Passive kimberlite intrusion into actively dilating dyke–fracture arrays: evidence from fibrous calcite veins and extensional fracture cleavage

Calcite veins are invariably associated with en-echelon kimberlite dyke–fracture arrays. A detailed microstructural study of veining indicates four vein types. Type I stretched or ataxial veins are defined by high aspect ratio calcite fibers that are crystallographically continuous with calcite of the kimberlite matrix wall rock, by elongated phenocrystic phlogopite with sharp crystal terminations centered on contacts between adjacent calcite fibers and by phenocrystic phlogopite that grows or extends across these veins. Type I vein mineralogy indicates syn-dilational crystallization of vein minerals in local tensional areas within the kimberlite. Vein Types II (stretched to syntaxial elongate-blocky) and III (antitaxial) indicate late crystallization vein mineral growth during subsequent or repeated dilation. Calcite fibers in Type I to Type III veins are orthogonal to the contacts of their host dykes regardless of the orientation of vein margins. Type IV calcite veins, with blocky or mosaic/polycrystalline textures, are attributed to minor post-intrusion extension, which was potentially accompanied by repeated kimberlite intrusion within a given dyke array. Syn-crystallization/syn-intrusion Type I veins and an ubiquitous dyke-parallel fracture cleavage, in a zone up to 4 m on either side of dyke contacts, suggest that en-echelon kimberlite dyke–fracture arrays occupied the approximate center of zones of active dilation within the brittle carapace of the upper crust. Type II and III veins indicate that extension or dilation continued, independently of an occupying kimberlite fluid phase, after initial intrusion. Arrested mobile hydrofracturing, under low differential stress within the upper brittle or seismic carapace of the continental crust, followed by repeated dilation of the dyke–fracture system, is proposed as a mechanism for producing the features observed in this study. The conditions constrained in this study indicate passive dyke intrusion into dilating fracture arrays during crustal extension.     

网络安全动态防御体系研究及应用

在分析P2DR2模型的基础上,阐述了发展网络安全动态防御体系的重要性,讨论了其功能需求,提出了改进的IDS分析响应系统模型,并以其为核心构建了网络安全动态防御体系,还讨论了实现的关键技术并给出了应用实例.     

景宁地区变质岩划分及时代归属

景宁地区1：5万区域地质调查资料表明，该地区变质宕系实为不同时代和不同成因的产物。既存在中下元古代变质基底，相当于下元古界八都群，中元古界龙泉群及吕梁期侵入岩；也存在浅变质岩即中生代地层遭受热动力变质而成。原“鹤溪群”应予摒弃。     

与侵入岩有关的金矿体系

与侵入岩有关的金矿体系的主要特点 :1.大地构造位置是会聚板块边缘的内侧。这种部位的大陆岩浆作用往往形成了同时代的碱性、偏铝钙碱性和过铝成分的侵入岩 ;2 .显生宙 ,尤其是海西期和燕山期形成的侵入岩是与侵入岩金矿床有关的最佳侵入岩 ,其中最有利的部位是已知钨、锡矿床产出部位 ;3.成矿母岩是中性到酸性成分的偏铝、次碱性侵入岩 ,介于钛铁矿系列与磁铁矿系列之间 ;4 .成矿流体是富碳的热流体 ;5 .金属组合是 Au与 Bi、W、As、Mo、Te或 Sb组合 ,贱金属含量低 ;6 .硫化物含量低 ,一般低于 5 % ,显示还原性质的矿石矿物组合 ,特征的矿物组成是毒砂和磁黄铁矿 ,缺失磁铁矿和赤铁矿 ;7.除了浅成条件下形成的金矿床 ,该金矿体系的热液蚀变较弱 ,常见的蚀变产物是白云母 -绢云母 -绿泥石 -碳酸盐集合体。     

Textural development in sulfide-matrix ore breccias in the Voisey's Bay Ni-Cu-Co deposit,Labrador, Canada

Magmatic Ni-Cu sulfide ores at Voisey’s Bay contain complex assemblages of extremely heterogeneous rocks. These range from polymict breccias, with rock fragments in sulfide-rich and/or sulfide-poor matrices, to heterogeneous “vari-textured” gabbros with rapid short range variations in grain size and content of hydrous phases. Rock fragment populations in the breccias include endogenous olivine gabbros (cumulate and non-cumulate) and cumulate peridotites along with extensively depleted plagioclase-hercynite gneisses interpreted as restites from extensive partial melting of country rock quartzo-feldspathic paragneisses. Using a combination of desk-top microbeam XRF mapping at cm scale and 3D X-ray tomography, we show that both sulfide-poor and sulfide-rich breccias comprise heterolithic assemblages of clasts within a matrix of olivine gabbro. This matrix is characterised by an interconnected 3D framework of plagioclase crystals, highly variable in grain size at mm to cm scale, with interstitial olivine and poikilitic clinopyroxene, and is texturally indistinguishable from clast-free olivine gabbro. Sulfide forms interconnected networks at cm to dm scale and possibly larger. Much of the plagioclase developed by outgrowth from the margins of paragneiss xenoliths when the porosity was occupied by silicate melt. The observed range of textures is explained by a model of percolation of molten sulfide through variably crystalline inter-clast matrix, displacing the silicate melt to leave the refractory plagioclase-olivine or in some cases plagioclase-only component, now entirely within a sulfide matrix. The process is analogous to that believed to have formed interspinifex ore in komatiite-hosted deposits. Biotite rims on plagioclase enclosed in sulfide are interpreted as the result of reaction between plagioclase, olivine and a hydrous component derived from the sulfide melt itself, with a possible component of migrating residual silicate melt wicking along sulfide-silicate contacts. This sulfide infiltration model offers an alternative to the current model for upward emplacement of a slurry of silicate melt, sulfide melt and breccia fragments as a late stage injection into the dyke-sill complex. The preserved range of textures is interpreted as being due to gravity-driven percolation of sulfide liquid through a pre-existing partially molten intrusion breccia. In this model, the breccia serves as a physical trap site, accumulating downward migrating sulfide liquid. However, the invariable close mutual association of sulfide and rock fragments at Voisey’s Bay implies a common derivation.     

藏南冈底斯岩基东段米林地区晚侏罗世-白垩纪侵入岩的岩石成因和地球动力学意义

冈底斯岩基东部的米林地区发育辉长质片麻岩和花岗质片麻岩近垂向相间排布的侵入杂岩体及东侧未变形闪长岩体。野外穿切关系和锆石SHRIMP U-Pb年龄结果表明：早期辉长质片麻岩(146.3±1.6Ma)被晚期花岗质片麻岩(141.7±2.0Ma)侵入,并一起经历了后期变质作用(~90Ma)和晚白垩世闪长质岩浆作用(87.8±1.1Ma)。辉长质片麻岩具有E-MORB特征,经历了富Ti矿物相的堆晶作用,母岩浆主要来源于板片流体交代上覆亏损地幔楔物质(ε_Hf(t)=+9.9~+14.5;ε_Nd(t)=+3.0~+4.1)。花岗质片麻岩具有岛弧型岩浆岩的地球化学特征,同时伴有Fe-Ti氧化物的分离结晶,源区物质主要为部分熔融的初生下地壳(ε_Hf(t)=+10.9~+15.1;ε_Nd(t)=+4.1~+4.3)。闪长岩具有弱的Eu正异常,暗示源区存在斜长石的堆晶作用,其母岩浆来源于板片流体交代上覆亏损地幔楔物质(ε_Hf(t)=+12.2~+15.6),并在岩浆演化的过程中混入地壳物质。冈底斯岩基南缘发育晚侏罗世的辉长岩和早白垩世花岗可能是第一次新特提斯洋北向俯冲即将终止的产物。晚白垩世岩浆岩是与新特提斯洋再次俯冲引起的峰期岩浆活动的标志,可能是板块回撤引发软流圈上涌的产物。

     

Erosion of bentonite particles at the interface of a compacted bentonite and a fractured granite

Compacted bentonite has been considered as a candidate buffer material in the underground repository for the disposal of high-level radioactive waste. An erosion of bentonite particles caused by a groundwater flow at the interface of a compacted bentonite and a fractured granite was studied experimentally under various geochemical conditions. The experimental results showed that bentonite particles could be eroded from a compacted bentonite buffer by a flowing groundwater depending upon the contact time, the flow rate of the groundwater, and the geochemical parameters of the groundwater such as the pH and ionic strength.

A gel formation of the bentonite was observed to be a dominant process in the erosion of bentonite particles although an intrusion of bentonite into a rock fracture also contributed to the erosion. The concentration of the eroded bentonite particles eroded by a flowing groundwater was increased with an increasing flow rate of the groundwater. It was observed from the experiments that the erosion of the bentonite particles was considerably affected by the ionic strength of a groundwater although the effect of the pH was not great within the studied pH range from 7 to 10. An erosion of the bentonite particles in a natural groundwater was also observed to be considerable and the eroded bentonite particles are expected to be stable at the given groundwater condition.

The erosion of the bentonite particles by a flowing groundwater did not significantly reduce the physical stability and thus the performance of a compacted bentonite buffer. However, it is expected that an erosion of the bentonite particles due to a groundwater flow will generate bentonite particles in a given groundwater condition, which can serve as a source of the colloids facilitating radionuclide migration through rock fractures.     

与侵入岩有关的脉型金矿:类型、构造岩浆背景及与造山带金矿的区别

一些金矿化类型表明它们与侵入岩有关。这些矿床产于侵入岩内部、附近或环绕单个侵入体 ,包括斑岩型、角砾岩型、矽卡岩型、交代型和脉型。其中由于脉型金矿多为中温热液金矿而使其在生成模式上最有争议 ,这就是由 Groves等 (1998)提出的造山带金矿。由于缺少任何与侵入岩有直接联系的流体证据 ,普遍认为造山带金矿是在挤压变形和区域变质作用期间或之后生成的。据矿脉矿物学及金属元素组合特征 ,可将与侵入岩有关的脉型金矿分为 5种类型及相应的金属元素组合 :Au Fe氧化物 Cu,Au CuMo Zn,Au As Pb Zn Cu,Au Te Pb Zn Cu和 Cu As BiSb类型。     

Spatial Constraints on Magma Chamber Replenishment Events from Textural Observations of Cumulates: the Rum Layered Intrusion, Scotland

The Eastern Layered Series of the Rum Layered Suite is formedof 16 macro-units each comprising a lower peridotite and anoverlying feldspar-rich layer (the local term is allivalite).The origin of the peridotite layers is unresolved, with twocontrasting models. The earlier of the two is based on repeatedreplenishment of an open-system magma chamber with depositionof fractionated material on the chamber floor. The second isbased on the early formation of a troctolitic complex, whichis then repeatedly intruded by sills of replenishing picriticmagma to form the peridotite horizons. The lack of resolutionof this fundamental problem is a consequence of the relianceof previously published studies on field observations. I presentevidence to show that the clinopyroxene in the allivalites preservesinformation about the distribution of the last melt to solidify,permitting determination of not only the extent of super-solidustextural equilibration but also the sub-solidus history of theallivalite horizons. Comparison of profiles of clinopyroxene–plagioclase–plagioclasemedian dihedral angle across allivalite units demonstrates thatit is possible to distinguish between those that were intrudedby later picrite sills and those adjacent to peridotite horizonsformed by replenishment and subsequent deposition of fractionatedcrystals above the pre-existing pile. In the region studied,only the main peridotite body of Unit 9 was intruded into apre-existing allivalitic mush. KEY WORDS: Rum Layered Intrusion; chamber replenishment; dihedral angles; cumulates     

Improvement of groundwater quality due to fresh water ingress in Potharlanka Island, Krishna delta, India

Hydrochemical study had been carried out on the groundwater resources of Potharlanka Island, Krishna delta, India. Groundwater samples were collected and analyzed at 42 sites in December 2001 and October 2006. A comparative study of hydrochemical data indicates: groundwater is mildly alkaline with a pH of 7.0–8.2; electrical conductivity (EC) varies from 605 to 5,770 μS/cm in December 2001, and 652–5,310 μS/cm in October 2006. More than 62% of the groundwater samples in 2006 have TDS value <2,000 mg/l, which is within permissible limit of potable water, but 57% of the samples in 2001, are higher than the maximum permissible limit. Extremely low HCO₃/Cl and variable high Mg/Ca (molar ratios) had been indicated the transformation of the fresh groundwater aquifer systems to saline in 2001. Groundwater of this Island is mainly classified as Na–Cl and mixed types. A high percentage of Na–Cl type of these waters indicates the possibility of seawater ingression/intrusion process during 2001 and comparatively mixed water type indicates the dilution activities of groundwater. Excessive withdrawal of groundwater has caused the increase of saline water intrusion. Improvement of groundwater quality in this Island due to artificial recharge structures made by NGRI under RGNDWM project and affects of the flood due to heavy rainfall of the months of September–October 2005 are discussed in this paper.