辽宁盖县梁屯—矿洞沟碱性正长岩杂岩体的U—Pb和Sm—Nd年龄及其地质意义

辽宁梁屯 -矿洞沟杂岩体主要由辉石正长岩、霓辉正长岩和霓辉角闪正长岩等碱性岩石组成 ,具有全岩 Rb- Sr等时线年龄 186 6± 115 Ma和 ISr=0 .70 4 9的同位素特征 ,是我国目前报道的最古老的碱性正长岩类。本文报道了该岩体的锆石U- Pb和全岩 Sm- Nd同位素测试资料 ,获得了锆石 U- Pb同位素年龄为 185 7± 2 0 Ma、Sm- Nd等时年龄为 1787± 180 Ma、εNd(t) =- 4 .8～ - 5 .0的数据。它们反映出该杂岩体形成年龄的上限为 185 7± 2 0 Ma、下限不小于 1787± 180 Ma,来源于富集地幔物质。基于这些数据并结合区域地质资料分析 ,作者提出了华北地台北缘古元古宙存在有富集地幔储库 ,以及辽河群主体形成于 190 0 Ma以前的认识     

Estimating the surface wind speed over drifting pack ice from surface weather charts

Routine surface wind speed data, vital for the study of drifting pack ice, are not available for the polar oceans. Over sea, it has been demonstrated by Hasse that estimates of surface wind speed may be obtained from the geostrophic wind speed using linear formulae. Comparing estimated with observed data for six sites in Canada, it is found that the formulae may also be applied to obtain estimates of surface wind speed over pack ice.     

On fitting the log-linear model to wind speed and temperature profiles over a melting glacier

The profile structure of wind speed and temperature in katabatic flow over a melting glacier is analyzed within the log-linear framework. Similarity between windspeed and temperature profiles is indicated but the log-linear model should be restricted to heights within 1.5 m of the ice. Marked deviation from the model occur at greater heights, probably due to the effects of flux divergence.Unlike results from other stable atmospheres, a decreases with increasing stability. This may arise from the use of the Obukhov length L. When the height H at which the wind speed reaches its maximum value is used instead, does not vary with stability. It has mean values of 4.5 and 4.3 for windspeed and temperature profiles, respectively.     

Ecometrics and the paleoecological implications of Pleistocene faunas from the western coastal plains of the Cape Floristic Region,South Africa

The Pleistocene ungulate communities from the western coastal plains of South Africa's Cape Floristic Region (CFR) are diverse and dominated by grazers, in contrast to the region's Holocene and historical faunas, which are relatively species-poor and dominated by small-bodied browsers and mixed feeders. An expansion of grassy habitats is clearly implied by the Pleistocene faunas, but the presence of ruminant grazers that cannot survive the summer dry season typical of the region today suggests other important paleoecological changes. Here we use dental ecometrics to explore the paleoecological implications of the region's Pleistocene faunas. We show that the dental traits (hypsodonty and occlusal topography) of the ungulates that occurred historically in the CFR track annual and summer aridity, and we use these relationships to reconstruct past aridity. Our results indicate that the Pleistocene faunas signal paleoenvironments that were on average less arid than today, including during the summer, consistent with other lines of evidence that suggest a higher water table and expansion of well-watered habitats. Greater water availability can be explained by lower temperature and reduced evapotranspiration during cooler phases of the Pleistocene, probably coupled with enhanced groundwater recharge due to increased winter precipitation.     

The detection of fast-moving asteroids and comets by IRAS

The Infrared Astronomical Satellite (IRAS) was used to search for fast-moving objects in the inner Solar System. The selection effects and limitations of the search are examined with particular reference to the objects which may be present in the moving-object data base at JPL. It is shown that the two new Apollo asteroid discoveries are in fair agreement with the discovery rate by ground-based telescopes. IRAS discovered six comets which is also consistent with the discovery rate for ground-based searches. It is estimated that there are 20–30 comets but no Apollo asteroids in the hours-confirmed moving-object data base established by the IRAS project.     

Spectrophotometry of the small satellites of Saturn and their relationship to Iapetus, Phoebe, and Hyperion

We have obtained broadband spectrophotometric observations of four of the recently discovered small satellites of Saturn (Gladman et al., 2001, Nature 412, 163-166). The new data enable an understanding of the provenance, composition, and interrelationships among these satellites and the other satellites of Saturn, particularly Iapetus, Phoebe, and Hyperion. Temporal coverage of one satellite (S21 Tarvos) was sufficient to determine a partial rotational lightcurve. Our major findings include: (1) the satellites are red and similar in color, comparable to D-type asteroids, some KBOs, Iapetus, and Hyperion; (2) none of the satellites, including those from the “Phoebe Group” has any spectrophotometric relationship to Phoebe; and (3) S21 Tarvos exhibits a rotational lightcurve, although the data are not well-constrained and more observations are required to fit a definitive period. Dust created by meteoritic impacts and ejected from these satellites and additional undiscovered ones may be the source of the exogenous material deposited on the low-albedo side of Iapetus. Recent work which states that the small irregular satellites of Saturn have impacted Phoebe at least 6-7 times in the age of the Solar System (Nesvorny et al., 2003, Astron. J. 126, 398-429), suggests that such collisions may have propelled additional material from both Phoebe and the small irregular satellites toward Iapetus. The accretion of material from outer retrograde satellites may be a process that also occurs on Callisto and the uranian satellites.     

A first approach to assessing future climate states in the UK over very long timescales: Input to studies of the integrity of radioactive waste repositories

Projected timescales for the transport of radionuclides from an undisturbed undergound nuclear waste repository to the surface are in the range of tens of thousands to millions of years. Over these timescales major natural and potentially major anthropogenic changes in climate can be expected. As part of the UK disposal safety assessment programme, time-dependent models of the repository environment are being developed. The Climatic Research Unit has undertaken a study of relevant climatic change and climatic effects. This has required assessment of the probable range, succession and duration of major climate states likely to be experienced in the UK over very long timescales, up to 10⁶ yr. Two methodologies have been employed. The first uses the Milankovitch theory, which is considered to be the major cause of the Pleistocene glacial/interglacial cycles. The second involves empirical analysis of the long-term reconstructed climate record: no assumptions about the specific causes or mechanisms are made. A period of sub-tropical climate is included in the sequence to represent a period of anthropogenically-induced greenhouse warming. The climate sequence established using these methods will form the basis for studying related processes, such as erosion and groundwater movement and transfer by vegetation, and their implications for radioactive waste disposal. This has involved the construction of instrumental climate analogues.     

The Othris Ophiolite, Greece: A snapshot of subduction initiation at a mid-ocean ridge

The mantle section of the Tethyan-type Othris Ophiolite, Greece, records tectono-magmatic processes characteristic of both mid-ocean ridges and supra-subduction zones. The Othris Ophiolite is a remnant of the Jurassic Neotethys Ocean, which existed between Eurasia and Gondwanaland. Othris peridotites range from fertile plagioclase lherzolites to depleted harzburgites. Abundances of Al₂O₃ and CaO show well-defined inverse linear correlations with MgO, suggesting that the Othris peridotites formed as residua from variable degrees of partial melting.

Peridotites from the Fournos Kaïtsa and western Katáchloron sub-massifs are similar to abyssal peridotites and can be explained by a multistage model with some melting in the garnet stability field followed by moderate degrees of anhydrous near-fractional melting in the spinel stability field. In contrast, the peridotites from the Metalleio, Eretria, and eastern Katáchloron sub-massifs, and the Vourinos ophiolite are highly depleted and have extremely low concentrations of Al₂O₃ and heavy rare earth elements. These peridotites have enriched light REE contents compared to the middle REE. These residua are best modelled by hydrous melting due to a flux of slab-derived fluid to the mantle wedge during melting.

The occurrence of both styles of melting regimes within close spatial and temporal association in the same ophiolite is explained by intra-oceanic thrusting and forced subduction initiation at (or near) a mid-ocean ridge. Thus, the Othris Ophiolite, and probably Tethyan-type ophiolites in general, represent a transient phase of plate tectonic reorganisation rather than quasi-steady state plate tectonics.     

Magma source components in an arc-continent collision zone: the Flores-Lembata sector,Sunda arc,Indonesia

Major, trace-element, and Sr-, Nd-and Pbisotope data are presented for volcanics from 12 active or recently active volcanoes from the islands of Flores, Adonara, Lembata and Batu Tara in the eastern Sunda are. The volcanics vary in composition from low-K tholeiite, through medium-and high-K calcalkaline types to the K-rich leucite basanites of Batu Tara. From the tholeiites to the leucite basanites there are marked increases in the concentrations of LILE (K, Rb, Ba, Sr), LREE and La/Yb, and all the volcanics have high Ba/ Nb, La/Nb and Ba/La compared with mid-ocean ridge and intraplate eruptives. K/Cs values are generally lower than OIB values, and overlap those of other arc volcanics and northeast Indian Ocean sediments. The volcanics exhibit a broad range of ⁸⁷Sr/⁸⁶Sr (0.70468–0.70706), ¹⁴³Nd/¹⁴⁴Nd (0.512946–0.512447), and a moderate range in ²⁰⁶Pb/²⁰⁴Pb (18.825–19.143), ²⁰⁷Pb/ ²⁰⁴Pb (15.643–15.760) and ²⁰⁸Pb/²⁰⁴Pb (38.97–39.51). Trace-element and isotopic data suggest that the mantle beneath the eastern Sunda arc is a complex heterogeneous mixture of 3 or 4 major source components: MORB-source or depleted MORB-source, OIB-source and subducted Indian Ocean sediment. The low-K tholeiites were probably formed by relatively large degrees of melting of depleted MORB-source mantle, modified by subduction-related fluids, whereas the trace-element and isotopic characteristics of the K-rich volcanics suggest that they were derived from an OIB source which and been modified by a subduction-related melt component. The source components of the medium-to high-K calcalkaline rocks are more difficult to determine, and probably include mixtures of MORB-source or OIB-source, and melt/fluid derived from subducted oceanic sediment. Minor-and trace-element modelling calculations indicate substantial difficulties in producing the relatively low Ti-contents of arc volcanics by melting OIB-source mantle. Where OIB mantle is considered to be an important component of arc magmas it is suggested that the HFSE are buffered to relatively low concentration by a residual Ti-rich accessory phase.