Non‐equilibrium concepts lead to a unified explanation of the formation of chondrules and chondrites

Abstract— Calculations of the formation of seven types of chondrules in Semarkona from a gas of solar composition were performed with the FACT computer program to predict the chemistries of oxides (including silicates), developed by the authors and their colleagues. The constrained equilibrium theory was used in the calculations with two nucleation constraints suggested by nucleation theory. The first constraint was the blocking of Fe and other metal gaseous atoms from condensing to form solids or liquids because of very high surface free energies and high surface tensions of the solid and liquid metals, respectively. The second constraint was the blocking of the condensation of solids and the formation of metastable liquid oxides (including silicates) well below their liquidus temperatures. Our laboratory experiments suggested subcooling of type IIA chondrule compositions of 400 degrees or more below the liquidus temperature. The blocking of iron leads to a supersaturation of Fe atoms, so that the partial pressure of Fe (p_Fe) is larger than the partial pressure at equilibrium (p_Fe(eq)). The supersaturation ratio S = p_Fe/p_Fe(eq) becomes larger than 1 and increases rapidly with a decrease in temperature. This drives the reaction Fe + H₂O ? H₂ + FeO to the right. With S = 100, the activity of FeO in the liquid droplet is 100 times as large as the value at equilibrium. The FeO activities are a function of temperature and provide relative average temperatures of the crystallization of chondrules. Our calculations for the LL3.0 chondrite Semarkona and our study of some non‐equilibrium effects lead to accurate representations of the compositions of chondrules of types IA, IAB, IB, IIA, IIAB, IIB, and CC. Our concepts readily explain both the variety of FeO concentrations in the different chondrule types and the entire process of chondrule formation. Our theory is unified and could possibly explain the formation of chondrules in all chondritic meteorites as well as provide a simple explanation for the complex chemistries of chondrites, and especially for type 3 chondrites.     

(Ruby--Sapphire)--Chromian Mica--Tourmaline Rocks from Westland, New Zealand

Boulders of the assemblage ruby—sapphire corundum, chromianmuscovite, margarite, tourmaline (chromian chlorite, Zn—Mnchromite and Mn—Ti magnetite) occur in glacial moraineand rivers of north Westland, South Island of New Zealand. Thelocation, Cr-rich composition of the boulders and the presenceof rare serpentinite rinds indicate that they are derived fromultramafic rocks (Pounamu Ultramafics) that occur within AlpineSchist of the Southern Alps. The largest sample is progressivelyzoned outwards from a corundum—margarite core, throughan intermediate zone of Cr-muscovite, to an outer zone of Cr-chloritethat is in contact with serpentinite. Most finds consist oferosion-resistant corundum-rich cores. In the corundum, Cr₂O₃content ranges from 0.5 to 13%, with red coloration becomingmore intense with increasing Cr. In addition to the dominantCr³⁺ Al³⁺ substitution, those of (Fe, V)³⁺ Cr³⁺ and (Ti⁴⁺+Fe²⁺) 2Cr³⁺ result in spectacular colour zoning from colourlessto deep ruby red-carmine and pale blue to dark blue—violet.Corundum has grown by replacement of the micaceous matrix thatconsists of chromian muscovite (0.10–4.10% Cr₂O₃) andchromian margarite (0.46–1.20% Cr₂O₃). Both micas containa significant paragonite component (up to 21.5% in muscoviteand up to 40.8% in margarite). Late phase muscovite is Ba richwith up to 4.77% BaO, and margarite has up to 0.66% SrO. Tourmalineoccurs as veins, vein outgrowths and larger poikilitic crystalsthat replace the mica matrix. Chromium content ranges between0.82 and 3.6% Cr₂O₃. High bulk rock Al (up to 78% Al₂O₃), K,Ca, Cr and Na, and low Si (14.5–23.1% SiO₂), suggest thatthe corundum—Cr-silicate rocks are the products of extrememetasomatic alteration of quartzofeldspathic schist enclavesin serpentinite. Isocon analysis indicates that conversion ofthe schist to the micaceous matrix of the corundum rocks involvesconservation of Ca, Al, K, volatiles and Sr, a mass loss of59% and a volume reduction of 69% consequent on removal of 70–80%Si and all other elements (most >80%), with enrichment ofbetween 900 and 1800% Cr. The formation of corundum from themica matrix involved a further mass—volume reduction anddecrements in Si, Ca, K, volatiles and Sr from reaction sites.Concentric mineral zonation in single rock samples and zoning—replacementin minerals, e.g. Cr in corundum and chromite, Ti, Fe²⁺ in corundum,Ba in muscovite, Sr in margarite, and Mn and Zn in chromiteand magnetite, imply element redistribution during metasomatism.Experimental reaction between quartzofeldspathic schist andserpentinite at 450C and 2 kbar produced reaction sequencescontaining newly formed Ca-plagioclase—phlogopitic micachloriteand muscovite—chlorite that in terms of composition areanalogous with the observed (corundum—margarite)—muscovite—chloritezonation. The temperature of metamorphism of garnet zone rocks(45020C) that contain the corundum—Cr-silicate rocksis well below that of the breakdown of muscovite and margariteto form corundum and indicates the importance of fluid composition,particularly the cation—hydrogen variables a_Ca²⁺/H⁺, aK⁺/H₊and a_S1O2. Introduction of boron into the schist (from serpentinite),and boron released from the breakdown of original tourmalinein the schist, resulted in tourmaline veining and reaction ofthe mica matrix to form tourmaline that invoved both a massand volume increase and addition of Fe, Mg together with B. KEY WORDS: corundum—Cr-silicate rocks; metasomatism; New Zealand; Southern Alps ^*Corresponding author.     

High-resolution shallow seismic identification of gas escape features in the sediments of Loch Tay, Scotland: tectonic and microbiological associations

High-resolution seismic reflection profiles (3·5 kHz) have revealed the presence of extensive interstitial gas accumulation within the sedimentary sequences of Loch Tay, Scotland, as identified by acoustic turbidity masking the seismic stratigraphy. Within the central section of the loch, in the deepest water area directly above the zone of the seismically active Loch Tay Fault, focused flows of gas through the sediment pile to the loch bed via chimneys and pockmarks, together with gas seeps within the water column, have been identified. Microbiological observations indicate that the gas is biogenic CH₄, produced by both chemoautotrophic (which use CO₂ as a source of carbon and H₂ as a source of energy) and aceticlastic species (which use acetate as a source of carbon and energy) of methanogens in the fine-grained, organic rich deposits that have been focused into the zone of accumulation in the deep central part of the loch. The spatial distribution of the gas escape features suggests that earthquake movements along the Loch Tay Fault are responsible for facilitating focused gas escape in this part of the loch, by the creation of new pathways and conduits through the sediment pile, along which gas can migrate upwards and exit into the water column. Relict pockmarks and associated chimneys identified in the seismic records indicate that gas escape has been taking place since Pleistocene times though the precise timings cannot be ascertained. This is the first time that such features have been reported from a lake in the UK.     

Determination of Fluorine in Eighty International Geochemical Reference Samples by Proton Induced Gamma Ray Emission Spectrometry (PIGE)

Fluorine content has been determined non destructively in eighty international geochemical reference samples (GRS) including rocks, soils, sediments, minerals and ores, by proton induced gamma ray emission spectrometry (PIGE) using the nuclear reaction ¹⁹F(p,αγ) ¹⁶O. Under our operating conditions, the detection limit is around 25 ppm. Our analytical results are compared with the presently preferred values when available or with other published data. The general agreement between this work and reported values is reasonably good. The present paper includes results on several GRS for which existing data are rather scarce or even inexistant.     

Petrology,chemistry, and isotopic compositions of the lunar highland regolith breccia Dar al Gani 262

Abstract— Lunar meteorite Dar al Gani 262 (DG 262)—found in the Libyan part of the Sahara—is a mature, anorthositic regolith breccia with highland affinities. The origin from the Moon is undoubtedly indicated by its bulk chemical composition; radionuclide concentrations; noble gas, N, and O isotopic compositions; and petrographic features. Dar al Gani 262 is a typical anorthositic highland breccia similar in mineralogy and chemical composition to Queen Alexandra Range (QUE) 93069. About 52 vol% of the studied thin sections of Dar al Gani 262 consist of fine-grained(100 μm) constituents, and 48 vol% is mineral and lithic clasts and impact-melt veins. The most abundant clast types are feldspathic fine-grained to microporphyritic crystalline melt breccias (50.2 vol%; includes recrystallized melt breccias), whereas mafic crystalline melt breccias are extremely rare (1.4 vol%). Granulitic lithologies are 12.8 vol%, intragranularly recrystallized anorthosites and cataclastic anorthosites are 8.8 and 8.2 vol%, respectively, and (devitrified) glasses are 2.7 vol%. Impact-melt veins (5.5 vol% of the whole thin sections) cutting across the entire thin section were probably formed subsequent to the lithification process of the bulk rock at pressures below 20 GPa, because the bulk rock never experienced a higher peak shock pressure. Mafic crystalline melt breccias are very rare in Dar al Gani 262 and are similar in abundance to those in QUE 93069. The extremely low abundance of mafic components and the bulk composition may constrain possible areas of the Moon from which the breccia was derived. The source area of Dar al Gani 262 must be a highland terrain lacking significant mafic impact melts or mare components. On the basis of radionuclide activities, an irradiation position of DG 262 on the Moon at a depth of 55–85 g/cm³and a maximum transit time to Earth <0.15 Ma is suggested. Dar al Gani 262 contains high concentrations of solar-wind-implanted noble gases. The isotopic abundance ratio ⁴⁰Ar/³⁶Ar < 3 is characteristic of lunar soils. The terrestrial weathering of DG 262 is reflected by the occurrence of fractures filled with calcite and by high concentrations of Ca, Ba, Cs, Br, and As. There is also a large amount of terrestrial C and some N in the sample, which was released at low temperatures during stepped heating. High concentrations of Ni, Co, and Ir indicate a significant meteoritic component in the lunar surface regolith from which DG 262 was derived.     

UNDERGROUND GRAVITY SURVEY IN ALPINE REGIONS*

An underground gravity study was carried out under extreme conditions of the Alpine regions. The lead–zinc mine Bleiberg, Carinthia, was selected as an example to show the possibilities and limitations of the subsurface gravity method. For in situ density determinations, gravity measurements were made in two vertical mine shafts passing through Triassic sedimentary rocks of the Bleiberg Unit. The main prblem in gravity data reduction in extremely rugged topography is the accurate calculation of the terrain effect on underground stations. A general discussion of the various corrections required for the gravity measurements in the mine is presented. The mean interval densities in the two shafts, in limestone, dolomite, and schists formations, were determined as 2.76 and 2.77 g/cm³, respectively, with an accuracy of better than 0.01 g/cm³ for a depth interval of 50 m. The interval densities provide valuable information about the lithological and structural changes in the shaft surroundings and also agree well with the representative hand sample densities. In the second part, the applications of subsurface horizontal gravity surveys in exploration are discussed. Since the influence of topography is less underground because of the greater distance to the surface, subsurface surveys have definite advantages over surface surveys and can be very helpful in locating anomalous density zones in the mines. An example of gravity survey with a station spacing of 10 m at a depth of about 540 m is presented.     

The Quadrennial Ozone Symposium 2016

<正>1.Overview The 2016 Quadrennial Ozone Symposium(QOS-2016)was held on 4–9 September 2016 in Edinburgh,UK.The Symposium was organized by the International Ozone Commission(IO3C),the NERC Centre for EcologyHydrology and the University of Edinburgh,and was co-sponsored by the International Union of Geodesy and Geophysics,the International Association of Meteorology and Atmospheric     

An interdisciplinary study of weathering effects in ordinary chondrites from the Acfer region,Algeria

Abstract— Weathering effects on meteorite finds from the Acfer region were studied by various analytical techniques and in dependence on the depth of sampling. In thin sections of weathered meteorites, weathering effects usually decrease from the outside to the interior of the meteorite. The results of evolved gas analysis indicate that variation in weathering between surface and core is not significant in respect to the formation of Fe-oxyhydroxides. The secondary alteration effects in the noble gases are distributed unevenly throughout the specimens, as seen in the nonsystematic differences observed for the heavy noble gases. Chemical analyses show significant enrichment of Ba and Sr in the outer parts of the weathered samples due to element contamination through aqueous solution. Iron, Ni, and Co are partly flushed from the system as the metal oxidation proceeds. Oxygen isotopes show increases in δ¹⁸O and δ¹⁷O with increasing terrestrial age. For a set of H3 chondrites, the degree of weathering determined from the water content was correlated with terrestrial ages and is discussed with respect to possible weathering mechanisms.