Carbonate metasomatism of the oceanic mantle beneath Fernando de Noronha Island, Brazil

Evidence is presented for a carbonate-immiscibility phenomena in the upper mantle based on data from a set of strongly metasomatized xenoliths in a basanitic lava flow from Fernando de Noronha Island (southwest Atlantic). A petrological and geochemical study of lherzolitic and harzburgitic xenoliths reveals that the oceanic mantle of this region has been affected by very strong carbonate metasomatism. The metasomatism led to wehrlitization of the primary mantle mineral assemblage (ol, opx, sp). The wehrlitization was the result of interaction between a possibly ephemeral sodic dolomitic melt or fluid with the mantle peridotite according to the following reactions, which include sodic components: 4MgSiO₃+CaMg(CO₃)₂=2Mg₂SiO₄+CaMgSi₂O₆+2CO2 3CaMg(CO₃)₂+CaMgSi₂O₆=4CaCO₃+2Mg₂SiO₄+2CO₂ The olivine has abundant micro-inclusions consisting of Na-Al-Si-rich glass, Fe, Ni and Cu-monosulfide, Ca-rich carbonate and dense CO₂. The interrelationships between the glass, sulfide and carbonate inclusions permit speculation that silicate, sulfide, and Ca-rich carbonatite melts were in equilibrium with each other and originated from partial melting of metasomatized and wehrlitized peridotite underneath Fernando de Noronha Island. These results support a two-stage model of Ca-rich carbonatite formation: first stage - metasomatic wehrlitization and carbonatization of mantle rocks; second stage - partial melting of the carbonate-bearing wehrlitic rock resulting in the formation of immiscible silicate, sodic carbonate and sulfide liquids and the ultimately generation of calciocarbonatites.     

The upper mantle beneath Kapfenstein and the Transdanubian volcanic region,E Austria and W Hungary: A comparison

Summary A representative suite of ultramafic xenoliths from Kapfenstein, Austria, has been investigated petrographically. Textures and mineral chemistries are compared with published data on Hungarian xenoliths and discussed within the framework of the hypothesis of a mantle diapir beneath the Transdanubian Volcanic Region (TVR) of E Austria and W Hungary. We succeeded in recognizing important differences which seem to support the TVR mantle diapir concept. Below the external part of the TVR (Kapfenstein) the upper mantle seems to be essentially untectonized and lithologically rather monotonous (e.g., Type II clinopyroxenites are absent). In contrast, both deformed (equigranular) and undeformed (protogranular) peridotite xenoliths occur in the internal part (Balaton area) where Type II clinopyroxenite xenoliths as well as Type I/Type II composite rocks are present. It is remarkable that at Gérce (Hungary), situated approximately mid-way between the internal and external regions, almost exclusively porphyroclastic xenoliths occur.The undeformed xenoliths from Kapfenstein are largely unfractionated. A small proportion exhibits depletions in basaltic component or some mild influence of mantle metasomatism. Several mineral chemical parameters, such asmg-number of olivine, Al₂O₃ content of spinel and clinopyroxene, apparent pyroxene equilibration temperature, etc., show a narrow distribution with a pronounced maximum in the undeformed Kapfenstein xenoliths. By contrast, the deformed xenoliths from the internal TVR show a much broader range of values with no distinct maximum, attesting to a more complex chemical and physical evolution. Thus a direct relationship between deformation and chemistry seems to be confirmed. The deformed rocks can be extreme in two ways: they can either be strongly depleted or strongly enriched as documented by the high contents of clinopyroxene in equigranular xenoliths from Szigliget. Tectonization apparently opens the way for mass transport in either direction.

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Der obere Mantel unterhalb Kapfenstein und der Transdanubischen Vulkanischen Region, E-Österreich und W-Ungarn: Ein Vergleich

Zusammenfassung Eine repräsentative Suite von ultramafischen Xenolithen von Kapfenstein, Steiermark, wurde petrologisch untersucht. Die Gefüge und Mineralchemismen werden mit publizierten Daten von ungarischen Vorkommen verglichen und im Rahmen der Mantel-Diapir-Hypothese für die Transdanubische Vulkanische Region (TVR) diskutiert. Der Vergleich ergab wesentliche Unterschiede, welche das TVR-Mantel-Diapir-Konzept unterstützen. Der Mantel unterhalb des äußeren Teiles der TVR (Kapfenstein) ist praktisch untektonisiert und lithologisch monoton (z.B. fehlen Typ II Klinopyroxenite). Im Gegensatz dazu finden sich im inneren Teil (Balaton-Region) sowohl deformierte (equigranulare) als auch nicht-deformierte (protogranulare) Xenolithe zusammen mit Typ II Klinopyroxeniten. Auch zusammengesetzte Xenolithe, bestehend aus Typ I und Typ II Gesteinen sind vorhanden. Bemerkenswert ist, daß bei Gérce (Ungarn), eine Lokalität, welche sich zwischen dem inneren und äußeren Teil der TVR befindet, fast ausschließlich nur porphyroklastische Xenolithe vorkommen.Die undeformierten Xenolithe von Kapfenstein sind größtenteils unfraktioniert. Einige wenige zeigen Verarmungen oder geringfügige metasomatische Anreicherungen. Histogramme mineralchemischer Parameter zeigen sehr deutlich die Unterschiede zwischen den undeformierten Kapfenstein Xenolithen und den deformierten der inneren TVR. Die Kapfenstein Xenolithe zeigen typischerweise regelmäßige Verteilungen mit einem deutlichen Maximum. Die Xenolithe der inneren TVR hingegen zeigen eine flache Verteilung und weisen damit auf eine wesentlich komplexere chemische Entwicklung hin. Unsere Daten scheinen einen direkten Zusammenhang zwischen Deformation und chemischer Veränderung aufzuzeigen. Die deformierten Gesteine können in dieser Hinsicht zwei Extreme annehmen: Sie können entweder stark verarmt oder stark angereichert sein. Letzeres wird z.B. beeindruckend durch die hohen Gehalte an Klinopyroxen der equigranularen Xenolithe von Szigliget dokumentiert. Tektonisierung scheint die Wege für Massen-Transporte in beiden Richtungen zu öffnen.

     

Mineralogical alteration of artificial meteorites during atmospheric entry. The STONE-5 experiment

The generic concept of the artificial meteorite experiment STONE is to fix rock samples bearing microorganisms on the heat shield of a recoverable space capsule and to study their modifications during atmospheric re-entry. The STONE-5 experiment was performed mainly to answer astrobiological questions. The rock samples mounted on the heat shield were used (i) as a carrier for microorganisms and (ii) as internal control to verify whether physical conditions during atmospheric re-entry were comparable to those experienced by “real” meteorites. Samples of dolerite (an igneous rock), sandstone (a sedimentary rock), and gneiss impactite from Haughton Crater carrying endolithic cyanobacteria were fixed to the heat shield of the unmanned recoverable capsule FOTON-M2. Holes drilled on the back side of each rock sample were loaded with bacterial and fungal spores and with dried vegetative cryptoendoliths. The front of the gneissic sample was also soaked with cryptoendoliths.

The mineralogical differences between pre- and post-flight samples are detailed. Despite intense ablation resulting in deeply eroded samples, all rocks in part survived atmospheric re-entry. Temperatures attained during re-entry were high enough to melt dolerite, silica, and the gneiss impactite sample. The formation of fusion crusts in STONE-5 was a real novelty and strengthens the link with real meteorites. The exposed part of the dolerite is covered by a fusion crust consisting of silicate glass formed from the rock sample with an admixture of holder material (silica). Compositionally, the fusion crust varies from silica-rich areas (undissolved silica fibres of the holder material) to areas whose composition is “basaltic”. Likewise, the fusion crust on the exposed gneiss surface was formed from gneiss with an admixture of holder material. The corresponding composition of the fusion crust varies from silica-rich areas to areas with “gneiss” composition (main component potassium-rich feldspar). The sandstone sample was retrieved intact and did not develop a fusion crust. Thermal decomposition of the calcite matrix followed by disintegration and liberation of the silicate grains prevented the formation of a melt.

Furthermore, the non-exposed surface of all samples experienced strong thermal alterations. Hot gases released during ablation pervaded the empty space between sample and sample holder leading to intense local heating. The intense heating below the protective sample holder led to surface melting of the dolerite rock and to the formation of calcium-silicate rims on quartz grains in the sandstone sample.     

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Moldavites from Austria

Abstract— Several moldavites have been discovered in the northern part of Lower Austria. Tektites from two new locations (Altenburg and Radessen) have been analyzed. These new finds lend credibility to old reports about tektites from Lower Austria, some of which are associated with artefacts of prehistoric cultures. The new locations are situated between the Bohemian and Moravian parts of the moldavite strewn field, which is thus shown to extend further south than previously known. Most of the samples show clear indications of surface alterations by water and/or humic substances, and one sample shows signs of fluviatile transport. The geological setting of the moldavite-bearing sediments is similar to the Czechoslovakian occurrences but is probably less disturbed. Chemically the samples show considerable variations even within one location. No unambiguous association with either the Bohemian or the Moravian group is evident either for the major or trace element abundances.     

Overcoming cross-scale challenges to climate change adaptation for local government: a focus on Australia

This paper aims to identify key cross-scale challenges to planned adaptation within the context of local government in Australia, and suggest enabling actions to overcome such challenges. Many of the impacts of climate change and variability have or will be experienced at the local level. Local governments are embedded in a larger governance context that has the potential to limit the effectiveness of planned adaptation initiatives on the ground. This study argues that research on constraints and barriers to adaptation must place greater attention to understanding the broader multi-governance system and cross-scale constraints that shape adaptation at the local government scale. The study identified seven key enabling actions for overcoming cross-scale challenges faced by local governments in Australia when undertaking climate change adaptation planning and implementation. A central conclusion of this study is that a cooperative and collaborative approach is needed where joint recognition of the scale of the issue and its inherent cross-scale complexities are realised. Many of the barriers or constraints to adaptation planning are interlinked, requiring a whole government approach to adaptation planning. The research suggests a stronger role at the state and national level is required for adaptation to be facilitated and supported at the local level.