Geochemical and Isotopic Heterogeneities along an Island Arc-Spreading Ridge Intersection: Evidence from the Lewis Hills, Bay of Islands Ophiolite, Newfoundland

This study focuses on the origin of magma heterogeneity andthe genesis of refractory, boninite-type magmas along an arc–ridgeintersection, exposed in the Lewis Hills (Bay of Islands Ophiolite).The Lewis Hills contain the fossil fracture zone contact betweena split island arc and its related marginal oceanic basin. Threetypes of intrusions, which are closely related to this narrowtectonic boundary, have been investigated. Parental melts inequilibrium with the ultramafic cumulates of the PyroxeniteSuite are inferred to have high MgO contents and low Al₂O₃,Na₂O and TiO₂ contents. The trace element signatures of thesePyroxenite Suite parental melts indicate a re-enriched, highlydepleted source with 0·1 x mid-ocean ridge basalt (MORB)abundances of the heavy rare earth elements (HREE). Initial_Nd values of the Pyroxenite Suite range from -1·5 to+0·6, which overlap those observed for the island arc.Furthermore, the Pyroxenite Suite parental melts bear strongsimilarities to boninite-type equilibrium melts from islandarc-related pyroxenitic dykes and harzburgites. Basaltic dykessplit into two groups. Group I dykes have 0·6 x MORBabundances of the HREE, and initial _Nd values ranging from +5·4to +7·5. Thus, they have a strong geochemical affinitywith basalts derived from the marginal basin spreading ridge.Group II dykes have comparatively lower trace element abundances(0·3 x MORB abundances of HREE), and slightly lower initial_Nd values (+5·4 to +5·9). The geochemical characteristicsof the Group II dykes are transitional between those of GroupI dykes and the Pyroxenite Suite parental melts. Cumulates fromthe Late Intrusion Suite are similarly transitional, with _Ndvalues ranging from +2·9 to +4·6. We suggest thatthe magma heterogeneity observed in the Lewis Hills is due tothe involvement of two compositionally distinct mantle sources,which are the sub-island lithospheric mantle and the asthenosphericmarginal basin mantle. It is likely that the refractory, boninite-typeparental melts of the Pyroxenite Suite result from remeltingof the sub-arc lithospheric mantle at an arc–ridge intersection.Furthermore, it is suggested that the thermal-dynamic conditionsof the transtensional transform fault have provided the prerequisitefor generating magma heterogeneity, as a result of mixing relationshipsbetween arc-related and marginal basin-related magmas. KEY WORDS: Bay of Islands ophiolite; transform (arc)–ridge intersection; boninites; rare earth elements, Nd isotopes     

华北地区成组地震前后的地电阻率异常特征

分析了自有地电阻率观测资料以来华北地区发生的三次成组地震前后的异常特征,其中包括1976年唐山地震组、1989年大同地震组和1998年张北地震组.结果发现(1)成组地震的地电阻率异常持续时间都比较长,主震发生后异常一般会继续下降或维持低值异常不恢复,整个成组地震的趋势背景非常清楚;(2)主震前异常台站范围比较广,异常台站数目比较多,后续地震的异常多集中在震源区;(3)成组地震结束后,异常一般都很快恢复.最后探讨了成组地震的地电阻率异常发展特征与孕震机理的关系.     

基于固体潮观测的高精度垂直摆倾斜仪

针对地球固体潮汐监测的要求，介绍了高精度垂直摆倾斜仪的组成和工作原理；论述了差动电容测微传感器技术在垂直摆倾斜仪中的应用；采用空间多体中心构形理论进行倾斜仪机械结构设计；利用复杂双摆理论分析了摆体的动力学特性，并进行了摆体摆动误差的分析计算；提出了用静电进行垂直摆倾斜仪的标定方法。同时，对垂直摆倾斜仪的使用环境和应用情况进行了说明。     

基于Java3D的网络地理信息可视化

在分析WebGIS中地理信息可视化研究现状的基础上，详细介绍了Java3D开发库的基本开发机制，并讨论其关键技术与解决方案，成功实现了基于Java3D的网络地理信息Web浏览器。实验表明，通过Java3D建立数字球面，并利用Java3D空间数据模型表达地理信息模型，实现在数字球面上映射地理信息，是实现网络地理信息可视化的新途径和新思路。     

数字地球网格计算雏议

数字地球将为人类提供关于我们地球的海量自然和人文数据与信息 ,是我们生活的行星的一个多分辨率 ,四维虚拟表达。网格计算被认为是解决数字地球问题的最好方法。数字地球问题的解决必须通过异构的计算资源 ,信息系统 ,设备 ,人之间的相互协作 ,而这些都是地理位置或组织结构分散的。本文介绍我们在生成用于解决数字地球问题的核心中间件的研究工作以及结果。因为网格计算本身是一门比较新的领域 ,网格计算与数字地球的有机结合将为数字地球提供一个全新的计算工具     

红地球葡萄栽培的气候适应性分析

美国红地球葡萄(RedGlobe)，是我国近几年引进的葡萄新品种，其对气象条件的要求较高。本文分别通过温度、湿度、光照等几个方面分析了红地球葡萄生长的适宜气象条件，以便于今后在葡萄的生产过程中趋利避害。     

我国第一颗业务型地球静止气象卫星FY-2C

20 0 4年 1 0月 1 9日 ,我国在西昌卫星发射中心成功发射了第一颗业务型地球静止轨道气象卫星FY 2C ,该星定位于 1 0 5°E赤道上空 ,工作状况良好。文章介绍了中国FY 2C卫星携带仪器的技术特点以及地面应用系统。     

Isotope Dilution MC-ICP-MS Rare Earth Element Analysis of Geochemical Reference Materials NIST SRM 610, NIST SRM 612, NIST SRM 614, BHVO-2G, BHVO-2, BCR-2G, JB-2, WS-E, W-2, AGV-1 and AGV-2

We present data for the concentrations of eleven rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb, Lu) in eleven international geochemical reference materials obtained by isotope dilution multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). We have analysed both rock powders and synthetic silicate glasses, and the latter provide precise data to support the use of these as reference materials for in situ trace element determination techniques. Our data also provide precise measurements of the abundance of mono-isotopic Pr in both glasses and powders, which allows more accurate constraints on the anomalous redox-related behaviour of Ce during geochemical processes. All materials were analysed in replicate providing data that typically reproduce to better than one percent. Sm/Nd ratios in all these materials also reproduce to better than 0.2% and are accurate to < 0.2% and can thus be used as calibrants for Sm-Nd geochronology. Our analyses agree well with existing data on these reference materials. In particular, for NIST SRM 610, USGS BHVO-2, AGV-1 and AGV-2, our measured REE abundances are typically within < 2% (and mostly 1%) of REE concentrations previously determined by isotope dilution analysis and thermal ionisation mass spectrometry, consistent with the higher degree of precision and accuracy obtained from isotope dilution techniques. Close agreement of results between basaltic glass reference materials USGS BHVO-2G and BCR-2G and the BHVO-2 and BCR-2 powders from which they were created suggests that little fractionation, concentration or dilution of REE contents occurred during glass manufacture.