FUV and X-ray absorption in the Warm-Hot Intergalactic Medium

The Warm-Hot Intergalactic Medium (WHIM) arises from shock-heated gas collapsing in large-scale filaments and probably harbours a substantial fraction of the baryons in the local Universe. Absorption-line measurements in the ultraviolet (UV) and in the X-ray band currently represent the best method to study the WHIM at low redshifts. We here describe the physical properties of the WHIM and the concepts behind WHIM absorption line measurements of H I and high ions such as O VI, O VII, and O VIII in the far-ultraviolet and X-ray band. We review results of recent WHIM absorption line studies carried out with UV and X-ray satellites such as FUSE, HST, Chandra, and XMM-Newton and discuss their implications for our knowledge of the WHIM.Comment: 26 pages, 9 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 3; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

Scandian Ultrahigh-Pressure Metamorphism of Proterozoic Basement Rocks on Fjortoft and Otroy, Western Gneiss Region, Norway

Electron microprobe mineral composition data are presented for samples of exsolved and recrystallized garnet websterites within the mantle-derived peridotite bodies and of external orthopyroxene eclogite lenses directly enclosed within the gneisses on the islands of Fjørtoft and Otrøy in the Western Gneiss Region of Norway. These data are utilized to obtain P-T estimates that lie within the coesite stability field, and are mostly also compatible with rare observations of microdiamond formation and preservation for the deformed and re-equilibrated garnet websterite assemblages in the peridotite bodies included within the basement gneiss sequences on both islands. Equivalent P-T estimates for external orthopyroxene eclogite lenses within the basement gneisses on both islands are mostly not well constrained due to fairly extensive modification of orthopyroxene compositions during amphibolite-facies retrogression. Nonetheless, P-T estimates for the least retrogressed samples again indicate the likelihood that these rocks underwent Scandian ultrahigh-pressure metamorphism. We thus conclude that, contrary to a previously published interpretation, both the Caledonian Blåhø nappe sequence and the underlying Proterozoic Baltica basement gneisses on Fjørtoft experienced Scandian ultrahigh-pressure metamorphism, thus denying a previous suggestion that a major, greater than normal continental crust thickness, tectonic break exists between these rock sequences on this island. Similarly, the Baltica basement gneiss sequence exposed on the northern side of Otrøy, with its comparable mantle-derived peridotite bodies and external orthopyroxene eclogite lenses, is also shown to have been subjected to the Scandian ultrahigh-pressure metamorphic event. Copyright © 2006 by V. H. Winston & Son, Inc. All rights reserved

Petrology and geochemistry of xenoliths from the northern Baltic Shield: evidence for partial melting and metasomatism in the lower crust beneath an Archaean terrane

Lower crustal xenoliths entrained in a Paleozoic ultramafic lamprophyre breccia pipe on Elovy island, Kola peninsula, Russia, represent some of the oldest lower crustal material yet investigated from Europe. The xenoliths vary from feldspar-poor, garnetrich rocks which resemble eclogites, to feldspar-rich garnet granulites. Quartz-rich felsic granulites, as well as pyroxenites and amphibole-rich rocks are also present. The mafic granulites/eclogites represent a suite of gabbros and norites that is related by olivine fractionation. The igneous protoliths may have formed in a manner analogous to lower crustal rocks from most other European xenolith localities, i.e. by basaltic underplating, but magmatic cumulates are not in evidence. The Kola lower crust was subjected to one or more metasomatic events which introduced up to 45% phlogopite and/or amphibole into both eclogites/granulites and pyroxenites. The resulting rocks have strong enrichments in Rb, Ba, and K, indicating that the lower crust is not uniformly depleted in LIL and heat-producing elements. Siliceous (65% SiO2) and mafic (< 50% SiO2) lithologies coexist in migmatitic xenoliths, which provide evidence for partial melting processes and restite formation in mafic metaigneous lower crust. The relationship, if any, between partial melting and metasomatism is unclear