Comparative Re-Os systematics of chondrites: Implications regarding early solar system processes

A suite of 47 carbonaceous, enstatite, and ordinary chondrites are examined for Re-Os isotopic systematics. There are significant differences in the ¹⁸⁷Re/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os ratios of carbonaceous chondrites compared with ordinary and enstatite chondrites. The average ¹⁸⁷Re/¹⁸⁸Os for carbonaceous chondrites is 0.392 ± 0.015 (excluding the CK chondrite, Karoonda), compared with 0.422 ± 0.025 and 0.421 ± 0.013 for ordinary and enstatite chondrites (1σ standard deviations). These ratios, recast into elemental Re/Os ratios, are as follows: 0.0814 ± 0.0031, 0.0876 ± 0.0052 and 0.0874 ± 0.0027, respectively. Correspondingly, the ¹⁸⁷Os/¹⁸⁸Os ratios of carbonaceous chondrites average 0.1262 ± 0.0006 (excluding Karoonda), and ordinary and enstatite chondrites average 0.1283 ± 0.0017 and 0.1281 ± 0.0004, respectively (1σ standard deviations). The new results indicate that the Re/Os ratios of meteorites within each group are, in general, quite uniform. The minimal overlap between the isotopic compositions of ordinary and enstatite chondrites vs. carbonaceous chondrites indicates long-term differences in Re/Os for these materials, most likely reflecting chemical fractionation early in solar system history.A majority of the chondrites do not plot within analytical uncertainties of a 4.56-Ga reference isochron. Most of the deviations from the isochron are consistent with minor, relatively recent redistribution of Re and/or Os on a scale of millimeters to centimeters. Some instances of the redistribution may be attributed to terrestrial weathering; others are most likely the result of aqueous alteration or shock events on the parent body within the past 2 Ga.The ¹⁸⁷Os/¹⁸⁸Os ratio of Earth’s primitive upper mantle has been estimated to be 0.1296 ± 8. If this composition was set via addition of a late veneer of planetesimals after core formation, the composition suggests the veneer was dominated by materials that had Re/Os ratios most similar to ordinary and enstatite chondrites.     

Inelastic dynamic analysis of RC bridges accounting for spatial variability of ground motion,site effects and soil–structure interaction phenomena. Part 1: Methodology and analytical tools

During strong ground motion it is expected that extended structures (such as bridges) are subjected to excitation that varies along their longitudinal axis in terms of arrival time, amplitude and frequency content, a fact primarily attributed to the wave passage effect, the loss of coherency and the role of local site conditions. Furthermore, the foundation interacts with the soil and the superstructure, thus significantly affecting the dynamic response of the bridge. A general methodology is therefore set up and implemented into a computer code for deriving sets of appropriately modified time histories and spring–dashpot coefficients at each support of a bridge with account for spatial variability, local site conditions and soil–foundation–superstructure interaction, for the purposes of inelastic dynamic analysis of RC bridges. In order to validate the methodology and code developed, each stage of the proposed procedure is verified using recorded data, finite‐element analyses, alternative computer programs, previous research studies, and closed‐form solutions wherever available. The results establish an adequate degree of confidence in the use of the proposed methodology and code in further parametric analyses and seismic design. Copyright © 2003 John Wiley & Sons, Ltd.     

Eocene-Pliocene time scale and stratigraphy of the Upper Rhine Graben (URG) and the Swiss Molasse Basin (SMB)

We present a general stratigraphic synthesis for the Upper Rhine Graben (URG) and the Swiss Molasse Basin (SMB) from Eocene to Pliocene times. The stratigraphic data were compiled both from literature and from research carried out by the authors during the past 6 years ; an index of the stratigraphically most important localitites is provided. We distinguish 14 geographical areas from the Helvetic domain in the South to the Hanau Basin in the North. For each geographical area, we give a synthesis of the biostratigraphy, lithofacies, and chronostratigraphic ranges. The relationships between this stratigraphic record and the global sea-level changes are generally disturbed by the geodynamic (e.g., subsidence) evolution of the basins. However, global sea-level changes probably affected the dynamic of transgression–regression in the URG (e.g., Middle Pechelbronn Beds and Serie Grise corresponding with sea-level rise between Ru1/Ru2 and Ru2/Ru3 sequences, respectively) as well as in the Molasse basin (regression of the UMM corresponding with the sea-level drop at the Ch1 sequence). The URGENT-project (Upper Rhine Graben evolution and neotectonics) provided an unique opportunity to carry out and present this synthesis. Discussions with scientists addressing sedimentology, tectonics, geophysics and geochemistry permitted the comparison of the sedimentary history and stratigraphy of the basin with processes controlling its geodynamic evolution. Data presented here back up the palaeogeographic reconstructions presented in a companion paper by the same authors (see Berger et al. in Int J Earth Sci 2005).     

Origin of chondritic forsterite grains

Iron-poor and refractory lithophile element (RLE) rich forsterite grains occur in all major types of unequilibrated chondrites. In our laser ablation inductively coupled mass spectrometry (LA-ICPMS) minor and trace element study we show that refractory forsterites (RF) from carbonaceous (CC), unequilibrated ordinary (UOC) and a Rumuruti chondrite (RC) have similar chemical compositions with high RLE concentrations and low concentrations of Mn, Fe, Co and Ni. Fractionation of RLEs and rare earth elements (REEs) is in agreement with formation by crystallization from a RLE rich silicate melt. Low concentrations and the fractionation of moderately siderophile elements (Fe, Co, Ni) in RFs suggests formation at low oxygen fugacity, possibly in equilibrium with primitive Fe,Ni metal condensates in a gas of solar composition. Anomalously high Ti in the parental melt can be explained by Ti³⁺/Ti⁴⁺ ∼1.5, supporting formation of RF in highly reducing conditions. Low Mn concentrations indicate formation at high temperatures (>∼1160 K). The model of formation of RFs and the accompanying physico-chemical conditions during their formation as well as their relation to non refractory olivine are discussed.     

Human-biometeorological assessment of heat waves in Athens

The goal of this study is the analysis of heat waves and their impact on humans, using human biometeorological indices, which are based on the energy balance of the human body. The implications for humans are not only described through the intensity of the heat waves, but also through their duration over consecutive days. Both intensity and duration were analyzed for the Greater Athens Area during the period 1955 to 2001. The analysis was carried out using the daily physiologically equivalent temperature and the daily minimum air temperature. Based on these two parameters, the results showed an increase in the average duration of heat waves. Furthermore, the use of the Gaussian filter revealed the intra-annual variation of heat stress conditions and their relevance to humans. The results could be used for the management of the negative consequences of heat waves in cities suffering from environmental pollution and also for climate impact studies.     

Climatology of Ozone, PAN, CO, and NMHC in the Free Troposphere Over the Southern North Atlantic

Free tropospheric measurements of ozone, peroxyacetylnitrate andprecursors (CO, NMHC) that were made within the framework of the EUROTRACsub-project TOR (Tropospheric Ozone Research) between 1990 and 1995 at theGAW station Izana, Tenerife (28°18N, 16°30W) arediscussed. The average annual cycles reveal the importance of transport fromnorthern mid-latitudes and the role of photo-chemistry. According toair-mass trajectories, which were supplied to us from AEROCE(Atmosphere/Ocean Chemistry Experiment), transport from northernmid-latitudes is associated with high precursor concentrations in winter,whereas ozone concentrations in winter are not much influenced by transportpatterns, suggesting a rather uniform distribution over the northern part ofthe Northern Hemisphere around mean value of 43 ± 5 ppb. In summer,high ozone concentrations of up to 90 ppb are often encountered duringtransport from north, while the levels of precursors are much lower than inwinter, because of photochemical destruction. Trajectories from southerlylatitudes and the Sahara usually have the lowest ozone concentrationsassociated with them.