which favours the development of sector-zoning is discussed. The formation of augite rims around quartz-rich xenoliths and the compositional characteristics of the augites concerned are due to local high silica activities. Comments are made concerning some lunar pyroxenes in the light of the present study. 相似文献
7.
Petrogenesis and geochemical composition of biotites in rare-element granitic pegmatites in the southwestern Grenville Province,Canada 总被引:2,自引:0,他引:2
D. Lentz 《Mineralogy and Petrology》1992,46(3):239-256
Summary Field, mineralogical, and chemical determinations of biotite from late-tectonic rare-element (U, Th, Mo, Nb, REE) Grenville pegmatites are used to characterize and evaluate their petrogenesis in part of the southwestern Grenville Province. These pegmatites occur within middle to upper amphibolite facies rocks along and adjacent to shear zones and have hybridized margins because of interaction with their host rocks. Endo- and exomorphic biotite forms by the mechanical incorporation or hydrothermal replacement of pre-existing biotite, hornblende, Ca pyroxene and/or feldspar; accompanied by chemical re-equilibration, an increase in grain size, and inherit some of the chemical characteristics of the pegmatite. In general, the Fe/(Fe + Mg) ratio ranges between 0.22 and 0.86. The most highly fractionated biotites have high Fe/(Fe + Mg), Al, Mn, Rb, Nb, and Zn and low Ba. The chemical compositions of biotite from unzoned, partially-zoned, and zoned pegmatites indicate a trend of increasing chemical fractionation based on LIL enrichment.Overlap in calculated log
(3.2 to 4.7) and log
(1.3 to 2.8) for biotite (@ 600°C) among the different pegmatites is extensive. Commonly, magnetite and microcline coexist with biotites having an Fe/(Fe + Mg) between 0.54 to 0.65. Volatile enrichment and vapor-phase saturation are probably responsible for the development of zonation in the pegmatites. The diffusive loss of H2 at or near H2O vapor saturation at high H2O/Fe2+ may be responsible for the oxidized nature of some pegmatites.Rare-element enrichment due to pegmatite fractionation combined with partitioning of rare-elements from the pegmatite melt into the volatile phase and subsequent interaction with the host rocks is key to the formation of these rare-element mineral deposits.
With 9 Figures 相似文献
Petrogenese und geochemische Zusammensetzung von Biotiten in seltenen Element-führenden granitischen Pegmatiten der südwestlichen Grenville Provinz, Kanada
Zusammenfassung Die Ergebnisse von Geländearbeiten, sowie von mineralogischen und geochemischen Untersuchungen an Biotit aus spättektonischen seltenen Element-Pegmatiten (U, Th, Mo, Nb, REE) von Grenville-Alter bilden die Basis einer Diskussion ihrer Petrogenese in der südwestlichen Grenville Provinz. Diese Pegmatite kommen in Gesteinen der mittleren bis oberen Amphibolit-Fazies längs und in der Nähe von Shearzonen vor und haben hybridisierte Ränder, die auf Interaktion mit ihren Wirtsgesteinen zurückgehen. Endo- und exomorphe Biotite sind durch mechanische Einschließung oder durch hydrathermale Verdrängung von Biotiten, Hornblenden, Kalziumpyroxenen und/oder Feldspäten gebildet worden. Dies wird durch chemische Reequilibrierung, eine Zunahme der Korngröße und durch Übernahme einiger chemischer Charakteristika der Pegmatite begleitet. Im allgemeinen schwanken die Fe/(Fe + Mg) Verhältnisse von 0.22 bis 0.68, die am stärksten fraktionierten Biotite haben hohe Fe/(Fe + Mg), Al, Mn, Rb, Nb und Zn Gehalte und niedrige Ba Gehalte. Die chemische Zusammensetzung von Biotit aus nicht zonierten, teilweise zonierten und zonierten Pegmatiten zeigt einen Trend mit zunehmend chemischer Fraktionierung, die auf einer Anreicherung von LIL-Elementen basiert.Beträchtliche überschneidungen in den berechneten log (3.2 bis 4.7) und log (1.3 bis 2.8) für Biotit (600°C) von verschiedenen Pegmatiten sind zu erkennen. Im allgemeinen koexistiert Magnetit und Mikroklin mit Biotiten von Fe/ (Fe + Mg) Verhältnissen zwischen 0.54 und 0.65. Anreicherung von volatilen Phasen und eine Sättigung der Dampfphase sind wahrscheinlich für die Entwicklung der Zonierung der Pegmatite verantwortlich. Der Verlust von H2 durch Diffusion im Bereich der H2O Dampfsättigung bei hohen H2O/Fe2+ Werten dürfte für die oxidierte Natur einiger Pegmatite verantwortlich sein.Wichtigster Faktor für die Bildung dieser Lagerstätten seltener Elemente ist die Anreicherung von seltenen Elementen durch Pegmatit-Fraktionierung, wobei diese von der Pegmatit-Schmelze in die volatile Phase gehen, und die anschließende Interaktion mit den Nebengesteinen.
With 9 Figures 相似文献
8.
J. Vander Auwera 《Contributions to Mineralogy and Petrology》1993,114(2):203-220
In the Rogaland granulites of Southern Norway, thin anhydrous pyroxene-bearing margins (5–10 mm) are observed mainly in migmatitic banded gneisses at the contact between hornblende-rich metabasites and charnockites. According to field data, the development of these margins post-dates any deformation. Petrographic data show that they are zoned. Three different types have been recognized:
- Metabasite/plagioclase + orthopyroxene/plagioclase + clinopyroxene/gneiss
- Metabasite/plagioclase + orthopyroxene + clinopyroxene/plagioclase + clinopyroxene/gneiss
- Metabasite/plagioclase + orthopyroxene/gneiss
9.
Amphibole composition in tonalite as a function of pressure: an experimental calibration of the Al-in-hornblende barometer 总被引:66,自引:3,他引:63
Max W. Schmidt 《Contributions to Mineralogy and Petrology》1992,110(2-3):304-310
The Al-in-hornblende barometer, which correlates Altot content of magmatic hornblende linearly with crystallization pressure of intrusion (Hammarstrom and Zen 1986), has been calibrated experimentally under water-saturated conditions at pressures of 2.5–13 kbar and temperatures of 700–655°C. Equilibration of the assemblage hornlende-biotite-plagioclase-orthoclasequartz-sphene-Fe-Ti-oxide-melt-vapor from a natural tonalite 15–20° above its wet solidus results in hornblende compositions which can be fit by the equation: P(±0.6 kbar) = –3.01 + 4.76 Al
hbl
tot
r
2=0.99, where Altot is the total Al content of hornblende in atoms per formula unit (apfu). Altot increase with pressure can be ascribed mainly to a tschermak-exchange (
) accompanied by minor plagioclase-substitution (
). This experimental calibration agrees well with empirical field calibrations, wherein pressures are estimated by contact-aureole barometry, confirming that contact-aureole pressures and pressures calculated by the Al-in-hornblende barometer are essentially identical. This calibration is also consistent with the previous experimental calibration by Johnson and Rutherford (1989b) which was accomplished at higher temperatures, stabilizing the required buffer assemblage by use of mixed H2O-CO2 fluids. The latter calibration yields higher Altot content in hornblendes at corresponding pressures, this can be ascribed to increased edenite-exchange (
) at elevated temperatures. The comparison of both experimental calibrations shows the important influence of the fluid composition, which affects the solidus temperature, on equilibration of hornblende in the buffering phase assemblage. 相似文献
10.
Paolo A. Sossi John D. Foden Galen P. Halverson 《Contributions to Mineralogy and Petrology》2012,164(5):757-772
This study presents accurate and precise iron isotopic data for 16 co-magmatic rocks and 6 pyroxene–magnetite pairs from the classic, tholeiitic Red Hill sill in southern Tasmania. The intrusion exhibits a vertical continuum of compositions created by in situ fractional crystallisation of a single injection of magma in a closed igneous system and, as such, constitutes a natural laboratory amenable to determining the causes of Fe isotope fractionation in magmatic rocks. Early fractionation of pyroxenes and plagioclase, under conditions closed to oxygen exchange, gives rise to an iron enrichment trend and an increase in $ f_{{{\text{O}}_{2} }} $ of the melt relative to the Fayalite–Magnetite–Quartz (FMQ) buffer. Enrichment in Fe3+/ΣFemelt is mirrored by δ57Fe, where VIFe2+-bearing pyroxenes partition 57Fe-depleted iron, defining an equilibrium pyroxene-melt fractionation factor of $ \Updelta^{57} {\text{Fe}}_{{{\text{px}} - {\text{melt}}}} \le - 0.25\,\permille \times 10^{6} /T^{2} $ . Upon magnetite saturation, the $ f_{{{\text{O}}_{2} }} $ and δ57Fe of the melt fall, commensurate with the sequestration of the oxidised, 57Fe-enriched iron into magnetite, quantified as $ \Updelta^{57} {\text{Fe}}_{{{\text{mtn}} - {\text{melt}}}} = + 0.20\,\permille \times 10^{6} /T^{2} $ . Pyroxene–magnetite pairs reveal an equilibrium fractionation factor of $ \Updelta^{57} {\text{Fe}}_{{{\text{mtn}} - {\text{px}}}} \approx + 0.30\,\permille $ at 900–1,000?°C. Iron isotopes in differentiated magmas suggest that they may act as an indicator of their oxidation state and tectonic setting. 相似文献
11.
Genesis of the calc-alkaline igneous rock suite 总被引:11,自引:1,他引:11
A high pressure experimental study of the partial melting fields of synthetic high-alumina olivine tholeiite, high-alumina quartz tholeiite, basaltic andesite, andesite, dacite and rhyodacite under dry and wet
conditions has been conducted in order to investigate possible origins of the calc-alkaline series from the upper mantle. Detailed analyses of crystallizing phases using the electron microprobe has enabled calculation of the liquid line of descent in these compositions at various pressures.At 27–36 kb garnet and clinopyroxene are the liquidus or near-liquidus phases in dry tholeiite, basaltic andesite and andesite, while quartz is the liquidus phases in dry dacite and rhyodacite. Under wet conditions at 27 kb garnet, not quartz, is the liquidus phase in the dacite. Qualitatively these results show that the low melting fraction of a quartz eclogite at 27–36 kb under dry conditions is of andesitic composition whereas under wet conditions it is rhyodacitic or granodioritic. At these pressures under dry conditions the andesite liquidus lies in a marked low temperature trough between the more basic and more acid compositions. Quantitatively, the calculated compositions of liquid fractionates for varying degrees of melting of the quartz eclogite bulk composition broadly follow the calc-alkaline trend.At 9–10 kb under wet conditions
sub-silicic amphibole and pyroxenes are the near-liquidus phases in tholeiite and basaltic andesite compositions. Calcic plagioclase and garnet occur nearer the solidus. The calculated liquid fractionates follow the calc-alkaline trend and demonstrate that the calc-alkaline series may be derived by the partial melting of amphibolite at lower crustal depths under wet conditions
, Or by the fractional crystallization of a hydrous basalt magma at similar depths.These experimental results support two complementary hypotheses for the derivation of the calc-alkaline igneous rock suite from the mantle by a two stage igneous process. In the first stage of both hypotheses large piles of basalt are extruded on the earth's surface. Subsequently this pile of basalt may, under dry conditions, transform to quartz eclogite, sink into the mantle and finally undergo partial melting at 100–150 kms depth. This partial melting gives rise to the calc-alkaline magma series leaving a residuum of clinopyroxene and garnet. Alternatively, if wet conditions prevail in the basalt pile and the geotherms remain high, partial melting of the basalt may take place near the base of the pile, at about 10 kb pressure
. The liquids so formed constitute the calc-alkaline suite and the residuum consists of amphibole, pyroxenes and possibly minor garnet and calcic plagioclase. Both models may be directly linked to the hypothesis of sea-floor spreading. 相似文献
12.
M. E. Fleet 《Contributions to Mineralogy and Petrology》1974,44(4):259-274
The partition of Si, Al, Ti, Fe3+, Mg, Fe2+, Mn, Ca and Na between coexisting Ca-rich and Ca-poor pyroxenes from a wide variety of igneous and metamorphic rocks have been investigated systematically. Many of the distributions, and especially those for the partition of Ti, Mg, Fe2+, Mn and Na, indicate characteristic trends for pyroxenes from the various petrologic groups identified. The partition of Mg, Fe2+ and Mn correlate with inferred cooling rates, the partition co-efficients of pyroxenes from extruded and other quickly cooled rocks most nearly approaching unity. In contrast, the partition of Si and Ti and the absolute amounts of Al may be related to the physicochemical conditions prevailing during original crystallisation; Ti being particularly relatively enriched in Ca-rich pyroxenes of ultramafic associations. The trends of the compositions of the Ca-rich pyroxenes plotted in the pyroxene quadrilateral also correlate with cooling rates and comparison with the limited data available on the phase relations of coexisting pyroxenes suggests that sub-solidus chemical readjustments have occurred in both phases. 相似文献
13.
Yamuna Singh Anubhooti Saxena A K Bhatt R Viswanathan T S Shaji L K Nanda 《Journal of Earth System Science》2018,127(1):4
Crystallochemical data on metamict davidite from albitites and albitised rocks from the Bichun area (Jaipur district, Rajasthan, India) of Banded Gneissic Complex (BGC) are provided. Davidite occurs as euhedral, subhedral to anhedral crystals in the form of disseminated grains and also as fracture filled veins. The crystals of davidite are up to 8 cm in length and 6 cm in width. The powder X-ray diffraction (XRD) pattern of the heat-treated davidite (at \(900{^{\circ }}\hbox {C}\)) reveals well-defined reflections of crystallographic planes. The calculated unit-cell parameters of the heat treated davidite are: \(\hbox {a}_{0} = \hbox {b}_{0} = 10.3556 \, \text {\AA }\) and \(\hbox {c}_{0} = 20.9067 \, \text {\AA }\), with unit-cell volume \(\hbox {(V)} = 1941.6385 \, \text {\AA }^{3}\); and \({\upalpha }={\upbeta }= 90^{\circ }\) and \({\upgamma }= 120^{\circ }\), which are in agreement with the values of davidite standard. Geochemical data reveals that the investigated davidite contains 51.5–52.6% \(\hbox {TiO}_{2}\), 14.8–15.1% \(\hbox {Fe}_{2} \hbox {O}_{3}\), 9.8–10.2% FeO, 6.97–7.12% \(\hbox {U}_{3} \hbox {O}_{8}\), 6.72–6.92% \(\hbox {RE}_{2} \hbox {O}_{3}\), 3.85–3.61% \(\hbox {K}_{2}\hbox {O}\), 0.9–1.4% \(\hbox {Al}_{2} \hbox {O}_{3}\), and 0.8–1.2% \(\hbox {SiO}_{2}\). The calculated structural formulae of the two davidite crystals are: D-1: \(\hbox {K}_{0.0044/0.004} \hbox {Ba}_{0.0044/0.005} \hbox {Ca}_{0.20/0.20} \hbox {Na}_{0.012/0.012} \hbox {Mn}_{0.053/0.053} \hbox {Mg}_{0.14/0.14} \hbox {Pb}_{0.0076/0.008} \hbox {Fe}_{2.675/2.675} \hbox {Fe}_{1.59/1.59} \hbox {Y}_{0.1175/0.118} \hbox {P}_{0.053/0.053} \hbox {Nb}_{0.008/0.008} \hbox {Sn}_{0.001/0.001} \hbox {Zr}_{0.033/0.033} \hbox {U}_{0.468/0.468} \hbox {Th}_{0.009/0.009} \,\,\hbox {REE}_{0.6829/0.683})_{6.05/6.05} (\hbox {Ti}_{12.15/12.15}\,\, \hbox {Fe}_{1.9022/1.903} \hbox {Si}_{0.372/0.372}\,\, \hbox {Al}_{0.517/0.517}\,\, \hbox {Cr}_{0.018/0.018} \hbox {Co}_{0.009/0.009} \hbox {Ni}_{0.027/0.027})_{15/15} \hbox {O}_{36/36} (\hbox {OH}_{0.319/0.319[]1.681/1.681})_{2/2}\) and D-2: \((\hbox {K}_{0.004/0.004} \hbox {Ba}_{0.005/0.005} \hbox {Ca}_{0.20/0.20} \hbox {Na}_{0.012/0.012} \hbox {Mn}_{0.05/0.05} \hbox {Mg}_{0.094/0.094} \hbox {Pb}_{0.007/0.007} \hbox {Fe}_{2.58/2.58} \hbox {Fe}_{1.71/1.71} \hbox {Y}_{0.112/0.112} \hbox {P}_{0.106/0.106} \hbox {Nb}_{0.006/0.006} \hbox {Sn}_{0.001/0.001} \hbox {Zr}_{0.03/0.03} \hbox {U}_{0.48/0.48} \hbox {Th}_{0.009/0.009} \hbox {REE}_{0.665/0.665})_{6.088/6.088} (\hbox {Ti}_{12.48/12.48} \hbox {Fe}_{1.87/1.87} \hbox {Si}_{0.249/0.249} \hbox {Al}_{0.334/0.334} \hbox {Cr}_{0.019/0.019} \hbox {Co}_{0.008/0.008} \hbox {Ni}_{0.04/0.04})_{15/15} \hbox {O}_{36/36} (\hbox {OH}_{0.098/0.098[]1.90/1.90})_{2/2}\). The calculated structural formulae are not fully stoichiometric, which could be due to metamict nature of davidite. The characteristic feature of distribution pattern of REE in davidite is unusually high concentration of LREE and HREE and substantially low content of MREE. It may be due to the occupation of REEs in two distinct crystallographic sites in davidite structure, i.e., M(1) and M(O) sites. Chondrite-normalised plot of davidite reveals a pronounced negative Eu-anomaly (\(\hbox {Eu}/\hbox {Eu}^{*} = 0.30{-}0.39\)), which suggests extremely fractionated nature of the metasomatising fluids from which davidite had crystallized. Metamict davidite-bearing U ores not only from Rajasthan, but also from other parts of India are likely to yield very high U leachability, thereby making them attractive sources of U, which otherwise are ignored by mineral engineers as uneconomic U ores. 相似文献
14.
The temperature-sensitive Fe,Mg exchange equilibrium,
相似文献
15.
Volker von Seckendorff Hugh St. C. O'Neill 《Contributions to Mineralogy and Petrology》1993,113(2):196-207
The partitioning of Mg and Fe2+ between coexisting olivines and orthopyroxenes in the system MgO-FeO-SiO2 has been investigated experimentally at 1173, 1273, 1423 K and 1.6 GPa over the whole range of Mg/Fe ratios. The use of barium borosilicate as a flux to promote grain growth, and the identification by back-scattered electron imaging of resulting growth rims suitable for analysis by electron microprobe, results in coexisting olivine and orthopyroxenene compositions determined to a precision of±0.003 to 0.004 in molar Fe/(Mg+Fe). Quasi-reversal experiments were performed starting with Mg-rich olivine and Fe-rich orthopyroxene (low KD) and vice versa (high KD), which produced indistinguishable results. The distribution coefficient, KD, depends on composition and on temperature, but near Fe/(Mg+Fe)=0.1 (i.e. mantle compositions) these effects cancel out, and KD is insensitive to temperature. The results agree well with previous experimental investigations, and constrain the thermodynamic mixing properties of Mg-Fe olivine solid solutions to show small near-symmetric deviations from ideality, with
between 2000 and 8000 J/mol. Multiple non-linear least squares regression of all data gave a best fit with
(implying 5450 J/mol at 1 bar) and
, but the two W
G
parameters are so highly correlated with each other that our data are almost equally well fit with
, as obtained by Wiser and Wood. This value implies
, apparently independent of temperature. Our experimental results are not compatible with the assessment of olivine-orthopyroxene equilibria of Sack and Ghiorso. 相似文献
16.
Shock-induced melt veins in amphibolites from the Nördlinger Ries often have chemical compositions that are similar to bulk rock (i.e., basaltic), but there are other veins that are confined to chlorite-rich cracks that formed before the impact and these are poor in Ca and Na. Majoritic garnets within the shock veins show a broad chemical variation between three endmembers: (1) \({}^{\text{VIII}}{{\text{M}^{2+}}_3} {}^{\text{VI}}{\text{Al}}_{2} ({}^{\text{IV}}{\text{SiO}}_{4} )_{3}\) (normal garnet, Grt), (2) \({}^{\text{VIII}}{{\text{M}^{2+}}_3} {}^{\text{VI}}[{\text{M}}^{2 + } ({\text{Si,Ti}})]({}^{\text{IV}}{\text{SiO}}_{4} )_{3}\) (majorite, Maj), and (3) \({}^{\text{VIII}}({{\text {Na} {\text M}^{2+}}_2}) {}^{\text{VI}}[ ({\text{Si,Ti}}){\text {Al}}]({}^{\text{IV}}{\text{SiO}}_{4} )_{3}\) (Na-majorite50Grt50), whereby M2+ = Mg2+, Fe2+, Mn2+, Ca2+. In particular, we observed a broad variation in VI(Si,Ti) which ranges from 0.12 to 0.58 cations per formula unit (cpfu). All these majoritic garnets crystallized during shock pressure release at different ultrahigh pressures. Those with high VI(Si,Ti) (0.36–0.58 cpfu) formed at high pressures and temperatures from amphibole-rich melts, while majoritic garnets with lower VI(Si,Ti) of 0.12–0.27 cpfu formed at lower pressures and temperatures from chlorite-rich melts. Furthermore, majoritic garnets with intermediate values of VI(Si,Ti) (0.24–0.39) crystallized from melts with intermediate contents of Ca and Na. To the best of our knowledge the ‘MORB-type’ Ca–Na-rich majoritic garnets with maximum contents of 2.99 wt% Na2O and calculated crystallisation pressures of 16–18 GPa are the most extreme representatives ever found in terrestrial shocked materials. At the Ries, the duration of the initial contact and compression stage at the central location of impact is estimated to only ~ 0.1 s. We used a ~ 200-µm-thick shock-induced vein in a moderately shocked amphibolite to model its pressure–temperature–time (P–T–t) path. The graphic model manifests a peak temperature of ~ 2600 °C for the vein, continuum pressure lasting for ~ 0.02 s, a quench duration of ~ 0.02 s and a shock pulse of ~ 0.038 s. The small difference between the continuum pressure and the pressure of majoritic garnet crystallization underlines the usefulness of applying crystallisation pressures of majoritic garnets from metabasites for calculation of dynamic shock pressures of host rocks. Majoritic garnets of chlorite provenance, however, are not suitable for the determination of continuum pressure since they crystallized relatively late during shock release. An extraordinary glass- and majorite-bearing amphibole fragment in a shock-vein of one amphibolite documents the whole unloading path. 相似文献
17.
Jing-Hua Wu Huan Li Xiao-Shuang Xi Hua Kong Qian-Hong Wu Neng-Li Peng Xi-Ming Wu Jing-Ya Cao Jillian Aira S Gabo-Ratio 《Journal of Earth System Science》2017,126(5):64
The Taipusi area in the Bainaimiao Arc Belt is located in the northern margin of the North China Craton, at the southern margin of the middle Central Asian Orogenic Belt. It is characterized by large exposures of mafic dikes. In this contribution, we present first-hand whole-rock major and trace elements, zircon U–Pb geochronology and in situ trace element geochemistry data for these mafic rocks, which reveal their petrogenesis and tectonic evolution. These mafic dikes display varied compositions of \(\hbox {SiO}_{2}\) (49.42–54.29%), \(\hbox {TiO}_{2}\) (0.63–1.08%), \(\hbox {Al}_{2}\hbox {O}_{3}\) (13.94–17.60%), MgO (4.66–10.51%), \(\hbox {Fe}_{2}\hbox {O}_{3}\) (1.59–3.07%), FeO (4.60–6.90%), CaO (4.57–8.91%), \(\hbox {Na}_{2}\hbox {O}\) (1.61–4.26%), \(\hbox {K}_{2}\hbox {O}\) (0.92–2.54%) and \(\hbox {P}_{2}\hbox {O}_{5}\) (0.11–0.29%). They are mainly of high-K calc-alkaline series with indistinct Eu anomalies, enriched in large ion lithophile elements (e.g., Rb, Ba, K and Sr) but depleted in high field strength elements (e.g., Nb, P and Ti). These suggest that the crystallizing magma was derived from enriched mantle altered by metasomatic fluids in a subduction setting with imprints of active continental margin features. The high concentrations of Hf, U, Th, Pb and Y, pronounced positive Ce but slightly negative Eu anomalies in zircons indicating that the magma underwent a fractional crystallization and crustal contamination process, with medium to high \(f\hbox {O}_{2}\). Zircon LA–ICP–MS U–Pb dating yielded concordant ages of 437–442 Ma for these mafic dikes, which is consistent with the early Paleozoic volcanic arc magmatic activity in the Bainaimiao area. Hence, we conclude that the Bainaimiao Arc Belt is a continental arc formed by the southward subduction of the Paleo-Asian ocean during early Paleozoic. 相似文献
18.
H. de Almeida Sampaio Filho G. P. Sighinolfi E. Galli 《Contributions to Mineralogy and Petrology》1973,38(4):279-290
Chemical analyses and crystallographic and some optical data have been obtained for 28 samples of beryl from Bahia State, Brazil. The larger range of variability in the chemical composition is shown by Mg, Fe and Li. Sodium is the more diffuse alkali element. Potassium is always very limited. Calcium appears in noticeable amounts only in three samples. The Ti, Cr, Rb, and Cs elements were also tested. The samples studied here can be defined as sodium-potassium beryls with low alkali content. Unit cell parameters show the following ranges: a=9.210–9.245 and c=9.190–9.220 Å. From a statistical analysis of these data it may be seen that: an increase of Fe and (Fe+Mn+Mg) percentage has a positive correlation with a, but no influence on c, which in turn has a close positive correlation with Li and is negatively correlated with Be. Less negative correlations also exist between the pairs {Be, Li}, {a,Al}, {Al, Fe} and {Al, (Fe+Mn+Mg)}. A positive correlation also exists between sodium and the parameter a. 相似文献
19.
Fe-Ti oxide minerals from regionally metamorphosed quartzites of western New Hampshire 总被引:3,自引:0,他引:3
Douglas Rumble III 《Contributions to Mineralogy and Petrology》1973,42(3):181-195
The assemblages rutile-hematite, hematite, hematite-magnetite, hematite-ilmenite-magnetite, and ilmenite-magnetite occur in sillimanite- and kyanite-grade quartzites exposed in western New Hampshire. Different assemblages are found in interlayered sedimentary beds of single outcrops. Magnetites are nearly pure Fe3O4 and contain trace amounts of Al, Si, Ti, V, Cr, Mn, and Ni. Magnetites in contact with hematites contain up to 0.4 weight % MnO, but magnetites in contact with ilmenites containing up to 2.3 weight % MnO have no detectable Mn. Ilmenite is enriched in Mn relative to coexisting hematite, and hematite is so enriched with respect to magnetite. Systematic partitioning of elements between oxide minerals and absence of crossing tie lines suggest that the minerals attained chemical equilibrium during regional metamorphism. None of the assemblages are divariant because of the presence of components in addition to FeO, Fe2O3, and TiO2; therefore, none of them constitute oxygen buffers. Nevertheless, gradients in
between adjacent sedimentary beds can be measured using variations of oxide mineral composition in trivariant and quadrivariant phase assemblages. Oxygen behaved as an initial value component or inert component during regional metamorphism. It is likely that the
gradients are due to differences in bulk composition of sedimentary beds at the time of deposition. 相似文献
20.
D. A. F. Hendry A. R. Chivas S. J. B. Reed J. V. P. Long 《Contributions to Mineralogy and Petrology》1982,78(4):389-403
The Koloula Igneous Complex comprises 26 different intrusive phases that have been divided into two major magmatic episodes — cycle 1 intrusions (4.5 Ma) and cycle 2 intrusions (2.4 to 1.5 Ma). The cycle 2 intrusions are further divided into the Inamumu Zoned Pluton (IZP) which is composed of 6 concentrically disposed quartz diorite and tonalite units; and several satellite intrusions. The IZP is host to porphyry-copper mineralization, whereas the cycle 1, and cycle 2 satellite intrusions are barren. Presently exposed mineralization in the IZP (A system) represents the deeply eroded core of a porphyry copper system, where widely-spaced veinlet alteration envelopes ( 1 mm thick) are separated by large volumes of unaltered rock.Compositional trends in biotites and amphiboles from both individual grains and throughout the differentiation series of the IZP, indicate fluctuating but generally increasing
existed through the sequence from early magmatic late magmatic early hydrothermal conditions. In amphiboles, compositional domains (Mg-rich) that are indicative of high
are correlated with episodes of fluid exsolution, independent evidence of which is provided by multiple generations of fluid inclusions in quartz phenocrysts. These high
domains in amphiboles have higher Si, Mn, and Ca contents, but are depleted in Fe, Ti, Na, K, and Cl relative to the less oxidizing domains. The latter elements are those that are known from veinlet alteration assemblages and fluid-inclusion evidence to have been preferentially partitioned into the co-existing fluid phase (late magmatic hydrothermal solution).By contrast, amphiboles from barren rock types that are slightly older than, and of the same age as the IZP, exhibit restricted compositional ranges, and are more Fe-rich. Some individual grains and two cycle 2 satellite intrusions indicate Fe-enrichment during progressive crystallization. Siliceous deuteric amphiboles are commonly as Mg-rich as the high
amphibole domains from the IZP, but are easily distinguished from them by their lack of smooth compositional trends versus Si, and by their highly variable Mg and Fe contents.Biotites from the IZP also indicate progressive oxidation, whereas biotites from the barren rock types show either little compositional variation or progressive Fe-enrichment. Biotites from the barren intrusions are richer in Cl, Li and Rb and poorer in Ba than those of the mineralizing intrusions. fHF was very low ( 0.003 bars) in both barren and mineralizing intrusions. During progressive differentiation, Rb content decreased and Ba content increased in IZP biotites, which is atypical, yet explicable owing to the former presence of a competing fluid phase during biotite crystallization.Because
is a function of degree of fluid exsolution, then in igneous systems with sufficient Cu, Cl, and ultimately S, progressively higher
should potentially lead to more mineralized intrusions. Higher
is reflected by steeper Fe versus Si gradients in amphibole domains. Indeed, such a graph for amphiboles from 5 igneous complexes, indicates that two economically mineralized units produced steeper FeSi than those from weakly mineralized intrusions. Steep FeSi trends that do not continue to amphibole domains more siliceous than Si=7.3 (atoms per 23 oxygens) are unlikely to have resulted from subsolidus crystallization and these intrusions are unlikely to be strongly mineralized. 相似文献
|