On the Kuril Islands there are 85 volcanoes, 39 of which are active. Hot springs and mud pots are wide spread in this area and have significant inputs on the chemical composition of the surrounding surface waters and environment. We present results of trace elements as well as data on H, O, S, and He isotope ratios for hydrothermal systems of the Mendeleev Volcano (Kunashir Island) and surrounding surface waters. Water and gas samples were taken from springs and holes as well as creeks and the Lesnaya River. Among the thermal water types, three main groups can be distinguished. The first group includes the waters, in which SO4^- ion predominant. The water temperature on the surface reaches 97℃, and TDS varies from a few g/L to 7 g/L. These waters are acid to superacid with pH values ranging 0.6 to 2.3. The second group is sodium-chloride waters. A maximum TDS is 14.2 g/L. The waters are neutral or alkaline; pH varies from 6.9 to 8.2. The third group is the sodium-chloride-sulfate-bicarbonate water. The Stolbovskie springs, located in the periphery of the Mendeleev Volcano are representative of this type. The pH of these waters is close to neutral. TDS is 1.9 g/L. They are rather the derivatives of sodium-chloride waters arisen from dilution of them by subsurface waters. The Kuslyi Creek and Lesnaya River are located near the Mendeleev Volcano. The most acid springs discharge into the Kislyi Creek as a result pH of this creek being 2.5, and contents of most elements rather high. For example, the contents of dissolved solids of Si, Fe, Al, Mn, Zn, in waters of the Kislaya Creek are 22.1, 8.1, 6.2, 1.29, and 0.28 mg/L, and correspondently. The water of the Lesnaya River, (Before the Kislyi Creek, pH is about 8 with TDS 102 mg/L, but after the Kuslyi Creek, pH decreases and the concentrations of chemical elements increase. Debit of the Kislayi Creek in summer season is about 370 L/sec. It means that every day only this small creek inputs in the Lesnay River about 706 kg of Si; 相似文献
Crystallization under confinement conditions is a very important process in geochemistry and geophysics. Computer simulations of fluids in nanometer scale pore spaces can provide a unique microscopic insight into the structure, dynamics and forces arising from the crystallization process. We discuss in this paper molecular dynamics computer simulations of crystallization in pores of nanometer dimensions. The crystallization pressure due to the freezing of a model of Argon in a nanopore is computed using molecular dynamics simulations. We also investigate the influence of pore geometry in determining the dynamics of confined fluids, as well as mass separation in binary mixtures. It turns out that the pore geometry reveals itself as an important variable, leading to 1) new mechanisms for fast diffusion in confined spaces, and 2) accumulation of solute in specific regions inside the pore. 相似文献
The paragenesis of monazite in metapelitic rocks from the contact aureole of the Harney Peak Granite, Black Hills, South Dakota, was investigated using zoning patterns of monazite and garnet, electron microprobe dating of monazite, bulk-rock compositions, and major phase mineral equilibria. The area is characterized by low-pressure and high-temperature metamorphism with metamorphic zones ranging from garnet to sillimanite zones. Garnet porphyroblasts containing euhedral Y annuli are observed from the garnet to sillimanite zones. Although major phase mineral equilibria predict resorption of garnet at the staurolite isograd and regrowth at the andalusite isograd, textural and mass balance analyses suggest that the formation of the Y annuli is not related to the resorption-and-regrowth of garnet having formed instead during garnet growth in the garnet zone. Monazite grains in Black Hills pelites were divided into two generations on the basis of zoning patterns of Y and U: monazite 1 with low-Y and -U and monazite 2 with high-Y and -U. Monazite 1 occurs in the garnet zone and persists into the sillimanite zone as cores shielded by monazite 2 which starts to form in the andalusite zone. Pelites containing garnet porphyroblasts with Y annuli and monazite 1 with patchy Th zoning are more calcic than those with garnet with no Y annuli and monazite with concentric Th zoning. Monazite 1 is attributed to breakdown of allanite in the garnet zone, additionally giving rise to the Y annuli observed in garnet. Monazite 2 grows in the andalusite zone, probably at the expense of garnet and monazite 1 in the andalusite and sillimanite zones. The ages of the two different generations of monazite are within the precision of chemical dating of electron microprobe. The electron microprobe ages of all monazites from the Black Hills show a single ca. 1713 Ma population, close to the intrusion age of the Harney Peak Granite (1715 Ma). This study demonstrates that Y zoning in garnet and monazite are critical to the interpretation of monazite petrogenesis and therefore monazite ages. 相似文献
Ultrahigh-pressure (UHP) metamorphic terranes reflect subduction of continental crust to depths of 90–140 km in Phanerozoic contractional orogens. Rocks are intensely overprinted by lower pressure mineral assemblages; traces of relict UHP phases are preserved only under kinetically inhibiting circumstances. Most UHP complexes present in the upper crust are thin, imbricate sheets consisting chiefly of felsic units ± serpentinites; dense mafic and peridotitic rocks make up less than 10% of each exhumed subduction complex. Roundtrip prograde–retrograde P–T paths are completed in 10–20 Myr, and rates of ascent to mid-crustal levels approximate descent velocities. Late-stage domical uplifts typify many UHP complexes.
Sialic crust may be deeply subducted, reflecting profound underflow of an oceanic plate prior to collisional suturing. Exhumation involves decompression through the P–T stability fields of lower pressure metamorphic facies. Scattered UHP relics are retained in strong, refractory, watertight host minerals (e.g., zircon, pyroxene, garnet) typified by low rates of intracrystalline diffusion. Isolation of such inclusions from the recrystallizing rock matrix impedes back reaction. Thin-aspect ratio, ductile-deformed nappes are formed in the subduction zone; heat is conducted away from UHP complexes as they rise along the subduction channel. The low aggregate density of continental crust is much less than that of the mantle it displaces during underflow; its rapid ascent to mid-crustal levels is driven by buoyancy. Return to shallow levels does not require removal of the overlying mantle wedge. Late-stage underplating, structural contraction, tectonic aneurysms and/or plate shallowing convey mid-crustal UHP décollements surfaceward in domical uplifts where they are exposed by erosion. Unless these situations are mutually satisfied, UHP complexes are completely transformed to low-pressure assemblages, obliterating all evidence of profound subduction. 相似文献
The evaluation of seismic site response in the urban area of Catania was tackled by selecting test areas having peculiar lithological
and structural features, potentially favourable to large local amplifications of ground motion. The two selected areas are
located in the historical downtown and in the northern part of Catania where the presence of a fault is evident. Site response
was evaluated using spectral ratio technique taking the horizontal- to-vertical component ratio of ambient noise. Inferences
from microtremor measurements are compared with results from synthetic accelerograms and response spectra computed at all
drillings available for this area. Such method is particularly suitable in urban areas where the nature of the outcropping
geological units is masked by city growth and anthropic intervention on the surface geology. The microtremor H/V spectral
ratios evaluated at soft sites located within the downtown profile tend to be smaller than that usually reported in the literature
for such soils. A tendency for amplifications to peaks near 2 Hz is observed only in some sites located on recent alluvial
deposits. Evidences for amplifications of site effects (frequency range 4–8 Hz) were observed in the sampling sites located
on the fault, with a rapid decrease of spectral amplitude just a few tenths of metres away from the discontinuity. Numerical
simulations evidenced the importance of geolithological features at depth levels even greater than 20–30 m. Besides this,
the results strongly confirm the importance of the subsurface geological conditions, in the estimate of seismic hazard at
urban scale. 相似文献