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21.
A large number of calcrete samples from topsoils of the Doukkâli area, western Morocco, were studied by U-disequilibrium series methods. The 230Th/234U ages are rather uniformly distributed between>350 and 2 ka BP. Homologous samples for occurrence and structure display quite different ages, the 230Th/234U ages are considered apparent. This is explained by repeated deposition of secondary calcite in the calcrete pores, which caused lowering of the original ages. However, the apparent ages may be considered minimum ages of the calcrete formation, indicating that calcium carbonate mobilization and deposition has been taking place repeatedly since >350 ka.
The age range obtained is quite comparable with that of calcretes from southern Spain, suggesting similar conditions for the calcrete formation in the two areas. 相似文献
22.
Earthquake Damage Scenarios of the Building Stock of Potenza (Southern Italy) Including Site Effects 总被引：3，自引：0，他引：3
Mauro Dolce Angelo Masi Maria Marino Marco Vona 《Bulletin of Earthquake Engineering》2003,1(1):115-140
Damage scenarios relevant to the building stock of the town of Potenza, Southern Italy, are presented. A procedure for the
preparation of scenarios has been purposely set up. In the first step, the inventory of the building stock has been made.
Location and characteristics of buildings have been obtained from a survey carried out after the 1990 Potenza earthquake and
further updated in 1999. In the second step, the absolute vulnerability of the buildings has been evaluated. A hybrid technique
has been used, where typological analyses and expert judgement are combined together. Beyond the classes of vulnerability
A, B and C of the MSK scale, the class D of EMS98 scale, for the less vulnerable buildings, has been considered. The third
step has been the selection of the reference earthquakes by including also local amplification effects. Two events with 50
and 475 years return periods have been chosen as representative, respectively, of a damaging and of a destructive seismic
event expected in Potenza. The sites that may exhibit important amplification effects have been identified using the first
level method of the TC4 Manual. Damage scenarios of dwelling buildings have been prepared in the fourth step and reported
in a GIS. They are relevant to the selected reference earthquakes, taking into account or not site effects. The generally
low vulnerability of buildings results in a limited number of damaged buildings for the lower intensity earthquake, and of
collapsed buildings, for the higher intensity earthquake. The influence of site effects on the damage distribution is significant.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
23.
Stable isotope evidence for a marine origin of ophicalcites from the north-central Apennines (Italy) 总被引：1，自引：0，他引：1
Carbon and oxygen isotope ratios of 59 samples of Mesozoic ophicalcites from the north-central Apennines were measured. Strontium content and isotope ratios were only determined for selected samples.
The data obtained (−4.1 ≤ δ 13C ≤ + 3.0; 16.5 ≤ δ 18O ≤ 30.1; 0.7076 ≤ 87Sr/86Sr ≤ 0.7086; 60 ≤ Sr ppm ≤ 1140) suggest that the carbonate cement of the Apennines ophicalcites had a marine origin.
The 18O/16O values of most of the carbonates studied, however, indicate that the rocks have interacted with hydrothermal fluids, dominantly represented by sea water. In particular, the rocks from the northern section of the Apennines apparently reequilibrated their δ 18O content at higher temperature than those from the central zone.
Strontium isotope ratios, close to the Cretaceous—Cenozoic ocean water values, are well in agreement with such a kind of sea water/ophicalcites interaction, even if the carbonate cement formed earlier during the Jurassic period. 相似文献
24.
Sr content was measured in 6 fluorite and 7 calcite samples from an epithermal deposit of fluorite at Monte delle Fate near Cerveteri (Latium, Italy). Sr isotope ratios were obtained from two selected samples. Sr contents of calcite range from 1,200 to 2,620 ppm and of fluorite from 10 to 360 ppm. 87Sr/86Sr values of calcite and fluorite are 0.7087 and 0.7091, respectively. Such isotope ratios clearly indicate that the bulk of strontium present in both minerals was provided by marine sedimentary reservoirs. According to the Sr distribution coefficient, the low contents measured in fluorite, which formed after calcite, clearly prove that the mineral was not deposited by the same kind of waters from which calcite originated. The high Sr contents of calcite suggest that the bicarbonate-bearing waters have largely interacted with Ca-sulphate evaporites of Upper Triassic age. On the contrary, the waters from which fluorite precipitated were apparently involved in a more superficial circulation through post-Triassic sedimentary formations.
Résumé On a determiné la teneur de strontium dans 6 échantillons de fluorite et 7 échantillons de calcite d'un gisement à fluorite près de Monte delle Fate, Cerveteri (Latium; Italie centrale). De plus les rapports isotopiques du même élément ont été mésurés pour deux échantillons choisis. Les teneurs du strontium dans la calcite et la fluorite varient de 1 200 à 2 620 ppm et de 10 à 360 ppm, respectivement. La valeur du rapport 87Sr/86Sr est pour la calcite 0,7087 et pour la fluorite 0,7091. Ces rapports indiquent que les sédiments marins ont été la source de la plupart du strontium dans les deux minéraux. Selon le coefficient de distribution du strontium, la fluorite, de déposition postérieure à la calcite, n'a pas pu précipiter de la même eau de la calcite. Les teneurs élevées de l'élément dans la calcite sont la conséquence de l'interaction des eaux bicarbonatées avec les sédiments sulfate-évaporitiques du Triassique supérieur. Au contraire les eaux primaires de la fluorite ont circulé dans les sédiments post-Triassiques.相似文献
25.
Carbon, oxygen and hydrogen isotope variations have been measured in samples from the epithermal fluorite vein deposit at Monte delle Fate, Latium. The ranges in 13C and 18O of calcite are –1.3 to 3.4 and 9.5 to 17.3, respectively. D values of water extracted from fluid inclusions are –49 to –39 for calcite and –41 to –34 for fluorite. Fluid inclusion filling temperatures (225°–240°C) and salinites (3.75) are nearly the same for both fluorite and sparry calcite. An elongated form of calcite, of minor abundance, precipitated at lower temperatures. The data indicate that (1) the CO2 involved in the mineralization was provided by the local marine limestones, (2) the waters were meteoric in origin and underwent an 18O shift of 10 permil by exchange with marine country rocks, and (3) all geochemical features can be explained by the action of two hydrothermal fluids. Hot brines recently discovered in the Cesano geothermal area, 30 km to the east, have temperatures and some chemical characteristics similar to the hydrothermal fluids at Monte delle Fate. 相似文献
26.
The role of site effects in the comparison between code provisions and the near field strong motion of the Emilia 2012 earthquakes 总被引：1，自引：1，他引：0
Maria Rosaria Gallipoli Leonardo Chiauzzi Tony Alfredo Stabile Marco Mucciarelli Angelo Masi Carmine Lizza Luigi Vignola 《Bulletin of Earthquake Engineering》2014,12(5):2211-2230
A damaging seismic sequence hit a wide area mainly located in the Emilia-Romagna region (Northern Italy) during 2012 with several events of local magnitude \(\hbox {M}_\mathrm{l} \ge 5\) , among which the \(\hbox {M}_\mathrm{l}\) 5.9 May 20 and the \(\hbox {M}_\mathrm{l}\) 5.8 May 29 were the main events. Thanks to the presence of a permanent accelerometric station very close to the epicentre and to the temporary installations performed in the aftermath of the first shock, a large number of strong motion recordings are available, on the basis of which, we compared the recorded signals with the values provided by the current Italian seismic regulations, and we observed several differences with respect to horizontal components when the simplified approach for site conditions (based on Vs30 classes) is used. On the contrary, when using the more accurate approach based on the local seismic response, we generally obtain a much better agreement, at least in the frequency range corresponding to a quarter wavelength comparable with the depth of the available subsoil data. Some unresolved questions still remain, such as the low frequency behaviour ( \(<\) 1 Hz) that could be due either to complex propagation at depth larger than the one presently investigated or to near source effects, and the behaviour of vertical spectra whose recorded/code difference is too large to be explained with the information currently available. 相似文献
27.
28.
Castorina Francesca Magganas Andreas Masi Umberto Kyriakopoulos Konstantinos 《Mineralogy and Petrology》2020,114(1):39-56
Mineralogy and Petrology - Geochemistry and Sr-Nd isotopes were determined in Triassic calcalkaline metalava and metapyroclastic rocks from Attica and Argolida, central Greece, to ascertain their... 相似文献
29.
Summary ?Major and trace element contents and Sr–Nd isotope ratios of selected volcanics of Pliocene age from the Almopia area, central
Macedonia, Greece, have been determined. These rocks are mainly distinguished as two groups based on geographical, petrological
and isotopic data: a) the east–central western group (E–CW) and b) the south western group (SW). The absence of contemporaneous
basic volcanics in the Almopia area coupled with the considerable scatter of elements in variation diagrams rule out fractional
crystallization as the dominant differentiation process. Instead, disequilibrium textures along with the positive correlation
of Sr-isotope ratios with differentiation suggest mixing between a basic and an acid component combined with assimilation
and fractionation.
The spider diagrams of the most silica-poor volcanics show evidence of subduction-related processes, indicating that the parental
magmas may have been derived from partial melting of mantle wedge enriched in LILE and LREE by subducted slab-derived fluids.
Previous data on the oxygen isotope composition of the same volcanics are consistent with this genetic hypothesis. Lastly,
the relatively high 87Sr/86Sr and low 143Nd/144Nd ratios (0.7080 and 0.512370, respectively) of the volcanic sample inferred to be compositionally the closest one to the
parental magma of Almopia rocks suggest that the incompatible element enrichment of the mantle source is old, probably of
Proterozoic age.
Received December 12, 2001; revised version accepted June 20, 2002
Published online November 29, 2002 相似文献
30.
M. Dominik U.G. Jrgensen N.J. Rattenbury M. Mathiasen T.C. Hinse S. Calchi Novati K. Harpse V. Bozza T. Anguita M.J. Burgdorf K. Horne M. Hundertmark E. Kerins P. Kjrgaard C. Liebig L. Mancini G. Masi S. Rahvar D. Ricci G. Scarpetta C. Snodgrass J. Southworth R.A. Street J. Surdej C.C. Thne Y. Tsapras J. Wambsganss M. Zub 《Astronomische Nachrichten》2010,331(7):671-691
Within less than 15 years, the count of known planets orbiting stars other than the Sun has risen from none to more than 400 with detections arising from four successfully applied techniques: Doppler‐wobbles, planetary transits, gravitational microlensing, and direct imaging. While the hunt for twin Earths is on, a statistically well‐defined sample of the population of planets in all their variety is required for probing models of planet formation and orbital evolution so that the origin of planets that harbour life, like and including ours, can be understood. Given the different characteristics of the detection techniques, a complete picture can only arise from a combination of their respective results. Microlensing observations are well‐suited to reveal statistical properties of the population of planets orbiting stars in either the Galactic disk or bulge from microlensing observations, but a mandatory requirement is the adoption of strictly‐deterministic criteria for selecting targets and identifying signals. Here, we describe a fully‐deterministic strategy realised by means of the ARTEMiS (Automated Robotic Terrestrial Exoplanet Microlensing Search) system at the Danish 1.54‐m telescope at ESO La Silla between June and August 2008 as part of the MiNDSTEp (Microlensing Network for the Detection of Small Terrestrial Exoplanets) campaign, making use of immediate feedback on suspected anomalies recognized by the SIGNALMEN anomaly detector. We demonstrate for the first time the feasibility of such an approach, and thereby the readiness for studying planet populations down to Earth mass and even below, with ground‐based observations. While the quality of the real‐time photometry is a crucial factor on the efficiency of the campaign, an impairment of the target selection by data of bad quality can be successfully avoided. With a smaller slew time, smaller dead time, and higher through‐put, modern robotic telescopes could significantly outperform the 1.54‐m Danish, whereas lucky‐imaging cameras could set new standards for high‐precision follow‐up monitoring of microlensing events (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献