An Unusual Enstatite-Forsterite Basalt from Kolbeinsey Island, North of Iceland

This is the first account of volcanic rocks erupted from a northernextension of the MidAtlantic Ridge to a locality between Icelandand Jan Mayen. The islet of Kolbeinsey (67° 08' N., 18°36' W.) is being rapidly eroded and now measures 52x36 m, andreaches only to 7.5m above sea level. Two identical specimensof vesicular basalt were collected by the Icelandic Coastguardvessel Aegir in 1962, and have now been chemically analysed.The mineral compositions were determined by electron microprobeanalysis. The rock carries micro-phenocrysts of highly magnesianolivine (Fo_{98 8}) and of plagioclase (An₈₅ to An₃₀). Brown andlemon-yellow grains of augite (Wo₄₂ En₄₅ Fs₁₃) are accompaniedby pale-yellow, euhedral to subhedral, groundmass orthopyroxenesof highly magnesian composition (Wo₄ En₈₈ Fs₈) and with a calciumcontent higher than found previously in enstatites. The chemistryof the basalt, also, is unusual in showing Fe₂O₃ = 8.98 percent and FeO = 0.38 per cent. The high state of oxidation isconsidered in relation to the production of forsterite and enstatitefrom basalt magma. Historic submarine volcanism in the regionis discussed in relation to bathymetric and geophysical data.     

Quantitative Constraints on Metamorphism in the Variscides of Southern Brittany--a Complementary Pseudosection Approach

Previous studies of metapelitic rocks from the core of the southernBrittany metamorphic belt suggest a complex clockwise P–Tevolution. We use pseudosections calculated for an average subaluminousmetapelite composition in the MnNCKFMASH system and averageP–T calculations to investigate in more detail the metamorphicevolution of these rocks. For migmatites, sequential occurrenceof kyanite, kyanite + staurolite and sillimanite suggests thata prograde evolution to P > 8 kbar at T     

Entry dynamics and acoustics/infrasonic/seismic analysis for the Neuschwanstein meteorite fall

Abstract— We have analyzed several types of data associated with the well‐documented fall of the Neuschwanstein meteorites on April 6, 2002 (a total of three meteorites have been recovered). This includes ground‐based photographic and radiometer data as well as infrasound and seismic data from this very significant bolide event (Spurný et al. 2002, 2003). We have also used these data to model the entry of Neuschwanstein, including the expected dynamics, energetics, panchromatic luminosity, and associated fragmentation effects. In addition, we have calculated the differential efficiency of acoustical waves for Neuschwanstein and used these values to compare against the efficiency calculated using available ground‐based infrasound data. This new numerical technique has allowed the source height to be determined independent of ray tracing solutions. We have also carried out theoretical ray tracing for a moving point source (not strictly a cylindrical line emission) and for an infinite speed line source. In addition, we have determined the ray turning heights as a function of the source height for both initially upward and downward propagating rays, independent of the explicit ray tracing (detailed propagation path) programs. These results all agree on the origins of the acoustic emission and explicit source heights for Neuschwanstein for the strongest infrasonic signals. Calculated source energies using more than four different independent approaches agree that Neuschwanstein was certainly <500 kg in initial mass, given the initial velocity of 20.95 km/s, resulting in an initial source energy ≤0.0157‐0.0276 kt TNT equivalent (4.185 times 10¹² J). Local source energies at the calculated infrasonic/seismic source altitudes are up to two orders of magnitude smaller than this initial source energy.     

The fall of the Grimsby meteorite—I: Fireball dynamics and orbit from radar,video, and infrasound records

Abstract– The Grimsby meteorite (H4–6) fell on September 25, 2009. As of mid‐2010, 13 fragments totaling 215 g have been recovered. Records of the accompanying fireball from the Southern Ontario Meteor Network, including six all‐sky video cameras, a large format CCD, infrasound and radar records, have been used to characterize the trajectory, speed, orbit, and initial mass of the meteoroid. From the four highest quality all‐sky video records, the initial entry velocity was 20.91 ± 0.19 km s^?1 while the derived radiant has a local azimuth of 309.40° ± 0.19° and entry angle of 55.20° ± 0.13°. Three major fragmentation episodes are identified at 39, 33, and 30 km height, with corresponding uncertainties of approximately 2 km. Evidence for early fragmentation at heights of approximately 70 km is found in radar data; dynamic pressure of this earliest fragmentation is near 0.1 MPa while the main flare at 39 km occurred under ram pressures of 1.5 MPa. The fireball was luminous to at least 19.7 km altitude and the dynamic mass estimate of the largest remaining fragment at this height is approximately several kilograms. The initial mass is constrained to be <100 kg from infrasound data and ablation modeling, with a most probable mass of 20–50 kg. The preatmospheric orbit is typical of an Apollo asteroid with a likely immediate origin in either the 3:1 or ν₆ resonances.     

HYDROCHEMISTRY AS AN INDICATOR OF SUBGLACIAL DRAINAGE SYSTEM STRUCTURE: A COMPARISON OF ALPINE AND SUB-POLAR ENVIRONMENTS

The anion compositions (SO²₄, HCO⁻₃ and Cl⁻) of runoff from the Haut Glacier d'Arolla, Switzerland and Austre Brøggerbreen, Svalbard are compared to assess whether or not variations in water chemistry with discharge are consistent with current understanding of the subglacial drainage structure of warm- and polythermal-based glaciers. These glacial catchments have very different bedrocks and the subglacial drainage structures are also believed to be different, yet the range of anion concentrations show considerable overlap for SO²⁻₄ and HCO⁻₃. Concentrations of Cl⁻ are higher at Austre Brøggerbreen because of the maritime location of the glacier. Correcting SO²⁻₄ for the snowpack component reveals that the variation in non-snowpack SO²⁻₄ with discharge and with HCO⁻₃ is similar to that observed at the Haut Glacier d'Arolla. Hence, if we assume that the provenance of the non-snowpack SO²⁻₄ is the same in both glacial drainage systems, a distributed drainage system also contributes to runoff at Austre Brøggerbreen. We have no independent means of testing the assumption at present. The lower concentrations of non-snowpack SO²⁻₄ at Austre Brøggerbreen may suggest that a smaller proportion of runoff originates from a distributed drainage system than at the Haut Glacier d'Arolla.     

The Lilloise Intrusion, East Greenland: Fractionation of a Hydrous Alkali Picritic Magma

The Lilloise is an 8 km4 km layered mafic intrusion which cutsthe plateau basalts of the East Greenland Tertiary province.Lilloise was intruded at 50 Ma, 4–5 Ma after cessationof the voluminous tholeiitic magmatism which accompanied riftingof the East Greenland continental margin. Lilloise is unusualamong layered intrusions in the province because it had a hydrousalkali picrite parent magma and generated a late-stage effluxof magmatic water from the intrusion into the aureole rocks.The three major subdivisions of the layered rocks are: olivine-clinopyroxene,olivine-clinopyroxene-plagioclase and plagioclase-amphibolecumulates. Massive subsidence of the intrusion before completesolidification resulted in deformation of the internal layeringand downturn of the bedding in the surrounding basalts. A strikingfeature of the intrusion is the injection of the layered rocksby a plexus of magmatic sheets which formed at the time of subsidence.The composition of these sheets is representative of the fractionationtrend of the intrusion and ranges from hawaiite to mildly saturatedquartz trachyte. The fractionation trend is successfully explainedby extraction of cumulus minerals of the layered rocks froma parent magma represented by alkali picrite dykes of a contemporaneousregional dyke swarm. Saturated to mildly over-saturated syenitesare a major component of the East Greenland province and theLilloise intrusion is illustrative of an important magmatictrend towards such compositions at this stage in the openingof the North Atlantic. KEY WORDS: Lilloise intrusion; East Greenland; alkali picrite magma; layered intrusion; magmatic differentiation ^*Corraponding author