Advances in our understanding of the gem corundum deposits of the West Pacific continental margins intraplate basaltic fields   总被引：2，自引：1，他引：1  

Ian Graham  Lin Sutherland  Khin Zaw  Victor Nechaev  Alexander Khanchuk 《Ore Geology Reviews》2008,34(1-2):200

Recent discoveries over the last decade of new gemfields, exploitation of new and existing deposits, and application of relatively new techniques have greatly increased our knowledge of the basalt-derived gem sapphire–ruby–zircon deposits. In this paper we focus on the Late Mesozoic to Cenozoic intraplate basaltic fields of the West Pacific continental margins. We review advances made in understanding the genesis of these deposits, based on the application of newer techniques. We also critically review existing data on the gem corundum deposits, in order to further refine a model for their origin.In some of the intraplate basaltic fields, corundum-bearing xenoliths have been found showing a range of PT formation conditions from 790 °C at 0.85 GPa to as much as 1100 to 1200 °C at 1.0 to 2.5 GPa. Although most magmatic sapphires contain syngenetic inclusions of columbite-group phases, zircon, spinel and rutile, some contain additional nepheline and K-feldspar, suggesting crystallization from more undersaturated alkaline magma while the Weldborough field of NE Tasmania also contains molybdenite and beryl, suggesting at least some interaction with more fractionated ‘granitic-type’ magmas. There is a large range in PT conditions calculated for the metamorphic rubies (from 780 to 940 °C, through 800 to 1150 °C up to 1000 to 1300 °C). Fluid/melt inclusion studies on magmatic corundums generally suggest that they formed in a CO₂-rich environment from a ‘syenitic’ melt under a range of T conditions from 720 to 880 °C up to 1000 to 1200 °C. Oxygen isotope studies reveal that typical magmatic corundums have values of + 4.4 to 6.9‰, whereas metamorphic corundums from the same basaltic host have lower values of + 1.3 to 4.2‰.Geochronological studies have shown that some fields produced a simple eruptive and zircon/corundum crystallization event while others had multiple eruptive events but only one or two zircon crystallization events. For a few fields, some corundums/zircons crystallized in storage regions and then remained relatively inert for periods of 200 to 400 Ma without significant change before transport to the surface in the Cenozoic. Tectonic studies of the Australian region suggest that many of the corundums crystallized from magmas related to episodic basaltic volcanism in a tectonic regime of extension, associated with the opening of the Tasman and Coral Seas. For the Asian region, the magmatic–polygenetic corundums within the basaltic fields largely crystallized in a tectonic regime of distributed E–W extension, whereas the metamorphic-metasomatic corundums crystallised in a transpressional regime associated with the collision of the Indian Plate with the Eurasian Plate (e.g., [Garnier, V., Giuliani, G., Maluski, H., Ohnenstetter, D., Deloule, E., 2003. Ar–Ar and U–Pb ages of marble-hosted ruby deposits from Central and South-east Asia. Geophysical Research Abstracts 5, 03751; Garnier, V., Giuliani, G., Ohnenstetter, D., and Schwarz, D., 2004. Les gisements de corindon: classification et genese. Les placers a corindon gemme. Le Regne Mineral 55, 7-47; Garnier, V., Ohnenstetter, D., Giuliani, G., Maluski, H., Deloule, E., Phan Trong, T., Pham Van, L., Hoang Quang, V., 2005a. Age and significance of ruby-bearing marble from the Red River Shear Zone, Northern Vietnam. Canadian Mineralogist 43, 1315–1329]).  相似文献   

Brine-pool deposition for the Zn–Pb–Cu massive sulphide deposits of the Bathurst mining camp, New Brunswick, Canada. II. Ocean anoxia during mineralisation     

Mike Solomon   《Ore Geology Reviews》2008,33(3-4):352-360

Current models of massive sulphide ore genesis in the Bathurst mining camp, New Brunswick, involve settling of sulphide particles from a stagnating, low-salinity hydrothermal plume spreading laterally in an anoxic ocean layer with minimal sulphate content. There is fragmentary evidence of ocean anoxia in the form of local fine lamination in the shales that host some of the deposits but the total organic carbon, S, Fe, U/Th, Ni/Co, V/Ni and V/Cr relationships indicate deposition under oxic or dysoxic conditions. Vanadium and Mn values range from oxic to anoxic and sulphate-reducing to non-sulphate reducing but Mn may be anomalously low due to derivation by erosion of acidic volcanic rocks. The somewhat equivocal physical and chemical data, combined with the likely disturbing effects of penecontemporaneous volcanism, considerably weaken the case for an anoxic bottom layer in a static ocean. The presence of barite with ambient seawater ³⁴S values in Brunswick no. 12 ore, and the abundance of sulphate in modern euxinic basin waters, make a sulphate-free layer unlikely, even if anoxic. Sulphate-bearing, low-salinity fluids mixing with seawater would lead to growth of barite-bearing chimneys and baritic rubble mounds, which are not observed. A model involving brine-pool deposition better explains the major features of the Bathurst ores.  相似文献   

安徽省黄山地区唐家坞组生物地层   总被引：2，自引：0，他引：2  

孙乘云  杜森官  王有生 《地层学杂志》2008,32(3)

安徽省南部黄山市刘村一带唐家坞组的时代以往归为晚志留世,新近在唐家坞组中采获腕足类、瓣鳃类、腹足类等多门类化石,并首次采获胞石、鹦鹉螺等化石,其中胞石Conochitina(Densichitana)dens的时代为兰多维列世末至文洛克世初期,含这些化石的层位相当于秀山动物群的层位。结合地质情况分析,唐家坞组时限主要属于早志留世。  相似文献   

新疆塔中南坡奥陶系的地层缺失和沉积相变化   总被引：4，自引：0，他引：4  

蔡习尧  李越 《地层学杂志》2008,32(4)

按照奥陶系内部6个组沉积的时间片段拟定塔中南坡不同区块存在不同程度的缺失。部分关键层段的牙形石和几丁虫组合特征证明一间房组和恰尔巴克组在塔中部分井区是存在的,但恰尔巴克组的分布范围最狭窄。总体上,塔中南坡隆起区地层缺失较多,古城墟隆起基本完整。据缺失状况和岩相展布,显示塔中南坡的沉积单元具有由东往西迁移的特征,且各时段迁移的距离与速度存在较大差异。  相似文献   

贵州青岩剖面青岩阶上部牙形石的发现及其意义     

武桂春  姚建新  纪占胜  王立亭 《地质学报》2008,82(2):145-154

在贵州青岩剖面的青岩组之上,原被认为是拉丁期的垄头组下部的层段中发现了牙形石动物群,除少量的分枝分子外,都归属于Neogondolella属,可鉴定为4个种,即Neogondolella bifurcata,N.constricta,N.mombergensis和N.navicula.建立了2个牙形石带,自下而上是Neogondolella bifurcata带和N.cinstricta带.牙形石面貌证明这段地层在时代上非常接近但尚未进入拉丁阶,属于安尼期中晚期,进一步的牙形石工作将很有可能在目前发现的牙形石层段的上部寻找到安尼阶和拉丁阶之间的界限,从而为青岩阶顶界的限定提供可靠的牙形石证据.此外,牙形石的发现还初步实现了青岩阶2大主导门类化石--牙形石和菊石在同一剖面的直接对比关系.  相似文献   

扬子及周缘地区上奥陶统-下志留统烃源岩发育环境及其控制因素   总被引：6，自引：0，他引：6  

严德天  王清晨  陈代钊  汪建国  王卓卓 《地质学报》2008,82(3):321-327

扬子地区下古生界发育了上奥陶统五峰组和下志留统龙马溪组两套有效烃源岩,查清其发育环境及其控制因素具有重要的科学理论和油气勘探意义.晚奥陶世开始,扬子地区进入碎屑岩陆棚演化阶段;五峰期-龙马溪期,扬子地区主体为局限的深水陆棚环境,总体呈现出浅水陆棚、深水陆棚、次深海共存的古地理格局.沉积体系展布和沉积演化主要受扬子陆块与华夏陆块的汇聚作用控制.扬子地区上奥陶统-下志留统烃源岩的形成与生烃母质生物的高生产力和高埋藏率、冰期-冰后期之交的气温快速转暖、海平面快速上升以及粘土矿物在有机质富集保存过程中的赋存驻留作用等密切相关.  相似文献   

鄂尔多斯盆地东缘煤储层微孔隙结构特征及其影响因素   总被引：2，自引：0，他引：2  

张松航  汤达祯  唐书恒  许浩  林文姬  张彪 《地质学报》2008,82(10):1341-1349

在对鄂尔多斯盆地东缘58套采自不同层位不同地域煤样显微组分测试和低温液氮比表面测试的基础上,从比表面积、吸附曲线形态、阶段孔径结构分布、阶段孔径比表面积贡献、FHH分形特征几个方面刻画了煤储层微孔隙特征。同时,就“孔比表面积—孔隙结构—煤物质组成与化学结构”这一因果链,分析了鄂尔多斯盆地东缘煤微孔隙特征与煤变质程度、煤岩显微组分以及矿物组分与类型的关系。研究发现,Ro在0.60%~1.91%范围内,比表面积及FHH分形分维数先明显降低,Ro至1.3%后又略有回升,同时吸附回线“滞后环”及分形尺度对应的压力范围明显减小,孔径3~4 nm“墨水瓶”型孔明显减少乃至消失,并成为比表面积减少的主要贡献者。在相似煤级条件下,惰质组分较镜质组分有更多的比表面积贡献。粘土矿物组分含量>10%时,孔径3~4 nm“墨水瓶”型孔对比表面贡献明显,且随煤级增高影响作用相对加大。  相似文献   

Mobilization analysis of the dolmen of Dombate (Northwest Spain)     

Vicente Navarro  Luis E. Romera  ngel Yustres  Miguel Candel 《Engineering Geology》2008,100(1-2):59-68

This paper presents an analysis of the mobilization of the dolmen of Dombate, a megalithic monument situated in the Northwest of Spain. The study is founded on simple static principles, with the application of basic concepts of soil mechanics (soil reactions were computed by the reaction modulus method) and rock mechanics (a simple secant approach was adopted to model the contact between orthostats). In addition, a simplified geometric model for dolmens was adopted. On the basis of these concepts, a numerical solver able to provide quick estimations of the system's mobilization was developed. Using this tool, a number of sensitivity analyses were conducted to estimate the mobilization that could be caused by a conservation project currently under consideration. It was found that mobilization might be excessive, and therefore, a safer procedure is proposed. In short, this paper puts forth a new rational approach for archaeological practices which may help to estimate the possible consequences of excavations and rehabilitations on megalithic structures.  相似文献   

Structural elements of the Makran region, Oman sea and their potential relevance to tsunamigenisis     

Mohammad Mokhtari  Iraj Abdollahie Fard  Khaled Hessami 《Natural Hazards》2008,47(2):185-199

The character of convergence along the Arabian–Iranian plate boundary changes radically eastward from the Zagros ranges to the Makran region. This appears to be due to collision of continental crust in the west, in contrast to subduction of oceanic crust in the east. The Makran subduction zone with a length of about 900 km display progressively older and highly deformed sedimentary units northward from the coast, together with an increase in elevation of the ranges. North of the Makran ranges are large subsiding basins, flanked to the north by active volcanoes. Based on 2D seismic reflection data obtained in this study, the main structural provinces and elements in the Gulf of Oman include: (i) the structural elements on the northeastern part of the Arabian Plate and, (ii) the Offshore Makran Accretionary Complex. Based on detailed analysis of these data on the northeastern part of the Arabian Plate five structural provinces and elements—the Musendam High, the Musendam Peneplain, the Musendam Slope, the Dibba Zone, and the Abyssal Plain have been identified. Further, the Offshore Makran Accretionary Complex shown is to consist Accretionary Prism and the For-Arc Basin, while the Accretionary Prism has been subdivided into the Accretionary Wedge and the Accreted/Colored Mélange. Lastly, it is important to note that the Makran subduction zone lacks the trench. The identification of these structural elements should help in better understanding the seismicity of the Makran region in general and the subduction zone in particular. The 1945 magnitude 8.1 tsunamigenic earthquake of the Makran and some other historical events are illustrative of the coastal region’s vulnerability to future tsunami in the area, and such data should be of value to the developing Indian Ocean Tsunami Warning System.  相似文献   

湖南石门杨家坪下寒武统杷榔组三段混合沉积研究   总被引：5，自引：1，他引：4  

董桂玉  何幼斌  陈洪德  罗进雄  秦志勇 《地质论评》2008,54(5):593-601

湖南石门杨家坪下寒武统杷榔组三段发育陆源碎屑与海相碳酸盐的混合沉积。综合前人研究成果,通过对研究区野外露头资料的详细观测和室内样品分析及数据统计等工作,对研究区杷榔组三段混合沉积进行了详细的研究。研究区混合沉积特征宏观上表现为由陆源碎屑与混积物交互沉积、碳酸盐与混积物交互沉积和不同类型混积物本身的交互沉积构成的混积层系,微观上表现为陆源碎屑组分与碳酸盐组分混合沉积所形成混积岩;混合沉积类型主要为内潮汐沉积作用和浊流沉积作用形成的复合式混合沉积Ⅱ,次为深水原地沉积作用形成的渐变式混合沉积,但是不同成因的沉积作用形成的混合沉积类型往往叠加在一起,形成复合式混合沉积Ⅱ+渐变式混合沉积的混合沉积复合体;混合沉积环境为深水斜坡,发育内波、内潮汐混合沉积微相、深水原地混合沉积微相和远源浊流混合沉积微相等类型;在沉积环境分析的基础上,根据内波、内潮汐沉积特征,剖析了混合沉积的沉积机理;结合混合沉积的成因、沉积机理、产出部位及沉积环境等因素,以沉积学原理为指导,建立了研究区杷榔组三段的混合沉积模式。  相似文献