661 research outputs found
1.90-1.88Ga arc magmatism of central Fennoscandia: geochemistry, U-Pb geochronology, Sm-Nd and Lu-Hf isotope systematics of plutonic-volcanic rocks from southern Finland
The earliest Svecofennian magmatism in southern Finland has been dated at 1.90-1.88Ga. As an example of this, the OrijĂ€rvi (ca. 1.89Ga) and Enklinge (ca. 1.88Ga) volcanic centres comprise bimodal plutonic batholiths surrounded by volcanic rocks of comparable ages and chemical compositions. Here, we report geochemical and Sm-Nd isotope data from intrusive and extrusive samples, combined with zircon U-Pb and Lu-Hf isotopes for granodiorites from both study areas. The samples range from gabbros to granites and indicate a subduction-related continental margin setting. The zircons from the OrijĂ€rvi granodiorite define an age of 1892±4Ma whereas the Enklinge granodiorite yields an age of 1882±6Ma. Several inherited ages of 2.25-1.95Ga as well as younger ages of 1.86-1.80Ga were found in the Enklinge granodiorite. The initial ΔNd values from the mafic rocks from both locations fall in the range +1.1 to +2.9 whereas the felsic rocks exhibit initial ΔNd values of -0.4 to +1.2. The magmatic zircons from the OrijĂ€rvi and Enklinge granodiorites show average initial ΔHf values of -1.1 (at 1892Ma) and zero (at 1882Ma), respectively, each with a spread of about 7 Δ-units. The initial ΔHf values for the inherited zircons from Enklinge range from +3.5 to +7.6 with increasing age. The Sm-Nd data indicate that the mafic rocks were derived from a âmildly depletedâ mantle source while the felsic rocks show larger crustal contribution. Also, the variation in ΔHf values indicates minor mixing between mildly depleted mantle derived magmas and crustal sources. U-Pb ages and Hf isotopes for inherited zircons in the Enklinge granodiorite suggest the presence of juvenile Svecofennian âproto-crustâ at depth
A 1.85 Ga volcanic arc offshore the proto-continent Fennoscandia in southern Sweden
The Fröderyd Group forms part of the Vetlanda-Oskarshamn belt (also known as the Oskarshamn-Jönköping Belt), which is a piece of Palaeoproterozoic crust that is completely encapsulated by 1.81â1.77 Ga granitoids of the Transscandinavian Igneous Belt in the southern part of the Fennoscandian Shield. New U-Pb zircon data from a felsic metavolcanic rock in the Fröderyd Group have been acquired using LA-ICP-MS single collector. The age is determined to 1853 ± 11 Ma. The Fröderyd Group is interpreted to represent a volcanic arc that was located southwest of the margin to the proto-continent Fennoscandia. Tonalitic magma, identified in the Eksjö-BĂ€ckaby regions, formed the middle crust in this arc complex and intruded the volcanic arc rocks at ca. 1.83â1.82 Ga. When this arc complex gradually approached the margin to the proto-continent Fennoscandia, parts of it were uplifted above sea level and initiated lacustrine sedimentation in restricted basins, which now are found in the Vetlanda region. Parallel with the development of this arc complex, 1.86â1.85 Ga granitoids intruded the margin to the proto-continent Fennoscandia and 1.87â1.86 Ga clastic metasedimentary rocks in the VĂ€stervik area in an Andean-type active continental margin.It can be concluded that the Vetlanda and VĂ€stervik sedimentary basins formed in two completely different geological environments during two separate events. The VĂ€stervik sediments formed along the margin to the proto-continent Fennoscandia before the Fröderyd arc system had developed while the Vetlanda sediments formed in a post-arc environment outboard to the southwest of the margin to the proto-continent Fennoscandia. It is suggested that the mafic volcanic rocks close to the lake Nömmen should be excluded from the Vetlanda supergroup and instead be related in time to the Fröderyd Group. This paper presents an interpretation of the tectonic evolution including volcanic arc and rifted volcanic arc during the 1.87 to 1.77 Ga time span with relevance to the evolution of the active southwestern margin of the proto-continent Fennoscandia depicted as a sequence of schematic profiles.</p
The lead and copper isotopic composition of copper ores from the Sierra Morena (Spain)
The paper presents lead and copper isotope analyses of 51 copper ore samples from the Sierra Morena, South of Spain. They are from ancient mines of the Iberian Peninsula collected by Claude Domergue during various field campaigns in the central Sierra Morena from 1965 to 1975. Most samples consist of copper oxide minerals such as malachite, azurite and chrysocolla and stem from the surficial sections of the ore deposits. The aim of the study was to supplement the existing reference data bank on lead isotopic compositions of ancient copper mines from the Iberian Peninsula. This is particularly important for the Sierra Morena for which data exist mostly for lead-zinc but not for copper ores. The lead isotope ratios range from 18.165 to 19.712 (206Pb/204Pb), 0.797 to 0.859 (207Pb/206Pb) and 1.955 to 2.108 (208Pb/206Pb). Two separate fields can be distinguished with a major field intermediate between the ore deposits from SW and SE Spain and a second at higher 208Pb/206Pb values. Copper isotopes were analysed additionally to provide further constraints for provenance studies. The copper isotope ratios δ65Cu of the copper oxide samples are mostly positive and higher on average than those of sulphide minerals. They are a potential tool to distinguish between either sulphide ore or oxide ore deposit derived artefacts.En este artĂculo, presentamos los resultados de los anĂĄlisis isotĂłpicos (plomo y cobre) llevados a cabo sobre 51 muestras de mineral de cobre de Sierra Morena, Sur de España. Las muestras provienen de minas antiguas de la PenĂnsula IbĂ©rica, que habĂan sido recogidas por Claude Domergue en el curso de sus prospecciones en Sierra Morena central, entre 1965 y 1975. La mayorĂa de las muestras consiste de minerales de Ăłxido de cobre como malaquita, azurita y crisocola que se encuentran en la superficie de los depĂłsitos. El objetivo de este estudio es de contribuir a la base hoy disponible de datos de isĂłtopos de plomo de las antiguas minas de cobre en la PenĂnsula IbĂ©rica. Este objetivo es particularmente importante puesto que la mayorĂa de los datos publicados de Sierra Morena se refieren a minerales de plomo-zinc. Las proporciones de isĂłtopos de plomo varĂan entre 18.165 y 19.713 206Pb/204Pb, de 0.797 a 0.859 207Pb/206Pb, y de 1.955 a 2.108 208Pb/206Pb. Se pueden distinguir dos zonas independientes: una zona principal que se sitĂșa entre los depĂłsitos de España del sudoeste y sudeste y una segunda zona con las proporciones de isĂłtopos de plomo mĂĄs altas. AdemĂĄs, los isĂłtopos del cobre fueron analizados para suplir restricciones adicionales en los estudios de proveniencia. Las proporciones de isĂłtopos de cobre, δ65Cu/63Cu, fueron analizadas en los Ăłxidos de cobre y son en la mayor parte positivas y mas altas en medio que las proporciones δ65Cu de los sulfuros de cobre. Los resultados presentan un instrumento eficiente para distinguir los artefactos elaborados de minerales de sulfuros de cobre o de minerales de Ăłxido de cobre
Lithium isotopes in fluid inclusions as tracers of crustal fluids: An exploratory study
Lithium isotopes are extensively used to trace fluid migration and fluid-rock interactions in the shallow Earth's crust. Although, Li isotope systematics might give important information about deep crustal fluids, this stable isotope system remains surprisingly under exploited in fluid inclusions. Here, twenty-three samples from a variety of deep environments, from diagenetic, metamorphic to magmatic-hydrothermal conditions (~150 to 600°C), have been investigated in order to provide the first exploratory overview of the range in Li isotopic composition of fluid inclusions. From 1 to 2g of hydrothermal quartz or dolomite, cation analysis (Na, K, Ca, Mg, Sr, Li), Li fraction recovery and Li isotopic analysis of bulk fluid inclusion leachates were carried out by using an innovative approach coupling crush-leach extraction, high performance ion chromatography and MC-ICPMS analysis. Reconstructed Li concentrations and ÎŽ7Li values of these fluid inclusions (respectively 12 to 653mg/l and â1.4±0.2â° to +41.3±0.8â°) are compatible with previously proposed models for the origin of the fluids and fluid-rock interactions. ÎŽ7Li values are independent from other tracers (Br/Cl, I/Cl) and parameters such as temperature, salinity, and cation content (Na/Ca, Na/K, Na/Mg, Na/Li, Na/Sr ratios). The results show that, in conjunction with other parameters, the Li isotopic compositions of fluid inclusions are potentially powerful source and process tracers of deep crustal fluids within a wide range of geological environments and related ore-forming systems, for example in from sedimentary basins, seafloor hydrothermal systems and subduction zones
Lithosphere 2016: Ninth symposium on the Structure, Composition and Evolution of the Lithosphere in Fennoscandia
The geochemical composition of seven post-kinematic mafic dykes in southern part of Central Svecofennia have been studied. Two dykes have been selected for in situ zircon U-Pb geochronology and one for in situ zircon Lu-Hf isotope analysis.These c. 1.86 Ga dykes can be divided into two subgroups by their geochemical characteristics: i) an enriched type with Nb contents up to 42 ppm, high contents of certain fluid mobile elements such as F, Ba, Sr, K2O and LREE and elevated contents of Fe2O3, Ti2O and P2O5, and ii) a primitive type with high MgO and Cr content. The primitive dyke exhibit positive, average c. +3, initial ΔHf values. The geochemical data combined with the petrological and the field observations suggest that the dykes are juvenile and derived from a subduction-enriched mantle source in a within-plate environment during the post-kinematic stage of the Svecofennian orogeny.</p
Novel Mechanism of Supersolid of Ultracold Polar Molecules in Optical Lattices
We study the checkerboard supersolid of the hard-core Bose-Hubbard model with
the dipole-dipole interaction. This supersolid is different from all other
supersolids found in lattice models in the sense that superflow paths through
which interstitials or vacancies can hop freely are absent in the crystal. By
focusing on repulsive interactions between interstitials, we reveal that the
long-range tail of the dipole-dipole interaction have the role of increasing
the energy cost of domain wall formations. This effect produces the supersolid
by the second-order hopping process of defects. We also perform exact quantum
Monte Carlo simulations and observe a novel double peak structure in the
momentum distribution of bosons, which is a clear evidence for supersolid. This
can be measured by the time-of-flight experiment in optical lattice systems
Coherent collapse of a dipolar Bose-Einstein condensate for different trap geometries
We experimentally investigate the collapse dynamics of dipolar Bose- Einstein
condensates of chromium atoms in different harmonic trap geometries, from
prolate to oblate. The evolutions of the condensates in the unstable regime are
compared to three-dimensional simulations of the Gross-Pitaevskii equation
including three-body losses. In order to probe the phase coherence of collapsed
condensates, we induce the collapse in several condensates simultaneously and
let them interfere
Cooling a nanomechanical resonator with quantum back-action
Quantum mechanics demands that the act of measurement must affect the
measured object. When a linear amplifier is used to continuously monitor the
position of an object, the Heisenberg uncertainty relationship requires that
the object be driven by force impulses, called back-action. Here we measure the
back-action of a superconducting single-electron transistor (SSET) on a
radiofrequency nanomechanical resonator. The conductance of the SSET, which is
capacitively coupled to the resonator, provides a sensitive probe of the
latter's position;back-action effects manifest themselves as an effective
thermal bath, the properties of which depend sensitively on SSET bias
conditions. Surprisingly, when the SSET is biased near a transport resonance,
we observe cooling of the nanomechanical mode from 550mK to 300mK-- an effect
that is analogous to laser cooling in atomic physics. Our measurements have
implications for nanomechanical readout of quantum information devices and the
limits of ultrasensitive force microscopy (such as single-nuclear-spin magnetic
resonance force microscopy). Furthermore, we anticipate the use of these
backaction effects to prepare ultracold and quantum states of mechanical
structures, which would not be accessible with existing technology.Comment: 28 pages, 7 figures; accepted for publication in Natur
d-wave collapse and explosion of a dipolar Bose-Einstein condensate
We investigate the collapse dynamics of a dipolar condensate of 52Cr atoms
when the s-wave scattering length characterizing the contact interaction is
reduced below a critical value. A complex dynamics, involving an anisotropic,
d-wave symmetric explosion of the condensate, is observed. The atom number
decreases abruptly during the collapse. We find good agreement between our
experimental results and those of a numerical simulation of the
three-dimensional Gross-Pitaevskii equation, including contact and dipolar
interactions as well as three-body losses. The simulation indicates that the
collapse induces the formation of two vortex rings with opposite circulations.Comment: 4 pages, 4 figure
Age and geochemistry of granitoids in the Precambrian basement of Ăland, SE Sweden â implications for the extension of the Transscandinavian Igneous Belt in the Baltic Sea region
The Precambrian crust in the Baltic
Sea region is mostly covered by Phanerozoic sedimentary rocks but can be
studied in drill cores. Two granitoids from the crystalline basement below
Ăland were collected from the archives of the Geological Survey of Sweden and
analyzed for geochemistry and dated with the U-Pb method on zircons. The Böda
Hamn granitoid (northern Ăland) has a monzodioritic composition and an age of
1799.8±3 Ma while the ValsnĂ€s granitoid (central Ăland) has a quartz monzonitic
composition and an age of 1784.9±5.7 Ma. These geochemical-isotopic
characteristics are compatible with those of generation 1 of the
Transscandinavian Igneous Belt (TIB) in the Fennoscandian Shield, â„30 km west
of Ăland.A more detailed review of the TIB-1
generation shows that two
sub-generations (1a and 1b) can
be distinguished on each respective side of the Oskarshamn-Jönköping Belt
(OJB). Sub-generation 1a (north of OJB) has an age span of 1794-1808 Ma while sub-generation
1b (south of OJB) has an age span of 1769-1793 Ma. According to this subdivision, the Böda Hamn monzodiorite belongs to sub-generation 1a, which also can be followed to southernmost Gotland
(Sundblad et al. 2003) and the ValsnÀs quartz monzonite belongs to sub-generation 1b, which can be followed to
the Latvian/Lithuanian border, where a marginally younger granitoid was
reported from off shore drill core E-7 (Salin et al. 2016). Taken
together, these data suggest that the Transscandinavian Igneous Belt can
be traced across the Baltic Sea from the exposed parts within the Fennoscandian
Shield to the Latvian/Lithuanian border.Salin, E.,
Sundblad, K., Woodard, J. and Lahaye, Y. 2016: The Precambrian crust in the
Baltic Sea region. Bulletin of the Geological Society of Finland, 32nd Nordic
Geological Winter Meeting, Helsinki. Abstract volume, p. 162.Sundblad, K., Claesson, S.
& Gyllencreutz, R. 2003: The Precambrian of
Gotland â a key to the understanding of the geologic environment for granitoids
in the Baltic Sea region. Granitic systems â State of the art and future
avenues. An international symposium in honor of professor Ilmari Haapala.
Abstract volume, Helsinki, 102Ââ106.
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