Metamorphic Evolution of the Middle Seve Nappe in the Snasahögarna area, Scandinavian Caledonides

In the Snasahögarna area, situated in the central Scandinavian Caledonides, the Middle Seve Nappe Complex mainly consists of pelitic gneisses. Within these garnet and kyanite bearing gneisses the first discovery of metamorphogenic diamond in Sweden has been confirmed by micro raman spectroscopy. The garnet hosted diamond together with associated carbonate and fluid inclusions were deposited by carbon saturated fluids at a pressure exceeding 3.1 GPa. The peak mineral assemblage, Phg Mgs-Sid Grt Ky Jd Rt Coe (Dia), is constrained by microscopic observations and thermodynamic phase equilibrium modeling. Modeled garnet cores equilibrated at c. 750°C and 1.3 GPa together with phengite rims. This early exhumation stage was followed by heating reaching a peak temperature of 880-910°C at 1.05-1.18 GPa. Partial melting following the increased temperature is confirmed by anatectic segregations and microscopic melt related textures in the paragneiss. A fluid restricted environment at the late high temperature stage is inferred from mineral textures, mineral chemistry and low bulk rock loss on ignition. This is in agreement with thermodynamic models

Metamorphic Evolution of the Middle Seve Nappe in the Snasahögarna area, Scandinavian Caledonides

In the Snasahögarna area, situated in the central Scandinavian Caledonides, the Middle Seve Nappe Complex mainly consists of pelitic gneisses. Within these garnet and kyanite bearing gneisses the first discovery of metamorphogenic diamond in Sweden has been confirmed by micro raman spectroscopy. The garnet hosted diamond together with associated carbonate and fluid inclusions were deposited by carbon saturated fluids at a pressure exceeding 3.1 GPa. The peak mineral assemblage, Phg Mgs-Sid Grt Ky Jd Rt Coe (Dia), is constrained by microscopic observations and thermodynamic phase equilibrium modeling. Modeled garnet cores equilibrated at c. 750°C and 1.3 GPa together with phengite rims. This early exhumation stage was followed by heating reaching a peak temperature of 880-910°C at 1.05-1.18 GPa. Partial melting following the increased temperature is confirmed by anatectic segregations and microscopic melt related textures in the paragneiss. A fluid restricted environment at the late high temperature stage is inferred from mineral textures, mineral chemistry and low bulk rock loss on ignition. This is in agreement with thermodynamic models

Metamorphic evolution of the Seve Nappe Complex in the Snasahögarna area, Swedish Caledonides abstract /

Tyt. z nagłówka.Bibliogr. s. 522.The Middle Seve Nappe in the Snasahögarna mountains, western Jämtland, Sweden, is composed of high grade metamorphic rocks emplaced in far-travelled nappes. The investigation of these paragneisses, derived from the Baltica margin, can contribute information about the subduction and exhumation processes, which controlled the formation of the Seve Nappe Complex (SNC) in the Scandinavian Caledonides. Recent studies in other parts of the orogen have shown that the rocks of the SNC likely have experienced pressures higher than what was previously described (Janák et al. 2012, Klonowska et al. in press). These latest PT studies along with geochronological dates available suggest that the collision between Baltica and Laurentia has commenced c. 30 m.y. earlier (at ca. 450 Ma) than generally accepted. Samples of kyanite- and garnet-bearing meta-sediments were collected along a profile at Tväraklumparna (Snasahögarna area) and investigated in thin sections using light microscopy followed by BSE imaging, WDS analysis and Raman spectroscopy. Preliminary results show that dominant garnet reaches up to 7 mol. % of Grs content. The garnet commonly contains inclusions of quartz surrounded by radial cracks and grains of polycrystalline quartz. More rare are inclusions of kyanite and white mica with a Si-contents reaching 3.34 a.p.f.u. Detailed studies of garnet revealed dense areas of micrometer size inclusions exhibiting negative crystal shape present in the core regions. Raman studies suggest these inclusions are at least partly formed by microdiamond. Textural evidence of peak metamorphic conditions reaching the stability field of coesite together with microdiamonds preserved in garnet cores confirms that the Seve Nappe crustal rocks of the Snasahögarna area has undergone ultrahigh pressure metamorphism.Dostępny również w formie drukowanej.KEYWORDS: western Jämtland, metamorphic rocks, SNC, Scandinavian Caledonides

Metamorphic Evolution of the Middle Seve Nappe in the Snasahögarna area, Scandinavian Caledonides

In the Snasahögarna area, situated in the central Scandinavian Caledonides, the Middle Seve Nappe Complex mainly consists of pelitic gneisses. Within these garnet and kyanite bearing gneisses the first discovery of metamorphogenic diamond in Sweden has been confirmed by micro raman spectroscopy. The garnet hosted diamond together with associated carbonate and fluid inclusions were deposited by carbon saturated fluids at a pressure exceeding 3.1 GPa. The peak mineral assemblage, Phg Mgs-Sid Grt Ky Jd Rt Coe (Dia), is constrained by microscopic observations and thermodynamic phase equilibrium modeling. Modeled garnet cores equilibrated at c. 750°C and 1.3 GPa together with phengite rims. This early exhumation stage was followed by heating reaching a peak temperature of 880-910°C at 1.05-1.18 GPa. Partial melting following the increased temperature is confirmed by anatectic segregations and microscopic melt related textures in the paragneiss. A fluid restricted environment at the late high temperature stage is inferred from mineral textures, mineral chemistry and low bulk rock loss on ignition. This is in agreement with thermodynamic models

Quenched primary melt in Ramlat as Sahmah 517 – Snapshot of ureilite anatexis in the early solar system

Ureilites are the second largest group of achondrite meteorites but consensus is still lacking on the nature of their precur- sors, melting processes, and the genetic relationship between monomict ureilites and brecciated ureilites. The recently found ureilite Ramlat as Sahmah 517 is of special interest in this context. This meteorite lacks shock features in its primary silicates and belongs to a rare augite- and chromite-bearing subset of the monomict ferroan ureilites. It hosts abundant intergranular glass veinlets speckled with pyroxene and metal globules. Detailed petrographic investigations show that the Si-Al-rich glass represents quenched anatectic melt that was present prior to formation of the reduced olivine rims by incomplete low-pressure equilibration (smelting) of carbon and silicates. The melt facilitated smelting which, along with rapid crystallization of sec- ondary pyroxene, modified the originally trachyandesitic melt. Melt-silicate equilibrium preceding these events is constrained by modelling using MELTS and the first reported in-situ measurements of LREE-enriched glass that is largely complementary to the depleted mafic silicates in monomict ureilites. The inferred major element composition of the partial melt that formed in RaS 517 is similar to that of trachyandesite in Almahata Sitta but RaS 517 lacks phosphates which are abundant in the Alma- hata Sitta trachyandesite and in alkali-rich feldspathic clasts in polymict ureilites. The LREE-depletion in the dominant monomict ferroan ureilite population can be explained by the formation of melt fractions similar to the glass in RaS 517 after initial rapid melting of phosphates. These finds provide evidence for a genetic relationship between ferroan ureilites and lithologies similar to the Almahata Sitta trachyandesite and further suggest that these ureilites formed by partial melting of P- and alkali-rich precursors with trace element concentrations similar to equilibrated ordinary chondrites. Quenched Si-Al-rich glass also occurs in magnesian ureilites but has lower concentrations of alkalis and LREE-depleted trace element signatures which can reflect more depleted compositions at the onset of partial melting. The evidence presented here favors a scenario in which the primary ureilite differentiation was driven by gradual heating from radioactive decay with resulting tem- peratures (>1100 C) being maintained until disruption of the ureilite parent asteroid

Primary crystallization and partial remelting of chondrules in the protoplanetary disk: Petrographic, mineralogical and chemical constraints recorded in zoned type-I chondrules

Chondrules from unequilibrated ordinary chondrites are among the oldest Solar system materials and preserve mineralogical, chemical and isotopic signatures that link them to their primary formation mechanisms and environments in the early Solar System. Some chondrules record features indicating modifications by high- to low-temperature processes throughout their residence time in the protoplanetary disk. Chondrules that were partially modified after their primary formation record chemical, isotopic and textural information on their initial formation conditions and subsequent reprocessing that are essential to reconstruct their formation environments and interpret the ages recorded by individual chondrules correctly. The detailed textural and major, minor and trace element analyses of two type-I chondrules from the low petrologic type ordinary chondrites MET 00526 and MET 00452 (L/LL3.05) reveal complex chemical and textural systematics bearing testimony of their multi-stage high temperature evolution, including reheating and partial remelting, in the evolving protoplanetary disk prior to accretion into their parent bodies. During primary crystallization of chondrule MET00526_Ch43, mineral growth, including incipient formation of feldspar in the outer parts of the chondrule, led to the fractionation of melt, eventually resulting in a chemical gradient in the mesostasis. During a later punctuated reheating that ultimately led to partial remelting of the outer parts of the chondrule, mesostasis and low-Ca pyroxene remelted partially. This partial remelting enhanced the chemical differences within the mesostasis and led to the formation of two chemically distinct mesostases in the inner and the outer zone of the chondrule with almost complementary abundances of Rb, Na, K, Ba, Sr and Eu. The calculated bulk mesostasis composition reveals chondritic relative abundances of these elements in the bulk chondrule with a slight depletion of the most volatile elements. Chemical and textural observations further indicate that this disequilibrium remelting occurred under more reducing conditions than the primary melting event preserved in the chondrule centre, allowing for the crystallization of a second generation of low-Ca pyroxene in the outer parts of the chondrule. Very similar processes are also recorded in chondrule MET00452_Ch22 with the degree of remelting being more extensive. A previously determined young 26Al-26Mg age of ∼3 Ma after CAIs determined for chondrule MET00452_Ch22 dates the time of the chondrule remelting rather than its primary formation. This is evidence for a late thermal event in the protoplanetary disk and generally indicates that multiple, distinct thermal pulses occurred in the chondrule forming region of the protoplanetary disk throughout the time of chondrule formation. The nonconcentric secondary outer zone around a spherical inner zone may indicate a directed heat source as the cause of partial remelting and reprocessing of primary chondrules.ISSN:0016-7037ISSN:1872-953

X-ray Photoelectron Spectroscopy of Ti3AlC2, Ti3C2Tz, and TiC Provides Evidence for the Electrostatic Interaction between Laminated Layers in MAX-Phase Materials

The inherently nanolaminated Ti3AlC2 is one of the most studied MAX-phase materials. MAX-phases consists of two-dimensional Mn+1Xn-layers (e.g., T3C2-layers) with strong internal covalent bonds separated by weakly interacting A-layers (e.g., Al-layers), where the repetitive stacking of the Mn+1Xn-layers and the A-layers suggests being the foundation for the unusual but attractive material properties of the MAX-phases. Although being an important parameter, the nature of the bonding between the Mn+1Xn-layers and the A-layers has not yet been established in detail. The X-ray photoelectron spectroscopy data presented in this paper suggest that the weak interaction between the Ti3C2-layers and the Al-layers in Ti3AlC2 is through electrostatic attraction facilitated by a charge redistribution of the delocalized electrons from the Ti3C2-layers to the Al-layers. This charge redistribution is of the same size and direction as between Ti atoms and Al atoms in TiAl alloy. This finding opens up a pathway to predict and improve MAX-phase materials properties through A-layer alloying, as well as to predict new and practically feasible MXene compounds.Funding Agencies|Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [EM160004]; Swedish Research Council (VR)Swedish Research Council [6422013-8020]; KAW Fellowship/Scholar program</p

Meteorite terrestrial ages in Oman based on gamma spectrometry and sediment dating, focusing on the Ramlat Fasad dense collection area

We combine the search for young meteorites in the Omani-Swiss collection (~1140 fall events collected 2001–2018) using 22Na and 44Ti with luminescence and 14C sediment ages from the Ramlat Fasad (RaF) dense collection area (DCA) of Oman to obtain combined terrestrial ages and maximum accumulation times, and test whether the proportion of young meteorites is consistent with the models of meteorite flux and weathering. Gamma-ray spectrometry data for 22Na show that two (0.17%) of the meteorites in the collection fell during the 20 yr preceding this study, consistent with the rates of meteorite accumulation. In the RaF DCA, meteorites are found on Quaternary to Neogene sediments, providing constraints for their maximum terrestrial ages. 44Ti activities of the RaF 032 L6 strewn field found on deflated parts of active dunes indicate an age of 0.2–0.3 ka while dune sand optically stimulated luminescence ages constrain an upper age of 1.6 ka. Extensive sediment dating using luminescence methods in the RaF DCA area showed that all other meteorite finds were made on significantly older sediments (>10 ka). Dense accumulations of meteorites in RaF are found on blowouts of the Pliocene Marsawdad formation. Our combined results show that the proportion of meteorites with low terrestrial ages is low compared to other find areas, consistent with the previously determined high average terrestrial age Oman meteorites and significantly older than suggested by models of exponential decay. Oman meteorites may commonly have been buried within dunes and soils over extended periods, acting as a temporary protection against erosion

Formation of RuO(OH)(2) on RuO2-Based Electrodes for Hydrogen Production

The catalytic and durable electrode coating of ruthenium dioxide (RuO2), applied on nickel (Ni) substrates, is today utilized as electrocatalytic cathodes for hydrogen production, e.g., in the chlor-alkali process and alkaline water electrolysis. The drawback is, however, the sensitivity to reverse currents obtained during power shutdowns, e.g., at maintenance, where the RuO2-based electrodes can be severely damaged unless polarization rectifiers are employed. Through the material characterization techniques X-ray diffraction and X-ray photoelectron spectroscopy, we can now reveal that RuO2 coatings, when exposed to hydrogen evolution at industrially relevant conditions, transforms into ruthenium oxyhydroxide (RuO(OH)(2)). The study further shows that as the hydrogen evolution proceeds the formed RuO(OH)(2) reduces to metallic ruthenium (Ru)