Home About us Contact
|
Home About us Contact | ||
|
|
||
Electron Microprobe (electron + microprobe)
Terms modified by Electron Microprobe Selected AbstractsMicro-Raman spectroscopic study of El Gasco pumice, western SpainJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2007F. Rull Abstract A micro-Raman spectroscopic study of pumice materials from El Gasco (Sierra de Gata, Spain) has been performed for the first time. The obtained spectra allow the precise identification of the minerals, quartz, haematite, magnetite, ilmenite, rutile and anatase, in general agreement with results obtained by complementary techniques of X-Ray Diffraction (XRD) and Electron Microprobe. Also, fayalite and ferroan ringwoodite have been identified. The presence of high-pressure polymorphs indicates that the pumice rocks were subjected to high-pressure conditions quite similar to those observed in shock-induced molten and recrystallised materials, such as some meteorites and impact-related rocks. Copyright © 2006 John Wiley & Sons, Ltd. [source] Provenance and microprobe assays of phyllite-tempered ceramics from the uplands of central ArizonaGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 2 2008David R. Abbott The ceramics in use across a broad upland zone of central Arizona during the early Classic period (ca. A.D. 1100,1300) were characterized by a lack of mineralogical variability; nearly all of the clay containers were tempered with one rock type, phyllite. Consequently, nearly all of the upland pottery is assigned to a single pottery type, Wingfield Plain. This compositional uniformity has frustrated ceramic provenance studies, and, as a result, little has been learned previously about the organization of ceramic production and exchange in the upland territory. There are, however, considerable and interpretable chemical differences in the phyllite-tempered wares, as shown with microanalyses of the temper fragments and pottery clay fractions with an electron microprobe. The chemical patterning is useful for investigating issues pertaining to the upland zone, including the organization of ceramic manufacture, community arrangements, and pottery transactions during a time of prevalent hostilities in central Arizona. © 2008 Wiley Periodicals, Inc. [source] An electron microprobe study of P645/T390: Evidence for an Early Helladic III Lerna,Aegina connectionGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 8 2002Michael J. Dorais Middle Helladic Aeginetan Ware is widely distributed throughout the Aegean. It is characterized by a "gold mica or volcanic ash" fabric and is abundant at Lerna on the Argive plain, Greece, in the Middle Helladic and Late Helladic I periods. A group of Early Helladic III ceramics at Lerna includes P645/T390, which also has a volcanic fabric. We have sampled all the major rock types of the separate volcanic episodes on Aegina, Methana, and Poros and analyzed the constituent minerals with the electron microprobe. These analyses provide a reference standard against which the mineralogy of P645/T390 and other potential Aeginetan wares can be compared. The compositions of amphibole, clinopyroxene, plagioclase, and biotite in P645/T390 are identical to the same minerals in dacites on Aegina, suggesting an origin on that island. Compositional mismatches with the minerals of Methana and Poros indicated the ceramic was not manufactured at these locations. This narrow-necked jar represents the earliest occurrence of Aeginetan Ware on mainland Greece that has been confirmed by a quantitative method. © 2002 Wiley Periodicals, Inc. [source] Geochemical and mineralogical distinctions between Bonnin and Morris (Philadelphia, 1770,1772) porcelain and some contemporary British phosphatic waresGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2001J. Victor Owen The major element compositions of 15 ceramic sherds from the Bonnin and Morris factory site were determined by electron microprobe. Thirteen samples are phosphatic; the others consist of (a) "soapstone" (magnesian/plombian) and (b) true porcelain, and are interpreted as exotic artifacts, as is one compositionally distinct (relatively SiO2 -poor, P2O5+CaO-rich) phosphatic sample. Although long considered to be virtually indistinguishable from Bow porcelain (London: ca. 1747,1776), the phosphatic Philadelphia wares have a relatively low mean CaO/P2O5 ratio (3.3 versus 3.8; molecular proportions) and high alumina content (6.6 versus 5.4 wt % Al2O3). Furthermore, unlike Bow, the Bonnin and Morris samples contain calcic plagioclase (bytownite), and in some instances, an orthoclase-rich ternary feldspar. The preservation of calcic plagioclase indicates that Philadelphia porcelain was fired at (rather than above) the thermal minimum in the An-SiO2 -C3P system, although the presence of Na (and other fluxes) in these wares precludes the exact determination of the maximum firing temperature from this phase diagram. These wares are also distinctive insofar as the phosphate and melt phases can contain small amounts of lead; they have bulk lead contents of approximately 0.1,1.2 wt % PbO. This component has not been detected in the body of Bow or other contemporary British phosphatic porcelains. Their principal similarity lies in the fact that both wares contain sulfate. In addition, the glazes on Bonnin and Morris porcelain (e.g., PbO , 35,50 wt %; SnO2 , 1,2%) compositionally resemble those used at Bow. If feldspar is formed at all, then Al-poor phosphatic porcelain (or those with low CaO/P2O5 ratios) will have comparatively low modal calcic plagioclase contents, thereby allowing the rapid depletion of this mineral via resorption by the melt phase during vitrification. Such appears to have been the case for analyzed Bow porcelain, which is therefore interpreted to have been overfired (sensu lato) relative to its Philadelphia counterpart. Conceivably, calcic plagioclase could be preserved in low-Al wares that were fired only briefly at vitrification temperatures. Given the role of firing history in governing the mineralogy of porcelain, compositional criteria are more reliable for distinguishing these wares. © 2001 John Wiley & Sons, Inc. [source] Preparation of a Synthetic Titanite Glass Calibration Material for In Situ Microanalysis by Direct Fusion in Graphite Electrodes: A Preliminary Characterisation by EPMA and LA-ICP-MSGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 2 2005Magne Ødegård matériaux de calibration; microanalyse; fusion directe; électrodes de graphite; verre de titanite This paper describes a technique for the preparation of a titanite (CaTiSiO5) glass calibration material for use in in situ microanalysis of major, minor, and trace elements in geological materials. The starting composition was a titanite matrix doped with minor and trace elements at , 200 ,g g -1. The elements Sc, Y, REEs, Th and U were added in the form of nitrates in solution, and the elements V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Hf and W were added as solid oxides. The synthetic titanite glass was produced by direct fusion by resistance heating in graphite electrodes at 1600-1700 °C, and quenched in air. Backscattered electron images indicate good homogeneity, with no signs of separate phases or vesicles, and analysis of the major elements Ca, Ti and Si by electron microprobe showed relative standard deviations between 0.5 and 0.7%, based on six independent measurements. Deviations from nominal concentrations for Ca, Si and Ti were measured to -1.2, -3.3 and -0.8%, respectively. The homogeneity of the trace elements in the glass was assessed by LA-ICP-MS analyses, using NIST SRM 610, 612 and 616 as external calibrators, and Ca as the internal standard element. Determinations were made both with a quadrupole mass spectrometer and a sector field instrument, and both raster and spot modes of analysis were used. For the majority of doped elements, precision was better than 10%, and relative deviations from nominal values were, with few exceptions, between 5 and 10%. Cet article décrit une technique de préparation d'un verre de composition CaTiSiO5 (titanite) pour l'utiliser comme matériau de calibration lors de microanalyses in situ des éléments majeurs, mineurs et en trace dans des matériaux géologiques. La composition de départ a une matrice de titanite, dopée avec des éléments mineurs et en trace à une concentration de , 200 ,g g-1. Les éléments Sc, Y, REE, Th et U ont été ajoutés sous forme de nitrates en solution et les éléments V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Hf et W sous forme d'oxydes solides. Le verre synthétique de titanite a été produit par fusion directe avec un chauffage par des résistances dans des électrodes de graphite à 1600-1700 °C suivi d'un refroidissement rapide à l'air. Les images obtenues par électrons rétrodiffusés montrent que le verre présente une bonne homogénéité, sans aucun signe de phases individualisées ou de vésicules, et l'analyse des éléments majeurs Ca, Ti et Si par microsonde électronique a des déviations standard relatives (RSD) entre 0.5 et 0.7% provenant de six mesures indépendantes. Les déviations par rapport aux concentrations calculées, pour Ca, Si et Ti, sont de -1.2, -3.3 et -0.8% respectivement. L'homogénéité de répartition des éléments en trace dans le verre a été vérifiée par des analyses LA-ICP-MS, en utilisant les matériaux de référence NIST SRM 610, 612 et 616 pour la calibration externe et Ca comme élément standard interne. Les déterminations ont été faites avec un spectromètre de masse de type quadrupôle et un autre de type secteur magnétique, par des analyses à la fois en mode balayage et en mode ponctuel. Pour la majorité des éléments dopés, la précision est meilleure que 10% et les déviations standard relatives par rapport aux valeurs calculées sont, à quelques exceptions près, entre 5 et 10%. [source] Eclogites from the Chinese continental scientific drilling borehole, their petrology and different P-T evolutionsISLAND ARC, Issue 4 2007Yong-Feng Zhu Abstract Four phengite-bearing eclogites, taken from different depths of the Chinese continental scientific drilling (CCSD) borehole in the Sulu ultrahigh pressure terrane, eastern China, were studied with the electron microprobe. The compositional zonations of garnet and omphacite are moderate, whereas phengite compositions generally vary significantly in a single sample from core to rim by decrease of the Si content. Various geothermobarometric methods were applied to constrain the P-T conditions of these eclogites on the basis of the compositional variability of the above minerals. The constrained P-T path for sample B218 is characterized by pressure decrease from ca 3.0 GPa (ca 600°C) to 1.3 GPa (ca 550°C). Eclogite B310 yielded P-T conditions of 3.0 GPa and 750°C. The path for eclogite B1008 starts at about 650°C and 3.6,3.9 GPa (stage I) followed by a pressure decrease to 2.8,3.0 GPa and a significant temperature rise (stages II and IIIa, 750,810°C). Afterwards, this rock cooled down to 620,660°C at still high pressures (2.5,2.7 GPa, stage IIIb). Retrograde conditions were about 670°C and 1.3 GPa (stage IV). Eclogite B1039 yielded a P-T path starting at ca 600°C and 3.3,3.9 GPa (stage I). A pressure decrease to about 3.0 GPa (stage II, 590,610°C) and then a moderate isobaric temperature increase to ca 630°C (stage III) followed. Stage IV is characterized by temperatures of 650°C at pressures close to 1.3 GPa. During and after this stage (hydrous) fluids partially rich in potassium penetrated the rocks causing minor changes. Relatively high oxygen fugacities led to andradite and magnetite among the newly formed minerals. We think that the above findings can be best explained by mass flow in a subduction channel. Thus, we conclude that the assembly of UHP rocks of the CCSD site, eclogites, quartzofeldspathic rocks, and peridotites, cannot represent a crustal section that was already coherent at UHP conditions as it is the common belief currently. The coherency was attained after significant exhumation of these UHP rocks. [source] Application of otolith microchemistry to estimate the migratory history of Japanese eel Anguilla japonica on the Sanriku Coast of JapanJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2 2004A. Kotake Summary The age and migratory history of the Japanese eel, Anguilla japonica Temminck & Schlegel, collected in Miyako Bay along the Sanriku coast of Japan, was examined using the otolith microstructure and analysis of strontium (Sr) and calcium (Ca) concentrations conducted with wavelength dispersive X-ray spectrometry by an electron microprobe. The line analysis of Sr : Ca ratios along the life history transect of each otolith showed a peak (ca. 15,17 × 10,3) which corresponded with the period of their leptocephalus and early glass eel stages in the ocean. The mean Sr : Ca ratios from the elver mark to the otolith edge indicated that there were eels with several general categories of migratory history, including sea eels that never entered freshwater (average Sr : Ca ratios, ,6.0 × 10,3), and others that entered freshwater for brief periods but returned to the estuary or bay. This evidence of the occurrence of sea eels in this northern area indicates that Japanese eels of the Sanriku coast do not necessarily migrate into freshwater rivers during recruitment as do glass eels at the beginning of their growth phase; even those that do enter freshwater may later return to the marine environment. Thus, anguillid eel migrations into freshwater are clearly not an obligatory migratory pathway, but rather a facultative catadromy with seawater or estuarine residents as an ecophenotype. [source] Fluid flow and Al transport during quartz-kyanite vein formation, Unst, Shetland Islands, ScotlandJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2010C. E. BUCHOLZ Abstract Quartz-kyanite veins, adjacent alteration selvages and surrounding ,precursor' wall rocks in the Dalradian Saxa Vord Pelite of Unst in the Shetland Islands (Scotland) were investigated to constrain the geochemical alteration and mobility of Al associated with channelized metamorphic fluid infiltration during the Caledonian Orogeny. Thirty-eight samples of veins, selvages and precursors were collected, examined using the petrographic microscope and electron microprobe, and geochemically analysed. With increasing grade, typical precursor mineral assemblages include, but are not limited to, chlorite+chloritoid, chlorite+chloritoid+kyanite, chlorite+chloritoid+staurolite and garnet+staurolite+kyanite+chloritoid. These assemblages coexist with quartz, white mica (muscovite, paragonite, margarite), and Fe-Ti oxides. The mineral assemblage of the selvages does not change noticeably with metamorphic grade, and consists of chloritoid, kyanite, chlorite, quartz, white mica and Fe-Ti oxides. Pseudosections for selvage and precursor bulk compositions indicate that the observed mineral assemblages were stable at regional metamorphic conditions of 550,600 °C and 0.8,1.1 GPa. A mass balance analysis was performed to assess the nature and magnitude of geochemical alteration that produced the selvages adjacent to the veins. On average, selvages lost about ,26% mass relative to precursors. Mass losses of Na, K, Ca, Rb, Sr, Cs, Ba and volatiles were ,30 to ,60% and resulted from the destruction of white mica. Si was depleted from most selvages and transported locally to adjacent veins; average selvage Si losses were about ,50%. Y and rare earth elements were added due to the growth of monazite in cracks cutting apatite. The mass balance analysis also suggests some addition of Ti occurred, consistent with the presence of rutile and hematite-ilmenite solid solutions in veins. No major losses of Al from selvages were observed, but Al was added in some cases. Consequently, the Al needed to precipitate vein kyanite was not derived locally from the selvages. Veins more than an order of magnitude thicker than those typically observed in the field would be necessary to accommodate the Na and K lost from the selvages during alteration. Therefore, regional transport of Na and K out of the local rock system is inferred. In addition, to account for the observed abundances of kyanite in the veins, large fluid-rock ratios (102,103 m3fluid m,3rock) and time-integrated fluid fluxes in excess of ,104 m3fluid m,2rock are required owing to the small concentrations of Al in aqueous fluids. It is concluded that the quartz-kyanite veins and their selvages were produced by regional-scale advective mass transfer by means of focused fluid flow along a thrust fault zone. The results of this study provide field evidence for considerable Al mass transport at greenschist to amphibolite facies metamorphic conditions, possibly as a result of elevated concentrations of Al in metamorphic fluids due to alkali-Al silicate complexing at high pressures. [source] Occurrence of calcite in Sanbagawa pelitic schists: implications for the formation of garnet, rutile, oligoclase, biotite and hornblendeJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2002A. Goto Abstract The frequency of occurrence of minerals in 1876 samples of Sanbagawa pelitic schist in central Shikoku is summarized on the basis of microscopic observation accompanied, in part, by use of an electron microprobe. All samples contain quartz, plagioclase, phengite, chlorite and graphite. More than 90% of samples contain clinozoisite, titanite and apatite. Garnet is present in 95% of samples from the garnet zone, and biotite is present in 64% of samples from the albite-biotite zone. Calcite is found in about 40% of samples of the pelitic schist collected from outcrop, but occurs in 95% of the pelitic schist from drill cores. Calcite was apparently ubiquitous in the pelitic schist during the Sanbagawa metamorphism, but must have been dissolved recently by the action of surface or ground water. The mineral assemblages of the Sanbagawa pelitic schist have to be analyzed in the system with excess calcite, quartz, albite (or oligoclase), clinozoisite, graphite and fluid that is composed mainly of H2O, CO2 and CH4. In the presence of calcite, reactions that produce garnet, rutile, oligoclase, biotite and hornblende, some of which define isograds of the metamorphic belt, should be written as mixed volatile equilibria that tend to take place at lower temperature than the dehydration reactions that have been proposed. The presence of calcite in pelitic schist suggests that fluid composition is a variable as important in determining mineral assemblages as pressure and temperature. Thus Ca-bearing phases must be taken into account to analyze the phase relations of calcite-bearing pelitic schist, even if CaO content of Sanbagawa pelitic schist is low. As calcite is a common phase, the mineral assemblages of the biotite zone pelitic schist may contravene the mineralogical phase rule and warrant further study. [source] Tephrological implications of beam size,sample-size effects in electron microprobe analysis of glass shardsJOURNAL OF QUATERNARY SCIENCE, Issue 2 2001John B. Hunt Abstract This paper concerns the potential consequences of varying procedures for the determination of tephra geochemistry by electron microprobe. Application of electron probe microanalysis to tephrostratigraphical methods has increasingly facilitated the resolution and refinement of Quaternary chronology associated with records of proxy-environmental or proxy-climatic change. The geographical range over which tephras are recovered has expanded significantly with the identification and analysis of crypto (or hidden) tephras in areas far removed from tephra sources. These tephras are dominated by glass shards, which, in many distal environments, may be either small in size (,m) or may be highly pumiceous with low glass:void ratios and thin (<10 ,m) shard walls. We demonstrate that reducing the size of the electron beam used to analyse shard geochemistry cannot be used reliably to permit analysis of thin glass walls. This approach distorts the geochemical data, creating analytical differences that may generate inappropriate tephrogeochemical fingerprints. Additional distortion of the geochemical fingerprint in the form of hybrid analyses may be encountered in glass fragments containing micron-sized crystalline phases such as feldspar. Copyright © 2001 John Wiley & Sons, Ltd. [source] Carbonates in CM chondrites: Complex formational histories and comparison to carbonates in CI chondritesMETEORITICS & PLANETARY SCIENCE, Issue 4 2010Simone De LEUW Two different carbonate minerals (calcite/aragonite and dolomite) together constitute 1.4,2.8 vol% of CM chondrites. In contrast, CI chondrites contain four different carbonate minerals: calcite/aragonite, dolomite, breunnerite, and siderite. CI chondrites have abundant dolomite, a mineral that seems to be absent in the most aqueously altered CM chondrites. In this study, carbonates in seven CM chondrites (Y-791198, LaPaz Icefield 04796, Cold Bokkeveld, Nogoya, Queen Alexandra Range 93005, Allan Hills 83100, and Meteorite Hills 01070) were studied petrographically and by electron microprobe. The results indicate that carbonate formation in CM chondrites differs from that in CI chondrites and is more complex than previously recognized. Our studies of CM chondrites indicate that (1) carbonates formed on the parent asteroid in an aqueous environment that gradually changed in composition, (2) at some stage, Ca and Mg activities in the environment were high enough to form metastable dolomite, and (3) dolomites disappeared in the most aqueously altered CM chondrites. [source] Origin of kamacite, schreibersite, and perryite in metal-sulfide nodules of the enstatite chondrite Sahara 97072 (EH3)METEORITICS & PLANETARY SCIENCE, Issue 2 2010Stephen W. LEHNER We have measured concentrations of Ni, Cu, Ga, Au, Ir, Ru, and Pd in these minerals with laser ablation, inductively coupled plasma mass spectrometry (ICP-MS). We also measured their Fe, Ni, P, Si, and Co concentrations with electron microprobe. In kamacite, ratios of Ru/Ir, Pd/Ir, and Pd/Ru cluster around their respective CI values and all elements analyzed plot near the intersection of the equilibrium condensation trajectory versus Ni and the respective CI ratios. In schreibersite, the Pd/Ru ratio is near the CI value and perryite contains significant Cu, Ga, and Pd. We propose that schreibersite and perryite formed separately near the condensation temperatures of P and Si in a reduced gas and were incorporated into Fe-Ni alloy. Upon further cooling, sulfidation of Fe in kamacite resulted in the formation of additional perryite at the sulfide interface. Still later, transient heating re-melted this perryite near the Fe-FeS eutectic temperature during partial melting of the metal-sulfide nodules. The metal-sulfide nodules are pre-accretionary objects that retain CI ratios of most siderophile elements, although they have experienced transient heating events. [source] Ca,Al-rich inclusions in Rumuruti (R) chondritesMETEORITICS & PLANETARY SCIENCE, Issue 9 2008Surya Snata ROUT Many of these meteorites are breccias containing primitive type 3 fragments as well as fragments of higher petrologic type. Ca,Al-rich inclusions (CAIs) occur within all lithologies. Here, we present the results of our search for and analysis of Al-rich objects in Rumuruti chondrites. We studied 20 R chondrites and found 126 Ca,Al-rich objects (101 CAIs, 19 Al-rich chondrules, and 6 spinel-rich fragments). Based on mineralogical characterization and analysis by SEM and electron microprobe, the inclusions can be grouped into six different types: (1) simple concentric spinel-rich inclusions (42), (2) fassaite-rich spherules, (3) complex spinel-rich CAIs (53), (4) complex diopside-rich inclusions, (5) Al-rich chondrules, and (6) Al-rich (spinel-rich) fragments. The simple concentric and complex spinel-rich CAIs have abundant spinel and, based on the presence or absence of different major phases (fassaite, hibonite, Na,Al-(Cl)-rich alteration products), can be subdivided into several subgroups. Although there are some similarities between CAIs from R chondrites and inclusions from other chondrite groups with respect to their mineral assemblages, abundance, and size, the overall assemblage of CAIs is distinct to the R-chondrite group. Some Ca,Al-rich inclusions appear to be primitive (e.g., low FeO-contents in spinel, low abundances of Na,Al-(Cl)-rich alteration products; abundant perovskite), whereas others were highly altered by nebular and/or parent body processes (e.g., high concentrations of FeO and ZnO in spinel, ilmenite instead of perovskite, abundant Na,Al-(Cl)-rich alteration products). There is complete absence of grossite and melilite, which are common in CAIs from most other groups. CAIs from equilibrated R-chondrite lithologies have abundant secondary Ab-rich plagioclase (oligoclase) and differ from those in unequilibrated type 3 lithologies which have nepheline and sodalite instead. [source] In-situ doping and implantation of GaN layers with MnPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009k Sofer Abstract In this paper we present a growth of Ga1,xMnxN layers by MOVPE and ion implantation of GaN layers with Mn. The Mn concentration detected by electron microprobe and PIXE was well below the solubility limit, ranging from 0.2 to 1.1 at.%. Implanted doses of Mn ions were in the range 1x1016 -5x1016 Mn atoms.cm,2 with energy of 330 keV. The analysis of the MOVPE deposition process of Ga1,xMnxN thin films revealed an unfavorable ratio between the apparent Mn concentration in the gas phase and its doping level in the deposited layer. On the other hand, the incorporation of Mn has a positive effect on the resulting surface morphology. The optimal deposition temperature of 1000 °C was found out as a compromise between the layer quality and Mn concentration. In both in-situ grown and implanted samples, a ferromagnetic component persisting up to room temperature and a prevailing paramagnetic phase were observed. The ferromagnetic moment observed in implanted samples was influenced by free carrier concentration in GaN layers which were used for implantation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Chemical Composition of Rock-Forming Minerals in Copper,Gold-Bearing Tonalite Porphyries at the Batu Hijau Deposit, Sumbawa Island, Indonesia: Implications for Crystallization Conditions and Fluorine,Chlorine FugacityRESOURCE GEOLOGY, Issue 2 2007Arifudin Idrus Abstract Copper,gold mineralization at the world-class Batu Hijau porphyry deposit, Sumbawa Island, Indonesia, is closely related to the emplacement of multiple stages of tonalite porphyries. Petrographic examination indicates that at least two texturally distinct types of tonalite porphyries are currently recognized in the deposit, which are designated as "intermediate tonalite" and "young tonalite". They are mineralogically identical, consisting of phenocrysts of plagioclase, hornblende, quartz, biotite and magnetite ± ilmenite, which are set in a medium-coarse grained groundmass of plagioclase and quartz. The chemical composition of the rock-forming minerals, including plagioclase, hornblende, biotite, magnetite and ilmenite in the tonalite porphyries was systematically analyzed by electron microprobe. The chemical data of these minerals were used to constrain the crystallization conditions and fluorine,chlorine fugacity of the corresponding tonalitic magma during its emplacement and crystallization. The crystallization conditions, including temperature (T), pressure (P) and oxygen fugacity (fO2), were calculated by applying the hornblende,plagioclase and magnetite,ilmenite thermometers and the Al-in-hornblende barometer. The thermobarometric data indicate that the tonalite porphyries were emplaced at 764 ± 22°C and 1.5 ± 0.3 × 105 kPa. If the pressure is assumed to be lithostatic, it is interpreted that the rim of hornblende and plagioclase phenocrysts crystallized at depths of approximately 5.5 km. As estimated from magnetite,ilmenite thermometry, the subsolidus conditions of the tonalite intrusion occurred at temperatures of 540,590°C and log fO2 ranging from ,20 to ,15 (between Ni-NiO and hematite,magnetite buffers). This occurred at relatively high fO2 (oxidizing) condition. The fluorine,chlorine fugacity in the magma during crystallization was determined on the basis of the chemical composition of magmatic biotite. The calculation indicates that the fluorine,chlorine fugacity, represented by log (fH2O)/(fHF) and (fH2O)/(fHCl) in the corresponding tonalitic magma range from 4.31 to 4.63 and 3.62 to 3.79, respectively. The chlorine fugacity (HCl) to water (H2O) is relatively higher than the fluorine fugacity (HF to water), reflecting a high activity of chlorine in the tonalitic magma during crystallization. The relatively higher activity of chlorine (rather than fluorine) may indicate the significant role of chloride complexes (CuCl2, and AuCl2,) in transporting and precipitating copper and gold at the Batu Hijau deposit. [source] THE PIEDMONT WHITE MARBLES USED IN ANTIQUITY: AN ARCHAEOMETRIC DISTINCTION INFERRED BY A MINERO-PETROGRAPHIC AND C,O STABLE ISOTOPE STUDY*ARCHAEOMETRY, Issue 6 2009A. BORGHI The metamorphic rocks outcropping in the Western Alps are characterized by a great variety of white marbles, which have been poorly studied in the archaeometric field even though they have been used since antiquity. Typical examples are the Arc of August of Roman times in Susa (Piedmont, Italy) and lots of monuments and historical buildings of Turin (Italy). A multi-analytical approach based on petrographic (optical and scanning electron microscopy), electron microprobe and stable isotope analysis of Piedmont white marbles has been performed in order to carry out a detailed description, summarizing their main microtextural, mineralogical and isotopic features. Eight historical Piedmont marbles have been sampled from well-known quarry sites belonging to different metamorphic geological units of the Western Alps (Ornavasso, Crevola, Pont Canavese, Foresto, Chianocco, Prali, Brossasco and Garessio marbles). Their different metamorphic conditions, ages and structural evolution allowed us to draw a discriminative flowchart based on microscopic and minero-chemical data. [source] Chemical U-Th-Pb Monazite Dating of Deformations versus Pluton Emplacement and the Proterozoic History of the Arkansas River Region, Colorado, USAACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009Hui CAO Abstract: Five lengthy periods involving multiple phases of cordierite and andalusite growth were revealed by detailed studies of foliation inflection/intersection axes (FIA) preserved in porphyroblasts in schists from the Arkansas River region in Colorado, USA. The regionally consistent character of the succession of five different FIA trends enabled the relative timing of each FIA with respect to the next to be determined. The FIA succession from first to last is: FIA 1 trending W-E, FIA 2 trending SSW-NNE, FIA 3 trending NNW-SSE, FIA 4 trending NW-SE and FIA 5 trending SW-NE. For four of the FIA sets, samples were found containing monazite grains preserved as inclusions. These were dated on an electron microprobe. The ages obtained concur exactly with the FIA succession, with FIA 1 at 1506 ± 15 Ma, FIA 2 at 1467 ± 23 Ma, FIA 3 at 1425 ± 18 Ma, FIA 4 not dated and FIA 5 at 1366 ± 20 Ma. These ages are directly reflected in a succession of plutons in the surrounding region dated by other isotopic approaches, suggesting that deformation, metamorphism and pluton emplacement occurred together episodically, but effectively continuously, for some 140 Ma. [source] Special Xenoliths in an Aegirine-Augite Syenite Porphyry in Liuhe, Yunnan, China: Discovery and ImplicationsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Xianfan LIU Abstract: Three special types of xenoliths have recently been found in an aegirine-augite syenite porphyry in Liuhe, Yunnan, China. Petrographical, petrochemical, electron microprobe, and scanning electron microscopy studies indicate that pure calcite xenocrysts and quartz-bearing topaz pegmatite xenoliths result from the degassing of mantle fluids during their migration, and that black microcrystalline iron-rich silicate-melt xenoliths are the product of the extraction of mantle fluids accompanying degassing and are composed dominantly of quartz, chlorite, and iron-rich columnar and sheet silicate minerals with characteristic minerals, such as native iron, apatite, and zircon. According to the bulk-rock chemical and mineral compositions and crystallization states, the microcrystalline melt xenoliths are not the product of conventional magmatism, and especially the existence of native iron further proves that the xenoliths were mantle fluid materials under reduction or anoxic conditions. The study of the special xenoliths furnishes an important deep-process geochemical background of polymetallic mineralization in different rocks and strata in the study area. [source] Tin(II) Doped Anatase (TiO2) Nanoparticles: A Potential Route to "Greener" Yellow PigmentsCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2009Moumita Ghosh Dr. Abstract Benign by design: Tin(II) doped anatase TiO2 nanoparticles, a potential candidate as environmentally benign yellow pigments, have been synthesized. The presence of Sn2+ in anatase structure has been confirmed by various analytical techniques including optical and 119Sn Mössbauer spectroscopy. During our exploration of compounds in the SnII -TiIV -O system, we discovered that hydrolysis of titanium alkoxide solution in the presence of SnII salts resulted in stable deep-yellow colored anatase nanoparticles. The samples were characterized by X-ray powder diffraction, electron microprobe, thermal analysis, transmission electron microscopy, and 119Sn Mössbauer spectroscopy. Mössbauer data of the yellow colored samples showed the presence of both SnII and SnIV in a distorted environment as expected in the anatase structure. It is suggested that the cationic charge imbalance is compensated by oxygen vacancies and/or hydroxyl groups as evidenced by Mössbauer data which show two types of SnII environments. When heated in air to 300,°C the samples changed color to completely white and 119Sn Mössbauer data of these samples showed only the presence of SnIV. These observations indicate that the origin of the yellow color in our Sn doped anatase nanoparticles arises from filled Sn 5s states just above the O 2p band, thus decreasing the band gap. The SnII doped anatase TiO2 nanoparticles reported here can potentially lead to environmentally benign yellow pigments. The simplistic nature of the synthetic procedure could easily be adapted to large-scale industrial manufacture. [source] | |||||||||||||||||||