Authigenic Gypsum in Gas-Hydrate Associated Sediments from the East Coast of India (Bay of Bengal)

Authigenic gypsum crystals, along with pyrite and carbonate mineralization, predominantly calcites were noticed in distinct intervals in a 32 m long piston core, collected in the gas hydrate- bearing sediments in the northern portion of the Krishna-Godavari basin, eastern continental margin of India at a water depth of 1691 m. X-ray diffraction and energy dispersive spectrum studies confirm presence of pyrite, gypsum, calcite, and other mineral aggregates. The occurrence of gypsum in such deep sea environment is intriguing, because gypsum is a classical evaporite mineral and is under saturated with respect to sea water. Sedimentological, geochemical evidences point to diagenetic formation of the gypsum due to oxidation of sulphide minerals (i.e. pyrite). Euhedral, transparent gypsum crystals, with pyrite inclusions are cemented with authigenic carbonates, possibly indicating that they were formed authigenically in situ in the gas hydrate-influenced environment due to late burial diagenesis involving sulphate reduction and anaerobic oxidation of methane (AOM). Therefore, the authigenic gypsums found in sediments of the Krishna-Godavari and Mahanadi offshore regions could be seen as one of the parameters to imply the presence of high methane flux possibly from gas hydrate at depth.     

石灰岩介质中地下核试验熔岩的矿物研究及其形成过程

The melt rocks produced during an underground nuclear explosion in the limestone medium may be classified into three types in the light of thin-section examinations and chemical compositions. One of them is the carbonate melt rock which is distributed widely and very large in quantities. About 20 kinds of monominerals were identified by X-ray powder and electron microprobe techniques. Some minerals, such as moissanite, brownkillerite, Ca12Ah14O33, etc., are rare or have not yet been discovered in nature. In addition, this paper presents the four stages of formation of the melt rocks, i.e., the vaporization-liquefaction stage, the initial crystallization-cavity stripping stage, the crystallization stage, and the chimney formation-thermal metamorphism stags. Furthermore, preliminary theoretical analysis was carried out of the physico-chemical process of mineral formation.     

Zircon Geochronology and Trace Element Geochemistry from the Xiaozhen Copper Deposit, North Daba Mountain: Constraints on Albitites Petrogenesis

Albitite often accompanies with various metal and gem mineral deposits and a large number of occurrences have been reported globally, including the South Qinling orogen, China. The Xiaozhen copper deposit is a typical deposit in the North Daba Mountain area of the South Qinling orogen whose distribution is controlled by albitite veins and fractures. As there are few studies on the petrogenesis of albitite in Xiaozhen copper deposit, this paper focuses on the petrogenesis of albitite and its mineralization age. Detailed fieldwork and mineral microscopic observations initially suggest that albitite from the Xiaozhen copper deposit is igneous in origin. Further zircon trace element geochemistry studies indicate that these zircons have high Th/U ratios(0.5), low La content, high(Sm/La)N and Ce/Ce*values, and a strong negative Eu anomaly, which are commonly seen in magmatic zircons. The chondrite–normalized rare earth element(REE) patterns are consistent with magmatic zircons from throughout the world, and they fall within or near the field of magmatic zircons on discriminant diagrams. The calculated average apparent Ti–in–zircon temperature for young zircons is 780°C, consistent with magmatic zircon crystallization temperatures. Therefore, zircon geochemistry indicates that the albitite origin is magmatic. SIMS U–Pb dating on nine magmatic zircons yielded a concordia age of 154.8±2.2 Ma, which represents the formation of albitite and the metallogenic age. More importantly, it is consistent with the ages of Yanshanian magmatism and metallogenesis in the South Qinling orogen, so formation of the Xiaozhen copper deposit may be a closely related geological event.     

Speciation of sulfate components in size-fractionated aerosol particles using sulfur K-edge X-ray absorption near-edge structure （XANES）

Sulfates are a main constituent of aerosols, which sulfate aerosols, it is necessary to determine what can cause various environmental problems sulfate ions are contained in these aerosols In the evaluation of the influence of In this study, sulfur K-edge XANES was used to determine sulfate species present in size-fractionated aerosol particles based on the post-edge structure after the main absorption peak in the XANES region. Aerosol samples were collected as part of the Japan-China joint project, ＂Asian Dust Experiment on Climate Impact＂ using a low-volume Andersen-type air sampler. XANES was measured at Beamline BL-9A at Photon Factory, Japan. A comparison of the XANES spectra of reference sulfate materials and aerosol samples collected in Tsukuba in Japan clearly showed that （NH4）2SO4 was the main sulfur species in particles with a smaller diameter and gypsum was the main sulfur species in particles with a larger diameter. A simulation of the XANES spectra by reference materials allows us to obtain the quantitative mixing ratios of the different sulfate species present in the aerosol samples. The presence of minor sulfur species other than （NH4）2SO4 and gypsum at the surface of mineral aerosols is suggested in our simulations and by a surface-sensitive conversion electron/He-ion yield XANES. In the absence of a contribution from a large dust event, the mole concentration of gypsum in the mineral aerosol fraction determined by XANES is similar to that of Ca which is determined independently using ion chromatography. This shows that the Ca and sulfate in the mineral aerosols are present only as gypsum. Considering that calcite is the main Ca mineral in the original material arising from an arid and semi-arid area in China, it is strongly suggested that gypsum is formed in aerosol during its long-range transportation by a reaction between calcite and sulfate ions.     

Geochemical reasons for high vulnerability of northern taiga ecosystems on hard gypsum outcrops

Northern taiga ecosystems on hard gypsum outcrops were studied at the area of Plnega State Reserve in the Arkhangelsk region of Russia. Landscapes on gypsum outcrops are very specific and characterized by a dissected karst topography and predominance of soils formed on hard gypsum. Phytocenoses confined to soils on hard gypsum are oligotrophic and significantly differ from generally known boreal forests. In the northern taiga, these are open woodlands characterized by the prevalence of suppressed pines and larches and the presence of rare arcto-alpine species （e.g. Gypsophylla uralensis subsp, pinegensis） in the lower tiers. It was found that ecosystems on gypsum outcrops are very vulnerable for fires with slow processes of vegetation recovery. Chemical methods of rocks, soils and plants samples investigation include pH （potentiometrically）, humus （T＇urin＇s method）, nitrogen （K＇eldal＇s method） and total content of other 20 macro- and microelements （X-ray fluorescence analysis）. The analysis of hard gypsum and the local geochemical background of the Pinega region （glacial loamy deposits） showed that gypsum rock is enriched only in S, Ca, and Sr： it consists of 99% CaSO4＊2H2O and is non-calcareous according to pH levels and negative result of qualitative reaction with HCl. The contents of Br, Pb and N are close to those of moraine. But most of nutrients have concentrations insufficient for normal plant growth, e.g. K and Mn are found in quantities of 1/400 and less than 1/1000 of their contents in silicate loamy soils of the study area. Distribution of all chemical elements in the profiles of soils formed on gypsum shows that there is no accumulation of any eluvium during soil formation because of total dissolution of disintegrated gypsum material. In this specific soil litter is the main horizon of most of nutrient concentration and, therefore, its role for plants nutrition became more important than in soils on glacial loams. The fires destroying soil litter, which is extremely precious for the whole ecosystem on geochemically pure gypsum, also causes an intensive denudation of organic horizons on slopes of karst landforms.     

Discovery,Genesis and Significance of Metallic Minerals in Evaporate Series in the Kuqa Basin

A large-scale evaporate series is developed in Paleogene-Neogene strata in the Kuqa basin. The series is composed mainly of evaporate with thin beds of clastic rock (mainly mudstone and siltstone). In grayish white medium- and coarse-grained sandstone in Miocene strata, the formation of copper minerals is in close connection with brine. In joint planes, which are developed in vertical strata, are filled with gypsum. Gypsum and copper-mineralized sandstone contains enormous copper minerals, mainly atacamite. According to the SEM analysis for salt rock, gypsum rock, limestone, grayish green siltstone, grayish white medium-coarse-grained sandstone, some minerals are composed of metallic elements including Au, Ag, Cu, Zn, Pb, Co, Ni and U etc., in which Au occurs in a native form, Cu occurs in a native form or as atacamite in salt rock, gypsum rock and limestone, Ag occurs as silver sulfide in gypsum, and Zn, Pb, Co, Ni, U occur as compounds along with the above metallic ions in evaporate or clastic rock. From SEM images, we can see that metallic elements or their compounds (oxides or sulfides) “take root” as grains in salt or gypsum crystals, which belong to primary chemical sedimentation along with evaporate, while some grains “float” on surface of salt or gypsum. In the former case, mineral grains were formed together with salt (gypsum) crystals; while in the latter case, minerals were enriched from internal metallic ions (Paleogene evaporate samples) or external metallic ions (Neogene gypsum samples) in the late stage of evaporate formation. The metallic ions in Paleogene evaporate samples might originate from weathered or denudated materials in the south Tianshan Mountains. The metallic ions in the Neogene evaporate samples might be from metal-bearing brine, which migrated upward to surface along fractures and leached into evaporate (gypsum). Occurrence of metallic minerals and their compounds (elementary substance) in Paleogene evaporate proves that diversified metallic minerals exist in evaporate. The source of metallic ions in the Neogene evaporate series shows that evaporate could provide materials for late-stage metallic mineralization.     

Origin of Peridotites and Chromitites in the Pozanti-kar Santi Ophiolite, Turkey

The Pozanti-Karsanti ophiolite(PKO)in Turkey’s eastern Tauride belt comprises mantle peridotites,ultramafic to mafic cumulates,isotropic gabbros,sheeted dikes and pillow lavas.The mantle peridotites are dominated by spinel harzburgites with minor dunites.The harzburgites and dunites have quite depleted mineral and whole-rock chemical composition,suggesting high degrees of partial melting.Their PGEs vary from Pd-depleted to distinct Pd-enriched patterns,implying the crystallization of interstitial sulphides from sulphur-saturated melts(e.g.MORB-like forearc basalt).U-shaped or spoon-shaped REE patterns indicate that the PKO peridotites may have also been metasomatized by the LREE-enriched fluids released from a subducting slab in a suprasubduction zone.Based on the mineral and whole-rock chemical compositions,the PKO peridotites show affinities to forearc peridotites.Chromitites occur both in the mantle peridotites and the mantle-crust transition zone horizon(MTZ).Chromitites from the two different horizons have different textures but similar mineral compositions,consistent with typical high-Cr chromitites.Chromitites hosted by mantle harzburgites generally have higher total platinum-group element(PGE)contents than those of the MTZ chromitites.However,both chromitites show similar chondritenormalized PGE patterns characterized by clear IPGEs,Rh-enrichments relative to Pt and Pd.Such PGE patterns indicate no or only minor crystallization of Pt-and Pd enriched sulphides during formation of chromitites from a sulphur-undersaturated melt(e.g.boninitic or island arc tholeiitic melt).Dunite enveloping chromitite lenses in the ho*s ting harzburgite resulted from melt-rock reaction.We have performed mineral separation work on samples of podiform chromitite hosted by harzburgites.So far,more than200 grains of microdiamond and more than 100 grains of moissanite(Si C)have been separated from podiform chromitites.These minerals have been identified by EDX and Laser Raman analyses.The diamonds and moissanite are accompanied by large amounts of rutile.Additionally,zircon,monazite and sulphides are also common phases within the heavy mineral separates.Both diamond and moissanite have been analyzed for carbon and nitrogen isotopic composition using the CARMECA 1280-HR large geometry Secondary Ion Mass Spectrometer at the Helmholtz Zentrum Potsdam.In total,61δ13CPDB results for diamond were acquired,exhibiting a range from-28.4‰to-18.8‰.31δ13CPDB results for Moissanite vary between-30.5‰to-27.2‰,with a mean value of-29.0‰.Diamond has relatively large variation in nitrogen isotopic composition with 40δ15NAIR results ranging from-19.1‰to 16.6‰.The discovery of diamond,moissanite and the other unusual minerals from podiform chromitite of the Pozanti-Karsanti ophiolite provides new support for the genesis of ophiolitic peridotites and chromitites under high-pressure and ultra-high reducing conditions.Considering the unusual minerals,the high Mg#silicate inclusions,and the needle-shaped exsolutions in the PKO chromitites,the parental melts of these chromitites may have been mixed with deep asthenospheric basaltic melts that had assimilated materials of the descending slab when passing through the slab in a subduction zone environment.We suggest melt-rock reactions,magma mixing and assimilation may have triggered the oversaturation of chromites and the formation of PKO chromitites.     

Crystal Growth and Crystallization Time Scales of the Panzhihua Layered Intrusion: Constraint from Crystal Size Distribution

The Panzhihua layered intrusions is generated closely related to the Emeishan LIPs. This paper analyzes the spatial distribution of plagioclase and pyroxene. The quantitative texture analysis of 2209 plagioclase shows that the characteristic length of plagioclase is 0.54 to 0.96 mm, the intercept variation range is large, from ?0.67 to 0.96, and the slope is ?1.85 to ?1.04, the Aspect Ratio shows from 1.84 to 2.59 and fractal dimension D is 1.908–1.933. The quantitative texture analysis of 2342 pyroxene shows that the characteristic length of pyroxene is 0.38–0.64 mm, the intercept shows from 0.46 to 2.26, The slope ranges from ?2.6 to ?1.47, the Aspect Ratio value varies from 1.53 to 1.71, the fractal dimension D is 0.93 to 1.13. All the CSDs results of the Panzhihua intrusions indicate that plagioclase and pyroxene form in an open magma system and undergo four replenishment of magma injection. The plagioclase crystals do not grow as the lathlike shape, and the fractal growth leads to complex crystal surface. The plagioclase undergoes deformation compaction during the crystal process, and then is oriented. The pyroxene crystals grow along an approximately triaxial ratio and undergo texture adjustment and small crystal dissolution reabsorption. When all crystals in magma system grows up to 2 mm, the pyroxene undergoes cumulation in the Panzhihua layered intrusions. The plagioclase crystallization time scale is 171.23–304.41 years, representing that the crystallization is the more uniform in central part of the melt. The nucleation density continuously increases during the crystallization process of the magma system. The time scale to reach the final maximum crystal nucleation density is 15.28–58.98 years.     

Introduction to thematic section on hydrodynamic ;tudies of mineralization

1.Introduction Most metallic mineral deposits formed from hydrothermal fluids,and the mineralization processes include both chemical (e.g.,fluid-rock and fluid-fluid interactions)and physical(e.g., fluid flow)aspects.More attention has been paid to the chemical processes than the physical ones,even though the latter is equally important in controlling the formation of mineral deposits and their localization.Nevertheless,a number of studies have been carried out regarding the hydrodynamics of fluid flow associated with ore mineralization(e.g.,Cathles,1981,1997; Garven and Raffensperger,1997;Cathles and Adams,2005; Cox,2005;Ingebritsen et al.,2006),and it is timely to eval-     

Strategies towards robust interpretations of in situ zircon Lu-Hf isotope analyses

The combination of U-Pb and Lu-Hf compositions measured in zircon crystals is a remarkably powerful isotopic couplet that provides measures on both the timing of mineral growth and the radiogenic enrichment of the source from which the zircon grew.The U-Pb age documents the timing of zircon crystallization/recrystallization and Hf isotopes inform on the degree to which the host melt was derived from a radiogenic reservoir(e.g.depleted mantle) versus an unradiogenic reservoir(e.g.ancient continental crust),or some mixture of these sources.The ease of generating large quantities of zircon U-Pb and Lu-Hf data has been in large part facilitated by instrument advances.However,the dramatic increase in time constrained zircon Lu-Hf analyses in the Earth science community has brought to the fore the importance of careful data collection and reduction workflows,onto which robust geological interpretations may be based.In this work,we discuss the fundamentals of Lu-Hf isotopes in zircon,which then allows us to provide a robust,accessible,methodology for the assessment of data quality.Additionally,we discuss some novel techniques for:data visualization—that facilitates better transparency of data interpretation;integration of geographic information—that may reveal spatial trends where temporal trends were only apparent before;and some novel statistical evaluation tools—that may provide more rigorous interand intra-sample comparisons.     

Late Triassic Intraoceanic Arc Aystem within Neotethys: Evidence from Cumulate Hornblende Gabbro in Gangdese Belt, South Tibet

The Neotethys plays an important role in shaping the Gangdese magmatic belt,southern Tibet.However,the initial time of spreading and subduction of the Neotethys remains contentious.In this study,a suite of late Triassic cumulate hornblende gabbro was identified in the southern margin of the Gangdese magmatic belt.The gabbro exhibits cumulate structure,with hornblende and plagioclase as the primary mineral phases.Isotopic data indicate a hydrous magma source derived from a depleted mantle wedge that has been modified by slab dehydration.Geochemical discriminations suggest that the gabbro was formed in an intraoceanic arc setting,with crystallization ages of ca.220-213 Ma.Hornblende,hornblendelagioclase and ilmenite thermometers reveal that the crystallization temperature of 900-750°C for the gabbro.Hornblende and hornblende-plagioclase geobarometers yield an emplacement depth at ca.14.5-19.5 km.This gabbro constitutes a line of evidence for an intraoceanic arc magmatism that is coeval with the counterparts in the southern Turkey,revealing an intraoceanic subduction system within the Neotethys from west to east in the Late Triassic and that the oceanization of the Neotethys was much earlier than previous expectation.     

论姑山铁矿床的形成条件

On the basis of geological characteristics the Gushan iron deposit should be assigned to volcano-hydruthermal type with hematite qusrtz as its principal mineral assemblage.Iron concentration of the ore-forming fluid has been estimated from the ratio of hematite to quartz in the ores. By using experimental and thermodynamic data the soinbilities of iron minerals at elevated temperatures and pressures are calculated in the system FeO-Fe2O3-NaCl-HCl-H2O. The effect of T, P, pH, fe2 and total concentration of chlorine on the solubilities of iron minerals are discussed. Thermodynamic calculations based on presumed physicochemical conditions for the ore-forming solutions are in good agreement with geological observation. The calculation shows that iron minerals were deposited at log fo2=-21--25, log(mKCl mbl^ ) =-2,5--3, P=1-0.75 (or 0.5) Kb,T=400-350℃. It is believed that the original fluid was an acid NaCl-bearing solution of magmatic derivation. However, iron in the solution was enriched with falling temperature by dissolving pre-exist iron minerals in the consolidated rocks rather than extracted directly from the magma. Either decreasing temperature (below 400℃) or pressure is capable of depositing iron minerals from the solution, but the ratio of Fe to Si in the ore is dependent mainly upon the pH. The widespread silica vein at later stages is a reflection of decreasing acidity of the solution. Increase in fo2 will also favor the deposition of iron minerals. The hypabyssal occurrence and the existance of the Huangmaqing shale contribute greatly to the formation of hematite.     

Distribution of Palygorskite in the Lingtai Profile of Chinese Loess Plateau： Its Paleoclimatic Implications

Palygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess-red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate.In this paper,field emission scanning electron microscope and high-resolution transmission electron microscope observations on the red clay-loess-paleosol of the Renjiapo profile at Lingtai,Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma,but no occurrence has been found in eolian sediments since 3.2 Ma.Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis,and transformed from illite-montmorillonite under the pore water action.In the Lingtai profile,the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility,dust flux and depositional rate.The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon,when changes took place in the East Asia paleoclimate pattern,i.e.a high-frequency strong fluctuation alternative evolution of the environment. Therefore,palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time.     

A Study of Near- and Super-Critical Fluids Using Diamond Anvil Cell and in-Situ FT-IR Spectroscopy

The phase relation and solution structure of water and NaCl aqueous solution have been observed and examined by using the hydrothermal diamond anvil cell (HDAC) at elevated temperatures and pressures and the in situ FT-IR spectroscopy. The temperature of observations ranges from 25 to 850° C and the pressure up to 10 or 30 kb. At first, we observed the phase transition process from halite+liquid+vapour (H+L+V) to L+H, then to L (or supercritical fluid, SCF), and another path: H+L+V? L+V? L (or SCF) in heating process. By means of the visual microscope, the authors found that in the L+V immiscibility field L+V exhibits an ordered structure, i.e. a large visual cluster of solvent around ions. The liquid phase is manifested by vapour bubbles. When phase transitions are observed, the authors examined their infrared spectra by using the FT-IR microscopy simultaneously. In the case of the phase transition from liquid (L) to liquid + vapor (L+V) immisciblity field of NaCl solutions, a sudden change (strong frequency shift) of infrared spectra of the aqueous solution is observed near the critical temperature of water as the temperature is raised from 25 to 650° C. The frequency of the maximum intensity of OH symmetric and asymmetric vibration varies with respect to temperature. The sharp peak of the OH stretching vibration of the maximum intensity appears in an interval from 300 to 400° C. It is indicated that the hydrogen bonding network is weakened and broken at last near the critical point of water, which causes the aqueous solution to become more associated. Besides, a pressure indicator (a mineral or compound) was introduced to the HDAC.     

Anomalous Enrichment of Silver in Organic Matter of the Songxi Shale-hosted Ag-Sb Deposit in Northeastern Guangdong

The silver contents of organic matter in the host rocks of the Songxi shale-hosted Ag-Sb deposit of northeastern Guangdong, South China, have been directly determined using the electron microprobe technique. The silver contents in two types of organic matter, marine vitrinite and solid bitumen, vary in the range from 100×10-6to 350×10-6, which are from tens of times to thousands of times higher than those of the host rocks in the ore deposit. The average silver content of the organic matter is also several times higher than the pay grade of silver for commercial mining of the ore deposit. It is quite obvious that the organic matter of the host rocks in the ore district is characterized by an anomalous enrichment of silver. The results of this study indicate that the silver anomalies in the organic matter have been derived from both the host rocks and the silver-bearing fluids of the Songxi black shale ore source. In the course of sedimentation and later hydrothermal reworking, organic matter was able     

Distribution of Palygorskite in the Lingtai Profile of Chinese Loess Plateau: Its Paleoclimatic Implications

Palygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess-red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate. In this paper, field emission scanning electron microscope and high-resolution transmission electron microscope observations on the red clay-loess-paleosol of the Renjiapo profile at Lingtai, Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma, but no occurrence has been found in eolian sediments since 3.2 Ma. Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis, and transformed from iilite-montmorilionite under the pore water action. In the Lingtai profile, the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility, dust flux and depositional rate. The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon, when changes took place in the East Asia paleoclimate pattern, i.e. a high-frequency strong fluctuation alternative evolution of the environment. Therefore, palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time.     

我国铁矿床的一种新类型——弓长岭式含石墨的富磁铁矿矿床及其成因

Graphite has been identified for the first time from rich magnetite ores in Gongehangling,Northeast China.It is suggested that the deposit is originated from siderite of sedimentary origin through regional metamorphism.In view of the unique charaeteristics of its geologieal setting and mineral assemblage this deposit should be elassified as a new type in China     

CHARACTERIZATION OF DEFORMATION AND X-RAY PETROFABRICS IN THE MIDDLE PART OF THE WAHONGSHAN FAULT ZONE, QINGHAI PROVINCE, NORTHWESTERN CHINA

The Wahongshan fault zone in Qinghai province is one of the most important faults in westem China. In this paper, deformation and X-ray petrofabrics have been studied in the middle segment of the fault. The results show that the formation of the fault zones can be divided into two major stages: ductile shear deformation stage and brittle deformation stage. The early stage ductile shearing leads to the formation of the NW-NNW trending mylonite zones along the fault, which is intensely cut by the late-formed brittle faults. X-ray petrofabrics of rocks near the faults indicate that the minerals in the tectonites show a great degree of orientation in the alignment. The quartz, which is a very important mineral in the tectonites, is deformed by basal face gliding or near basal face gliding, and sometimes by prismatic face sliding, which indicates that the rocks are deformed in epithermal to mesothermal or mesothermal environment, and the dynamic recrystallization also plays an important role in the formation     

莱河矿稳定性的热力学分析

Laihunite, a mineral of ferric and ferrous iron silicate discovered in China in recent years, occurs in high grade metamorphic BIF coexisting with magnetite, quartz,fayaiite, ferrosilite and almandine. Complete nets based on Sehreinemakers bundles and partial nets with maximum closure after the method described by H. W. Day have been constructed by taking into account the existance of this minertl in order to illustrate phase relations for the (n 3) multisystem in the system of Fe2O3-FeO-SiO2. Judging from Lindsley‘s experimental data on ferrosilits, laihunite is expected to be stable at pressures probably higher than 15 Kb. Two-pyroxene and olivine-clinopyroxene geothermometere give temperatures of formation between 600--700℃. Free energy of laihunite calcultted according to the method of Chert and estimated values of heat capacity allow oxygen fugacity to be plotted against temperature at different total pressures with respect to a number of univariant reactions in which lailunite is involved. The log fo2 -T diagram demonstrates that to a first approximation the stability flels of laihunite overlaps the upper part of the magnetite field, but its upper limit is a little beyond the hematite-magnetite equilibrium. The three major requirements for laihunite stability, i.e., an unusual high pressure, a temperature in the order of 600--700℃ and a relatively higher oxygen fugacity are mutually, exclusive in common geological environment, which may probably account for the rare occurrence of this mineral in nature. For the BIF in which laihunite occurs, the pressure caused by the weight of overlying strata is not high enough to give rise to its formation even in the extreme case of geothermal gradient.So it is suggested that additional tectonic pressure in response to plate activity might have been involved.     

吉林陨石中包裹体特征，形成温度及其意义的探讨

Glass and gas inclusions have been observed in olivine and other minerals in 30 doubly polished tin sections of Jilin meteorites, indicating that there must have been melting And condensation stages during the process of meteorite formation. Temperatures of formation have been determined by homogenization and quenching runs,giving 1050-200℃ and 502℃ for glass and gas inclusions respectively, Meanwhile,the fibrous radial crystals of pyroxene have been notieed to grow when heated over 800℃. These observations are in general agreement with the available experimental data and theoretical calculations regarding meteorite.