Amplitude curves of longitudinal waves for several three-dimensional models of the upper mantle     

Jiří Vaněk 《Studia Geophysica et Geodaetica》1966,10(3):350-359

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Computation of diffracted rays in inhomogeneous media with curved interfaces     

Vlastislav Červený  Ivan Pšenčík  Reviewer J. Vaněk 《Studia Geophysica et Geodaetica》1972,16(4):356-366

Summary A method for computing certain types of diffracted rays and corresponding travel-time curves in laterally inhomogeneous media with slightly curved interfaces is suggested. Numerical examples are presented.Dedicated to Academician Alois Zátopek on His 65th Birthday  相似文献   

Age differences between Rb---Sr whole rock and U---Pb zircon ages of syn- and postorogenic Svecokarelian granitoids in Sottunga, SW Finland     

Eric Welin  Matti Vaasjoki  Veli Suominen 《Lithos》1983,16(4):297-305

The U---Pb age on pooled data of zircnos from the postorogenic Svecokarelian Mosshaga granite is 1788 ± 11 Ma (2 σ). The corresponding Rb---Sr whole rock age is 1742 ± 34 Ma (2 σ). The Mosshaga granite intrudes a synorogenic granodiorite, which has a U---Pb zircon age of 1889 ± 10 Ma and a Rb---Sr whole rock age of 1850 ± 28 Ma. The age differences between the U---Pb zircon ages and Rb---Sr whole rock ages are concluded to be geologically significant. It is shown that the Mosshaga pluton cooled rapidly and as a consequence the Rb---Sr isotopic system closed at a time very close to the crystallization of the zircons. A commonly observed feldspar and biotite alteration in Svecokarelian granitoids indicates migration of Rb and Sr isotopes in the whole rock system which may lead to apparently younger Rb---Sr ages.  相似文献   

Mixing rates in Shagawa Lake,Minnesota, sediments as determined from ¹⁰⁶Ru profiles     

John Van Sickle  Walter C. Weimer  David P. Larsen 《Geochimica et cosmochimica acta》1983,47(12):2189-2197

Rates of surficial sediment mixing and sediment burial are measured in Shagawa Lake, Minnesota, using radionuclide tracers. Based on ¹⁰⁶Ru profiles in 16 cores, mixing rates average 13 cm²/yr within the upper 9 cm of sediment. Two other nuclides, ²¹⁰Pb and ¹³⁷Cs, provide further evidence for calculation of mixing rates. In addition, ²¹⁰Pb profiles estimate sediment burial rates (about 0.4 cm/yr). Mixing estimates are shown to be fairly insensitive both to uncertainties in sediment burial rates and to temporal patterns of ¹⁰⁶Ru deposition.  相似文献   

Paleomagnetism of the latest Precambrian/Cambrian Unicoi basalts from the Blue Ridge, northeast Tennessee and southwest Virginia: evidence for Taconic deformation     

Peter M. Brown  Rob Van der Voo 《Earth and Planetary Science Letters》1982,60(3):407-414

Three components of magnetization have been observed in ninety-six samples (twelve sites) of amygdaloidal basalts and “sedimentary greenstones” of the Unicoi Formation in the Blue Ridge Province of northeast Tennessee and southwest Virginia. These components could be isolated by alternating field as well as thermal demagnetization. One component, with a direction close to that of the present-day geomagnetic field is ascribed to recent viscous remanent magnetizations; another component, with intermediate blocking temperatures and coercivities, gives a mean direction of D = 132°, I = +43°,α₉₅ = 9° for N = 10 sites before correction for tilt of the strata. This direction and the corresponding pole position are close to Ordovician/Silurian data from the North American craton and we infer this magnetization to be due to a thermal(?) remagnetization during or after the Taconic orogeny. This magnetization is of post-folding origin, which indicates that the Blue Ridge in our area was structurally affected by the Taconic deformation. The third component, with the highest blocking temperatures and coercivities, appears to reside in hematite. Its mean direction, D = 276°, I = ?17°,α₉₅ = 13.8° for N = 6 sites (after tilt correction) corresponds to a pole close to Latest Precambrian and Cambrian poles for North America. The fold test is inconclusive for this magnetization at the 95% confidence level because of the near-coincidence of the strike and the declinations. We infer this direction to be due to early high-temperature oxidation of the basalts, and argue that its magnetization may have survived the later thermal events because of its intrinsic high blocking temperatures. A detailed examination of the paleomagnetic directions from this study reveals that the Blue Ridge in this area may have undergone a small counterclockwise rotation of about 15°.  相似文献   

Editorial     

Eric Delmelle 《制图学和地理信息科学》2021,48(1)

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The use of electron backscatter diffraction and orientation contrast imaging as tools for sulphide textural studies: example from the Greens Creek deposit (Alaska)     

Katja?Freitag  Alan?P.?BoyleEmail author  Eric?Nelson  Murray?Hitzman  James?Churchill  Magda?Lopez-Pedrosa 《Mineralium Deposita》2004,39(1):103-113

The Greens Creek polymetallic massive sulphide deposit is hosted in a typical polyphase deformed lower greenschist facies orogenic setting. The structure of the host rocks is well constrained, exhibiting a series of three superimposed ductile deformations followed by two brittle episodes. The ore is found both in fold hinges where early-formed depositional features are preserved and in fold limbs where primary features are typically strongly modified or obliterated. Samples from both settings have been investigated using electron backscatter diffraction (EBSD) coupled with forescatter orientation contrast (OC) imaging in order to observe the effects of deformation and lower greenschist facies metamorphism on pyrite. Results suggest that colloform pyrite may preserve information relevant to palaeoenvironment, that apparently simple textures are generally more complex, and that pyrite can deform plastically by dislocation glide and creep processes at lower temperatures and/or strain rates than generally accepted. This analysis indicates that EBSD and OC imaging provide powerful tools for observing textural relationships in pyrite that are not shown by more traditional methods. They should become routine tools for pyrite texture analysis.Editorial handling: D. Lentz  相似文献   

Scientific drilling reveals geochemical heterogeneity within the Ko’olau shield,Hawai’i     

Haskins  Eric H.  Garcia  Michael O. 《Contributions to Mineralogy and Petrology》2004,147(2):162-188

The Koolau Scientific Drilling Project (KSDP) was initiated to determine if the distinctive geochemistry of Koolau lavas is a near-surface feature. This project successfully deepened a recent, ~351 m deep, tri-cone rotary-drilled water well by coring another ~328 m. Three Ar–Ar plateau ages of 2.8 to 2.9 Ma from the drill core section of 103 flows confirm stratigraphic interpretations that core drilling recovered the deepest and oldest subaerially erupted lavas yet sampled from this volcano. The petrography and geochemistry of the core, and cuttings from this and another new Koolau water well (~433 m deep) were determined. These analyses revealed that the geochemically distinct lavas of Koolau form a veneer only 175–250 m thick at the drill sites, covering flows with more typical Hawaiian tholeiite compositions. The compositional change occurred near the end of shield volcanism and is not abrupt. Thus, it is probably not related to a catastrophic event such as the collapse of the northeast flank of this volcano. The distinct geochemistry of surface Koolau lavas cannot be explained by melting pyroxenitic or combined pyroxenitic and peridotitic sources. Additional recycled oceanic crustal components, such as plagioclase-rich cumulates and sediment, were probably involved. As the Koolau volcano drifted off the Hawaiian hotspot and the overall degree of melting decreased, the proportion of melts from recycled oceanic crustal material increased relative to those from mantle peridotite.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Editorial responsibility: T.L. Grove  相似文献   

Distribution of heavy metals in marine bivalves, fish and coastal sediments in the Gulf and Gulf of Oman   总被引：2，自引：0，他引：2  

de Mora S  Fowler SW  Wyse E  Azemard S 《Marine pollution bulletin》2004,49(5-6):410-424

An assessment of marine contamination due to heavy metals was made in the Gulf and Gulf of Oman based on marine biota (fish and various bivalves) and coastal sediment collected in Bahrain, Oman, Qatar, and the United Arab Emirates (UAE) during 2000-2001. Sediment metal loadings were generally not remarkable, although hot spots were noted in Bahrain (Cu, Hg, Pb, Zn) and on the east coast of the UAE (As, Co, Cr, Ni). Concentrations of As and Hg were typically low in sediments and the total Hg levels in top predator fish commonly consumed in the region were < 0.5 microg g(-1) and posed no threat to public health. Very high Cd concentrations (up to 195 microg g(-1)) in the liver of some fish from southern Oman may result from food-chain bioaccumulation of elevated Cd levels brought into the productive surface waters by upwelling in the region. Very high As concentrations (up to 156 microg g(-1)) were measured in certain bivalve species from the region. Although not certain, the As is probably derived from natural origins rather than anthropogenic contamination.  相似文献   

Estrogen in a karstic aquifer     

Wicks C  Kelley C  Peterson E 《Ground water》2004,42(3):384-389

Adverse impacts on the health of some fish populations, such as skewed sex distributions, have been noted in surface waters and in laboratory experiments with relatively low concentrations (above 25 ng/L) of natural estrogen (17 beta-estradiol--E2). Sources of E2 to surface and ground waters can include avian, human, and mammalian waste products. The Ozark Plateau Aquifer (OPA) is a karstic basin that receives a significant portion of its water through losing reaches of rivers. Thus, there is a direct connection between surface water and ground water. The OPA was targeted for an E2 study to assess the potential for adverse health effects to aquatic organisms living in the system. Eight springs, which drain the aquifer, were sampled quarterly. The concentrations of E2 in the OPA ranged from 13 to 80 ng/L. For any one sampling event, the concentrations of E2 at the spring waters were statistically similar; however, the concentrations of E2 at all springs varied throughout the year. At Maramec Spring, one of the larger springs, the E2 concentration, was correlated with discharge. Based on the correlation between discharge and E2 concentration, aquatic organisms living in the plateau or in its discharged waters, including the threatened southern cavefish T. subterraneus, are exposed to concentration of E2 above 25 ng/L approximately 60% of the time. This implies that organisms living in karst basins throughout the OPA are likely exposed to E2 concentrations that may adversely impact their reproductive success for a significant portion of each year.  相似文献