Compositional trends among IID irons; their possible formation from the P-rich lower magma in a two-layer core

Group IID is the fifth largest group of iron meteorites and the fourth largest magmatic group (i.e., that formed by fractional crystallization). We report neutron-activation data for 19 (of 21 known) IID irons. These confirm earlier studies showing that the group has a relatively limited range in Ir concentrations, a factor of 5. This limited range is not mainly due to incomplete sampling; Instead, it seems to indicate low solid/liquid distribution coefficients reflecting very low S contents of the parental magma, the same explanation responsible for the limited range in group IVA. Despite this similarity, these two groups have very different volatile patterns. Group IVA has very low abundances of the volatile elements Ga, Sb and Ge whereas in group IID Ga and Sb abundances are the highest known in a magmatic group of iron meteorites and Ge abundances are the second highest (after group IIAB). Group IID appears to be the only large magmatic group having high volatile abundances but low S. In the volatile-depleted groups IVA and IVB it is plausible that S was lost as a volatile from a chondritic precursor material. Because group IID seems to have experienced minimal loss of volatiles, we suggest that S was lost as an early melt having a composition near that of the Fe–FeS eutectic (315 mg/g S). When temperatures had risen 400–500 K higher P-rich melts formed, became gravitationally unstable, and drained through the first melt to form an inner core that was parental to the IID irons. As discussed by [Kracher, A., Wasson, J.T., 1982. The role of S in the evolution of the parental cores of the iron meteorites. Geochim. Cosmochim. Acta 46, 2419–2426], it is plausible that a metal-rich inner core and a S-rich outer core could coexist metastably because stratification near the interface permitted only diffusional mixing. The initial liquidus temperature of the inner, P-rich core is estimated to have been 1740 K; after >60% crystallization the increase in P and the decrease in temperature may have permitted immiscibility with the S-rich outer core. We have not recognized samples of the outer core.     

Accretionary lapilli from the Sudbury impact event

Meteorite impact‐generated accretionary lapilli are not well studied. The recently discovered distal ejecta from the 1850 Ma Sudbury impact event contain abundant accretionary lapilli generated during the impact and deposited at great distances from the crater. We petrographically and geochemically examined lapilli from five sites (McClure, Connors Creek, Hwy 588, Pine River, and Grand Trunk Pacific, approximately 480–750 km from the center of the Sudbury structure). The compositions of quartz, K‐feldspar, calcite, biotite, and chlorite minerals are similar to each other in all of the samples, although the relative proportions of the minerals vary from site to site. The lapilli occur in a matrix of coarse‐grained quartz, carbonate, and feldspar grains. Zonation within lapilli appears to be due to grain size distribution rather than compositional variation. The inner zones are coarser grained than outer zones. The relative abundances of calcite, phyllosilicates, and feldspars are similar in each zone within individual lapilli. A meteoritic component is indicated by up to 1.8 ppb Ir in one lapillus from the Pine River site, and Ni and Cr ratios are on a chondritic trend line for many of the lapilli. Mechanisms previously proposed for accretionary lapilli formation seem inadequate to explain deposition of distal accretionary lapilli resulting from impact events. A new mechanism for upper atmospheric accretion is proposed, whereby ash ejected from impact events concentrates at altitudes of neutral buoyancy, where it then accretes and is deposited later than ballistically emplaced particles. Likely, multiple processes are taking place in the chaotic postimpact environment.     

North Atlantic climate impact on early late‐glacial climate oscillations in the south‐eastern Alps inferred from a multi‐proxy lake sediment record

High‐resolution multi‐proxy analyses of a sediment core section from Lake Jeserzersee (Saissersee) in the piedmont lobe of the Würmian Drau glacier (Carinthia, Austria) reveal pronounced climatic oscillations during the early late glacial (ca. 18.5–16.0k cal a BP). Diatom‐inferred epilimnetic summer water temperatures show a close correspondence with temperature reconstructions from the adjacent Lake Längsee record and, on a hemispheric scale, with fluctuations of ice‐rafted debris in the North Atlantic. This suggests that North Atlantic climate triggered summer climate variability in the Alps during the early late glacial. The expansion of pine (mainly dwarf pine) between ca. 18.5 and 18.1k cal a BP indicates warming during the so‐called ‘Längsee oscillation’. The subsequent stepwise climate deterioration between ca. 18.1 and 17.6k cal a BP culminated in a tripartite cold period between ca. 17.6 and 16.9k cal a BP with diatom‐inferred summer water temperatures 8.5–10 °C below modern values and a shift from wet to dry conditions. This period probably coincides with a major Alpine glacier advance termed the Gschnitz stadial. A warmer interval between ca. 16.9 and 16.4k cal a BP separates this cold phase from a second, shorter and less pronounced cold phase between ca. 16.4 and 16.0k cal a BP, which is thought to correlate with the Clavadel/Senders glacier advance in the Alps. The following temperature increase, coupled with wet (probably snow‐rich) conditions, caused the expansion of birch during the transition period to the late glacial interstadial. Copyright © 2011 John Wiley & Sons, Ltd.     

Field verification of a theoretical model to predict the dynamic response of a soft clay deposit

A 40-m thick clay deposit was subjected to sinusoidal excitations using a foundation block and an eccentric mass type vibrator. The response of the foundation block and the surrounding soil was measured using geophones inside the soil and on the surface. The phase shift between the excitation signal and the response signal, the accelerations of the foundation block and the particle velocities in the soil are compared with those obtained from a frequency-dependent numerical model based on the exact analytical solution for the boundary value problem of a rectangular foundation resting on a linear elastic halfspace.     

The historic and artistic heritage facing the earthquake risk: The Italian case

The problem of protection against earthquakes in Italy is made difficult by the presence of a huge historic and artistic heritage. Such a heritage is mainly made up of ancient buildings and monuments situated in the urban centres, which are densely distributed throughout Italy. Therefore, very complex problems are met in the determination of the value parameter concurring with the determination of seismic risk, in addition to hazard and vulnerability. An indication of the monetary value of a building is not sufficient as far as the cultural heritage is concerned: different criteria are necessary in order to distinguish which are the strategic buildings. If we consider that there are more than 2000 museums in Italy, most of which are placed inside historic buildings, it appears that museums should receive the highest priority in future initiatives for seismic rehabilitation.     

Dendrochronologie

Zusammenfassung Die Dendrochronologie arbeitet mit der Jahresschichtung des Holzes. Der Zuwachs gleichzeitig wachsender Hölzer ist ähnlich. Diese Forschungsrichtung braucht viel Material zur Herstellung typischer Mittelkurven. Mit Hilfe der Überbrückungsmethode kommt man örtlich sehr weit zurück. Schwierigkeiten liegen in der gesetzmäßigen Abnahme der Ähnlichkeit von Jahresringkurven mit der Entfernung voneinander. Neben einer absoluten Chronologie sind in Deutschland relative Chronologien aus Jungsteinzeit und Bronzezeit erarbeitet worden. Die Dendrochronologie kann gewisse Aussagen über Klimaschwankungen machen.