Advances in Global and Local Helioseismology: an Introductory Review

Helioseismology studies the structure and dynamics of the Sun's interior by observing oscillations on the surface. These studies provide information about the physical processes that control the evolution and magnetic activity of the Sun. In recent years, helioseismology has made substantial progress towards the understanding of the physics of solar oscillations and the physical processes inside the Sun, thanks to observational, theoretical and modeling efforts. In addition to the global seismology of the Sun based on measurements of global oscillation modes, a new field of local helioseismology, which studies oscillation travel times and local frequency shifts, has been developed. It is capable of providing 3D images of the subsurface structures and flows. The basic principles, recent advances and perspectives of global and local helioseismology are reviewed in this article.Comment: 86 pages, 46 figures; "Pulsation of the Sun and Stars", Lecture Notes in Physics, Vol. 832, Rozelot, Jean-Pierre; Neiner, Coralie (Eds.), 201

Tantalum mineralogy of rare-element granitic pegmatites from the Separation Lake area, northwestern Ontario

Abstract not available

Heterogeneity in southern Central Indian Ridge MORB: Implications for ridge-hot spot interaction

Between the Rodrigues Triple Junction and the Marie Celeste fracture zone, basalts from the Central Indian Ridge (CIR) exhibit an enrichment in incompatible elements that increases in intensity northward. In addition, H2O/TiO2, Al[8], and Dy/Yb ratios increase, while Na[8] remains unchanged and Fe[8] decreases. Evolution of the enriched magma appears to be affected by elevated water contents, which lower the mantle solidus, thereby increasing the initial depth of melting, as well as delaying plagioclase crystallization. However, the enrichment affecting the northern samples is not a just function of hydrous mantle melting and crystallization. Instead of trending toward a small melt fraction from the mantle, as predicted by hydrous melting models, the CIR samples lie on a mixing line between N-MORB and a source component that closely resembles present-day Réunion hot spot lavas. Thus it appears that while hydrous melting and crystallization affect the CIR, the enriched and wet mantle originates from the Réunion hot spot, where it migrates eastward toward the CIR, against the direction of motion of the lithosphere

Volcano-ice interactions at Prestahnukur, Iceland : rhyolite eruption during the last interglacial-glacial transition.

Prestahnukur is a 570m high rhyolite glaciovolcanic edifice in Iceland's Western Rift Zone with a volume of 0.6 km3. Uniform whole rock, mineral and glass compositions suggest that Prestahnukur was constructed during the eruption of one magma batch. Ar-Ar dating gives an age of 89+/-24 ka, which implies eruption during the transition (Oxygen Isotope substages 5d to 5a) between the Eemian interglacial and the Weichselian glacial period. Prestahnukur is unique among published accounts of rhyolite tuyas because a base of magmatically-fragmented tephra appears to be absent. Instead, basal exposures consist of glassy lava lobes and coarse hyaloclastite, above which are single and multiple lava sheets with matrix-supported basal breccias and hyaloclastite upper carapaces. Steepening ramp structures at sheet termini are interpreted as ice-contact features. Interactions between erupting magma and water/ice have affected all lithologies. A preliminary model for the construction of Prestahnukur involves an effusive subglacial eruption between 2 and 19 years duration which never became emergent, into an ice sheet over 700m thick. If 700m of ice had built up during this interglacial-glacial transition, this would corroborate models arguing for the swift accumulation of land-based ice in rapid response to global cooling

U-Pb columbite-tantalite chronology of rare-element pegmatites using TIMS and Laser Ablation-Multi Collector-ICP-MS

U-Pb isotopic analyses using TIMS and Laser Ablation-Multi Collector-ICP-MS were carried out on columbite-tantalite minerals from three suites of rare-element (Li, Cs, Ta) pegmatites in the Superior Province of Canada. Conventional TIMS analyses of these columbite-tantalite crystals produce scattered data and reverse discordance even after HF leaching of the grains prior to dissolution, possibly reflecting the incomplete removal of the open-system metamict segments during sample preparation. LA-MC-ICP-MS analyses of unleached, primary columbite free from inclusions and alteration give consistent and precise (<0.5%) Pb-Pb ages, demonstrating the utility of this approach. However, normal and reverse discordance is also observed in U-Pb data from LA-MC-ICP-MS analyses. This discordance represents either U-Pb mobilisation during recent weathering, sample preparation and/or an analytical artefact originating from variable elemental fractionation between U and Pb during ablation and ionisation that itself may have its origin in the contrasting metamictization of the dated columbite and the monazite standard used. Best age estimates of columbite from pegmatites in the Superior Province are; 2670±5 Ma for the Pakeagama Lake pegmatite, 2644±7 Ma for the Separation Rapids group, and 2665±8 Ma for the Mavis Lake group. The ages broadly show that the rare-element pegmatites are temporally synchronous with adjacent peraluminous granites

A Complex petrogenesis for an arc magmatic suite, St Kitts, Lesser Antilles

St Kitts forms one of the northern group of volcanic islands in the Lesser Antilles arc. Eruptive products from the Mt Liamuiga centre are predominantly olivine + hypersthene-normative, low-K basalts through basaltic andesites to quartz-normative, low-K andesites. Higher-Al and lower-Al groups can be distinguished in the suite. Mineral assemblages include olivine, clinopyroxene, orthopyroxene, plagioclase and titanomagnetite with rarer amphibole, ilmenite and apatite. Eruptive temperatures of the andesites are estimated as 963–950°C at fO2 NNO + 1 (where NNO is the nickel–nickel oxide buffer). Field and mineral chemical data provide evidence for magma mixing. Glass (melt) inclusions in the phenocrysts range in composition from andesite to high-silica rhyolite. Compositional variations are broadly consistent with the evolution of more evolved magmas by crystal fractionation of basaltic parental magmas. The absence of any covariation between 87Sr/86Sr or 143Nd/144Nd and SiO2 rules out assimilation of older silicic crust. However, positive correlations between Ba/La, La/Sm and 208Pb/204Pb and between 208Pb/204Pb and SiO2 are consistent with assimilation of small amounts (<10%) of biogenic sediments. Trace element and Sr–Nd–Pb isotope data suggest derivation from a normal mid-ocean ridge basalt (N-MORB)-type mantle source metasomatized by subducted sediment or sediment melt and fluid. The eruptive rocks are characterized by 238U excesses that indicate that fluid addition of U occurred <350 kyr ago; U–Th isotope data for mineral separates are dominated by melt inclusions but would allow crystallization ages of 13–68 ka. However, plagioclase is consistently displaced above these ‘isochrons’, with apparent ages of 39–236 ka, and plagioclase crystal size distributions are concave-upwards. These observations suggest that mixing processes are important. The presence of 226Ra excesses in two samples indicates some fluid addition <8 kyr ago and that the magma residence times must also have been less than 8 kyr