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171.
Júlia Dégi Rainer Abart Kálmán Török Dieter Rhede Elena Petrishcheva 《Mineralogy and Petrology》2009,95(3-4):219-234
We investigate the effects of xenolith–host basalt interaction on lower crustal mafic granulite xenoliths from the Central Pannonian Basin. The xenoliths are devoid of any signs of melting, nevertheless various phenomena are identified, which indicate that the original mineralogy and chemistry of the xenoliths was modified during interaction with the host basalt. The rock-forming silicates are only slightly affected by alteration, but the Fe–Ti-oxides are overprinted to a significant extent. Complex chemical zoning patterns are detected using high-resolution element mapping in ilmenites and in lamellar titanomagnetite–ilmenite intergrowths. The chemical alteration of the Fe–Ti-oxides was diffusion-controlled and, hence, time and temperature dependent. On the basis of diffusion profiles in titanomagnetite we estimate the duration of xenolith–host basalt interaction to be at least 9–20 h. This is comparable to the time necessary for the ascent of the host basalt to the surface. It is too short to reflect alteration during granulite facies metamorphism in the deep crust. The chemical alteration of the titanomagnetite thus reflects the total duration of the xenolith–host basalt interaction. 相似文献
172.
173.
Late Holocene tsunami traces on the western and southern coastlines of the Peloponnesus (Greece) 总被引:1,自引:0,他引:1
Anja Scheffers Dieter Kelletat Andreas Vtt Simon Matthias May Sander Scheffers 《Earth and Planetary Science Letters》2008,269(1-2):271-279
Greece, in particular the western and southern parts close to the subduction zone of the Hellenic Trench, experiences strong earthquakes and subsequent tsunamis. Nevertheless, field evidence of tsunamis from the late Holocene is extremely rare. Our research along the coastlines of the western and southern Peloponnesus resulted in new findings of tsunami impacts in the form of clusters and ridges of large boulders and thick tsunamigenic sand layers encountered in vibracores. Many boulders contained attached marine organisms, which prove that they were transported from the foreshore environment against gravity by extreme wave events. The attached organisms, which have been dated by 14C-AMS, suggest that historical tsunami events of great energy occurred around 1300 cal AD. A wood fragment found at the base of tsunami deposits in a vibracore from Cape Punta was dated to ~ 250 cal AD. 相似文献
174.
175.
The creatures that gaze back at us through the binocular microscope are so uniquely well‐preserved and life‐like that had we not known better we would have thought that they were modern. Instead they are half‐a‐billion‐year‐old arthropods extracted from Cambrian rocks of Sweden. The microscopic fossils, colloquially known as the ‘Orsten’ fossils, are now world‐famous and basking in the light of the research catwalk since their discovery in the 1970s. These fossils have provided significant insight into the long lost Cambrian biotas and early animal evolution. 相似文献
176.
Dieter Heymann 《Astrophysics and Space Science》2001,275(4):415-423
It is argued that the cycling of the atomic nuclei of`isotopically strange xenon' through carbon stars and its implantation intometeoritic nanodiamonds by low-energy stellar wind ions of such starslessens several difficulties of earlier theories. The isotopically strangexenon might be an abundant galactic constituent today, or have been suchduring the presolar past. 相似文献
177.
Abstract— Libyan Desert Glass (LDG) is an impact‐related, natural glass of still unknown target material. We have determined Rb‐Sr and Sm‐Nd isotopic ratios from seven LDG samples and five associated sandstones from the LDG strewn field in the Great Sand Sea, western Egypt. Planar deformation features were recently detected in quartz from these sandstones. 87Sr/86Sr ratios and ?‐Nd values for LDG range between 0.71219 and 0.71344, and between –16.6 and –17.8, respectively, and hence are distinct from the less radiogenic 87Sr/86Sr ratios of 0.70910–0.71053 and ?‐Nd values from –6.9 to –9.6 for the local sandstones from the LDG strewn field. Previously published isotopic ratios from the Libyan BP and Oasis crater sandstones are generally incompatible with our LDG values. LDG formation undoubtedly occurred at 29 Ma, but neither the Rb‐Sr nor the Sm‐Nd isotopic system were rehomogenised during the impact event, as we can deduce from Pan‐African ages of ?540 Ma determined from the regression lines from a total of 14 LDG samples from this work and the literature. Together with similar Sr and Nd isotopic values for LDG and granitoid rocks from northeast Africa west of the Nile, these findings point to a sandy matrix target material for the LDG derived from a Precambrian crystalline basement, ruling out the Cretaceous sandstones of the former “Nubian Group” as possible precursors for LDG. 相似文献
178.
Dieter Lorenz-Petzold 《Astrophysics and Space Science》1985,116(2):411-413
We make some comments concerning the magnetic perfect fluid Bianchi type-VIo solutions given recently by Royet al. (1985a). 相似文献
179.
Refractive index, density and infrared absorption studies of naturally and experimentally shocked-produced glasses formed from quartz, plagioclase, and alkali-feldspar confirm the existence of two main groups of amorphous forms of the framework silicates: solid-state and liquid-state glasses. These were apparently formed as metastable release products of high-pressure-phases above and below the glass transition temperatures. Solid-state glasses exhibit a series of structural states with increasing disorder caused by increasing shock pressures and temperatures. They gradually merge into the structural state of fused minerals similar to that of synthetic glasses quenched from a melt. Shock-fused alkali feldspars can, however, be distinguished from their laboratory-fused counterparts by infrared absorption and by higher density. It is concluded from recovery shock experiments on single crystals that solid-state glasses are formed by shock pressures between about 300 and 450 kb (feldspars) and 350 and 500 kb (quartz), whereas pressures exceeding some 430 kb (feldspars) and 500 kb (quartz) are necessary to produce liquid-state glasses 相似文献
180.
Dieter Heymann 《Meteoritics & planetary science》1979,14(1):43-50
The theory of 3He-rich flares by Colgate, Audouze, and Fowler implies that the composition of the solar cosmic ray-event associated with a 3He-rich flare is grossly non-solar. The relative abundances (relative to hydrogen) of carbon, nitrogen, and oxygen, as well as those of heavier elements are significantly reduced, and the isotopic compositions of virtually all elements are bound to be strongly anomalous. In addition, the abundances of 22Na, 26Al, and 10Be (of which there are approximately 1025atoms each in a 3He-rich flare) are at least comparable to the abundances of stable isotopes of these elements. Conditions for the detectability of the three radioactive species are discussed. 相似文献