Tufas, which are freshwater carbonates, are potential archives of terrestrial paleoclimate. Time series of stable isotopic compositions commonly show regular seasonal patterns controlled by temperature-dependent processes, and some perturbation intrinsic to the locality. We examined three tufa-depositing sites in southwestern Japan with similar temperate climates, to understand the origin of local characteristics in the isotopic records. Seasonal change in the oxygen isotope is principally reflected by temperature-dependent fractionation between water and calcite but was perturbed after heavy rainfalls overwhelming the stability of the δ18O value of the groundwater at one site. Isotopic mass balance indicates an undersaturated and relatively small aquifer at this locality. Water δ18O values at the other two sites were stable, reflecting a regular seasonal change in the δ18O value of tufa. Perturbation of the δ13C values in tufa is largely due to CO2 degassing from the stream, which significantly increases the δ13C values of dissolved inorganic carbon (DIC). At a site with remarkably high pCO2 in springwater and a sensitive response of flow rate to rainfall, the amount of CO2 degassing changed distinctly with flow rate. In contrast, the other two sites having low pCO2 springwater reflect a regular seasonal pattern of δ13C in DIC and tufa specimens. 相似文献
Recently, the Advanced Earth Observing Satellite 2 (ADEOS-2) was launched (December 14, 2002) successfully, and the Global Imager (GLI) onboard the ADEOS-2 satellite became operational in April 2003. In a first calibration checkup, the radiometric performance of GLI was compared relatively to that of other sensors on different satellites with different calibration backgrounds. As a calibration site, a large snowfield near Barrow, Alaska, was used, where space sensors in polar orbits view the same ground target on the same day with small differences in the local crossing times. This is why GLI, the Moderate Resolution Imaging Spectroradiometer (Terra, Aqua), the Sea-viewing Wide Field-of-view Sensor, the Advanced Very High Resolution Radiometer (N16, N17), the Medium Resolution Imaging Spectrometer, and the Advanced Along Track Scanning Radiometer datasets were selected for the following clear-sky condition days: April 14 and 26, 2003. At the same time, ground-truth experiments (e.g., measurements of ground reflectance, bidirectional reflectance distribution function, aerosol optical thickness) were carried out. Thereinafter, top-of-atmosphere (TOA) radiance/reflectance was forward calculated by means of radiative transfer code for each sensor, each band, and each day. Finally, the vicariously retrieved TOA signal was compared to TOA sensor Level 1B data. As a result, GLI's performance is encouraging at that time of the mission. GLI and the other seven sensors deliver similar sensor output in the range of about 5% to 7% around the expected vicariously calculated TOA signal. 相似文献
One of the keys to understanding the origin of Archaean greenstone belts lies in the geological relationships between mafic and ultramafic greenstones, felsic to intermediate volcanic rocks and terrigenous sediments. Traditional models for greenstone belt evolution have been based on in-situ stratigraphic relationships. Most of these models, for example an oceanic island-arc developed on oceanic basement, back-arc basins, and the recently popular plume model, predict concordant stratigraphic relationships among the various greenstone belt lithologies. However, rather than being depositional in nature, several authors have indicated that many of the relationships between the different lithologies in greenstone belts are in fact tectonic, suggesting an allochthonous origin for most greenstone sequences. All of these latter models make analogies to Phanerozoic tectonic processes involving accretion of oceanic materials with volcanism related to both plate subduction and rifting.
In this paper, we have evaluated the geological relationships between volcanic rocks and sediments in three regions in the Superior province, where the accretion of oceanic material can be documented, and direct comparisons are made to geological processes in Phanerozoic accretionary complexes. In the Malartic area in the southeastern Abitibi Subprovince, 3 to 4 km thick slices of komatiite and tholeiite, with intercalated terrigenous sediment, are tectonically imbricated and are overlain by calc-alkaline volcanics which postdate tectonic stacking. In both the Larder Lake region of the southwestern Abitibi belt and in the Beardmore-Geraldton belt, at the south-eastern limit of the Wabigoon belt, slices of iron-rich tholeiite and chemical sediments of an oceanic origin are tectonically imbricated with terrigenous sediment.
The Malartic-Val d'Or area is considered to be an example of accretion of an Archaean oceanic plateau, while the Larder Lake and the Beardmore-Geraldton regions are potentially typical of accretion of normal oceanic crust in an arc-environment. Phanerozoic accretion of oceanic crust is accompanied by a step-back in subduction, and in this paper we suggest that oceanic crust accretion may have been the principal mechanism by which the locus of subduction migrated towards the south of the Superior province. Asthenospheric upwelling associated with the isolated sinking plate may have been responsible for widespread late-magmatism. This scenario requires that magmas be erupted through previously accreted volcanic, plutonic and sedimentary material. Furthermore, later ridge subduction will result in transpressional tectonics and eruption of mafic sequences over mature and immature volcano-plutonic sequences. The combined result of the plate tectonic scenario envisaged would result in the well-described “cyclic stratigraphy” of many granite greenstone sequences. 相似文献
The Fe2+–Mg distribution coefficients between sapphirine and spinel:
were experimentally determined at pressures of 9–13 kbar and temperatures of 950–1150 °C using a natural ultrahigh-temperature (UHT) granulite with paragenesis of these minerals from the Napier Complex in East Antarctica [XMg = Mg / (Fe + Mg); XFe = Fe / (Fe + Mg)]. A new sapphirine–spinel geothermometer has been obtained as:
We applied the exchange thermometer to UHT or high-grade metamorphic rocks that were reported from various complexes in the world. If the KD values of 2.63–4.34 obtained from low-Cr mineral pairs such as XCrSpr < 0.016 and XCrSpl < 0.047 were substituted into the equation, their temperature conditions would be estimated as 806–1050 °C at 11 kbar. The XCr means Cr / (Al + Cr(+ Fe3+)). These temperatures are reasonable retrograde or near peak metamorphic condition. 相似文献
When a subduction-zone earthquake occurs, the tsunami height must be predicted to cope with the damage generated by the tsunami. Therefore, tsunami height prediction methods have been studied using simulation data acquired by large-scale calculations. In this research, we consider the existence of a nonlinear power law relationship between the water pressure gauge data observed by the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) and the coastal tsunami height. Using this relationship, we propose a nonlinear parametric model and conduct a prediction experiment to compare the accuracy of the proposed method with those of previous methods and implement particular improvements to the extrapolation accuracy.