塑膜温室油桃休眠期的温度变化     

孙智辉  吴刚  吴涛 《山西气象》2003,(4):15-16

本文详尽分析了冰岛低压和大西洋高压的长期变化规律，发现两者均具有明显的阶段性变化，而且冰岛低压和大西洋高压的强度具有明显的反相关。同时，还分析了大西洋高压和冰岛低压与我国气候的关系，发现大西洋高压与我国冬季气温基本呈正相关，而冰岛低压与我国气温大致呈反相关，但均没有显著影响，所以两者都不是影响我国气候变化的重要天气系统。  相似文献   

腾冲火山研究综述   总被引：3，自引：0，他引：3  

皇甫岗 《地震研究》1997,20(4):431-437

近３０年来，众多学对腾冲火山进行了大量的研究与考察工作，并在火山地质、地球化学、地热等方面取得了一批有价值的成果。本试图对部分有代表性的观点及研究成果进行综合性的介绍，供正在开展的《腾冲火山活动监测、预测与对策研究》重大项目的项专题研究参考。  相似文献   

火山作用—深成作用的相互联系     

高秉璋 《江西地质》1997,11(4):33-40

火山作用－深成作用的相互联系是研究岩浆活动从侵入到喷出，以及演化和发展的重要内容。高位深成岩体是其过渡类型，其中中心式环状杂岩体尤为重要，关键是要识别含棱角状捕掳体及破碎捕掳晶的侵入凝灰岩，包括侵入角砾岩，爆发角砾岩等一系列具侵入特征的火成碎屑岩类；大量的上覆火山岩碎块作为捕掳体出现在充气岩浆中，模糊了深成岩类和火山岩类，但根据产出形态及接触关系等特征仍可加以区别，本文对此问题作了明确的阐明，并以玉华山杂岩体为实例加以简要的论述  相似文献   

The color of pumice: case study on a trachytic fall deposit, Meidob volcanic field, Sudan   总被引：1，自引：0，他引：1  

H. Paulick  G. Franz 《Bulletin of Volcanology》1997,59(3):171-185

 This paper examines the cause of color variations of trachytic pumices which are essentially uniform in chemical composition and proposes a geological model for their formation. A pyroclastic sequence of distinct subunits with brown, buff, and black pumices was deposited during the 5000-B.P. eruption of a tuff ring in the central Meidob volcanic field (Sudan). Subunits of buff pumices locally contain minor amounts of streaky pumice with pale-gray and dark-gray domains. The combined evidence of petrographic studies, chemical analyses of whole pumices and groundmass separates, electron microprobe analyses, optical spectroscopy, transmission electron microscopy, and magnetic susceptibility measurements show that color variations of the pumice clasts are related to the size and distribution of Fe³⁺-rich oxide microcrysts. Buff pumice and light-gray domains of streaky pumice have a colorless, transparent groundmass with very few microcrysts. Dark-gray domains of streaky pumice contain abundant hematite and/or magnetite microcrysts visible in thin section within a transparent, colorless glass groundmass. The groundmass of the black pumice clasts is brown in thin section which is most likely caused by submicroscopic magnetite microcrysts. Brown pumice clasts have a mixed groundmass consisting of brown domains and domains with opaque microcrysts in transparent glass. Variations in the eruption dynamics have been inferred from lithological observations. Subunits of black pumices are related to eruption pulses with low magma discharge and high water/magma mass ratio, whereas subunits of buff pumice were deposited during eruption pulses with high magma discharge and low water/magma mass ratio. Brown pumices represent the top part of the magma body, and the initial stage of the eruption probably had a low magma discharge. Streaky pumices are interpreted as the product of syn-eruptive mixing of Fe³⁺-rich oxide microcryst-bearing magma and microcryst-free magma. Received: 3 February 1997 / Accepted: 28 July 1997  相似文献   

Gravity changes and present-day dynamics of the island of Pantelleria (Sicily Channel—Italy)     

Giovanna Berrino   《Journal of Volcanology and Geothermal Research》1997,78(3-4)

The island of Pantelleria is an active volcano located in the Sicily Channel (southern Italy), occurring in the middle of a continental rift system.Since the 1980's the island has been periodically surveyed by means of geodetic and geophysical methods to monitor the regional and local volcanic dynamics. Also, high-precision gravity measurements were started in 1990.The present paper is an analysis of the time-space gravity changes. Gravity measurements were carried out on a network presently formed by twenty stations. The gravity network was fully surveyed in June 1990 and June 1995 and partially surveyed in September 1993. Two absolute gravity stations were established in 1993 to provide a reference system and to check for long-term variations.The areal distribution of the gravity changes during the 1990–1995 time interval, obtained in the thirteen stations of the 1990 network, is strongly similar to the Bouguer anomaly field and to the large-scale features of the basement of the island. Otherwise, gravity changes are directly correlated with the Bouguer anomaly and inversely correlated with the altimetric variations. Comparison with the geological setting suggests that the present activity may be ascribed to the influence of the geodynamics of the Sicily Channel.  相似文献   

Magmatic effects of the lunar late heavy bombardment     

Linda T Elkins-Tanton 《Earth and Planetary Science Letters》2004,222(1):17-27

Large volumes of mare basalts are present on the surface of the moon, located preferentially in large impact basins. Mechanisms relating impact basins and mare basalt eruptions have previously been suggested: lunar impacts removed low-density material that may have inhibited eruption, and created cracks for fluid flow [Icarus 139 (1999) 246], and lunar basins have long been described as catchments for magma (e.g., [Rev. Geophys. Space Phys. 18 (1980) 107] and references therein). We present a new model for melt creation under near side lunar basins that is triggered by the impacts themselves. Magma can be produced in two stages. First, crater excavation depressurizes underlying material such that it may melt in-situ. Second, the cratered lithosphere rises isostatically, warping isotherms at the lithosphere-asthenosphere boundary which may initiate convection, in which adiabatic melting can occur. The first stage produces by far the largest volume of melt, but convective melting can continue for up to 350 Ma. We propose that giant impacts account for a large portion of the volume and longevity of mare basalt volcanism, as well as for several compositional groups, including high alumina, high titanium, KREEP-rich, and picritic magmas.  相似文献   

Hydrothermal Mineralization on the Mesoproterozoic Passive Continental Margins of China： A Case Study of the Langshan-Zha＇ertaishan Belt, Inner Mongolia, China     

PENGRunmin ZHAIYusheng 《《地质学报》英文版》2004,78(2):534-547

Most ore-forming characteristics of the Langshan-Zha‘ertaishan hydrothermal exhalation belt, which consists of the Dongshengmiao, Huogeqi, Tanyaokou and Jiashengpan large-superlarge Zn-Pb-Cu-Fe sulfide deposits, are most similar to those of Mesoproterozoic SEDEX-type provinces of the world. The characteristics include: (1) All deposits of this type in the belt occur in third-order fault-basins in the Langshan-Zha‘ertaishan aulacogen along the northern margin of the North China Platform; (2) these deposits with all their orebodies hosted in the Mesoproterozoic impure dolomite-marble and carbonaceous phyllite (or schists) have an apparent stratabound nature; ores display laminated and banded structures, showing clear depositional features; (3) there is some evidence of syn-sedimentary faulting, which to a certain extent accounts for the temporal and spatial distribution and the size of the orebodies in all deposits and the formation of intrabed conglomerates and breccias; (4) they show lateral and vertical zonation of sulfides; (5) The Cu/(Pb Zn Cu) ratio of the large and thick Pb Zn Cu orebodies gradually decreases from bottom to top; and (6) barite is interbedded with pyrites and sometimes with sphalerite. However, some characteristics such as the Co/Ni radio of the pyrites, the volcanism, for example, of the Langshan-Zha‘ertalshan metallogenic belt, are different from those of the typical SEDEX deposits of the world. The meta-basic volcanic rock in Huogeqi, the sodic bimodal volcanic rocks in the Dongshengmiao and potassic bimodal-volcanic rocks with blastoporphyfitic and blasto-glomeroporphyritic texture as well as blasto-amygdaloidal structure in the Tanyaokou deposits have been discovered in the only ore-bearing second formation of the Langshan Group in the past 10 years. The metallogeny of some deposits hosted in the Langshan Group is closely related to syn-sedimentary volcanism based on the following facts: most of the lead isotopes in sphalerite, galena, pyrite, pyrrhotite and chalcopyrite plot on both sides of the line for the mantle or between the lines for the mantle and lower crust in the lead isotope composition diagram; cobalt content of some pyrites samples is much higher than the nickel content (Co/Ni= 11.91-12.19). Some volcanic blocks and debris have been picked out from some pyritic and pyrrhotitic ores. All Zn-Pb-Cu-Fe sulfide orebodies in these deposits occur in the strata overlying metamorphic volcanic rocks in the only ore-bearing second formation. In the Jiashengpan deposit that lacks syn-sedimentary volcanic rocks in the host succession only Pb and Zn ores occur without Cu ore, but in the Dongshengmiao, Tanyaokou and Huogeqi deposits with syn-sedimentary volcanic rocks in the host succession Cu ores occur. This indicates a relatively higher ore-forming temperature. The process of synsedimentary volcanic eruption directly supplied some ore-forming elements, and resulted in secular geothermal anomaly favorable for the circulation of a submarine convective hydrothermal system, which accounts for the precipitation of deep mineralizing fluids exhaling into anoxidic basins along the syn-sedimentary fault system in the Langshan-Zha‘ertai rift. The Dongshengmiao, Tanyaokou, and Huogeqi deposits hosted in the Langshan Group appear to be a transitional type of mineral deposit between SEDEX and VMS-types but with a bias towards SEDEX, while the Jiashengpan deposit hosted in the Zha‘ertai Group is of a characteristic SEDEX type. This evidence, together with other new discoveries of Mesoproterozoic volcanic rocks and the features of lithogeny and metallogeny of the Bayun Obo deposit in the neighborhood emphasize the diversity, complexity and uniqueness of the Mesoproterozoic Langshan-Zha‘ertal-Bayun Obo ore belt.  相似文献   

The Significance of Multiple Saturation Points in the Context of Polybaric Near-fractional Melting   总被引：1，自引：0，他引：1  

ASIMOW  PAUL D.; LONGHI  JOHN 《Journal of Petrology》2004,45(12):2349-2367

Experimental petrologists have successfully located basalticliquid compositions parental to mid-ocean ridge basalt thatare, within experimental resolution, multiply saturated withthree-phase harzburgite or four-phase lherzolite assemblageson their liquidus at some elevated pressure. Such an experimentalresult is a necessary consequence of any paradigm in which eruptedbasalts derive from single-batch primary liquids that equilibratewith a mantle residue and undergo no subsequent magma mixingbefore differentiation and eruption. Here we investigate whether,conversely, such evidence of multiple saturation is sufficientto exclude dynamic melting models wherein increments of meltare mixed after segregation from residues, during melt transportor in magma chambers. Using two independent models of crystal–liquidequilibria to simulate polybaric near-fractional peridotitemelting, we find that aggregate liquids from such melting processescan display near-intersections of liquidus surfaces too closeto distinguish experimentally from exact multiple saturationpoints. Given uncertainties in glass compositions, fractionationcorrections, experimental temperature and pressure conditions,and achievement of equilibrium, these results suggest that polybaricmixtures can in fact masquerade as mantle-equilibrated single-batchprimary liquids. Multiple saturation points on the liquidussurfaces of primitive basalts do, however, preserve informationabout the average pressure of extraction of their constituentincrements of liquid. KEY WORDS: mantle melting; basaltic volcanism; experimental igneous petrology; thermodynamic modelling; inverse method  相似文献   

Petrogenesis of Tertiary Continental Intra-plate Lavas from the Westerwald Region, Germany   总被引：2，自引：2，他引：2  

HAASE  KARSTEN M.; GOLDSCHMIDT  BJORN; GARBE-SCHONBERG  C.-DIETER 《Journal of Petrology》2004,45(5):883-905

Tertiary volcanic rocks from the Westerwald region range frombasanites and alkali basalts to trachytes, whereas lavas fromthe margin of the Vogelsberg volcanic field consist of morealkaline basanites and alkali basalts. Heavy rare earth elementfractionation indicates that the primitive Westerwald magmasprobably represent melts of garnet peridotite. The Vogelsbergmelts formed in the spinel–garnet peridotite transitionregion with residual amphibole for some magmas suggesting meltingof relatively cold mantle. Assimilation of lower-crustal rocksand fractional crystallization altered the composition of lavasfrom the Westerwald and Vogelsberg region significantly. Thecontaminating lower crust beneath the Rhenish Massif has a differentisotopic composition from the lower continental crust beneaththe Hessian Depression and Vogelsberg, implying a compositionalboundary between the two crustal domains. The mantle sourceof the lavas from the Rhenish Massif has higher ²⁰⁶Pb/²⁰⁴Pband ⁸⁷Sr/⁸⁶Sr than the mantle source beneath the Vogelsbergand Hessian Depression. The 30–20 Ma volcanism of theWesterwald apparently had the same mantle source as the QuaternaryEifel lavas, suggesting that the magmas probably formed in apulsing mantle plume with a maximum excess temperature of 100°Cbeneath the Rhenish Massif. The relatively shallow melting ofamphibole-bearing peridotite beneath the Vogelsberg and HessianDepression may indicate an origin from a metasomatized portionof the thermal boundary layer. KEY WORDS: continental rift volcanism; basanites; trachytes; assimilation; fractional crystallization; partial melting  相似文献   

Hydrothermal alteration and tectonic evolution of an intermediate- to fast-spreading back-arc oceanic crust: Late Ordovician Solund-Stavfjord ophiolite, western Norway     

Hege  Fonneland-Jorgensen  Harald  Furnes  Karlis  Muehlenbachs  Yildirim  Dilek 《Island Arc》2005,14(4):517-541

Abstract The Solund‐Stavfjord ophiolite complex (SSOC) in western Norway represents a remnant of the Late Ordovician oceanic lithosphere, which developed in an intermediate‐ to fast‐spreading Caledonian back‐arc basin. The internal architecture and magmatic features of its crustal component suggest that the SSOC has a complex, multistage sea floor spreading history in a supra‐subduction zone environment. The youngest crustal section associated with the propagating rift tectonics consists of a relatively complete ophiolite pseudostratigraphy, including basaltic volcanic rocks, a transition zone between the sheeted dyke complex and the extrusive sequence, sheeted dykes, and high‐level isotropic gabbros. Large‐scale variations in major and trace element distributions indicate significant remobilization far beyond that which would result from magmatic processes, as a result of the hydrothermal alteration of crustal rocks. Whereas K₂O is strongly enriched in volcanic rocks of the extrusive sequence, Cu and Zn show the largest enrichment in the dyke complex near the dyke–volcanic transition zone or within this transition zone. The δ¹⁸O values of the whole‐rock samples show a general depletion structurally downwards in the ophiolite, with the largest and smallest variations observed in volcanic rocks and the transition zone, respectively. δ¹⁸O values of epidote–quartz mineral pairs indicate 260–290°C for volcanic rocks, 420°C for the transition zone, 280–345°C for the sheeted dyke complex and 290–475°C for the gabbros. The ⁸⁷Sr/⁸⁶Sr isotope ratios show the widest range and highest values in the extrusive rocks (0.70316–0.70495), and generally the lowest values and the narrowest range in the sheeted dyke complex (0.70338–0.70377). The minimum water/rock ratios calculated show the largest variations in volcanic rocks and gabbros (approximately 0–14), and generally the lowest values and range in the sheeted dyke complex (approximately 1–3). The δD values of epidote (?1 to ?12‰), together with the δ¹⁸O calculated for Ordovician seawater, are similar to those of present‐day seawater. Volcanic rocks experienced both cold and warm water circulation, resulting in the observed K₂O‐enrichment and the largest scatter in the δ¹⁸O values. As a result of metal leaching in the hot reaction zone above a magma chamber, Zn is strongly depleted in the gabbros but enriched in the sheeted dyke complex because of precipitation from upwelling of discharged hydrothermal fluids. The present study demonstrates that the near intact effect of ocean floor hydrothermal activity is preserved in the upper part of the SSOC crust, despite the influence of regional lower greenschist facies metamorphism.  相似文献