湖北省红石地区叶家小湾金矿基本特征及找矿模型     

刘忠明  黄国平等 《地质与勘探》2002,38(5):33-37

红石地区叶家小湾金矿形成于燕山晚期，成矿流体主要来自岩浆期后热液。断裂和岩浆岩是两大重要的成矿地质条件。控矿构造为北东向断裂，花岗岩是金矿的有利赋矿围岩。成矿物质来自深部，与燕山晚期 浆活动密切相关，叶家小湾金矿综合找矿模型的建立，对于在红石地区开展找金（银）工作具有重要指导作用。  相似文献   

Melt loss and the preservation of granulite facies mineral assemblages   总被引：29，自引：3，他引：29  

R. W. White  R. Powell 《Journal of Metamorphic Geology》2002,20(7):621-632

The loss of a metamorphic fluid via the partitioning of H₂O into silicate melt at higher metamorphic grade implies that, in the absence of open system behaviour of melt, the amount of H₂O contained within rocks remains constant at temperatures above the solidus. Thus, granulite facies rocks, composed of predominantly anhydrous minerals and a hydrous silicate melt should undergo considerable retrogression to hydrous upper amphibolite facies assemblages on cooling as the melt crystallizes and releases its H₂O. The common occurrence of weakly retrogressed granulite facies assemblages is consistent with substantial melt loss from the majority of granulite facies rocks. Phase diagram modelling of the effects of melt loss in hypothetical aluminous and subaluminous metapelitic compositions shows that the amount of melt that has to be removed from a rock to preserve a granulite facies assemblage varies markedly with rock composition, the number of partial melt loss events and the P–T conditions at which melt loss occurs. In an aluminous metapelite, the removal of nearly all of the melt at temperatures above the breakdown of biotite is required for the preservation of the peak mineral assemblage. In contrast, the proportion of melt loss required to preserve peak assemblages in a subaluminous metapelite is close to half that required for the aluminous metapelite. Thus, if a given proportion of melt is removed from a sequence of metapelitic granulites of varying composition, the degree of preservation of the peak metamorphic assemblage may vary widely.  相似文献   

On the relationship between kilometer-scale sheath folds, ductile thrusts and minor structures in the basal high-pressure units of the Cabo Ortegal complex (NW Spain)     

Josu Azcrraga  Benito balos  Jos Ignacio Gil Ibarguchi 《Journal of Structural Geology》2002,24(12)

Large sheath folds in the basal high-pressure nappes of the Cabo Ortegal complex are described and a kinematic interpretation provided. The principal penetrative and map structures relate to regional D2 deformation, which produced foliations (S2) bearing mineral and stretching lineations (L2) and several types of folds (a-type, sheath-like and ‘folded folds’). The latter structures are subparallel to the trend of the orogen. Their attitude suggests that the units involved shared a common tectonic evolution during progressive ductile deformation of an anisotropic medium. Reconstruction of major geological structures was accomplished through projection of map-scale features onto the ductile flow plane and the plane perpendicular to the ductile flow direction. The structures reconstructed illustrate their development in the deeper structural levels of an orogenic channel subjected to high-pressure metamorphism during the early phases of the Hercynian orogeny in NW Iberia. We argue that orogen-normal tectonic displacements (of up to a few hundreds of kilometers) represent the minor components of the transpression with possibly thousands of kilometers along-strike dextral displacement between the intervening plates (during subduction/collision).  相似文献   

在"数字国土工程"中我区地学数据库建设的现状及发展趋势     

张梅  胡凤翔 《内蒙古地质》2002,(2)

近年来,在国土资源部的高度重视下,我区相继建立了一系列地学数据库。这些地学数据库的建立不仅为地矿行业提供了基础性数据,也加速了"数字国土工程"和国土资源信息化建设的步伐。随着信息技术的高速发展,利用地理信息系统(GIS)将各类地学数据有机地结合起来,形成地学数据应用与管理系统,最终通过网络服务于社会,必将是各类地学数据发展的必然趋势。  相似文献   

Fluid-bearing alkaline carbonate melts as the medium for the formation of diamonds in the Earth''s mantle: an experimental study     

N. Pal''yanov  A. G. Sokol  M. Borzdov  A. F. Khokhryakov 《Lithos》2002,60(3-4):145-159

We have experimentally studied the formation of diamonds in alkaline carbonate–carbon and carbonate–fluid–carbon systems at 5.7–7.0 GPa and 1150–1700 °C, using a split-sphere multi-anvil apparatus (BARS). The starting carbonate and fluid-generating materials were placed into Pt and Au ampoules. The main specific feature of the studied systems is a long period of induction, which precedes the nucleation and growth of diamonds. The period of induction considerably increases with decreasing P and T, but decreases when adding a C–O–H fluid to the system. In the range of P and T corresponding to the formation of diamonds in nature, this period lasts for tens of hours. The reactivity of the studied systems with respect to the diamond nucleation and growth decreases in this sequence: Na₂CO₃–H₂C₂O₄·2H₂O–C>K₂CO₃–H₂C₂O₄·2H₂O–C>>Na₂CO₃–C>K₂CO₃–C. The diamond morphology is independent of P and T, and is mainly governed by the composition of the crystallization medium. The stable growth form is a cubo-octahedron in the Na₂CO₃ melt, and an octahedron in the K₂CO₃ melt. Regardless of the composition of the carbonate melt, only octahedral diamond crystals formed in the presence of the C–O–H fluid. The growth rates of diamond varied in the range from 1.7 μm/h at 1420 °C to 0.1–0.01 μm/h at 1150 °C, and were used to estimate, for the first time, the possible duration of the crystallization of natural diamonds. From the analysis of the experimental results and the petrological evidence for the formation of diamonds in nature, we suggest that fluid-bearing alkaline carbonate melts are, most likely, the medium for the nucleation and growth of diamonds in the Earth's upper mantle.  相似文献   

中条山西南段与变基性岩有关的铜矿地质特征及成因浅析     

薛克勤  赵月凤  董清雷 《华北地质》2002,(Z1)

与变基性岩有关的铜矿 ,是在中条山西南段新发现的一种新的铜矿类型 ,其形成是在原始基性岩浆侵入或喷发作用形成的矿源岩或矿化体基础上 ,经过区域变质和印支 -燕山期构造 -岩浆热液的改造加富而成 ,其成因应属与变基性岩有关的变质 -热液改造型铜 (镍、铁 )矿床。  相似文献   

内蒙古宝音图岩群变质基性火山岩锆石U-Pb年龄及意义     

张玉清  苏宏伟 《华北地质》2002,(Z1)

内蒙古达茂旗宝音图岩群是在达茂旗、查干呼绍地区 1:5万区调和白云鄂博幅 1:2 5万区调过程中从过去的巴特敖包群和白云鄂博群未分岩组解体出来的中级变质岩系。通过对宝音图岩群中阳起钠长片岩、二云片岩 (原岩均为基性火山岩 )进行单颗粒锆石U -Pb法年龄测定 ,获得了两条不一致线上交点年龄 (2 486± 42 )Ma、(2 496± 2 6 )Ma ,代表了宝音图岩群基性火山岩及宝音图岩群的形成时代 ;在不一致线之外不同成因的锆石的2 0 7Pb/ 2 0 6Pb表面年龄 (2 2 2 7± 15 )Ma ,寓示着 2 2 0 0Ma左右发生了一次区域性变质热事件 ;下交点年龄 (319±486 )Ma和 (40 6± 46 )Ma ,代表了 2 5 0～ 480Ma时期该区大面积岩浆侵位及宝音图岩群后期变形变质改造的时期 ,两个年龄样的获得为研究古元古代古陆的裂解及白云鄂博海槽的形成提供了直接依据。  相似文献   

国际地磁参考场在我国地磁基础研究中的应用     

王文 《国际地震动态》2002,(5):4-6,7

国际地磁参考场资料在我国得到广泛应用。利用国际地磁参考场资料，我国学者研究了高斯分析、地球磁场模型及其源场可能位置、重磁关系、核幔耦合、地磁场能量、地球非偶极子磁场西向漂移等。在绘制中国地磁等值图中也利用了某些国际地磁参考场资料。  相似文献   

Les dykes basiques du massif ancien de l'Ourika (Atlas de Marrakech,Maroc) : géochimie et significationThe basic dykes of the Ourika old massif (High Atlas of Marrakech): Geochemistry and significance     

Ahmed Barakat  Christian Marignac  Mohamed Bouabdelli 《Comptes Rendus Geoscience》2002,334(11):827-833

The Precambrian massif of Ourika is crosscut by two systems of basic dykes, striking N40°E and N90–120°E. Using incompatible trace elements, the two systems form two distinct chemical groups, displaying a continental tholeiitic affinity. The composition variations between the two defined groups can be due to heterogeneities of mantle sources and to contamination, during the magma ascent, by the continental crust. The emplacement of these basic dykes, before the late-PIII formations, can be related to the Neoproterozoic distension generalised to the Anti-Atlas chain. To cite this article: A. Barakat et al., C. R. Geoscience 334 (2002) 827–833.  相似文献   

城市基准地价评估的容积率内涵及其修正系数的确定--以石家庄市为例   总被引：6，自引：1，他引：6  

葛京凤  黄志英  梁彦庆 《地理与地理信息科学》2003,19(3):98-100,108

基淮地价评估是当前城市地价评估的主要形式。容积率既反映了土地的利用状况，同时也是影响地价的主要因素之一。该文阐述了容积率内涵，分析容积率与地价、环境的关系，探讨合理容积率的确定，以石家庄市为例，探索容积率修正系数确定的正确途径，避免在容积率概念、修正系数等问题上产生混淆。  相似文献