Synchronism in compression of the lithosphere in the central Atlantic and Western Tethys at the Tortonian-Messinian transition     

A. L. Knipper  Yu. N. Raznitsin 《Geotectonics》2008,42(1):21-30

The structure of anomalously uplifted areas in transverse ridges of the Vema, S o Paulo, and Romanche fracture zones is considered. It is concluded that their formation and eventual development in the present-day structure of the central Atlantic bottom proceeded during two stages. The first stage that corresponds to a short period at the Tortonian-Messinian transition (10 Ma ago) was marked by transportation of deep-seated rocks into the upper part of the lithosphere along thrust faults with mass motion in the meridional direction along the axis of the Mid-Atlantic Ridge. The second stage was characterized by contrasting highamplitude vertical movements from 10 to 3 Ma ago. It is suggested that near-meridional compression in the domains surrounding the Western Tethys in the Tortonian-Messinian resulted in deformation of the upper lithosphere within large transform fracture zones of the central Atlantic. The deformation that occurred 10 Ma ago was a manifestation of the global neotectonic epoch of the Earth.  相似文献   

Sorption of Ni on Na-rectorite studied by batch and spectroscopy methods     

Xiaoli Tan  Changlun Chen  Shaoming Yu  Xiangke Wang 《Applied Geochemistry》2008

Sorption of Ni²⁺ on Na-rectorite as a function of contact time, temperature, pH and fulvic acid (FA)/humic acid (HA) was studied under ambient conditions. A pseudo-second-order rate equation was used to simulate the kinetic sorption. The removal of Ni²⁺ increased with increasing pH. The presence of FA/HA enhanced the sorption of Ni²⁺ at low pH values, whereas no drastic effect of FA/HA on Ni²⁺ uptake to rectorite was found at high pH values. The diffuse layer model (DLM) fitted the experimental data of Ni²⁺ sorption in the absence and presence of FA/HA very well with the aid of FITEQL 3.2. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Ni²⁺ at different temperatures. The thermodynamic data (ΔH⁰, ΔS⁰, ΔG⁰) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of Ni²⁺ on rectorite was spontaneous and endothermic. The sorption and species of Ni²⁺ on rectorite in the presence and absence of FA/HA was also investigated and characterized by XPS. The spectroscopic analysis indicated no drastic structural changes of Na-rectorite and the sorption of Ni²⁺ mainly occurred on the surface and at the edge position of Na-rectorite.  相似文献   

The Ruiga intrusion: A typical example of a shallow-facies paleoproterozoic peridotite-gabbro-komatiite-basaltic association of the Vetreny Belt,Southeastern Fennoscandia     

V. S. Kulikov  Ya. V. Bychkova  V. V. Kulikova  Yu. A. Kostitsyn  O. S. Pokrovsky  M. V. Vasil’ev 《Petrology》2008,16(6):531-551

The Ruiga differentiated mafic-ultramafic intrusion in the northwestern part of the Vetreny Belt paleorift was described for the first time based on geological, petrological, geochronological, and geochemical data. The massif (20 km² in exposed area) is a typical example of shallow-facies peridotite-gabbro-komatiite-basalt associations and consists of three zones up to 810 m in total thickness (from bottom to top): melanogab-bronorite, peridotite, and gabbro. In spite of pervasive greenschist metamorphism, the rocks contain locally preserved primary minerals: olivine (Fo _75–86), bronzite, augite of variable composition, labradorite, and Cr-spinels. A mineral Sm-Nd isochron on olivine melanogabbronorite from the Ruiga Massif defines an age of 2.39 ± 0.05 Ga, while komatiitic basalts of the Vetreny Belt Formation were dated at 2.40–2.41 Ga (Puchtel et al., 1997). The rocks of the Ruiga intrusion and lava flows of Mt. Golets have similar major, rare-earth, and trace element composition, which suggests their derivation from a single deep-seated source. Their parent magma was presumably a high-Mg komatiitic basalt. In transitional crustal chambers, its composition was modified by olivine-controlled fractionation and crustal contamination, with the most contaminated first portions of the ejected melt. In terms of geology and geochemistry, the considered magmatic rocks of the Vetreny Belt are comparable with the Raglan Ni-PGE komatiite gabbro-peridotite complex in Canada (Naldrett, 2003).  相似文献   

Zr/Hf ratio as an indicator of fractionation of rare-metal granites by the example of the Kukulbei complex,eastern Transbaikalia     

G. P. Zaraisky  A. M. Aksyuk  V. N. Devyatova  O. V. Udoratina  V. Yu. Chevychelov 《Petrology》2008,16(7):710-736

The concept of granitic melt fractionation as the main process in the concentration of rare elements in granites calls for the development of a reliable method to determine the evolutionary sequences of granite series. We propose to use for this purpose a zirconium-hafnium indicator, the Zr/Hf weight ratio in granitic rocks (Zaraisky et al., 1999, 2000). By the example of three classic regions of rare-metal deposits, eastern Transbaikalia, central Kazakhstan, and Erzgebirge (Czech Republic and Germany), it was empirically shown that the Zr/Hf ratio of granites decreases during the fractional crystallization of granite magmas in the sequence granodiorite → biotite granite → leucogranite → lithium-fluorine granite. The reason is the higher affinity of Hf compared with Zr to a granite melt. This implies that the crystallization and settling of accessory zircon will cause the progressive enrichment of Hf relative to Zr in the residual melt. As a result, the Zr/Hf ratio decreases regularly in the series of sequential phases of granite intrusion related to a single magma chamber from granodiorite to biotite granite, leucogranite, and Li-F granite (from 45-30 to 10-2). Our experimental investigations supported the preferential enrichment of haplogranite melt in Hf and zircon crystals in equilibrium with melt in Zr (T= 800°C and P = 1 kbar). The Zr/Hf indicator was tested by the example of the wellknown Kukulbei rare-metal granite complex of eastern Transbaikalia (J3), which is unique in the degree of fractionation of initial granite melt with the formation of three phases of granite emplacement and vein derivatives. An important feature of the complex is its “short” differentiation trend. It was supposed that the granite magma of the first phase is parental, and the later phases forming small intrusive bodies in large massifs of biotite granites of the first phase are sequential products of its crystallization differentiation in a magma chamber. The biotite granites of the first phase are barren. The leucocratic granites of the second phase are accompanied by tin-tungsten greisen deposits (e.g., Spokoininskoe), and the upper part of cupola-like stocks of Li-F amazonite granites of the third phase host apogranite-type tantalum deposits (Orlovka, Etyka, and Achikan). In addition to three granite phases, the Kukulbei complex includes dikes of ongonites, elvans, amazonite granites, and chamber miarolitic pegmatites. All of the granitic rocks of the complex have similar isotopic ages of 142± 0.6 Ma. The Zr/Hf ratio decreases systematically from phase 1 (40–25), to phase 2 (20–10), and phase 3 (10–2). The ongonites, elvans, and pegmatites have similar Zr/Hf ratios (15-5), falling between the ranges of leucocratic muscovite granites and Li-F granites. Compared with other granite series, the granitic rocks of the Kukulbei complex show specific petrographic and geochemical features: they are strongly enriched in Rb, Li, Cs, Be, Sn, W, Mo, Ta, Nb, Bi, and F but depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From the early to late intrusion phases, the degree of enrichment and depletion in these element groups increases regularly. This is accompanied by a significant decrease (from 40 to 2) in Zr/Hf, which can be used as a reliable indicator of genetic relations, degree of fractionation, and rare-metal potential of granites. Granites with Zr/Hf values lower than 25 are promising for prospecting for Sn, W, Mo, and Be greisen deposits, whereas the formation of Ta deposits requires Zr/Hf values lower than 10.  相似文献   

Opacitization conditions of hornblende in Bezymyannyi volcano andesites (March 30, 1956 eruption)     

P. Yu. Plechov  A. E. Tsai  V. D. Shcherbakov  O. V. Dirksen 《Petrology》2008,16(1):19-35

The paper is devoted to the conditions under which opacite rims developed around hornblende grains in andesite of the catastrophic eruption (March 30, 1956) of Bezymyannyi volcano, Kamchatka. The opacite rims were produced by a bimetasomatic reaction between hornblende and melt with the development of the following zoning: hornblende → Px + Pl + Ti-Mag → Px + Pl → Px → melt. Biometasomatic reaction was accompanied by the active removal of CaO from the rim, addition of SiO₂, and more complicated behavior of other components. The hornblende also shows reactions of its volumetric decomposition under near-isochemical conditions. The opacite rims developed under isobaric conditions, at a pressure of approximately 6 kbar. The main reason for the instability of the hornblende was the heating of the magma chamber from 890 to 1005°C due to new hot magma portion injection. The time interval between the injection and the start of eruption was estimated from the thickness of the opacite rims and did not exceed 37 days. Hence, the March 30, 1956, eruption was not related to the volcanic activity in November of 1955 but to the injection of a fresh magma portion in February–March of 1956.  相似文献   

Numerical estimation of REV and permeability tensor for fractured rock masses by composite element method   总被引：2，自引：0，他引：2  

S.‐H. Chen  X.‐M. Feng  S. Isam 《国际地质力学数值与分析法杂志》2008,32(12):1459-1477

The Monte Carlo method is used to generate parent stochastic discrete fracture network, from which a series of fractured rock samples of different sizes and orientations are extracted. The fracture network combined with a regular grid forms composite element mesh of the fractured rock sample, in which each composite element is composed of sub‐elements incised by fracture segments. The composite element method (CEM) for the seepage is implemented to obtain the nodal hydraulic potential as well as the seepage flow rates through the fractured rock samples. The application of CEM enables a large quantity of stochastic tests for the fractured rock samples because the pre‐process is facilitated greatly. By changing the sizes and orientations of the samples, the analysis of the seepage characteristics is realized to evaluate the variation of the permeability components, the existence of the permeability tensor and the representative element volume. The feasibility and effectiveness are illustrated in a numerical example. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Biogeochemical characteristics of the Hetai goldfield, Guangdong Province, China     

Li Miao  Ruisong Xu  Yueliang Ma  Jinhong Xu  Jie Wang  Rui Cai  Yu Chen   《Journal of Geochemical Exploration》2008,96(1):43-52

In the Hetai goldfield, Guangdong Province, China, samples including rocks, soils and leaves of four plants (Pinus massoniana, Rhodomyrms tomenlosa, D. linearis var. dichotoma and Embelia laeta) collected from the gold mineralization zone and the background area were analyzed for Au, Ag, Cu, Pb, Zn, Hg, As and physiological parameters. The objective of this investigation is to study the geochemical and biogeochemical characteristics of studied plants, aiming at biogeochemical methods in Au exploration. The goldfield region shows geochemical and biogeochemical anomalies. Abundances of Au in rocks, soils, plants and the leaf pigments in the mineralized area are much higher than those in the surrounding region. The plants display unhealthy physiological and ecological characteristics in the Hetai goldfield area. The cell structures of the goldfield plants were anomalous and aberrant, and there were many nano-metal particles diffused in mitochondria and chloroplasts. Macro- and microscopic evidences of the vegetation in the goldfield areas are distinctly different from the background regions. The strongly anomalies in responses to Au are profound in further geochemical and botanic exploration studies.  相似文献   

华南前寒武系基底变质杂岩和中-新生代地幔岩的稀有气体同位素组成及其大地构造意义          下载免费PDF全文

谢窦克  邢光福  陆志刚  陈荣  周宇章 《地质科学》2008,43(1):175-204

对华南前寒武系变质岩浆杂岩稀有气体He、Ne、Ar和Xe的系统研究表明:扬子克拉通基底为含高³He的下地壳"原始岩石层",(³He/⁴He)×10^-6比值为2.8～4.6;而华夏板块基底变质岩浆杂岩则是在缺乏³He、低(³He/⁴He)×10^-8比值(3.15～17.7)的构造环境下形成的大陆中-上地壳变质岩浆杂岩层,反映出两者基底性质迥然不同。华南中-新生代爆破岩筒He同位素组成相反,相对稳定的扬子克拉通(³He/⁴He)×10^-8比值仅0.18～4.22,而郯庐-四会-吴川断裂以东,中-新生代活动地块(太平洋构造域)(³He/⁴He)×10^-8比值高达3.7～20.5。He同位素表明郯庐-四会-吴川断裂带为切割深至地幔的边界深大断裂,是扬子克拉通与华夏板块间的边界且控制了燕山期火山-侵入岩浆向西扩展。Ar同位素组成表明华南大陆中-新生代地幔形成接近"均一"的地幔组份。¹³⁶Xe/¹³⁰Xe-¹²⁹Xe/¹³⁰Xe相关组份表明它们具有地幔柱岩石同位素组成特征。  相似文献   

东营凹陷北部沙河街组四段深部储层多重成岩环境及演化模式   总被引：7，自引：0，他引：7       下载免费PDF全文

张善文  袁静  隋风贵  陈鑫 《地质科学》2008,43(3):576

主要通过薄片鉴定、扫描电镜观察、包裹体分析、粘土矿物分析、镜质体反射率测试和岩心物性分析等手段,结合构造发育史和有机质热演化史等研究成果,以揭示东营凹陷北带古近系深部碎屑岩储层成岩环境及演化模式为目的展开研究工作。结果表明:东营凹陷北带古近系深部碎屑岩储层存在酸性、碱性和酸性碱性交替等多重成岩环境。酸性成岩环境以碳酸盐矿物溶解、长石溶解蚀变为高岭石并伴生石英次生加大等为标志,碱性成岩环境以石英质颗粒及其次生加大边溶解、长石次生加大和晚期碳酸盐矿物沉淀为标志。研究区古近系深部碎屑岩储层成岩环境由浅至深大致经历了碱性—酸性—酸性碱性交替(局部碱性较强)—碱性—弱碱性的演化过程,并建立了沙河街组四段的成岩演化和储层改造模式。  相似文献   

松辽盆地三肇凹陷葡萄花油层成藏模式初探   总被引：11，自引：5，他引：6       下载免费PDF全文

孙雨  马世忠  刘云燕  刘宗堡  于利民 《地质科学》2008,43(4):746-757

运用源控含油气系统理论与综合分析技术,按成藏“层次分析”方法,通过对生、储、盖、圈(闭)静态要素及其内生、排、运、聚、散(失)动态过程的综合研究,对松辽盆地中央坳陷的三肇凹陷葡萄花油层成藏条件进行探讨,提出了以次级凹陷为中心、不同类型的油气聚集带紧邻并围绕次级凹陷最低部位呈环带状分布的大型凹陷内成藏模式,并进一步提出永乐次级凹陷中心及其三级聚油环带及徐家围子次级凹陷以西为"网式"运聚特征;在凹陷级成藏模式的指导下,通过对大面积密井网开发区综合解剖,提出三级构造带中单个的局部构造圈闭(群)、单个的(局部构造——)岩性圈闭(群)控油和成藏规律,为认识本区基本控油单元、油水分布规律、油气勘探及扩大新探区提供重要的理论依据。  相似文献