The Puu Oo eruption in the middle of Kilauea volcano's east rift zone provides an excellent opportunity to utilize petrologic constraints to interpret rift-zone processes. Emplacement of a dike began 24 hours before the start of the eruption on 3 January 1983. Seismic and geodetic evidence indicates that the dike collided with a magma body in the rift zone. Most of the lava produced during the initial episode of the Puu Oo eruption is of hybrid composition, with petrographic and geochemical evidence of mixing magmas of highly evllved and more mafic compositions. Some olivine and plagioclase grains in the hybrid lavas show reverse zoning. Whole-rock compositional variations are linear even for normally compatible elements like Ni and Cr. Leastsquares mixing calculations yield good residuals for major and trace element analyses for magma mixing. Crystal fractionation calculations yield unsatisfactory residuals. The highly evolved magma is similar in composition to the lava from the 1977 eruption and, at one point, vents for these two eruptions are only 200 m apart. Possibly both the 1977 lava and the highly evolved component of the episode 1 Puu Oo lava were derived from a common body of rift-zone-stored magma. The more mafic mixing component may be represented by the most mafic lava from the January 1983 eruption; it shows no evidence of magma mixing. The dike that was intruded just prior to the start of the Puu Oo eruption may have acted as a hydraulic plunger causing mixing of the two rift-zone-stored magmas. 相似文献
During the last two decades, extensive road-construction works in Northern France have allowed the discovery of numerous Middle Palaeolithic sites. Geological and multidisciplinary studies performed on these localities allowed the establishment of a precise chronostratigraphical and biostratigraphical framework of regional significance, which could be correlated to the global marine palaeoclimatic scale. Each human occupation layer has been linked to this regional framework, thus providing a stratigraphical age-control for the Middle Palaeolithic human settlements of this area.At the same time, a program of geochronological studies was developed using TL, OSL, U-series, ESR and, as often as possible, ESR/U-series methods. Hence, bones and teeth recovered from archaeological sites of Savy, Ault, Caours, Gentelles and La Celle-sur-Seine, were analyzed and the results compared to the chronostratigraphical ages. The age results are generally in good agreement with the geological data while bones and dental tissues display in some cases U-series ages higher that the EU-ESR ones, suggesting U-loss phenomena. 相似文献
The combined U-series/electron spin resonance (ESR) dating method was applied to nine teeth from two Early Pleistocene archaeological sites located in the Orce area (Guadix-Baza Basin, Southern Spain): Fuente Nueva-3 (FN-3) and Barranco León (BL). The combination of biostratigraphy and magnetostratigraphy places both sites between the Olduvai and Jaramillo subchrons (1.78–1.07 Ma).Our results highlight the difficulty of dating such old sites and point out the limits of the combined U-series/ESR dating method based on the US model. We identified several sources of uncertainties that may lead to inaccurate age estimates. Seven samples could not be dated because the dental tissues had (230Th/234U) activity ratios higher than equilibrium, indicating that uranium had probably leached from these tissues. It was however possible to calculate numerical estimates for two of the teeth, both from FN-3. One yielded a Middle Pleistocene age that seems to be strongly underestimated; the other provided an age of 1.19 ± 0.21 Ma, in agreement with data obtained from independent methods. The latter result gives encouragement that there are samples that can be used for routine dating of old sites. 相似文献
The choice of the ESR signal in the dating of speleothems is still debated. Among the peaks observed in speleothem ESR spectra, the most frequently signals used for the determination of the palaeodoses are the peaks at g=2.0007 (h3 line), g=2.0040 (Broad Line) and g=2.0057 (h1 line).
In order to determine the better analytical way to obtain reproducible DE values from these three ESR signals, successive additional annealing treatments ranging from 60–300 °C were performed on several samples of a stalagmitic floor from the Mousterian site of the Caverna delle Fate (Liguria, Italy), also dated by U-series between 90 and130 ka. The results confirm that DE values can be obtained from h3 and BL signals without annealing, while the h1 signal requires a thermal pre-treatment, to obtain the maximum intensity of this line. Then, on our samples, the DEvalues derived for the three lines are equivalent. It gives, hence, the opportunity to obtain data when the g=2.0007 line cannot be used. 相似文献
Climatic variability arising from the coupling between ocean temperature and sea-ice extent is studied in a spatially distributed system. A spatial degree of freedom is crudely introduced by the coupling, through energy transfer, of two box models each of which describes a different space region. The evolution equations are cast into a normal form and some qualitative features of this general class of models are predicted. It is shown, both analytically and numerically, that internally generated complexity in the form of aperiodic behaviour can be a natural consequence of spatially distributed systems. 相似文献