沉积物粒度分析在厦门市第四纪环境研究和地层划分对比中的应用   总被引：6，自引：0，他引：6  

张璞  陈建强  田明中  朱金芳  黄宗林  江春亮 《地球科学与环境学报》2005,27(1):88-94

采用MS2000型激光粒度分析仪进行测试，利用计算机粒度分析软件对数据进行整理和计算，绘制出样品的频率曲线、概率累积曲线以及粒度众数位值曲线等图件并进行沉积环境分析。厦门地区第四纪环境演化经历了中更新世同安组(含泥中粗砂、含泥细中砂、砂为主)海积一冲积一更新统上部龙海组(含泥粗中砂、含泥细中砂、含泥粗砂、粗砂、细中砂、含细砾中粗砂、中细砂等)冲积一洪冲积一更新世上部东山组(砂、砂砾、含泥中粗砂、粗砂、泥质中细砂、细砂、中粗砂等)冲洪积及部分海积(粉砂、细粉砂、含碳质泥、粘土、淤泥质粘土、粉砂质粘土等)一全新世长乐组(粉砂，淤泥质粘土、粉砂质粘土、碳质粘土、含砂淤泥质粘土，粉砂质亚粘土、粉细砂亚粘土等)海湾沉积。在解释环境变化的同时，说明粒度变化曲线在一定程度上可以作为地层划分的依据之一，并以此对研究区地层进行了详细划分。  相似文献   

Petrogenesis of andalusite–kyanite–sillimanite veins and host rocks, Sanandaj-Sirjan metamorphic belt, Hamadan, Iran     

A. A. Sepahi  D. L. Whitney  A. A. Baharifar 《Journal of Metamorphic Geology》2004,22(2):119-134

Quartz‐rich veins in metapelitic schists of the Sanandaj‐Sirjan belt, Hamadan region, Iran, commonly contain two Al₂SiO₅ polymorphs, and, more rarely, three coexisting Al₂SiO₅ polymorphs. In most andalusite and sillimanite schists, the types of polymorphs in veins correlate with Al₂SiO₅ polymorph(s) in the host rocks, although vein polymorphs are texturally and compositionally distinct from those in adjacent host rocks; e.g. vein andalusite is enriched in Fe₂O₃ relative to host rock andalusite. Low‐grade rocks contain andalusite + quartz veins, medium‐grade rocks contain andalusite + sillimanite + quartz ± plagioclase veins, and high‐grade rocks contain sillimanite + quartz + plagioclase veins/leucosomes. Although most andalusite and sillimanite‐bearing veins occur in host rocks that also contain Al₂SiO₅, kyanite‐quartz veins crosscut rocks that lack Al₂SiO₅ (e.g. staurolite schist, granite). A quartz vein containing andalusite + kyanite + sillimanite + staurolite + muscovite occurs in andalusite–sillimanite host rocks. Textural relationships in this vein indicate the crystallization sequence andalusite to kyanite to sillimanite. This crystallization sequence conflicts with the observation that kyanite‐quartz veins post‐date andalusite–sillimanite veins and at least one intrusive phase of a granite that produced a low‐pressure–high‐temperature contact aureole; these relationships imply a sequence of andalusite to sillimanite to kyanite. Varying crystallization sequences for rocks in a largely coherent metamorphic belt can be explained by P–T paths of different rocks passing near (slightly above, slightly below) the Al₂SiO₅ triple point, and by overprinting of multiple metamorphic events in a terrane that evolved from a continental arc to a collisional orogen.  相似文献   

Carbonate aeolianites of western Saurashtra,India: experimental decipherment of the depositional mechanisms     

PRABIR DASGUPTA  SUBIKASH BANDYOPADHYAY 《Sedimentology》2008,55(5):1361-1374

Granular carbonate deposits of Late Pleistocene to Early Holocene age, commonly referred to as ‘miliolite limestone’, occur in a linear belt, parallel to the southern coast of Saurashtra, India. In the present study area these carbonate deposits are found in select valleys between ridges and mounds of pyroclastic material present in the Deccan trap plateau. Two different depositional histories have been proposed for these sediments. The presence of marine bioclasts led to the postulation of a marine origin for these deposits. The second school of thought propounded redeposition of the coastal sediments by aeolian processes. Although a few features could not be explained by the proposed aeolian model, critical comparison of these two views favoured the aeolian origin. The mode of occurrence, lithological and structural attributes, and microscopic evidence presented here, also support a possible aeolian origin for these deposits. Experimental observation indicates that these carbonate aeolianites represent backflow deposits, which accumulated because of the flow separation caused by the presence of topographic highs. The conspicuous concave‐up geometry of the deposit conformed to the shape of the separation bulb. In view of the inferred depositional mechanism, the disposition of the deposits and the signature of the palaeoflow direction suggest that the carbonate particles were derived from the north‐western coast of Saurashtra by strong south‐easterly winds. Massive granular carbonates with outsized basement clasts appear to be the product of avalanching of granular material from the higher contours because of oversteepening of the primary deposit.  相似文献   

Asymmetrically zoned reaction rims: assessment of grain boundary diffusivities and growth rates related to natural diffusion-controlled mineral reactions   总被引：1，自引：0，他引：1  

L. M. KELLER  R. WIRTH  D. RHEDE  K. KUNZE  R. ABART 《Journal of Metamorphic Geology》2008,26(1):99-120

This study explores garnet coronas around hedenbergite, which were formed by the reaction plagioclase + hedenbergite→garnet + quartz, to derive information about diffusion paths that allowed for material redistribution during reaction progress. Whereas quartz forms disconnected single grains along the garnet/hedenbergite boundaries, garnet forms ～20‐μm‐wide continuous polycrystalline rims along former plagioclase/hedenbergite phase boundaries. Individual garnet crystals are separated by low‐angle grain boundaries, which commonly form a direct link between the reaction interfaces of the plagioclase|garnet|hedenbergite succession. Compositional variations in garnet involve: (i) an overall asymmetric compositional zoning in Ca, Fe²⁺, Fe³⁺ and Al across the garnet layer; and (ii) micron‐scale compositional variations in the near‐grain boundary regions and along plagioclase/garnet phase boundaries. These compositional variations formed during garnet rim growth. Thereby, transfer of the chemical components occurred by a combination of fast‐path diffusion along grain boundaries within the garnet rim, slow diffusion through the interior of the garnet grains, and by fast diffusion along the garnet/plagioclase and the garnet/hedenbergite phase boundaries. Numerical simulation indicates that diffusion of Ca, Al and Fe²⁺ occurred about three to four, four and six to seven orders of magnitude faster along the grain boundaries than through the interior of the garnet grains. Fast‐path diffusion along grain boundaries contributed substantially to the bulk material transfer across the growing garnet rim. Despite the contribution of fast‐path diffusion, bulk diffusion through the garnet rim was too slow to allow for chemical equilibration of the phases involved in garnet rim formation even on a micrometre scale. Based on published garnet volume diffusion data the growth interval of a 20‐μm‐wide garnet rim is estimated at ～10³–10⁴ years at the inferred reaction conditions of 760 ± 50 °C at 7.6 kbar. Using the same parameterization of the growth law, 100‐μm‐ and 1‐mm‐thick garnet rims would grow within 10⁵–10⁶ and 10⁶–10⁷ years respectively.  相似文献   

江西浒坑钨矿含矿石英脉的地质特征及成矿构造演化   总被引：7，自引：0，他引：7  

章伟 《地质学报》2008,82(11):1531-1539

位于赣西武功山地区的江西浒坑钨矿是一个大型石英脉型钨矿床,与赣南典型的“五层楼”模式不同,矿脉主要集中在岩体内接触带。含矿石英脉除了普通的块状构造以外,还普遍存在条带状构造。详细的野外编录和镜下研究表明含矿块状石英脉在形成后遭受不同程度的韧性剪切,从而形成不同成分的分异条带。剪切带以出现新生的面理和线理（拉伸线理）为特征。岩石学研究表明条带状矿石属于糜棱岩,具有丰富的塑性变形显微构造特征。通过对含矿石英脉的构造解析,认为与岩浆岩有关的原生节理系统基本上是同时形成的,沿节理充填的石英脉经历了长期的、多期次的构造运动,从而形成了复杂的石英脉和矿石类型。建立了原生节理形成→石英充填→韧性剪切发生→二期石英充填→脆性碎裂的矿区构造演化序列。韧性剪切作用的动力学背景可能是受后期岩浆侵入的影响,最后的脆性破裂应与区域上存在南北向的压应力有关。  相似文献   

江西省武功山地区浒坑钨矿床的Re-Os年龄及其地质意义   总被引：2，自引：0，他引：2  

刘珺 《地质学报》2008,82(11):1572-1579

浒坑钨矿床是位于江西省中部武功山成矿带的大型石英脉型黑钨矿床。为了确定该矿床的成矿时代,笔者选取了浒坑含钨石英脉中与黑钨矿共生的辉钼矿进行了高精度Re-Os同位素定年,并获得5个辉钼矿样品的Re-Os等时线年龄和模式加权平均年龄分别为150.2±2.2Ma和149.82±0.92Ma。测年数据表明浒坑钨矿床的成矿时代为150Ma左右,是华南地区中生代大规模成岩成矿作用高峰期的产物。辉钼矿含铼较低,表明成矿物质可能来自壳源,与形成浒坑花岗岩体的燕山期重熔S型花岗岩岩浆活动有关。该矿床形成于燕山期岩石圈伸展减薄环境。  相似文献   

The Ca-Eskola component in eclogitic clinopyroxene as a function of pressure, temperature and bulk composition: an experimental study to 15 GPa with possible implications for the formation of oriented SiO2-inclusions in omphacite     

Jürgen Konzett  Daniel J. Frost  Alexander Proyer  Peter Ulmer 《Contributions to Mineralogy and Petrology》2008,155(2):215-228

Experiments have been conducted in the P-T range 2.5–15 GPa and 850–1,500°C using bulk compositions in the systems SiO₂–TiO₂–Al₂O₃–Fe₂O₃–FeO–MnO–MgO–CaO–Na₂O–K₂O–P₂O₅ and SiO₂–TiO₂–Al₂O₃–MgO–CaO–Na₂O to investigate the Ca-Eskola (CaEs Ca_0.5□_0.5AlSi₂O₆) content of clinopyroxene in eclogitic assemblages containing garnet + clinopyroxene + SiO₂ ± TiO₂ ± kyanite as a function of P, T, and bulk composition. The results show that CaEs_ss in clinopyroxene increases with increasing T and is strongly bulk composition dependent whereby high CaEs-contents are favoured by bulk compositions with high normative anorthite and low diopside contents. In this study, a maximum of 18 mol% CaEs_ss was found at 6 GPa and 1,350°C in a kyanite-eclogite assemblage garnet + clinopyroxene + kyanite + rutile + coesite. By comparison, no significant increase in CaEs_ss with increasing P could be observed. If the formation of oriented SiO₂-rods frequently observed in eclogititc clinopyroxenes is due to the retrogressive breakdown of a CaEs-component then these textures are a cooling rather than a decompression phenomenon and are most likely to be found in kyanite-bearing eclogites cooled from temperatures ≥750°C. The presence of clinopyroxene with approx. 4 mol% CaEs_ss in an experiment conducted at 2.5 GPa/850°C confirms earlier suggestions based on field data that vacancy-rich clinopyroxenes are not necessarily restricted to ultrahigh pressure metamorphic conditions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Variation of infiltration rate through karstic surfaces due to land use changes: A case study in Murgia (SE-Italy)   总被引：1，自引：0，他引：1  

Filomena Canora  M. Dolores Fidelibus  Antonella Sciortino  Giuseppe Spilotro   《Engineering Geology》2008,99(3-4):210

Groundwaters of the Murgia carbonate aquifer represent the main groundwater resource of the Apulia region (SE Italy). In the highlands (Alta Murgia) karst crops out in different forms and textures which have been preserved up to the 1970s: little evolved agriculture and sheep rearing produced only a marginal modification of the epikarst while a high degree of division into parcels by drystone walls helped in preserving soils from erosion. In the last years the original scenery of the Alta Murgia changed due to widespread transformations of surface karstic textures for agricultural purposes, with undeniable negative consequences on the hydrogeological balance, concerning both the infiltration and the runoff terms. Stone shattering led to flattening and deep alteration of a large part of the original karstic landscape and to demolition of drystone walls.In a study area of about 139 km² located in the Alta Murgia, the comparison of aerial photos related to the period 1950–2001 indicated that stone shattering had occurred for about 42% of the area.The hydrological behaviour of the first soil layer of experimental parcels representing both shattered stone and natural karstic surface textures was analysed by using the numerical model Hydrus-2D with the aim of estimating the variation on infiltration rate due to stone shattering. Intensive field and laboratory measurements concerned soil texture, soil water content, pressure head, saturated hydraulic conductivity, pan evaporation and meteorological parameters.  相似文献   

江苏潮滩沉积物激光粒度仪与移液管-筛析分析结果的对比     

仝长亮  高抒 《沉积学报》2008,26(1):46-53

激光粒度仪的广泛应用带来了与历史数据的对比问题,因此需要建立激光粒度仪与早期分析结果之间的关系。根据江苏海岸潮滩沉积物样品的激光粒度仪和移液管-筛析法分析,对粒度参数、粒度组分等进行了对比,对两种方法的差异进行了分析。结果表明,对于江苏潮滩沉积物粒度参数中平均粒径的激光粒度仪与移液管-筛析分析结果之间有良好的线性关系;筛分法测得的粗颗粒物质较激光法偏少,而移液管法法测得的细颗粒物质较激光法偏多;将样品分类之后再进行两种方法所获粒度参数的回归分析,相关性得以提高,说明不同粒度组成的沉积物对分析结果的对比有不同的影响。两种方法之间的换算关系不仅与研究区域有关,而且与沉积物本身的粒度组成有关。  相似文献   

延边东部五道沟岩群的单颗粒锆石SHRIMP U-Pb 年代学及其地质意义   总被引：1，自引：0，他引：1  

逄 伟孙景贵  门兰静陈 雷 陈 冬 常 艳 梁树能 张 朋 聂喜涛 《中国地质》2008,35(6):1178-1184

通过对延边地区东部五道沟岩群黑云阳起石片岩的单颗粒锆石SHRIMP U-Pb年龄测定.获得21个单点年龄,其中包括7组谐和年龄和1组不谐和年龄.谐和年龄分别为1347.8 Ma、844.8 Ma、340.2～313.7 Ma(平均值为323±23 Ma,N=4,MSWD=0.23,置信度=0.88)、292.9～288.3 Ma(平均值=291±25 Ma,N=3,MSWD=0.031.置信度=0.86)、279.2～266.2 Ma(平均值为279±28 Ma,N=4,MSWD=0.031,置信度=0.86)、127.4～124.2 Ma(206Pb/208U年龄平均值为126.5±3.7 Ma,N=5,MSWD=0.12;置信度=O.97)、116.1～106.3 Ma(平均值为115±39 Ma,N=2,MSWD=1.2置信度=0.27),不谐和年龄的下交点年龄为(451±120)Ma、上交点年龄为(1811±400)Ma(MSWD=7.2);这一结果表明:阳起石片岩的原岩主要是来自中元古代、新元古代和早古生代的碎屑物,指示五道沟群的沉积成岩作用发生在石炭世(323±23 Ma),变质作用发生在晚二叠世(291±25 Ma),之后在279.2～266.2 Ma、126.5～106.3 Ma先后受两次岩浆用和蚀变作用的改造.  相似文献