华南东段加里东期花岗岩类形成构造背景探讨

根据近年对区域地质调查取得的认识和前人的研究成果,研究了华南东段加里东期花岗岩类的地质产状、分布规律、形成时代以及Nd、Sr同位素特征;结合研究区超镁铁质-镁铁质岩及火山岩的形成时代、震旦纪—奥陶纪的沉积环境、加里东期构造事件的构造变形特征,对加里东期花岗岩类的形成背景进行了探讨。结果表明,加里东期花岗岩类形成于410～460Ma,大部分岩体属于S型花岗岩,岩浆来源于地壳物质的部分熔融;极少数为I型花岗岩,有幔源物质参与。研究区在早古生代不存在与俯冲有关的弧火山岩,也不存在大面积的早古生代I型花岗岩,震旦纪—奥陶纪地层主要形成于浅海环境。研究提出,加里东期花岗岩类主体形成于板内构造环境。     

西藏南部二叠纪和早白垩世构造岩浆作用与特提斯演化:新观点

西藏高原前新生代时期的特提斯演化和新生代时期的高原隆升历史是西藏高原基础地质研究中两个长期被关注的重要科学问题,但迄今对西藏高原自身的物质组成和前新生代演化历史的认知程度仍然较低,直接限制了对新生代时期西藏高原隆升历史的更深入研究。新的地质和地球化学资料显示早—中二叠世时俯冲背景和伸展背景共存于现今的冈底斯带和喜马拉雅带,中二叠世末期(大约263Ma)侵位的皮康过铝质S型花岗岩以及同期发生的松多榴辉岩的高压变质作用和区域性角度不整合指示现今的冈底斯弧背断隆带在那时经历了同碰撞造山事件。中生代岩浆岩锆石U-Pb年龄和Hf同位素成分表明,冈底斯弧背断隆带和中冈底斯带存在以古元古代甚至太古宙物质为特征的古老基底物质,而北冈底斯带和南冈底斯则分别以中—新元古代新生地壳和显生宙新生地壳为特征。已有高质量年龄数据和锆石Hf同位素指示冈底斯带中北部地区在大约110Ma发生了带状岩浆大爆发并伴随着幔源物质显著增加。新的可靠的锆石U-Pb年龄指示喜马拉雅带东部措美(Comei)地区大面积出露的白垩纪火成岩侵位于132Ma左右,代表了新近在藏南和澳大利亚南西部识别出的经历了强烈变形和深位侵蚀的Comei-Bunbury大火成岩省的残余。以这些新资料为基础,讨论了西藏南部的晚古生代—中生代构造岩浆演化历史和特提斯演化过程。     

布什维尔德铂族元素矿床:铂族矿物赋存状态及其成因

总结南非布什维尔德杂岩体中Merensky Reef(简称MR矿层)和Platreef(简称PR接触带)两类铂族元素矿床的矿床地质、矿化特征以及铂族元素的赋存状态。MR矿床是典型的层状铂族元素(PGE)矿床,在杂岩体东部和西部发育,PGE总含量稳定,赋存在堆晶间隙硫化物中,常以PGE硫化物的形式产出。PR接触带型矿化集中在杂岩体北段,整体上不连续,各个矿床的具体特征由于底盘岩性的多变而不同,PGE主要赋存在碲化物和砷化物等半金属化合物中,可以脱离硫化物产在硅酸盐矿物中。相关的实验研究显示,PGE在岩浆结晶过程中发生分异,Pd/Ir比值体现了硫化物的分异程度;Pd比Pt更容易被氧化以及在热液中迁移,Pt/Pd比值体现了混染和热液的作用,这些因素造成了PR接触带与MR矿层中PGE赋存状态的差异。岩浆可能在侵入之前已经达到了硫饱和,岩浆房的压力变化和岩浆通道对于PGE的富集有重要意义,热液流体可以对已经形成的PGE矿化进行改造。     

构造煤化学结构演化与瓦斯特性耦合机理

煤是对应力和应变非常敏感的一种特殊岩石,在不同的应力-应变环境和构造应力作用下,煤的物理结构、化学结构及其光性特征等都将发生显著变化,从而形成具有不同结构特征的、不同类型的构造煤。构造煤在变形的过程中,镜质组反射率将发生规律性变化,并被较为广泛地应用于煤田构造的定量研究,高温高压变形实验也证实了这一现象。为了深入探讨煤镜质组光性组构变化的微观机理,将X-射线衍射、顺磁共振和核磁共振等技术应用于不同类型构造煤以及高温高压实验变形煤的化学结构研究。研究表明,构造煤化学结构演化与镜质组反射率的演化具有密切的内在联系,镜质组反射率的光性异常是构造煤化学结构演化在物理光学性质上的具体体现。不同类型的构造煤由于物理和化学结构上的不同,导致瓦斯含量和透气性等瓦斯特性上的重大差异,糜棱煤特殊的物理和化学结构决定了其高含气量和低透气性的特征,是矿井瓦斯突出的危险地带,因此,可以通过构造煤分布规律的研究,进行矿井瓦斯富集与突出危险性的评价与预测,为矿井瓦斯灾害的研究提供新的思路和方法。     

从滇黔桂“金三角”区域地层地球化学演化特征探讨卡林型金矿的物质来源

选用滇黔桂地区东经103°～110°,北纬22°～26°,面积约20万km2,34幅1∶20万水系沉积物统计结果资料,全面系统地探讨本区及其邻近区域地层地球化学特征及其与成矿的关系。结果表明:(1)与华南地区相比,本区存在Sb、As、Au、Hg等低温元素矿集区的地球化学块体,金具有深源性,而砷、锑、汞则是区域性的高背景,本区金与砷、锑、汞的相伴,既有必然性,又有偶然性;(2)与基性岩浆活动有关的亲基性场元素、氧化物、矿化剂高背景的形成,是本区右江裂谷带、富宁—关岭南北向断裂带、文山—富宁逆冲推覆构造带,特别是峨眉地幔柱所产生的基性岩浆喷溢及火山碎屑浊流沉积的客观地球化学反映;(3)黔西南地区二叠纪峨眉山玄武岩喷发导致二叠系和三叠系金及大量亲基性场元素的突变,右江裂谷活动至少始于寒武纪,随着时间的推移,由桂西往黔西南逐渐裂开;(4)滇黔桂"金三角"地区卡林型金矿的物源与裂谷、特提斯和区域性深大断裂和峨眉地幔柱长期活动相伴的基性火成岩及火山碎屑浊流沉积有关。     

Variations of Microbial Communities and the Contents and Isotopic Compositions of Total Organic Carbon and Total Nitrogen in Soil Samples during Their Preservation

Semi-sealed preservation of soil samples at different moisture of 4% and 23%,respectively, was simulated to observe the variations of soil microbial communities and determine the contents and isotopic compositions of the total organic carbon and total nitrogen on the 7th and 30th day, respectively.The results show that during preservation,the quantity of microbial communities tended to increase first and then decrease,with a wider variation range at higher moisture (23%).At the moisture content of 23%,th...     

Aerodynamic Characteristics of the Crest with Membrane Attachment on Cretaceous Pterodactyloid Nyctosaurus

The Nyctosaurus specimen KJ1 was reconstructed under the hypothesis that there is a membrane attached to the crest;the so-called headsail crest.The aerodynamic forces and moment acting on the headsail crest were analyzed.It was shown that KJ1 might adjust the angle of the headsail crest relative to the air current as one way to generate thrust (one of the aerodynamic forces,used to overcome body drag in forward flight) and that the magnitude of the thrust and moment could vary with the gesture angle and ...     

A Middle-Upper Devonian Boundary Section in the Open Platform,Platform Margin Facies of Guilin,South China

The Caiziyan Middle and Upper Devonian boundary section is located approximately 30 km northeast of Guilin.It hosts relatively abundant benthic and common-rare pelagic fossils,including brachiopods,corals,tentaculites,and conodonts,which may serve as a better suitable section for pelagic and neritic stratigraphic correlation.In this section,10"standard"conodont zones are recognized across the Givetian-Frasnian boundary,including,in descending order,the Lower hassi Zone,punctata Zone,transitans Zone,the U...     

Permeability Heterogeneity in a Fractured Sandstone–Mudstone Rock Mass in Xiaolangdi Dam Site, Central China

Abstract: Heterogeneity of permeability in fractured media is a hot research topic in hydrogeology. Numerous approaches have been proposed to characterize heterogeneity in the last several decades. However, little attention has been paid to correlate permeability heterogeneity with geological information. In the present study, several causes of permeability heterogeneity, that is, lithology, tectonism, and depth, are identified. The unit absorption values (denoted as ω), which are results obtained from the packer test, are employed to represent permeability. The variability of permeability in sandstone–mudstone is so significant that the value of unit absorptions span 3–4 orders of magnitude at any depth with several test sections. By declustering, it has been found that under a similar tectonic history, the means of permeability differ greatly at different formations as a result of different mudrock contents. It has also been found that in the same formation, permeability can be significantly increased as a result of faulting. The well-known phenomenon, the decrease in permeability with depth, is found to be caused by the fractures in the rock mass, and the relationship between permeability and depth can be established in the form of logω–logd. After subtracting the trend of ω with absolute depth, the mean of the residual value at each relative depth can be well correlated with the distribution of mudstone. The methods proposed in this paper can be utilized to research in similar study areas.     

Comparative Analysis of Sequence Characteristics among Different Superimposed Stages of the Chelif Basin,Algeria

Abstract: Superimposed basins were investigated with respect to tectonic evolution, sediment deposition and petroleum characteristics within a single superposition stage generally. The comparative study was seldom seen. Sequence characteristics were compared for two different superimposed stages – an expanding rifting stage and a depression-foreland transition stage – in the Chelif Basin during the Miocene in this paper. A model and mechanism for sequence evolution of superimposed basins in different dynamic situations are discussed with respect to sequence similarities and differences. The compared characters include sequence thickness, sequence boundaries and system tracts, as well as sediment deposition within sequences and sequence development patterns. Finally, some typical features of sequence development concomitant with changes of superimposed stages in the Chelif Basin are discussed.