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21.
During the process of continuous post-crystallization cooling, the degree of phase transformation in pyroxenes (ordering and decomposition of solid solutions) is determined by the total cooling time and by cooling rates at individual stages; this degree can also be applied to the estimation of the sub-solidus cooling time of pyroxenes and of rocks, genetically associated with them (geochronometer). The degree of Fe2+-Mg order in distribution between theM
1 andM
2 sites observed in orthopyroxenes can be used as the criterion for the sub-solidus cooling rates of orthopyroxenes. A technique for approximate estimation of cooling time (rates) of orthopyroxenes in the 1000–500°C interval is suggested on the basis of an ion exchange reaction kinetic model, with the adoption of a few assumptions. X-ray structural analysis study revealed the character of the Fe2+-Mg intersite distribution in the M-511 and M-533 orthopyroxenes from the Luna-20 regolith; the obtainedK
D values make 0.072(T
e
o
~ 460°C) and 0.06 (T
e
o
~ 480°C), respectively. The corresponding evaluation of the linear cooling rate in the 1000-500°C range, as inferred by the obtained data, gave the value of 0.2–0.25° h–1. Two features of the exosolution relate to the sub-solidus cooling rate of clinopyroxenes: the degree of phase separation by composition Wo and the exsolution scale . The monocrystal X-ray diffraction study, the transmission electron microscopy and the X-ray microprobe analysis produced the exsolution parameters for clinopyroxenes 2001-3, 2001-6 and 559 from the Luna-20 regolith: Wo 26%, 28% and 45% respectively; 300 Å, 1000 Å and 60 , respectively. The solvus temperatures (T
e) of the clinopyroxenes 2001-3 and 2001-6 make, respectively, 1100 ± 25°C and 1095 ± 45°C; the spinodal temperatures (T
s) areT
s =T
e – 50°C and represent quenching temperatures of the given pyroxenes in relation to the exsolution process. The cooling time fromT
cryst. toT
s was estimated and the value of the formal linear cooling rate was found to be ~ 90° h–1 (2001-3) and ~ 8° h–1 (2001-6). The average value of the pyroxene 559 sub-soldius cooling rate in the 1150–1000°C range was four orders less. The obtained data were discussed in view of the possible genesis of the studied Luna-20 pyroxenes. 相似文献
22.
Kotova G. A. Verigin M. I. Gombosi T. Kabin K. Bezrukikh V. V. 《Geomagnetism and Aeronomy》2020,60(2):162-170
Geomagnetism and Aeronomy - An analytical semiempirical model of the bow shock based on theoretical MGD calculations, accurate analytical solutions, and experimental data continues to be developed.... 相似文献
23.
24.
Johanna Lofi Philippe Pezard Frédéric Bouchette Olivier Raynal Pierre Sabatier Nataliya Denchik Arnaud Levannier Laurent Dezileau Raphaël Certain 《Ground water》2013,51(4):550-561
Most of the Mediterranean coastal porous aquifers are intensively exploited. Because of climatic and anthropogenic effects, understanding the physical and geological controls on groundwater distribution and flow dynamics in such aquifers is crucial. This study presents the results of a structural investigation of a system located along the coastline of the Gulf of Lions (NW Mediterranean). A key aspect of this study relies on an onshore‐offshore integrated approach combining outcrops, seismic profiles, and borehole data analysis. This multidisciplinary approach provides constraints on pore‐fluid salinity distribution and stratigraphic organization, which are crucial in assessing the modes of groundwater/seawater exchanges. Onshore, Lower Pliocene deposits dip gently seaward. They are unconformably overlain by Holocene clays in the lagoons. Offshore the Pliocene deposits either outcrop at the seabed or are buried below nonconsolidated sands infilling paleo‐valleys. Beneath the lido, the groundwater salinity distribution consists of salty pore water, overlying fresher pore water. Active circulation of groundwater masses is inferred from the geophysical results. In particular, offshore outcrops and paleo‐valleys may play an important role in salt water intrusion. 相似文献
25.
Hirotsugu Minami Kazuya Tatsumi Akihiro Hachikubo Satoshi Yamashita Hirotoshi Sakagami Nobuo Takahashi Hitoshi Shoji Young Keun Jin Anatoly Obzhirov Nataliya Nikolaeva Alexander Derkachev 《Geo-Marine Letters》2012,32(5-6):525-534
The Sakhalin Slope Gas Hydrate Project (SSGH) is an international collaborative effort by scientists from Japan, Korea, and Russia to investigate natural gas hydrates (GHs) that have accumulated on the continental slope off Sakhalin Island, Okhotsk Sea. From 2009 to 2011, field operations of the SSGH-09, -10, and -11 projects were conducted. GH-bearing and -free sediment cores were retrieved using steel hydro- and gravity corers. The concentrations of sulfate ions in sediment pore waters were measured to investigate sulfate concentration–depth profiles. Seventeen cores showed linear depth profiles of sulfate concentrations. In contrast, eight cores and two cores showed concave-up and -down profiles plausibly explained by sudden increase and decrease in methane flux from below, respectively, presumably caused by the formation of gas hydrate adjacent to the core sampling sites. 相似文献
26.
The initial stage of evolution of the displacement front is studied as a part of the nonlinear filtration model. Concentration and density profiles in the normal direction to the front are obtained. It turns out that the concentration changes relatively quickly, whereas the density rather slowly. The stability criterion of the displacement front is formulated. The conditions, under which the front retains the initial shape, are determined. 相似文献
27.
V. L. Khalipov A. E. Stepanov G. A. Kotova S. E. Kobyakova V. V. Bogdanov A. B. Kaisin V. A. Panchenko 《Geomagnetism and Aeronomy》2016,56(5):535-544
Vertical and horizontal plasma drifts are investigated during the polarization jet (PJ) detection in the F2 ionospheric layer based on the Doppler measurements at the Yakutsk meridian chain of subauroral ionospheric stations. It is shown that the velocities of vertical and horizontal drifts are significantly higher than the background motion during PJ observation periods. The ionospheric plasma motion direction changes from upward to downward on the polar edge of the main ionospheric trough. Doppler measurements on the DPS-4 ionosondes are compared with the simultaneous measurements of the plasma drift on the DMSP satellites during their passage near the Yakutsk meridian. The two kinds of measurements are in good agreement with each other. During the magnetic storm of June 23, 2005, by measurements of the DMSP satellites, the velocities of upward plasma flows were 1.0–1.4 km/s at a satellite altitude of 850 km. In the ionospheric F region, this speed corresponds to 150 m/s. According to satellite measurements, the westward drift velocity reached 2.5 km/s. The development of the polarization jet in the ionosphere was accompanied by a tenfold decrease in the electron density in 15–30 min. 相似文献
28.
A petrological and geochemical study on time-series samples from Klyuchevskoy volcano,Kamchatka arc 总被引：1，自引：0，他引：1
Olga?Bergal-Kuvikas Mitsuhiro?NakagawaEmail author Takeshi?Kuritani Yaroslav?Muravyev Nataliya?Malik Elena?Klimenko Mizuho?Amma-Miyasaka Akiko?Matsumoto Shunjiro?Shimada 《Contributions to Mineralogy and Petrology》2017,172(5):35
To understand the generation and evolution of mafic magmas from Klyuchevskoy volcano in the Kamchatka arc, which is one of the most active arc volcanoes on Earth, a petrological and geochemical study was carried out on time-series samples from the volcano. The eruptive products show significant variations in their whole-rock compositions (52.0–55.5 wt.% SiO2), and they have been divided into high-Mg basalts and high-Al andesites. In the high-Mg basalts, lower-K and higher-K primitive samples (>9 wt.% MgO) are present, and their petrological features indicate that they may represent primary or near-primary magmas. Slab-derived fluids that induced generation of the lower-K basaltic magmas were less enriched in melt component than those associated with the higher-K basaltic magmas, and the fluids are likely to have been released from the subducting slab at shallower levels for the lower-K basaltic magmas than for higher-K basaltic magmas. Analyses using multicomponent thermodynamics indicates that the lower-K primary magma was generated by ~13% melting of a source mantle with ~0.7 wt.% H2O at 1245–1260?°C and ~1.9 GPa. During most of the evolution of the volcano, the lower-K basaltic magmas were dominant; the higher-K primitive magma first appeared in AD 1932. In AD 1937–1938, both the lower-K and higher-K primitive magmas erupted, which implies that the two types of primary magmas were present simultaneously and independently beneath the volcano. The higher-K basaltic magmas evolved progressively into high-Al andesite magmas in a magma chamber in the middle crust from AD 1932 to ~AD 1960. Since then, relatively primitive magma has been injected continuously into the magma chamber, which has resulted in the systematic increase of the MgO contents of erupted materials with ages from ~AD 1960 to present. 相似文献
29.
Doklady Earth Sciences - 相似文献
30.
On the basis of petrochemical data, orthorocks are defined among highly metamorphosed sequences of the Landenpokh’ya Group attributed to the Kalevian and Svecofennian systems in the Ladoga region. The contents of major and trace elements in orthorocks, which constitute some volcanogenic sedimentary complexes in the western Ladoga region, are discussed. The volcanics of the first complex (Kukhka Island area) belong to the calc-alkaline series and are characterized by the presence of OIB-type basaltic andesites. The basites of the second complex (Kil’pola Island area) are attributed to the tuffaceous rocks of the WPB-type tholeiitic series. The volcanics of the third complex (Kuznechnoe-Khiitola area) are largely represented by dacites referred to the Svecofennian mature island arc. The presented geological and geochemical data imply that the first and second complexes, which include intraplate volcanics, could be formed on the basite Jatulian-Ludikovian basement (protolith). These Kalevian rocks of the western Ladoga region are correlated with the volcanogenic sedimentary complexes in the southern part of the Savo belt in Finland and belong to the Karelian province. 相似文献