四川开江恐龙骨骼化石矿物组分分离和微量元素组合的研究

文章详述了恐龙骨骼化石矿物组分的化学分离方法,同时对开江恐龙骨骼化石样品进行了分离和中子活化分析,通过对测试结果进行生物地球化学的对比研究.发现恐龙骨骼化石中某些微量元素异常明显,并推断其中的砷(As)、铬(Cr)、铷(Rb)的高异常含量和锌(Zn)的低异常含量极有可能是导致开江恐龙动物群集群死亡的原因之一。     

The system Ag-Fe-S: Phase equilibria and mineral assemblages

Phase relations in the Ag-Fe-S system were determined from 700 to 150 °C by quench experiments with the use of evacuated, sealed, silica tubes as reaction vessels; these data were then used to interpret various aspects of natural occurrences of Ag-Fe-S minerals (e.g. argentiferous pyrite). The assemblages Ag₂S+Fe_1–x S and Ag₂S+FeS₂ become stable, with decreasing temperature, at 622±2 ° and 607±2 °C, respectively; their establishments involve ternary invariant conditions. The three condensed phases Ag₂S+Fe_1–x S+FeS₂ become stable together at 532±2 °C through a ternary eutectic reaction near Ag₂S in composition. An invariant reaction at 248±8 °C results in the formation of the Ag+FeS₂ pair from the Ag₂S+Fe₇S₈ assemblage, which is stable at higher temperatures. The associations of native silver and pyrite are found in certain massive sulfide deposits, whereas natural coexistence of argentite and pyrrhotite has not been documented. Experiments demonstrate the feasibility of retrograde reequilibration in ores to produce the silver+pyrite pair from argentite+pyrrhotite. Less than 0.05 and 0.1 at. % Ag are soluble in FeS₂ and Fe_1–x S, respectively, at 600 °C and less than 0.8 at. % Fe in Ag₂S at 500 °C. Silver does not measurably affect the d _10.2 values of Fe_1–x S or the cell dimension of FeS₂ (a _{25 °C}=5.4175±0.0001 Å). This study also demonstrates that at low temperatures the binary fugacity data are applicable to ternary assemblages of the Ag-Fe-S system because of these very limited solubilities. The presence of Fe lowers the fcc bcc inversion temperature of Ag₂S more than 50 °C; the exact amount of lowering is dependent on the associated Ag-Fe-S phases. The bcc mono. inversion temperature, however, is not measurably affected. No ternary solid phases were encountered above 150 °C. Heating of sternbergite and argentopyrite (both AgFe₂S₃) mineral samples shows instability at 152 °C (e.g. partial breakdown of sternbergite in 405 days); rate studies show that a 10 °C temperature increase results in approximately a 5-fold increase in breakdown rate.

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Zusammenfassung Für die Interpretation von natürlichen Ag-Fe-S-Mineralen (z. B. silberhaltiger Pyrit) werden die Phasenbeziehungen im System Ag-Fe-S durch quenching Experimente bei Temperaturen von 700 ° bis 150 °C untersucht. Evakuierte und zugeschmolzene Quarzglasröhren dienen dabei als Reaktionsgefäße. Die Phasenassoziationen Ag₂S+Fe_1–x S (Argentit+Magnetkies) und Ag₂S+FeS₂ (Argentit+Pyrit) werden mit fallender Temperatur bei 622±2 °C und 607±2 °C stabil. Ihre Bildung ist nur unter ternären, invarianten Bedingungen möglich. Bei 532±2 °C bilden sich durch eutektische Reaktion (nahe der Ag₂S-Zusammensetzung) als stabile Phasen Ag₂S+Fe_1–x S+FeS₂. Bei 248±8 °C reagieren Ag₂S+Fe₇S₈, die zwischen Temperaturen von 292 °C bis 248 °C stabil sind, zu Ag+FeS₂. Paragenesen von gediegen Silber+Pyrit kommen in einigen massiven Sulfidlagerstätten vor; die Paragenese Argentit+Magnetkies ist dagegen noch nicht beobachtet worden. Die bisherigen experimentellen Ergebnisse machen eine retrograde Wiedereinstellung des Gleichgewichtes von gediegen Silber+Pyrit aus Argentit+Magnetkies wahrscheinlich. Bei 600 °C sind <0,05% bzw. 0,1% Ag in FeS₂ und Fe_1–x S löslich. Bei 500 °C lösen sich <0,8% Fe in Ag₂S. Die Zellkonstanten von Magnetkies (gemessen als d _10,2) und von Pyrit (a _{25 °C}=5,4175±0,0001 Å) werden durch die Aufnahme von Ag nicht meßbar beeinflußt. Die vorliegenden Ergebnisse zeigen, daß die Fugazitäten bei niederen Temperaturen entlang den binären Schnitten Fe-S und Ag-S auch auf das ternäre System Ag-Fe-S angewendet werden können, weil nur sehr beschränkte Mischbarkeiten existieren. Die Gegenwart von Fe erniedrigt die Inversions-temperatur fcc bcc für Ag₂S um mehr als 50 °C. Die genaue Inversions-temperatur wird durch die assozierten Ag-Fe-S Phasen festgelegt. Die bcc mono. Inversionstemperatur wird dagegen nicht meßbar beeinflußt. Oberhalb 150 °C werden keine ternären Phasen beobachtet. Sternbergit und Argentopyrit (beides AgFe₂S₃-Minerale) werden oberhalb 152 °C instabil (z. B. bricht Sternbergit teilweise nach 405 Tagen zusammen). Eine Temperaturerhöhung um ca. 10 °C erhöht die Zerfallsrate um ein Fünffaches.

     

Matrix analysis of metamorphic mineral assemblages and reactions

Assemblage diagrams are widely used in interpreting metamorphic mineral assemblages. In simple systems, they can help to identify assemblages which may represent equilibrium states; to determine whether differences between assemblages reflect changes in metamorphic grade or variations in bulk composition; and to characterize isograd reactions. In multicomponent assemblages these questions can be approached by investigating the rank, composition space (range) and reaction space (null-space) of a matrix representing the compositions of the phases involved. Singular value decomposition (SVD) provides an elegant way of (1) finding the rank of a matrix and detemining orthonormal bases for both the composition space and the reaction space needed to represent an assemblage or pair of assemblages; and (2) finding a model matrix of specified rank which is closest in a least squares sense to an observed assemblage. Although closely related to least squares techniques, the SVD approach has the advantages that it tolerates errors in all observations and is computationally simpler and more stable than non-linear least squares algorithms. Models of this sort can be used to interpret multicomponent mineral assemblages by straightforward generalizations of the methods used to interpret assemblage diagrams in simpler systems. SVD analysis of mineral assemblages described by Lang and Rice (1985) demonstrates the utility of the approach.     

Thermodynamic projection and extrapolation of high-variance mineral assemblages

A procedure is described whereby the effect of extra components on the plotting positions of minerals in projected phase diagrams may be accounted for rigorously. The method employs the equilibrium constraints of the mineral assemblage to extrapolate the compositions of the minerals to where the values of the extra components approach 0. The same procedure may also be used to extrapolate the compositions of natural assemblages over isothermal, isobaric composition diagrams or polythermal, polybaric diagrams.Examples from typical garnet-bearing pelite assemblages indicate that the extra components MnO and CaO dramatically shift the compositions of coexisting phases to lower Fe/Mg, even where the phase itself (e.g. chlorite or biotite) does not contain appreciable quantities of the extra component. Recognition of, and correction for, this effect is critical if projected phase diagrams are to be compared with experimentally calibrated phase diagrams in the chemical subsystem.     

青田石的宝石学特征与矿物组成

在野外地质调查的基础上,对40多个品种的近百块青田石样品进行了常规宝石学特征鉴定、X射线粉末衍射以及红外光谱的分析测试。研究结果表明,青田石的矿物成分及组合多种多样,大多数品种的青田石属于叶蜡石型,其他属于非叶蜡石型,包括伊利石型、地开石型和绢云母型。     

Equilibrium relations of prograde metamorphic mineral assemblages

¹⁸O of quartz, biotite, muscovite, garnet, ilmenite or magnetite, K-feldspar, and D of biotite from prograde metamorphic pelites of the Damara Orogen have been analyzed. The samples were taken from one stratigraphic unit which is exposed in the various stages from low-grade up to high-grade metamorphism with anatexis. Using the fractionation curves experimentally investigated up to now, it can be shown that equilibrium has been reached among the metamorphic assemblages in the low-grade and lower medium-grade metamorphism only. In the high-grade rocks only a partial equilibrium exists between those phases formed at the specific high-grade isogrades, i.e., K-feldspar, garnet, magnetite, or ilmenite, but not between these and the main reacting phase biotite. Biotite in equilibrium with these minerals is foundonly in anatectic rocks where new biotite crystallized from the melt.From this it is concluded that the¹⁸O/¹⁶O ratio of biotite is fixed at the time of crystallization and its initial composition is preserved when the temperature increases, unless the biotite recrystallizes. The isotopic temperatures derived from mineral pairs formed at specific isograds are in excellent agreement with temperatures derived from petrological investigations. The hydrogen isotoperatio of biotites decreases with increasing grade of metamorphism.     

Phase relations and mineral assemblages in the Ag-Bi-Pb-S system

Phase relations within the Ag-Bi-S, Bi-Pb-S, and Ag-Pb-S systems have been determined in evacuated silica tube experiments. Integration of experimental data from these systems has permitted examination and extrapolation of phase relations within the Ag-Bi-Pb-S quaternary system. — In the Ag-Bi-S system liquid immiscibility fields exist in the metal-rich portion above 597±3°C and in the sulfur-rich portion above 563±3°C. Ternary phases present correspond to matildite (AgBiS₂) and pavonite (AgBi₃S₅). Throughout the temperature range 802±2°C to 343±2°C the assemblage argentite (Ag₂S) + bismuth-rich liquid is stable; below 343°C this assemblage is replaced by the assemblage silver + matildite. — Five ternary phases are stable on the PbS-Bi₂S₃ join above 400°C — phase II (18 mol-% Bi₂S₃), phase III (27 mol-% Bi₂S₃), cosalite (33.3 mol-% Bi₂S₃), phase IV (51 mol-% Bi₂S₃), and phase V (65 mol-% Bi₂S₃). Phase IV corresponds to the mineral galenobismutite and is stable below 750±3°C. Phases II, III, and V do not occur as minerals, but typical lamellar and myrmekitic textures commonly observed among the Pb-Bi sulfosalts and galena evidence their previous existence in ores. Phase II and III are stable from 829±6°C and 816±6°C, respectively, to below 200°C; Phase V, stable only between 730±5°C and 680±5°C in the pure Bi-Pb-S system is stabilized to 625±5°C by the presence of 2% Ag₂S. Experiments conducted with natural cosalites suggest that this phase is stable only below 425±25°C in the presence of vapor. — In the Ag-Pb-S system the silver-galena assemblage is stable below 784±2°C, whereas the argentite + galena mineral pair is stable below 605±5°C. — Solid solution between matildite and galena is complete above 215±15°C; below this temperature characteristic Widmanstätten structure-like textures are formed through exsolution. Schematic phase relations within the quaternary system are presented at 1050°C, at 400°C, and at low temperature.

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Zusammenfassung Die Phasenbeziehungen in den Systemen Ag-Bi-S, Bi-Pb-S und Ag-Pb-S wurden durch Versuche in evakuierten Quarzglasröhrchen bestimmt. Die Auswertung aller experimentellen Daten gestattete eine Extrapolation der Phasenbeziehungen im quaternären System Ag-Bi-Pb-S. — Im System Ag-Bi-S besteht ein Zwei-Schemlzenfeld im metallreichen Teil über 597±3°C und im schwefelreichen Teil über 563±3°C. Die ternären Phasen entsprechen den Mineralien Schapbachit (AgBiS₂) und Pavonit (AgBi₃S₅). Zwischen 802±2°C und 343±2°C ist die Paragenese Silberglanz (Ag₂S) + Bi-reiche Schmelze stabil; unterhalb 343°C wird sie jedoch ersetzt durch die Paragenese Silber + Schapbachit. — Fünf ternäre Phasen sind stabil im Schnitt PbS-Bi₂S₃ oberhalb von 400°C: Phase II (18 Mol-% Bi₂S₃), Phase III (27 Mol-% Bi₂S₃), Cosalite (33.3 Mol-% Bi₂S₃), Phase IV (51 Mol-% Bi₂S₃) und Phase V (65 Mol-% Bi₂S₃). Phase IV entspricht dem Mineral Galenobismutit und ist stabil unterhalb 750±3°C. Die Phasen II, III und V kommen zwar nicht in der Natur vor, jedoch weisen typische myrmekitische und lamellare Gefüge, die man häufig in Pb-Bi-Sulfosalzen und deren Verwachsungen mit Bleiglanz beobachtet, auf die ehemalige Existenz solcher Phasen in diesen Erzen hin. Die Phasen II und III sind stabil von 829±6°C bzw. 816±6°C bis unter 200°C. Die Phase V, die im reinen System Bi-Pb-S zwischen 730±5°C und 680±5°C auftritt, wird in Gegenwart von 2% Ag₂S stabilisiert bis herab zu 625±5°C. Versuche mit natürlichen Cosaliten lassen darauf schließen, daß diese Phase nur unterhalb 425±25°C in Gegenwart einer Gasphase stabil ist. — Im System Ag-Pb-S ist die Paragenese Silber-Bleiglanz unterhalb von 784±2°C stabil, die Paragenese Silberglanz-Bleiglanz dagegen unterhalb 605±5°C. — Die Mischkristallreihe von Schapbachit und Bleiglanz ist vollständig oberhalb 215±15°C; unterhalb dieser Temperatur entstehen charakteristische Entmischungsgefüge ähnlich den Widmannstättenschen Figuren. Für das quaternäre System werden schematische Phasenbeziehungen für 1050°C, 400°C und eine noch tiefere Temperatur gegeben.

     

Melt loss and the preservation of granulite facies mineral assemblages

The loss of a metamorphic fluid via the partitioning of H₂O into silicate melt at higher metamorphic grade implies that, in the absence of open system behaviour of melt, the amount of H₂O contained within rocks remains constant at temperatures above the solidus. Thus, granulite facies rocks, composed of predominantly anhydrous minerals and a hydrous silicate melt should undergo considerable retrogression to hydrous upper amphibolite facies assemblages on cooling as the melt crystallizes and releases its H₂O. The common occurrence of weakly retrogressed granulite facies assemblages is consistent with substantial melt loss from the majority of granulite facies rocks. Phase diagram modelling of the effects of melt loss in hypothetical aluminous and subaluminous metapelitic compositions shows that the amount of melt that has to be removed from a rock to preserve a granulite facies assemblage varies markedly with rock composition, the number of partial melt loss events and the P–T conditions at which melt loss occurs. In an aluminous metapelite, the removal of nearly all of the melt at temperatures above the breakdown of biotite is required for the preservation of the peak mineral assemblage. In contrast, the proportion of melt loss required to preserve peak assemblages in a subaluminous metapelite is close to half that required for the aluminous metapelite. Thus, if a given proportion of melt is removed from a sequence of metapelitic granulites of varying composition, the degree of preservation of the peak metamorphic assemblage may vary widely.     

Evaluation of mineral thermometers and barometers applicable to garnet lherzolite assemblages

We have tested the ability of some 12 different barometer and 20 different thermometer formulations to reproduce the experimental P-T equilibration conditions of natural multi-component garnet lherzolite assemblages. For natural rock compositions it is essential to take account of the influence of both Cr and Fe on the garnet-orthopyroxene Al exchange reaction customarily used as a barometer for such assemblages and accordingly our results demonstrate that the formulation of Nickel and Green (1985) is the most satisfactory. No single thermometer formulation was judged to be reliable throughout the P-T range of interest. In our view equilibration temperatures are best assessed by consideration of a combination of the most satisfactory thermometer formulations, based on the two-pyroxene solvus and the Fe²⁺-Mg²⁺ exchange reactions between mineral pairs. Our results further indicate that use of the barometer (MacGregor 1974) and thermometer formulations recommended by Finnerty and Boyd (1984 and 1986) will lead to inaccurate assessment of the temperatures and pressures of equilibration for most garnet lherzolite xenolith assemblages and hence to incorrect interpretation of their depth of derivation within the mantle.     

Composition, mineral assemblages, and genesis of serendibite-bearing magnesian skarns

Variations in the composition and mineral assemblages of boronaluminosilciates (serendibite, grandidierite, kornerupine, and tourmaline) were studied in the abyssal and hypabyssal skarns of New York and California, United States, the Taezhnyi deposit of southern Yakutia, and deposits of the Pamirs, and compared to their occurrences around the world. The genesis of the boronaluminosilicates depends on the facies of the replaced skarns and the calcareous-skarn alteration of the primary composition of the host rocks. The substitution between Mg and Fe, as well as between Al, Si, and B, was studied in complex boronaluminosilciates and associated minerals. It was shown that f of serendibite is determined by that in the replaced skarn minerals (pyroxenes, spinel, sapphirine, and grandidierite) and is inherited in the replacing tourmaline and late silicates. Unlike serendibite, kornerupine is a typomorphic mineral of only bimetasomatic skarns of the abyssal facies. Serendibite, grandidierite, kornerupine, and tourmaline crystallized during the postmagmatic stage of the evolution of boron mineralization at skarn deposits of both the abyssal and the hypabyssal facies, at contact with magnesian carbonate sequences and desilicified aluminosilicate rocks.     

The Texture,Mineral Assemblages and Origin of Metamorphic Peridotite from Kuda Ophiolite,Xinjiang

There are two grades of network-type texture in metamorphic peridotite from the Kuda ophiolite,Xinjiang,China,The first graduation consists of coarse-grained olivine with plastic deformation fabrics,orthopyroxene and minor clinopyroxene and Cr-spinel.The second graduation consists of small minerals filling among the mineral grains of the first graduation.Four kinds of assemblages containing tremolite have been discovered in the second graduation,which were formed during mantle partial melting and mantle metasomatism of a highly depleted peridotite.     

Matrix analysis of metamorphic mineral assemblages and reactions: alternatives and extensions

Fisher (1989) advocated using the Singular Value Decomposition (SVD) of the composition matrix of a set of minerals for the determination of reactions between the minerals, and therefore of the compatibility relationships between mineral assemblages. The advantage of using the SVD for this is that an independent set of reactions, the left nullspace of the composition matrix, can be determined for a rank-deficient composition matrix which is close to, or within error of, the observed matrix. The zero singular values in the SVD can be identified by propagating the measurement uncertainties through to the singular values, and saying that singular values are zero if they are within error of zero. Having obtained an independent set of reactions, the reactions in the independent set can be combined linearly to find the full set of reactions. Propagating the measurement uncertainties through to the left nullspace of the composition matrix, the uncertainties in the coefficients of the reactions in the independent set can be determined. From these uncertainties, the uncertainties in all of the reactions can be determined, allowing the identification of reactions which are degenerate within error. This is important because it allows the identification of ambiguities in the compatibility relationships between mineral assemblages.     

The effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions

A series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates. The calculation assumes local equilibrium between phases, and that the system remains chemically closed during crystallization of the trapped liquid. The latter assumption is held to be valid on a scale of tens to hundreds of centimeters. It is not necessary to know the composition of the trapped liquid, as the calculation only requires an estimate of FeO content and trapping temperature.The change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift. Its magnitude depends on the modal proportions of cumulus phases and the initial porosity, and is only weakly dependent on initial phase compositions. Trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization. Crystallization of 30% trapped liquid gives rise to shifts of up to 10 mol. percent in Mg number of olivine or pyroxene. The size of the shift becomes greater when the initial cumulus assemblage has a lower total FeO+MgO content, and vice versa.As a result of the relationship between trapped liquid shift and cumulus mode, mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals. For example, in a cyclic unit grading from a pyroxenitic base to an anorthositic top, crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle, as has been observed in the Upper Critical Zone of the Bushveld Complex.     

桂林市红粘土的矿物组成与化学组成特征

讨论了粘土矿物成分与其成因的关系，指出红粘土的工程特性，是以伊利石为主，多数属于中等风化作用程度，具有中弱胀缩性。     

Influence of ferric iron on the stability of mineral assemblages

Ferric iron is present in all metamorphic rocks and has the ability to significantly affect their phase relations. However, the influence of ferric iron has commonly been ignored, or at least not been considered quantitatively, mainly because its abundance in rocks and minerals is not determined by routine analytical techniques. Mineral equilibria calculations that explicitly account for ferric iron can be used to examine its effect on the phase relations in rocks and, in principle, allow the estimation of the oxidation state of rocks. This is illustrated with calculated pseudosections in NCKFMASHTO for mafic and pelitic rock compositions. In addition, it is shown that ferric iron has the capacity to significantly increase the stability of the corundum + quartz assemblage, making it possible for this assemblage to exist at crustal P–T conditions in oxidized rocks of appropriate composition.     

Identifying provenance-specific features of detrital heavy mineral assemblages in sandstones

The composition of heavy mineral assemblages in sandstones may be heavily influenced by processes operating during transport, deposition and diagenesis. As a consequence, conventional heavy mineral data may not be a reliable guide to the nature of sediment source material. Certain features of heavy mineral suites, however, are inherited directly from the source area without significant modification, such as the varietal characteristics of individual mineral species. This paper describes an alternative approach to varietal studies that concentrates on relative abundances of minerals that are stable during diagenesis and have similar hydraulic behaviour. Ratios of apatite to tourmaline, TiO₂ minerals to zircon, monazite to zircon, and chrome spinel to zircon provide a good reflection of the source rock characteristics, because they are comparatively immune to alteration during the sedimentary cycle. These ratios are described as index values (ATi, RZi, MZi and CZi, respectively). This approach avoids some of the practical problems associated with varietal studies, such as the need to make subjective decisions about mineral properties or to use advanced analytical techniques that may not be accessible to the analyst. It also makes use of more components of the heavy mineral suite and thus provides a more balanced view of provenance characteristics. The use of these ratios is illustrated with examples from Upper Jurassic sandstones in the Outer Moray Firth area of the UK continental shelf and Triassic sandstones from onshore and offshore UK. Heavy mineral indices, notably ATi and MZi, show marked variations in Upper Jurassic Piper sandstones of the Outer Moray Firth. Main Piper sandstones have lower ATi and MZi values compared with Supra Piper sandstones, indicating significant stratigraphic evolution of provenance. The UK Triassic shows major regional variations in a number of index values, including ATi, MZi and CZi, demonstrating that sediment was supplied from several distinct source regions. This indicates a need for some modification of existing palaeogeographic models for the UK Triassic.     

梭菌SN-1菌株参与下形成的碳酸盐矿物组合及其主要矿物成分的动态变化

在Mg/Ca比值为6的Lagoa Vermelha改良培养基中,对分离自青海湖湖底沉积物的梭菌(Clostridiumsp.)进行了为期100 d的碳酸盐矿物培养实验,同时还完成了一组无菌对照实验。利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)分别对矿物成分和形态进行了测定和观察。实验结果表明:细菌培养实验的沉淀物数量始终多于无菌对照实验;在梭菌SN-1菌株作用下形成的碳酸盐矿物组合的变化趋势是方解石→方解石+单水碳钙石→单水碳钙石+方解石→单水碳钙石,而无菌对照实验产物中矿物的演化方向是单水碳钙石+方解石→方解石+单水碳钙石;在综合分析SEM和XRD观测结果的基础上,推测哑铃状矿物可能是高镁方解石,而球状矿物可能是单水碳钙石。