Petrology of lavas from episodes 2–47 of the Puu Oo eruption of Kilauea Volcano,Hawaii: Evaluation of magmatic processes

The Puu Oo eruption of Kilauea Volcano in Hawaii is one of its largest and most compositionally varied historical eruptions. The mineral and whole-rock compositions of the Puu Oo lavas indicate that there were three compositionally distinct magmas involved in the eruption. Two of these magmas were differentiated (<6.8 wt% MgO) and were apparently stored in the rift zone prior to the eruption. A third, more mafic magma (9–10 wt% MgO) was probably intruded as a dike from Kilauea's summit reservoir just before the start of the eruption. Its intrusion forced the other two magmas to mix, forming a hybrid that erupted during the first three eruptive episodes from a fissure system of vents. A new hybrid was erupted during episode 3 from the vent where Puu Oo later formed. The composition of the lava erupted from this vent became progressively more mafic over the next 21 months, although significant compositional variation occurred within some eruptive episodes. The intra-episode compositional variation was probably due to crystal fractionation in the shallow (0.0–2.9 km), dike-shaped (i.e. high surface area/volume ratio) and open-topped Puu Oo magma reservoir. The long-term compositional variation was controlled largely by mixing the early hybrid with the later, more mafic magma. The percentage of mafic magma in the erupted lava increased progressively to 100% by episode 30 (about two years after the eruption started). Three separate magma reservoirs were involved in the Puu Oo eruption. The two deeper reservoirs (3–4 km) recharged the shallow (0.4–2.9 km) Puu Oo reservoir. Recharge of the shallow reservoir occurred rapidly during an eruption indicating that these reservoirs were well connected. The connection with the early hybrid magma body was cut off before episode 30. Subsequently, only mafic magma from the summit reservoir has recharged the Puu Oo reservoir.     

Petrology and geochronology of eclogites from the Variscan Schwarzwald (F.R.G.)

The Moldanubian basement of the Schwarzwald contains basic to ultrabasic rocks of both crustal and mantle origin which display high-pressure mineral assemblages or relics of such. In order to constrain the P-T-t evolution of the crustal high-pressure rocks, petrological and geochronological studies have been carried out on three eclogite samples. Geothermobarometric estimations indicate minimum metamorphic pressures of 1.6 GPa and equilibration temperatures of 670 750°C. Reaction textures document various metamorphic stages during exhumation of the high-pressure rocks. The age of high-pressure metamorphism is constrained by Sm-Nd isochrons of 332±13 Ma, 334±11 Ma, and 337±6 Ma defined by garnet, whole rock and clinopyroxene. For one sample, large garnets show prominent growth zoning in terms of major elements, Sm, Nd, and inclusions, dividing the grains into two growth stages. Sm-Nd isotope analyses on these garnets indicate that the time span between the two growth stages is too small to be resolved, reflecting a rather rapid metamorphic evolution. This result is further constrained by a Rb-Sr isochron age of 325±6 Ma on retrograde biotite and whole rock on the same sample. For one of the studied eclogites, formation of the magmatic precursor rocks is possibly approximated by the Ordovician U-Pb upper intercept age of a discordia from zircons.     

Westerly jet stream and past millennium climate change in Arid Central Asia simulated by COSMO-CLM model

This study tackles one of the most debated questions around the evolution of Central Asian climate: the “Puzzle” of moisture changes in Arid Central Asia (ACA) throughout the past millennium. A state-of-the-art Regional Climate Model (RCM) is subsequently employed to investigate four different 31-year time slices of extreme dry and wet spells, chosen according to changes in the driving data, in order to analyse the spatio-temporal evolution of the moisture variability in two different climatological epochs: Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). There is a clear regime behavior and bimodality in the westerly Jet phase space throughout the past millennium in ACA. The results indicate that the regime changes during LIA show a moist ACA and a dry East China. During the MCA, the Kazakhstan region shows a stronger response to the westerly jet equatorward shift than during the LIA. The out-of-phase pattern of moisture changes between India and ACA exists during both the LIA and the MCA. However, the pattern is more pronounced during the LIA.     

Alpidische Gebirgsbildung in den Ostalpen: ein plattentektonisches Modell (Kurzfassung)

Zusammenfassung Plattentektonische Modelle stellen neue Hilfsmittel für die Interpretation der alpinen Orogenese dar. Die Bildung ozeanischer Kruste und ihre gleichzeitige oder nachfolgende Abführung (Subduktion) im alpinen Raum werden als Hauptmechanismen tektonischer Ereignisse angesehen.Der Ablauf der alpidischen Gebirgsbildung als plattentektonisches Modell kann in fünf Epochen eingeteilt werden: Oberes Perm bis Trias, erste Gliederung des Ost- und Südalpenraumes mit Ausbildung zweier Grabensysteme; Lias bis Malm die Öffnung des penninischen Ozeans und Trennung der Eurasischen Platte von der Ostalpin-Südalpin-Adriatischen Platte; Malm bis Unterkreide, Ausdehnung des penninischen Ozeans und Bildung ozeanischer Kruste; Genoman bis Eozän, Subduktion der penninischen ozeanischen Lithosphäre unter die Ostalpin-Südalpin-Adriatische Platte und oberes Eozän bis Pliozän, Kollision der kontinentalen Platten und zentralalpine Hebungen.

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A plate tectonics model has been applied to explain mountain building in the eastern Alps. The formation of ridge-type oceanic crust and its destruction in a subduction zone are regarded ast the main mechanisms for the alpine orogeny.The process can be divided into five tectonic epochs: Permo-Triassic ( 235-200 m. y.) first tectonic subdivision of the Eastern and Southern Alps and formation of two different rift systems; Liassic to Malm ( 195-150 m. y.) opening of the Penninic Ocean or Piemontais and separation of the Eurasian plate from the Austroalpine-Southalpine-Adriatic plate); Malm to Early Cretaceous ( 150-110 m. y.) formation of ridge-type oceanic crust in the Penninic Ocean; Cenomanian to Eocene ( 100-45 m. y.) subduction of the Penninic oceanic lithosphere under the Austroalpine-Southalpine-Adriatic plate; Late Eocene to Miocene ( 42-5 m. y.) collision of the two continental plates and vertical uplift.

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Résumé La formation d'une croûte océanique et sa subduction contemporaine et postérieure sont invoquées ici comme l'un des mécanismes essentiels de l'évolution tectonique des Alpes orientales.Utilisant, comme modèle, la tectonique des plaques, l'orogénèse alpine peut se diviser en cinq «époques»: Permien supérieur-Trias (env. 235-200 m. a.), première individualisation tectonique entre les Alpes orientales et méridionales et dévelopement de deux systèmes de grabens; Lias-Malm (env. 195-150 m. a.), ouverture de l'océan pennique et séparation des plaques «Eurasia» et «Austroalpine-Meridionale-Adriatique»; Malm — Crétacé inférieure (env. 150-110 m.a.); extension de l'océan pennique et formation d'une croûte océanique; Cénomanien-Eocène (env. 100-45 m. a.), subduction de la lithosphère océanique sous la plaque «Austroalpine-Meridionale-Adriatique» et Eocène supérieur-Pliocène (env. 42-5 m. a.), collision des plaques continentales et soulèvement des Alpes centrales.

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Vortrag, am 27. 2. 1975 auf der 65. Jahrestagung der Geologischen Vereinigung in Karlsruhe gehalten.     

Feeding behaviour of adult Centropages hamatus (Copepoda, Calanoida): Functional response and selective feeding experiments

The feeding behaviour of adults of the marine calanoid copepod Centropages hamatus was studied in laboratory experiments with ciliates and phytoplankton as food sources. The ingestion rate of algal (flagellates, diatoms) and ciliate prey (oligotrichs) as a function of prey concentration could be described by a Holling type III functional response, with close to zero ingestion rates at concentrations below 5 µg C l^− 1. In general, ingestion of ciliates was higher than ingestion of algae, and maximum feeding rates by adult males reached were half the feeding rates of adult females at prey concentrations exceeding 50 µg C l^− 1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as long as they contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching between suspension feeding and ambush predation. Therefore, the feeding behaviour of adult C. hamatus can be characterised as omnivorous with a preference for larger motile prey. This implies a trophic level above two, if there is a sufficient abundance of protozoan food available.     

228Ra, 226Ra, 224Ra and 223Ra in potential sources and sinks of land-derived material in the German Bight of the North Sea: implications for the use of radium as a tracer

Activities of the naturally occurring radium nuclides ²²⁸Ra, ²²⁶Ra, ²²⁴Ra and ²²³Ra were determined in waters of the open German Bight and adjacent nearshore areas in the North Sea, in order to explore the potential use of radium isotopes as natural tracers of land–ocean interaction in an environment characterised by extensive tidal flats, as well as riverine and groundwater influx. Data collected at various tidal phases from the Weser Estuary (²²⁸Ra: 46.3 ± 4.6; ²²⁶Ra: 17.1 ± 1.1; ²²⁴Ra: 26.1 ± 8.2 to 36.5 ± 6.1; ²²³Ra: 1.8 ± 0.1 to 4.0 ± 0.4), tidal flats near Sahlenburg (²²⁸Ra: 39.3 ± 3.8 to 46.0 ± 4.5; ²²⁶Ra: 15.5 ± 1.5 to 16.5 ± 1.7; ²²⁴Ra: 34.3 ± 2.2 to 85.3 ± 6.3; ²²³Ra: 3.6 ± 0.5 to 8.0 ± 1.2), freshwater seeps on tidal flats near Sahlenburg (²²⁸Ra: 42.1 ± 4.1; ²²⁶Ra: 21.3 ± 2.2; ²²⁴Ra: 5.1 ± 0.9; ²²³Ra: 2.6 ± 1.3) and also in permanently inundated parts of the North Sea (²²⁸Ra: 23.0 ± 2.3 to 28.2 ± 2.8; ²²⁶Ra: 8.2 ± 0.8 to 11.8 ± 1.2; ²²⁴Ra: 3.1 ± 1.0 to 10.1 ± 0.9; ²²³Ra: 0.1 ± 0.02 to 0.9 ± 0.05; units: disintegrations per minute per 100 kg water sample) reveal that, except for the fresh groundwater, the potential end-members of nearshore water mass mixing have quite similar radium signatures, excluding a simple discrimination between the sources. However, the decreasing activities of the short-lived ²²⁴Ra and ²²³Ra isotopes recorded towards the island of Helgoland in the central German Bight show a potential to constrain fluxes of land-derived material to the open North Sea. The largest source for all radium isotopes is generally found on the vast tidal flats and in the Weser Estuary. Future work could meaningfully combine this so-called radium quartet approach with investigations of radon activity. Indeed, preliminary data from a tidal flat site with fresh groundwater seepage reveal a ²²²Rn signal that is clearly lower in seawater.     

Hydrogen peroxide production rates in clean and polluted coastal marine waters of the Mediterranean, Red and Baltic Seas

The main aim of this study was to assess the hydrogen peroxide (HP) production rates (HPPR) related to anthropogenic pollution in coastal waters by laboratory and field experiments. HPPR's were assessed by simultaneous measurements of HP concentrations, cumulative solar UV irradiation and dissolved organic matter (DOM) fluorescence in the seawater samples at clean and polluted sites in the Mediterranean, Red and the Baltic Seas. The natural HP concentrations at all sites (8–100 nM) fall within the normal range recorded elsewhere, and follows a diurnal pattern. The polluted stations in the Mediterranean and Baltic Seas showed higher HPPR (3.2–16.6 nM m² W⁻¹ h⁻¹) than the clean stations, while in the Red Sea no significant differences were found because the station that was considered a priori polluted was actually rather clean (2–3 nM m² W⁻¹ h⁻¹). Laboratory experiments demonstrated that HPPR was positively linearly correlated to DOM fluorescence, however, this relationship was not found in the natural seawater samples examined in the field. The lack of relationship between HPPR and DOM in the field was attributed to enzymatic breakdown of HP as observed in dark decay experiments. HP dark decay rates were highest in polluted stations, probably due to larger bacterioplankton populations in these samples. Moreover, the HP dark decay rates were much lower in filtered than in non-filtered samples. Sun incubation of filtered (0.2 μm) seawater samples were performed to assess whether elimination of particles would yield higher HPPRs than in non-filtered samples. In the Baltic Sea (low UV irradiation) HPPR was higher in the filtered samples, while at sites with relatively high UV irradiation (Mediterranean and Red Seas), filtration of seawater did not stimulate HPPRs, probably due to UV-damage to planktonic microorganisms.     

The golden ark: arsenopyrite crystal plasticity and the retention of gold through high strain and metamorphism

Quantitative electron backscatter diffraction analysis and ion microprobe imaging of gold‐rich arsenopyrites provide the first insights into the crystal plasticity and element mobility behaviour of arsenopyrites through metamorphism (340°–460° and 2 kbar). Remarkably, the gold‐rich arsenopyrites remained structurally and chemically robust during high strain deformation. It was only during a superimposed lower strain deformation event, at a high angle to the preferred orientation of the arsenopyrites, that small amounts of crystal plasticity affected the arsenopyrites. During the low strain event, a dissolution–reprecipitation reaction resulted in loss of gold from the crystal lattice, facilitated by localised domains of recrystallisation, most likely due to fluid percolation along sub‐ and new grain boundaries. We suggest that the abundance and rheologically robust nature of gold‐rich arsenopyrite in giant gold deposits, affected by greenschist–amphibolite metamorphism, is actually critical in the preservation of those deposits.     

The trophic importance of epiphytic algae in a freshwater macrophyte system (<Emphasis Type="Italic">Potamogeton perfoliatus</Emphasis> L.): stable isotope and fatty acid analyses

Stable isotope and fatty acid analyses were used to study carbon sources for animals in a submerged plant bed. Epiphytes growing on Potamogeton perfoliatus, sand microflora, and alder leaves were the most important carbon sources. The most abundant macrophyte, P. perfoliatus was unimportant as a food source. Modelling (IsoSource) showed that epiphytes were the most important food source for the most abundant benthic invertebrates, the isopod Asellus aquaticus (annual mean contribution 64%), the amphipod Gammarus pulex (66%), and the gastropod Potamopyrgus antipodarum (83%). The mean annual contributions of sand microflora were, respectively, 21, 19, and 9%; and of alder leaves, 15, 15, and 8% for these three species. The relative importance of carbon sources varied seasonally. The relative contribution of epiphytes was lowest for all three grazer species in July: A. aquaticus 38%, G. pulex 43%, and P. antipodarum 42%. A decline in epiphyte biomass in summer may have caused this switch to less attractive food sources. P. perfoliatus provided habitat and shelter for consumers, but food was mainly supplied indirectly by providing space for attached epiphytes, which are fast-growing and provide a highly nutritious food source.