Experimental study of fluorine and chlorine contents in mica (biotite) and their partitioning between mica,phonolite melt,and fluid     

V. Yu. Chevychelov  R. E. Botcharnikov  F. Holtz 《Geochemistry International》2008,46(11):1081-1089

This paper reports the results of a study of the composition of mica (biotite) crystallizing in the system of phonolite melt-Cl- and F-bearing aqueous fluid at T ～ 850°C, P = 200 MPa, and \(f_{O_2 } \) = Ni-NiO, as well as data on F and Cl partitioning between coexisting phases. It was established that Cl content in mica is significantly lower than in phonolite melt and, especially, in fluid. Fluorine shows a different behavior in this system: its content in mica is always higher than in phonolite melt but lower than in fluid. The mica-melt partition coefficients of Cl and F also behave differently. The Cl partition coefficient gradually increases from 0.17 to 0.33 with increasing Cl content in the system, whereas the partition coefficient of F sharply decreases from 3.0 to 1.0 with increasing total F content. The apparent partition coefficients of F between biotite and groundmass (melt) in various magmatic rocks are usually significantly higher than the experimental values. It was supposed that the higher ^Bt/glassD_F values in natural samples could be related to the influence of later oxidation reactions, reequilibration of biotite at continuously decreasing \(f_{H_2 O} \)/f _HF ratio, and an increase in this coefficients with decreasing total F content in the system.  相似文献   

A strong temperature effect on U/Ca in planktonic foraminiferal carbonates     

Jimin Yu  Henry Elderfield  Linda Booth 《Geochimica et cosmochimica acta》2008,72(20):4988-5000

Three planktonic foraminiferal species Globigerina bulloides, Neogloboquadrina pachyderma (d), and Globorotalia inflata collected from core-tops spanning 35° to 65°N in the North Atlantic were used for U/Ca and Mg/Ca and foraminiferal shell weight analyses. Except for U/Ca in G. bulloides calcified under warm conditions (>∼13 °C), U/Ca ratios in all three studied species increase with decreasing latitude and show strong positive correlations with Mg/Ca ratios. A dissolution effect on planktonic U/Ca is suggested by decreased shell weight and U/Ca and Mg/Ca ratios for shells from very deep water depth (>4.4 km) along the latitudinal transect. G. bulloides from down core samples in the North Atlantic show low U/Ca ratios during the last glacial and high ratios during the Holocene, similar to the Mg/Ca evolution trend. In general, our data indicate that the U incorporation into planktonic foraminiferal carbonates is strongly influenced by calcification temperature, although U/Ca in G. bulloides may be affected by seawater carbonate ion concentration under warm conditions and/or other factors.  相似文献   

The posthumous tectonics and mechanism of exhumation of granitic plutons: The case of the Transbaikal region and the Tien Shan     

M. G. Leonov  Yu. A. Morozov  A. V. Nikitin 《Geotectonics》2008,42(2):81-104

The study of granitic plutons of the Baikal Highland and the Tien Shan has made it possible to establish new features of their posthumous (after incorporation into the consolidated Earth’s crust) structural reworking and to understand the implications of the cataclastic flow for the exhumation of the crystalline basement in the studied regions. It is shown that granitic plutons undergo appreciable structural transformation at the stages of tectonic reactivation that is significantly separated in time from the moment of formation of plutons as geological bodies. The 3D cataclastic deformation is the main mode of structural reworking of granitic plutons, while the cataclastic flow is the main form of their mobility. Newly recognized slice structures characterize the volumetric deformation of granites.  相似文献   

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   

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   

西秦岭温泉斑岩型钼矿床地质特征及成因浅析   总被引：7，自引：0，他引：7  

韩海涛  刘继顺  董新  欧阳玉飞 《地质与勘探》2008,44(4)

温泉钼矿位于甘肃省武山县温泉乡陈家大湾,大地构造位置属北秦岭加里东褶皱带西段,是2000年后发现并正在勘查的斑岩型钼矿床.含矿的温泉岩体为中浅成侵入杂岩体,从海西期到燕山期有四期10次侵入.主体相为印支期侵入的似斑状黑云母二长花岗岩,燕山期早期的花岗斑岩穿插于主体相中,花岗斑岩与矿化密切相关,矿(化)体产出于燕山期花岗斑岩和附近的围岩中.地袁矿化呈脉状零星分散、不连续,品位低.共圈出矿(化)体40条,在地表下20～50m深处矿化连成一体,构成面型矿化.已经控制矿体范围近0.3km2,南北长近800m,东西实际控制宽400m,控制厚度最大445m,最小37m.钼矿体主要由充填于各向原生节理、裂隙中的相互平行或网状含钼石英细脉组成,矿石矿物组合简单,围岩蚀变较弱.成矿物质来源于岩浆,成矿流体主要来源于岩浆混入了大气降水和地下水,Re-Os同位素模式年龄214±7.1Ma,属斑岩型钼矿床.  相似文献