Effects of early season defoliation ofAnthyllis cytisoides(a Mediterranean browse species) on further herbivore attack     

Concepción L. Alados  Fernando G. Barroso  Antonio Aguirre  Juan Escós 《Journal of Arid Environments》1996,34(4):455-463

To determine if defoliation of a woody plant affects foraging by folivorous insects, we examined the infection rate (number of leaves damaged per total number of leaves sampled on marked stems) ofAnthyllis cytisoidesunder three experimental treatments: 10, 50 and 90% plant defoliation. Observations were made for three age classes, established by trunk base perimeter (equal to or lower than 11 cm, between 11 and 20 cm, larger than 20 cm). Plants respond positively to artificial defoliation by increasing total vegetative length of the stem and total inflorescence length. This response is most evident in young individuals.Response to herbivory was measured as overall infection rate and also as infection rate by different feeding guilds—chewing, mining, or sucking insects. We found that increased defoliation elicited increased resistance of leaves to insect attack. This was particularly evident in young plants. Different insect guilds respond in different ways. Attack by chewing insects declines with defoliation for all plant age classes; only sucking insects which feed on the oldest plants reduce feeding rate with plant defoliation. Finally, mining insects present the opposite trend in young and senescent plants.  相似文献   

渗流场反分析及其在多孔介质中的应用     

许模 《地质灾害与环境保护》1996,(2)

本文讨论了复杂地质环境中渗流场的反分析问题，利用地下水流数值模拟结合最优化技术，通过对地下渗流场的模拟和寻优，求得描述地下含水介质非稳定渗流场的重要参位──渗透系数和给水度的模型解，并应用于各向同性的多孔介质渗流场反分析实例中。  相似文献   

山东荣成沽河流域水资源系统分析     

许模  费美高 《地质灾害与环境保护》1996,7(3):50-55,63

流域水资源系统由降水产流，以及通过水文下垫面的转换，形成的地表径流和地下水流流组成。本文将复杂的沽河流域水 资源系统分解成多个子系统，利用频谱分析方法对各个水资源子系统的转换功能进行定量的分析刻画，并利用地下含水介质子系统的转换特征函数－频率响应函数求取水文地质参数，丰富了水文地质参数的获取途径。  相似文献   

新疆哈密黄山─镜儿泉地区金矿床（点）矿物标型特征的研究     

唐菊兴  阳正熙  李承德  慕纪录 《矿物岩石》1996,(3)

本文通过镜下鉴定，结合电子探针分析、Ｘ衍射分析等，总结了研究区各金矿床（点）的矿物物性、成分、分布等特征。矿物学的研究表明，整个成矿过程和构造动力变质密切相关。  相似文献   

Bismuth and cobalt minerals as indicators of stringer zones to massive sulphide deposits, Iberian Pyrite Belt     

E. Marcoux  Y. Moëlo  J. M. Leistel 《Mineralium Deposita》1996,31(1-2):1-26

The stringer zones and commonly the interaction zone at the base of the massive sulphide mounds in the Iberian Pyrite Belt contain bismuth and cobalt minerals that are not found in the overlying massive sulphides. These are fairly rare cobalt sulphoarsenides (cobaltite, alloclasite, galucodot) that were formed at the beginning of the massive sulphide genesis, and fairly common bismuth sulphides (bismuthinite, hammarite, wittichenite, cosalite, kobellite, joseite, etc.), including species rare at world scale (nuffieldite, giessenite, jaskolskiite) that were deposited from last stage high-temperature (> 300 °C) copper-bearing fluids containing Bi (Te, Se). The last stage fluids precipitated chalcopyrite containing Cu, Bi, Te, (Se) sulphosalts at the base of the sulphide mound to form a high cupriferous zone. Their interaction with the massive sulphides is reflected by the formation of an exchange zone, a few metres thick, showing chalcopyrite disease textures, at the base of the mound; this zone forms the upper limit of potentially economic copper enrichment and of bismuth minerals. Gold is undoubtedly in part, if not totally, related to this last phase. The bismuth concentrations being equivalent in the massive sulphides and the stringers, the presence of bismuth minerals in the stringer zones results from high-temperature conditions combined with a rarity of galena, which impedes absorption of available Bi. The distribution of these bismuth minerals provides a basic mineralogical zoning in the stringer zone, with a deep, low-aS₂ zone containing native bismuth and tellurides and a shallow, higher-aS₂ zone in contact with the massive ore sensu stricto and containing complex bismuth sulphides. These results make it possible to distinguish between sulphide veinlets belonging to stockwork zones of massive orebodies and veinlets of an ambiguous nature, and provide mineralogical criteria for the proximity of copper-rich zones. They enrich the very complex mineralogy of the Iberian Pyrite Belt.  相似文献   

A mass transfer model of bauxite formation   总被引：1，自引：0，他引：1  

Josep M. Soler  Antonio C. Lasaga 《Geochimica et cosmochimica acta》1996,60(24):4913-4931

The formation of bauxite due to weathering of a granitic protolith has been simulated by means of a one-dimensional flow and reaction model based on the mass transfer principle. The model couples mineral dissolution and precipitation reactions, speciation in solution, and advective solute transport in a porous medium. A very important aspect of the modeling study is the use of mineral reaction rates determined experimentally in the laboratory. The important effects of solution saturation state and pH have been incorporated into the kinetic rate laws governing the heterogeneous reactions. The values of these parameters have been obtained from the scientific literature to guarantee that realistic reaction rates are used in the simulations. Albite and quartz are the minerals that make up the parent rock in the model. Gibbsite, kaolinite, and a Na-mica (as a surrogate for smectite) are the secondary minerals that have been taken into account. Long-term simulations (>1 Ma) have been run, and the formation of a bauxitic profile, with an upper gibbsite-rich and a lower kaolinite-rich zone, is predicted. In early stages of the process (up to a few hundreds of thousands of years), both gibbsite and kaolinite precipitate directly from solution as a consequence of albite dissolution. In later stages, the bulk of gibbsite precipitation derives from the incongruent dissolution of kaolinite, while kaolinite precipitation is still caused by the dissolution of albite. This is also reflected by the formation of two reaction fronts in the profile. These results are compared with weathering sequences from the Los Pijiguaos bauxite deposit, Venezuela. The overlap between the gibbsite and kaolinite zones and the replacement of kaolinite by gibbsite are consistent with model calculations. Mechanical denudation has to be called upon to explain the limited thicknesses of the weathering profiles in the field. The role of mechanical erosion is supported by the presence of microsedimentary structures in the bauxite and the balance between dissolved and suspended loads in the streams draining the area.  相似文献   

裂隙岩体中的对流扩散研究     

陈尤雯  莫海鸿 《岩土力学》1997,18(3):47-52

揭示一个基于代数拓扑理论的裂隙网络中物质弥散模型，还给出了应用于网络中的对流扩散的对应性原理的证明。应用拓扑理论给出的框架，使其起了一个数据结构的组织者的作用，由此得到网络中每一个分支上的浓度的解。这个解是在拉普拉斯空间上的解析解。网络中任意点在任何时刻的浓度可以很方便地用数值拉氏反变换求出。  相似文献   

冀西北东坪金矿床含金石英脉石英流体包裹体Rb-Sr等时线及其地质意义   总被引：8，自引：2，他引：8  

莫测辉  王秀璋  程景平  梁华英 《地球化学》1997,26(3):20-27

用石英流体包裹体Ｒｂ－Ｓｒ等时线法测得产于碱性岩体中具有超大型潜力的东坪金矿床含金石英脉的年龄为（１０３±８）Ｍａ，远晚于赋矿岩体的就位时间（元古宙），显示了成岩与成矿是两期不同构造运动的产物，两者之间没有直接的成因联系。８７Ｓｒ／８６Ｓｒ示踪结果显示成矿物质主要来源于赋矿碱性岩体。研究结果认为，东坪金矿是后期与大气降水热液有关的改造成矿作用的产物。  相似文献   

关于侵入岩体中金矿床成因研究若干问题的讨论   总被引：9，自引：1，他引：9  

莫测辉  王秀璋 《地质论评》1997,43(2):139-147

各时代、不同类型侵入岩中的金矿床是金矿的主要类型。关于金矿床与岩体的成因关系目前尚存在不同的看法，但传统的岩浆热液成因观点仍居统治地位，其原因往往在于不少研究者把岩液热液成因当成了固定模式应用于具体矿床的研究，而不是建立在综合研究的基础之上。本文结合近年来金矿的研究进展，强调侵入岩中金矿床的研究的研究要综合考虑成岩成矿的时代与时差，成矿流体和成矿物质的来源等各方面因素。金矿床定年的进展研究表明，矿  相似文献   

岩浆活动旋回与地球多层对流系统   总被引：2，自引：2，他引：2  

邓晋福  莫宣学  赵海玲  罗照华  赵国春 《地学前缘》1997,(Z2)

从地球历史的节律角度讨论岩浆活动旋回。岩浆活动旋回可按时间与空间分出相互对应的不同尺度，进而可与深度尺度不同的地球多层对流系统相互对应，从而给予了岩浆活动旋回的动力学意义。岩浆活动的时间周期愈长，空间尺度亦愈大，需要的维持岩浆源存在的热能、挥发分供给的数量与深度亦愈大。  相似文献