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151.
McGrath Annette Stouraiti Christina Windley Brian 《International Journal of Earth Sciences》2017,106(6):2067-2089
International Journal of Earth Sciences - The nature of the protolith(s) of high-grade gneisses from the Aegean Cycladic Basement Unit of the islands of Paros and Serifos is investigated using... 相似文献
152.
Least-squares collocation, geophysical inverse theory and geostatistics: a bird's eye view 总被引:1,自引:0,他引:1
Ute Christina Herzfeld 《Geophysical Journal International》1992,111(2):237-249
153.
The spatial and temporal discharge regime and its effects on benthic communities were studied in two small temporary karstic stream systems of the Paderborner Hochfläche (East Westphalia, Germany). Both streams are characterized by very small perennial springbrook sections. Benthic invertebrates were sampled three times at 12 sites and discharge was measured monthly from March to September 2000. The spatial extension of streamflow was observed regularly to evaluate the duration of drought. Both streams showed a longitudinal gradient of hydrological intermittency from very small perennial reaches with low intermittency to an extremely harsh hydrological situation. The benthic communities displayed a decreasing species richness at increasing intermittency. The different hydrological stream sections were colonized by different lotic communities, characterized by typical species of temporary streams and by several typical species of springs. Particularly the perennial springs and springbrooks are very important for the species richness in these karstic stream systems. 相似文献
154.
The UV edge in the electronic absorption spectra of minerals, in many cases influencing their colour, is generally interpreted
as the low-energy wing of very strong UV bands caused by ligand–metal charge transfer (CT) transitions (e.g. Burns 1993).
However, Mie scattering theory shows that the presence of randomly distributed submicroscopic inclusions with narrow size
distribution and a refractive index n
i
in a matrix with different refractive index n
m
may give rise to a λ-dependent, band-like scattering (e.g. Kortüm 1969). Such scattering bands have so far not been considered
as contributing to the UV edge. Single-crystal electronic absorption spectra of eight natural almandine-rich garnets (Alm60–Alm88), two synthetic almandine samples (Alm100), all of different colours, and synthetic spessartine were studied by means of a Zeiss microscope-spectrometer in the range
40 000–20 000 cm−1. Special techniques of spectral measurements with crossed analyzer and polarizer, which enable the registration of the scattering
effect directly, were used as well. Four of the above garnets were also investigated using transmission electron microscopy.
Different types of inclusions, from 10 to several 100 nm in size, were observed in the garnet matrices. They are abundant
in cores of synthetic garnets, but very rare in most natural almandines studied. Electronic absorption spectra of the natural
almandine garnets show largely varying UV edge position and, hence, intensity at a given wavenumber which correlates with
the intensities of spin-forbidden dd bands of Fe3+ ions at 27 000 and 28 000 cm−1, superimposed on the long energy slope of the UV absorption. There are also positive correlations between Ti4+ and Fe3+ content, the latter recalculated on the basis of garnet stoichiometry, and UV edge intensity. Thus, the presence of Ti4+ and Fe3+ ions in octahedra, even in very low concentrations (0.0n at. pfu), leads to CT phenomena, that probably involve Fe2+ ions in edge-shared dodecahedral position and intensifies ligand- to-metal CT. The different colours of natural almandine
garnets with similar Fe2+ contents studied here are caused by this effect. Consistent with the absence of inclusions in most natural garnets studied,
λ-dependent scattering plays no role in their UV absorption. In contrast, in synthetic almandine and spessartine crystals,
a different intensity of UV absorption was observed in inclusion-free rims and inclusion-enriched cores. Some of the latter
demonstrate typical scattering patterns when measured at crossed polarizers.
Received: 10 April 2001 / Accepted: 27 September 2001 相似文献
155.
Christina Widiwijayanti Christel Tiberi Christine Deplus Michel Diament Valentin Mikhailov Rmy Louat 《Tectonophysics》2004,386(3-4):203-222
In order to better understand the tectonic framework of the Northern Molucca Sea area, we inverted satellite and sea-surface gravity data into an iterative scheme including a priori seismological and geological data. The resulting 3-D density model images the various tectonic units from the surface down to 40 km. We proceed to various tests to assess the stability and robustness of our inversion. In particular, we performed an offset and average smoothing method to properly refine our results. The resulting model shows a striking vertical regularity of the structures through the different layers, whereas the density contrasts appear strongly uneven in the horizontal direction.The density model emphasizes the complexity of the upper lithospheric structure in the northern Molucca Sea, which is clearly dominated by the interaction between ophiolitic ridges, sedimentary wedges and rigid blocks of the Philippine Sea Plate. It also provides new, hard information that can be used in discussion of the evolution of the region.Large density variations are concentrated in the central part of northern Molucca Sea and dominate the upper lithospheric. North–south trending density structures along the Central Ridge and west dipping thrust faults on the western side of the region are clearly imaged. In the eastern part of the region, we distinguish several blocks, especially the Snellius Plateau which seems to be split into two parts. We interpret this as an oceanic plateau associated with thicker crust that previously belonged to the Philippine Sea Plate. This crust is now trapped between the Molucca Sea complex collision zone and the Philippine Trench, due to the development of a new subduction zone in its eastern side. 相似文献
156.
Devendra Lal Christina D. Gallup Loïc Vacher Anthony J.T. Jull Robert C. Speed Amos Winter 《Geochimica et cosmochimica acta》2005,69(24):5717-5728
We present results of measurements of cosmogenic 10Be, 26Al and 36Cl, and the indigenous (intrinsic) concentrations of the stable elements Be, Al and Cl in 120-200 kyr old corals from Barbados and Puerto Rico. The concentration levels of these radionuclides in the corals lie in the range 104 to 108 atoms/g. A comparison of the measured nuclide concentrations with those expected to be produced in the corals by nuclear interactions of energetic cosmic radiation shows that (i) the radionuclides 26Al and 36Cl are derived from in situ cosmic ray interactions in the corals after their formation, but that (ii) the radionuclide 10Be owes its provenance in the coralline lattice primarily due to incorporation of dissolved beryllium in seawater in the lattice structure of the corals. 相似文献
157.
Iron isotope fractionation during planetary differentiation 总被引:4,自引:0,他引:4
Stefan Weyer Ariel D. Anbar Carsten Münker Alan B. Woodland 《Earth and Planetary Science Letters》2005,240(2):251-264
The Fe isotope composition of samples from the Moon, Mars (SNC meteorites), HED parent body (eucrites), pallasites (metal and silicate) and the Earth's mantle were measured using high mass resolution MC-ICP-MS. These high precision measurements (δ56Fe ≈ ± 0.04‰, 2 S.D.) place tight constraints on Fe isotope fractionation during planetary differentiation.Fractionation during planetary core formation is confined to < 0.1‰ for δ56Fe by the indistinguishable Fe isotope composition of pallasite bulk metal (including sulfides and phosphides) and olivine separates. However, large isotopic variations (≈ 0.5‰) were observed among pallasite metal separates, varying systematically with the amounts of troilite, schreibersite, kamacite and taenite. Troilite generally has the lightest (δ56Fe ≈ − 0.25‰) and schreibersite the heaviest (δ56Fe ≈ + 0.2‰) Fe isotope composition. Taenite is heavier then kamacite. Therefore, these variations probably reflect Fe isotope fractionation during the late stage evolution and differentiation of the S- and P-rich metal melts, and during low-temperature kamacite exsolution, rather than fractionation during silicate-metal separation.Differentiation of the silicate portion of planets also seems to fractionate Fe isotopes. Notably, magmatic rocks (partial melts) are systematically isotopically heavier than their mantle protoliths. This is indicated by the mean of 11 terrestrial peridotite samples from different tectonic settings (δ56Fe = + 0.015 ± 0.018‰), which is significantly lighter than the mean of terrestrial basalts (δ56Fe = + 0.076 ± 0.029‰). We consider the peridotite mean to be the best estimate for the Fe isotope composition of the bulk silicate Earth, and probably also of bulk Earth. The terrestrial basaltic mean is in good agreement with the mean of the lunar samples (δ56Fe = + 0.073 ± 0.019‰), excluding the high-Ti basalts. The high-Ti basalts display the heaviest Fe isotope composition of all rocks measured here (δ56Fe ≈ + 0.2‰). This is interpreted as a fingerprint of the lunar magma ocean, which produced a very heterogeneous mantle, including the ilmenite-rich source regions of these basalts.Within uncertainties, samples from Mars (SNC meteorites), HED (eucrites) and the pallasites (average olivine + metal) have the same Fe isotope compositions as the Earth's mantle. This indicates that the solar system is very homogeneous in Fe isotopes. Its average δ56Fe is very close to that of the IRMM-014 standard. 相似文献
158.
The 1990 Kalapana flow field is a complex patchwork of tube-fed pahoehoe flows erupted from the Kupaianaha vent at a low effusion rate (approximately 3.5 m3/s). These flows accumulated over an 11-month period on the coastal plain of Kilauea Volcano, where the pre-eruption slope angle was less than 2°. the composite field thickened by the addition of new flows to its surface, as well as by inflation of these flows and flows emplaced earlier. Two major flow types were identified during the development of the flow field: large primary flows and smaller breakouts that extruded from inflated primary flows. Primary flows advanced more quickly and covered new land at a much higher rate than breakouts. The cumulative area covered by breakouts exceeded that of primary flows, although breakouts frequently covered areas already buried by recent flows. Lava tubes established within primary flows were longer-lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply; tubes within breakouts were never reoccupied once the supply was interrupted. During intervals of steady supply from the vent, the daily areal coverage by lava in Kalapana was constant, whereas the forward advance of the flows was sporadic. This implies that planimetric area, rather than flow length, provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes. 相似文献
159.
160.