Bascou J, Delpech G, Vauchez A, Moine B N, Cottin J Y, Barruol G, . (2008). An integrated study of microstructural, geochemical, and seismic properties of the lithospheric mantle above the Kerguelen plume (Indian Ocean)
. Geochem. Geophys. Geosyst., 9(4), Q04036–.
Abstract: Peridotite xenoliths brought up to the surface by the volcanism of the Kerguelen Islands represent a mantle that has been affected by a high degree of partial melting followed by intense melt percolation above the Kerguelen plume. These xenoliths are therefore particularly suitable to investigate effects of melt-rock interaction on crystallographic fabrics (lattice-preferred orientation (LPO)) of peridotite minerals and on the LPO-induced seismic properties of peridotites above a mantle plume. We have studied a suite of 16 ultramafic samples representative of different degrees of partial melting and magma-rock interaction among which the protogranular harzburgites are the least metasomatised xenoliths and dunites are the ultimate stage of metasomatism. Olivine LPO is characterized by high concentration of [010] axes perpendicular to the foliation and [100] axes close to the lineation or distributed in the foliation plane in harzburgites, whereas the high concentration of [100] axes is parallel to the lineation and [010] axes is perpendicular to the assumed foliation in dunites. Olivine LPO in harzburgites is interpreted as being due to a deformation regime in axial compression or transpression. The fabric strength of olivine decreases progressively from protogranular to poikilitic harzburgites and finally to dunites, for which it remains nevertheless significant (J index $\geq$ 3.8). Seismic properties calculated from LPO of minerals indicate that metasomatism at higher melt/rock ratio lowers the P wave velocities. The most significant difference between harzburgites and dunites corresponds to the distribution of S wave anisotropy. Harzburgites display the maximum of anisotropy within the foliation plane and the minimum of anisotropy perpendicular to the foliation plane, whereas the lowest anisotropy is parallel to the lineation for dunites. These modifications of seismic properties as a result of metasomatic processes may induce seismic heterogeneities in the mantle above the Kerguelen plume. In addition, assuming a lithospheric mantle primarily harzburgitic and structured with a horizontal foliation, the seismic properties calculated for the Kerguelen xenoliths reconcile the rather high anisotropy evidenced by the horizontally propagating surface waves with the apparent isotropy revealed by the absence of splitting of vertically propagating teleseismic SKS waves recorded by the GEOSCOPE Kerguelen station.
Keywords: Kerguelen, mantle plume, seismic anisotropy, metasomatism, crystallographic fabric, lithosphere, 8121 Tectonophysics: Dynamics: convection currents, and mantle plumes, 8030 Structural Geology: Microstructures, 7208 Seismology: Mantle,
Programme: 133;444
|
Xu, G.; Frey, F.A.; Weis, D.; Scoates, J.S.; Giret, A. (2007). Flood basalts from Mt. Capitole in the central Kerguelen Archipelago: Insights into the growth of the archipelago and source components contributing to plume-related volcanism. Geochem. Geophys. Geosyst., 8.
Abstract: The Kerguelen Archipelago, constructed on the submarine Northern Kerguelen Plateau, is attributed to Cenozoic volcanism arising from the Kerguelen hot spot. Geochemical studies of 325 to 1000 m thick lava sections of the ?30 to 25 Ma flood basalt forming the bulk of the archipelago show a temporal change from older tholeiitic basalt to younger slightly alkalic basalt. This compositional transition is expressed in a 630 m lava section at Mt. Capitole where the lava sequence is lowermost tholeiitic basalt overlain by slightly alkalic basalt overlain by plagioclase-rich cumulates that are mixtures of plagioclase-phyric basalt and more evolved magmas. During growth of the archipelago, magma supply from the hot spot was variable and at times sufficiently low to enable extensive crystal fractionation; e.g., at Mt. Capitole and nearby Mt. Tourmente only 10 of 120 lava flows have >6 wt% MgO. On the basis of this study and previous isotopic data for the ?34 Ma submarine lavas erupted on the Northern Kerguelen Plateau, other flood basalt sections in the Kerguelen Archipelago, and younger lavas erupted in the archipelago and at Heard Island, there is significant Sr, Nd, Hf, and Pb isotopic heterogeneity that can be explained by two stages of mixing. The first mixing event, best shown by the submarine lavas, is between components that are related to Indian Ocean mid-ocean ridge basalt (MORB) and the Kerguelen hot spot. From ?34 Ma to <1 Ma, on average the proportion of the MORB-related component decreased. Subsequently, a second mixing process involved addition of a component with relatively high 87Sr/86Sr (>0.7060) and low 143Nd/144Nd (<0.5125) and 176Hf/177Hf (<0.2827) and nonradiogenic Pb isotope ratios (<17.9 for 206Pb/204Pb). We infer that this component was lower continental crust.
Keywords: Kerguelen mantle plume; Kerguelen Archipelago; Mt. Capitole; lower continental crust; Sr; Nd; Hf; Pb isotopic ratios; 1037 Geochemistry: Magma genesis and partial melting; 1038 Geochemistry: Mantle processes; 1065 Geochemistry: Major and trace element geochemistry
Programme: 444
|
Garcia, S.; Angelier, J.; Bergerat, F.; Homberg, C.; Dauteuil, O. (2008). Influence of rift jump and excess loading on the structural evolution of northern Iceland. Tectonics, 27.
Keywords: rift jump; structural evolution; lava dip; dyke; fault; flexure zone; Iceland; 8010 Structural Geology: Fractures and faults; 8036 Structural Geology: Paleoseismology; 8178 Tectonophysics: Tectonics and magmatism; 8137 Tectonophysics: Hotspots, large igneous provinces, and flood basalt volcanism; 9325 Geographic Location: Atlantic Ocean
Programme: 316
|
. (2008). Ground-based measurements of spatial and temporal variability of snow accumulation in East Antarctica. Reviews of geophysics, 46.
Abstract: The East Antarctic Ice Sheet is the largest, highest, coldest, driest, and windiest ice sheet on Earth. Understanding of the surface mass balance (SMB) of Antarctica is necessary to determine the present state of the ice sheet, to make predictions of its potential contribution to sea level rise, and to determine its past history for paleoclimatic reconstructions. However, SMB values are poorly known because of logistic constraints in extreme polar environments, and they represent one of the biggest challenges of Antarctic science. Snow accumulation is the most important parameter for the SMB of ice sheets. SMB varies on a number of scales, from small-scale features (sastrugi) to ice-sheet-scale SMB patterns determined mainly by temperature, elevation, distance from the coast, and wind-driven processes. In situ measurements of SMB are performed at single points by stakes, ultrasonic sounders, snow pits, and firn and ice cores and laterally by continuous measurements using ground-penetrating radar. SMB for large regions can only be achieved practically by using remote sensing and/or numerical climate modeling. However, these techniques rely on ground truthing to improve the resolution and accuracy. The separation of spatial and temporal variations of SMB in transient regimes is necessary for accurate interpretation of ice core records. In this review we provide an overview of the various measurement techniques, related difficulties, and limitations of data interpretation; describe spatial characteristics of East Antarctic SMB and issues related to the spatial and temporal representativity of measurements; and provide recommendations on how to perform in situ measurements.
Keywords: surface mass balance; East Antarctica; measurements; ground-truthing; 0762 Cryosphere: Mass balance; 0726 Cryosphere: Ice sheets; 0794 Cryosphere: Instruments and techniques; 9310 Geographic Location: Antarctica; 1621 Global Change: Cryospheric change
Programme: 411;454
|
. (2007). Reviews of geophysics, 45.
Keywords: history; geomagnetism; paleomagnetism; 1599 Geomagnetism and Paleomagnetism: General or miscellaneous; 1714 History of Geophysics: Geomagnetism and paleomagnetism; 5440 Planetary Sciences: Solid Surface Planets: Magnetic fields and magnetism; 7999 Space Weather: General or miscellaneous; 9820 General or Miscellaneous: Techniques applicable in three or more fields
Programme: 139
|
. (2007). Comparison of polar ozone loss rates simulated by one-dimensional and three-dimensional models with Match observations in recent Antarctic and Arctic winters. J. Geophys. Res., 112.
Abstract: Simulations of ozone loss rates using a three-dimensional chemical transport model and a box model during recent Antarctic and Arctic winters are compared with experimental loss rates. The study focused on the Antarctic winter 2003, during which the first Antarctic Match campaign was organized, and on Arctic winters 1999/2000, 2002/2003. The maximum ozone loss rates retrieved by the Match technique for the winters and levels studied reached 6 ppbv/sunlit hour and both types of simulations could generally reproduce the observations at 2-sigma error bar level. In some cases, for example, for the Arctic winter 2002/2003 at 475 K level, an excellent agreement within 1-sigma standard deviation level was obtained. An overestimation was also found with the box model simulation at some isentropic levels for the Antarctic winter and the Arctic winter 1999/2000, indicating an overestimation of chlorine activation in the model. Loss rates in the Antarctic show signs of saturation in September, which have to be considered in the comparison. Sensitivity tests were performed with the box model in order to assess the impact of kinetic parameters of the ClO-Cl2O2 catalytic cycle and total bromine content on the ozone loss rate. These tests resulted in a maximum change in ozone loss rates of 1.2 ppbv/sunlit hour, generally in high solar zenith angle conditions. In some cases, a better agreement was achieved with fastest photolysis of Cl2O2 and additional source of total inorganic bromine but at the expense of overestimation of smaller ozone loss rates derived later in the winter.
Keywords: Ozone loss rates; transport model; trajectory model; 0340 Atmospheric Composition and Structure: Middle atmosphere: composition and chemistry; 0341 Atmospheric Composition and Structure: Middle atmosphere: constituent transport and chemistry; 3334 Atmospheric Processes: Middle atmosphere dynamics; 3360 Atmospheric Processes: Remote sensing; 3319 Atmospheric Processes: General circulation
Programme: 209
|
McCabe, J.R.; Thiemens, M.H.; Savarino, J. (2007). A record of ozone variability in South Pole Antarctic snow: Role of nitrate oxygen isotopes. J. Geophys. Res., 112.
Keywords: nitrate; isotopes; ozone; 1041 Geochemistry: Stable isotope geochemistry; 0305 Atmospheric Composition and Structure: Aerosols and particles; 3344 Atmospheric Processes: Paleoclimatology; 1610 Global Change: Atmosphere; 0776 Cryosphere: Glaciology
Programme: 1011
|
Tackett, P.J.; Cavender, A.E.; Keil, A.D.; Shepson, P.B.; Bottenheim, J.W.; Morin, S.; Deary, J.; Steffen, A.; Doerge, C. (2007). A study of the vertical scale of halogen chemistry in the Arctic troposphere during Polar Sunrise at Barrow, Alaska. J. Geophys. Res., 112.
Keywords: Arctic; halogen chemistry; vertical profiles; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0736 Cryosphere: Snow; 0738 Cryosphere: Ice; 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes; 0322 Atmospheric Composition and Structure: Constituent sources and sinks
Programme: 457
|
Magand, O.; Genthon, C.; Fily, M.; Krinner, G.; Picard, G.; Frezzotti, M.; Ekaykin, A.A. (2007). J. Geophys. Res., 112.
Keywords: surface mass balance; East Antarctica; data quality; 0762 Cryosphere: Mass balance; 9310 Geographic Location: Antarctica; 0736 Cryosphere: Snow; 0776 Cryosphere: Glaciology; 0794 Cryosphere: Instruments and techniques
Programme: 411;454
|
Preunkert, S.; Legrand, M.; Jourdain, B.; Moulin, C.; Belviso, S.; Kasamatsu, N.; Fukuchi, M.; Hirawake, T. (2007). J. Geophys. Res., 112.
Keywords: sulfur cycle; Antarctica; dimethylsulfure; 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes; 0330 Atmospheric Composition and Structure: Geochemical cycles; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry
Programme: 414
|
