华北克拉通-扬子克拉通与秦岭造山带古地幔组成及状态的对比

经研究，华北克拉通古地幔以含石榴石的二辉橄榄岩、方辉橄榄岩及纯橄榄岩为主．地幔交代作用强烈，岩石富集不相容元素，明显高于南非及西澳克拉通者．扬子克拉通古地幔主元素亏损程度差，交代作用较弱，岩石为石榴石／尖晶石二辉橄榄岩．秦岭造山带壳、幔交界带的岩石类型复杂，包括蛇纹石化尖晶石二辉橄榄岩（蛇纹岩）、石榴石辉石岩、榴闪岩、变辉长岩及变玄武岩等．蛇纹岩遭受强的塑性流变，剪切变形结构发育．与克拉通相比，地幔交代作用很弱．３个地幔域的古地温状态有差异，秦岭造山带最高，扬子克拉通居中，华北克拉通最低．上述结果表明，两克拉通的古地幔特征相差显著，暗示经历了不同的演化过程．交代作用可能发生在１７００Ｍａ以前和１１００～５００Ｍａ，后者强于前者．造山带地幔的剪切变形明显强于克拉通地幔     

Osmium-strontium-neodymium-lead isotopic covariations in mid-ocean ridge basalt glasses and the heterogeneity of the upper mantle

Osmium, strontium, neodymium, and lead isotopic data have been obtained for 30 hand picked samples of basaltic glass from the Pacific, Atlantic and Indian mid-oceanic ridges. Large variations in Os isotopic ratios exist in the glasses, from abyssal peridotite-like values to radiogenic compositions similar to oceanic island basalts (¹⁸⁷Os/¹⁸⁶Os and ¹⁸⁷Os/¹⁸⁸Os ratios range from 1.06 to 1.36 and from 0.128 to 0.163, respectively). Os isotopic and elemental data suggest the existence of mixing correlations. This relationship might be ascribed to secondary contamination processes; however, such a hypothesis cannot account for the negative correlation observed between Os and Nd isotopes and the existence of complementary covariations between Os and SrPb isotopes. In this case, OsSrNdPb isotopic variations are unrelated to late post-eruption or shallow level contamination. These relationships provide strong evidence that the Os isotopic composition of the samples are derived from the mantle and thus implies a global chemical heterogeneity of the oceanic upper mantle. The results are consistent with the presence of recycled oceanic crust in the mantle sources of mid-ocean ridge basalts, and indicate that the unique composition of the upper mantle below the Indian ocean results from its contamination by a mantle component characterized by radiogenic Os and particularly unradiogenic Nd and Pb isotopic compositions.     

Influence of the Load Wavelength on the Permeability of a Viscosity Interface in the Mantle

Assuming a radially stratified Newtonian mantle in a steady-state approximation, we demonstrate that the permeability of a viscosity interface at 660-km depth strongly depends on the wavelength of buoyancy forces driving the flow. The flow induced by long-wavelength loads penetrates through the boundary freely even if the viscosity increases by two orders. In contrast, the boundary is practically impermeable for short-wavelength loads located in the upper mantle. Thus, a stepwise increase of viscosity is a significant obstacle for small descending features in the upper mantle, but huge upper mantle downwellings, or upwellings formed in the-lower mantle can overcome it easily. This indicates that certain care is necessary in interpreting the seismic structure of the mantle by means of flow models. The global tomographic image includes only the first few degrees of the harmonic series and, consequently, its interpretation in terms of a present-day flow field results in a predominantly whole-mantle circulation even for extreme viscosity contrasts.     

Crustal structure of Dabieshan orogenic belt

The crustal structures ofP velocity and density on the deep seismic sounding profile across the Ilabieshan orogenic belt are presented. There is a 5-km-thick crustal “root” between the Yuexi and Xiaotian where the elevation is highest on the profile. An apparent Moho offset of 4. 5 km beneath the Xiaotian-Mozitan fault marks the paleo-suture of the Triassic collision. A high-velocity anomaly zone at the depth below 3 km beneath the ultra-high pressure (UHP) zone may be correlated to the higher content of UHP metamorphic rocks. Project supported by the National Natural Science Foundation of China and the Joint Earthquake Science Foundation.     

Interpretation of S-wave data from Tai’an-Xinzhou DSS profile and its relationship with Xingtai earthquakes

On the basis of S wave information from Tai’an-Xinzhou DSS profile and with reference to the results from P-wave interpretation, the 2-D structures, including S-wave velocity V _s, ratio γ between V _p and V _s; and Poisson’ s ratio σ, are calculated; the structural configuration of the profile is presented and the relevant inferences are drawn from the above results. Upwarping mantle districts (V _s≈4.30 km/s) and sloping mantle districts (V _s≈4.50 km/s) of the profile with velocity difference about −4% at the top of upper mantle are divided according to the differences of V _s, γ and σ in different media and structures, also with reference to the information of their neighbouring regions; the existence of Niujiaqiao-Dongwang high-angle ultra-crustal fault zone is reaffirmed; the properties of low and high velocity blocks (zones) including the crust-mantle transitionalzone and the boudary indicators of North China rift valley are discussed. A comprehensive study is conducted on the relation of the interpretation results with earthquakes. It is concluded that the mantle upwarps, thermal material upwells through the high-angle fault, the primary hypocenter was located at the crust-mantle juncture 30.0∼33.0 km deep, and additional stress excited the M _S=6.8 and M _S=7.2 earthquakes at specific locations around 9.0 km below Niujiaqiao-Dongwang, the earthquakes took place around the high-angle ultra-crustal fault and centered in the brittle media and rock strata with low γ and low σ values. This subject is part of the 85-907-02 key project during the “8th Five-Year Plan” from the State Science and Technology Commission.     

1995年日本阪神地震近场强地面运动的特征

分析了１９９５年日本阪神地震（Ｍ７．２）近场强地面运动特征．结果表明，震中附近地区水平加速度峰值达６００～８００ｇａｌ，竖向加速度峰值达３００ｇａｌ，强地面运动持续时间为１０～１５ｓ，加速度时程的卓越周期为０．２～２ｓ．谱分析的结果还表明，在较宽的频带范围内该次地震的近场地震动的强度都比较大．     

铝对铬成矿地球化学的依存性和对抗性

基于岩浆铬矿床与超镁铁质岩石的关系，从元素亲合性和共生规律的角度揭示了铝对铬成矿制约的主导作用，分析了铝和铬亲石、亲氧的二重性及其晶体化学的依存关系。论证了超镁铁Ｓｉ－Ｏ体系中铝丰度过高或过低均不利于铬的成矿。揭示了制约元素分散富集的因素都是在一定条件下互为依存和转化的，是在动态中的矛盾的对立和统一。     

联合古陆演化周期中超大型含煤及含油气盆地的形成

联合古陆———Ｐａｎｇｅａ的拼合与裂解反映了地球系统内部的巨大变革，这一过程根本上改变了浅部圈层的构造和环境。地史上超大型含煤盆地及含油气盆地与Ｐａｎｇｅａ的演化周期密切相关。在石炭纪及二叠纪拼合过程中形成了一系列超大型聚煤盆地；晚侏罗世Ｐａｎｇｅａ开始裂解，出现全球性裂陷作用期，大西洋张开，许多与裂陷有关的大型叠合盆地形成。在这些盆地中已发现十余个与晚侏罗世烃源岩有关的巨型含油气系统。上述情况表明Ｐａｎｇｅａ演化过程中出现了对能源资源聚集极为有利的古构造、古环境和古气候条件。     

地幔流体及其成矿作用

地幔流体作为一种重要成矿介质在某些矿床形成过程中起到过重要作用。根据目前地幔流体研究的某些成果，介绍了地幔流体可能与成矿的方式和成矿机制，并举例说明地幔流体与超大型，大型矿床之间的成因联系。     

The use of GPR and VES in delineating a contamination plume in a landfill site: a case study in SE Brazil

This paper presents the results of the application of the Ground Penetrating Radar (GPR) method, or Georadar, in outlining a zone of contamination due to solid residues at the waste burial site of Rio Claro in the state of São Paulo, SE Brazil. A total of eight GPR profiles with 50- and 100-MHz antennae were surveyed. Six profiles were located within the landfill site and the remaining two were outside. The main objective of the GPR survey was to evaluate the side extension of contamination. A Vertical Electric Sounding (VES) survey was performed at four points within the site in order to investigate the vertical extent of the contamination plume and to define the bottom of the landfill. Two additional VESs were done outside the landfill with the purpose of determining the top of the ground water table and the geoelectric stratigraphy of the background. From the interpretation of the GPR profiles, it was possible to locate the top of the contamination plume and to infer that it was migrating laterally beyond the limits of the waste disposal site. This was observed along the profile situated close to the highway SP-127, which was about 20 m from the limit of the site. The signature of the contaminant appears as a discontinuous reflector that is believed to be a shallow ground water table. The discontinuity is marked by a shadow zone, which is characteristic of conductive contaminant residues. The contamination did not move far enough to reach a sugar cane plantation located at approximately 100 m from the border of the site. In the regions free from contamination, the ground water table was mapped at approximately 10 m of depth, and it was characterized by a strong and continuous reflector. The radar signal penetrated deep enough and enabled the identification of a second reflector at approximately 14 m deep, interpreted as the contact between the Rio Claro and the Corumbataí formations. The contact is marked by the presence of gravel characterized by ferruginous concretes, which cause the strong amplitude reflection in the GPR profile. Within the landfill site, the quantitative interpretation of the VES results showed the contamination zone. The base of the landfill varies between 11 and 15 m deep. Outside the landfill site, the VES results showed no indication of contamination and allowed the determination of the top of the ground water table and the contact between the Rio Claro and the Corumbataí formations. The results of GPR and VES showed a good agreement and the integrated interpretations were supported by local geology and information from several boreholes, about 17 m depth, on average. The bottom of the landfill reaches a maximum of 14.5 m depth.