The great eclogite debate of the Western Gneiss Region, Norwegian Caledonides: The in situ crustal v. exotic mantle origin controversy

An entertaining debate arose in the latter half of the 20th century among scientists working on the spectacular eclogite facies rocks that occur within metamorphic rocks of the Western Gneiss Region (WGR) of the Norwegian Caledonides. It resulted in part from Eskola's influential publication “On the Eclogites of Norway” who concluded, incorrectly, that mafic eclogites within gneisses (external eclogites) and garnetiferous ultramafic rocks within peridotite lenses had a common origin. The debate featured two end‐member positions. One was that all these garnet‐bearing assemblages, regardless of association, had an exotic origin, where they recrystallized at extremely high pressures and temperatures (P–T) in the mantle and then were tectonically inserted upward into the crust. The other was the in situ origin where this recrystallization occurred within the enclosing gneisses during regional metamorphism. Garnet peridotites and pyroxenites have compositions identical to ultramafic xenoliths in kimberlites and define P–T conditions that are appropriate to the upper mantle. Therefore, peridotite lenses were generally (and correctly) interpreted to be mantle fragments. However, some extended this exotic origin to external eclogites, particularly coarse‐grained orthopyroxene‐ (and coesite‐) bearing eclogites, which also formed at extremely high P–T. They noted an apparent pressure and temperature disequilibrium between anhydrous eclogites and the surrounding amphibolite facies gneisses. It was generally accepted that eclogites could form only in “dry” environments (urn:x-wiley:02634929:media:jmg12314:jmg12314-math-0001 << Ptotal). Thus, eclogites had to form within the anhydrous mantle rather than the host hydrous crust. Finally, there was doubt as to whether the necessary P–T conditions could be generated in continental crust, even when tectonically thickened. The arguments for an in situ origin were based largely on external eclogites. Thin sections showed garnet cores with amphibolite facies inclusions and rims with eclogite facies minerals suggesting prograde metamorphism. Similarly, core to rim changes in mineral chemical composition were consistent with increasing P–T. Coesite and microdiamond were found in both eclogites and host gneisses. Finally, thermobarometry showed burial depths increased from SE to NW across the WGR. Breakthroughs occurred when old assumptions were discarded. Eclogite recrystallization actually can occur in the presence of water. Eclogites and garnet peridotite and pyroxenites had completely different histories. They give different ages, formed under different P–T conditions, and have different geochemical fingerprints. The debate was finally resolved when it became generally accepted that continental crust could subduct into the mantle. Thus, it could subduct to eclogite facies depths where, simultaneously, peridotites could be inserted from the overlying mantle wedge. Both sides of the debate were correct! However, eclogites recrystallized “in situ” only because the enclosing crust was deep in the mantle and garnet peridotites did invade continental crust as solids, but only because the crust was below a mantle wedge. The “Great Debate” was fierce at times, but it led to the modern understanding that continental subduction is a vital part of mountain building

Age-related changes in physical functioning: Correlates between objective and self-reported outcomes

Objectives: To quantify the variance attributable to age and estimate annual decline in physical function and self-reported health using a battery of outcome measures in healthy older females. To determine whether self-reported functional losses are similar to those measured objectively and which best represent overall physical capacity. Design: Experimental study, cross-sectional analysis. Setting: Human Performance Laboratory, University setting. Participants: Thirty-nine community-dwelling women (mean [SD] age. =. 71.5 [7.3] years, range 60 to 83 years) completed a battery of objective measures of function and a self-reported health status survey. Main outcome measures: Objective measures: gait speed; TUG test; sit-to-stand; concentric knee flexor and extensor moments; self-reported: the SF-36. Results: Using a cross-sectional approach, annual declines were estimated for: TUG time (2.1%); gait speed (1.2%); knee extensor (2.2%) and flexor moments (3.0%); and self-reported Physical Functioning (0.9 to 1.2%) (p≤0.001). Linear regression indicated that age explained moderate variance in the objective (R2=21 to 34%) and self-reported (R2=14 to 28%) outcomes. TUG time and gait speed was significantly correlated with all objective outcomes except sit-to-stand (r=0.46 to 0.83) and most of the self-reported (r=0.40 to 0.63) outcomes (p<0.01). Conclusions: Age-related functional deterioration was estimated precisely across both objective and self-reported outcomes. Greater strength losses for the knee flexors compared to the extensors indicate an unequal strength loss of antagonistic muscle pairs which has implications for the safe completion of many functional tasks including obstacle negotiation, stair locomotion, postural transitions, and ultimately knee joint stability. Furthermore, walking speed and TUG time correlated most strongly with many of the outcomes highlighting their importance as global indicators of physical capacity

Structural, petrological and chemical analysis of syn-kinematic migmatites: insights from the Western Gneiss Region, Norway.

International audienceEvidence of melting is presented from the Western Gneiss Region (WGR) in the core of the Caledonian orogen, Western Norway and the dynamic significance of melting for the evolution of orogens is evaluated. Multiphase inclusions in garnets that comprise plagioclase, potassic feldspar and biotite are interpreted to be formed from melt trapped during garnet growth in the eclogite facies. The multiphase inclusions are associated with rocks that preserve macroscopic evidence of melting, such as segregations in mafic rocks, leucosomes and pegmatites hosted in mafic rocks and in gneisses. Based on field studies, these lithologies are found in three structural positions: (1) as zoned segregations found in high-pressure (HP) (ultra) mafic bodies, (2) as leucosomes along amphibolite facies foliation and in a variety of discordant structures in gneiss, and (3) as undeformed pegmatites cutting the main Caledonian structures. Segregations post-date the eclogite facies foliation and predate the amphibolite facies deformation, whereas leucosomes are contemporaneous with the amphibolite facies deformation and undeformed pegmatites are post-kinematic and were formed at the end of the deformation history. Geochemistry of the segregations, leucosomes and pegmatites in the WGR defines two trends, which correlate with the mafic or felsic nature of the host rocks. The first trend with Ca-poor compositions represents leucosome and pegmatite hosted in felsic gneiss, whereas the second group with K-poor compositions corresponds to segregation hosted in (ultra) mafic rocks. These trends suggest partial melting of two separate sources: the felsic gneisses and also the included mafic eclogites. The REE patterns of the samples allow distinction between melt compositions, fractionated liquids and cumulates. Melting began at high pressure and affected most lithologies in the WGR before or during their retrogression in the amphibolite facies. During this stage, the presence of melt may have acted as a weakening mechanism that enabled decoupling of the exhuming crust around the peak pressure conditions triggering exhumation of the upward-buoyant crust. Partial melting of both felsic and mafic sources at temperatures below 800°C implies the presence of an H2O-rich fluid phase at great depth to facilitate H2O-present partial melting

Observation of associated near-side and away-side long-range correlations in √sNN=5.02 TeV proton-lead collisions with the ATLAS detector

Two-particle correlations in relative azimuthal angle (Δϕ) and pseudorapidity (Δη) are measured in √sNN=5.02  TeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1  μb-1 of data as a function of transverse momentum (pT) and the transverse energy (ΣETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Δη|<5) “near-side” (Δϕ∼0) correlation that grows rapidly with increasing ΣETPb. A long-range “away-side” (Δϕ∼π) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ΣETPb, is found to match the near-side correlation in magnitude, shape (in Δη and Δϕ) and ΣETPb dependence. The resultant Δϕ correlation is approximately symmetric about π/2, and is consistent with a dominant cos⁡2Δϕ modulation for all ΣETPb ranges and particle pT

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table, submitted to European Physical Journal

Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS

Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations

Measurement of χ c1 and χ c2 production with s√ = 7 TeV pp collisions at ATLAS

The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at s√ = 7 TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → μ + μ −) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured

Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at s√=8 TeV with the ATLAS detector

The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy s√=8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb−1. No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R c = 950 GeV for a cut-off scale times radius (ΛR c) of approximately 30