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根据主量元素、微量元素和Sr-Nd同位素地球化学研究结果,觉罗塔格构造带中企鹅山群火山岩企鹅山群火山岩分为拉斑玄武岩和钙碱性玄武岩,拉斑玄武岩和钙碱性玄武岩均具有高铝、低钛和相对富集轻稀土元素（LREE）、大离子亲石元素的特征,与典型的岛弧玄武岩相似。钙碱性玄武岩具有显著的Eu的负异常,其不相容元素含量显著高于拉斑玄武岩,在La/Sm-La图解中,钙碱性玄武岩为结晶分异作用的产物,拉斑玄武岩则为平衡部分熔融的产物。Sr-Nd同位素特征表明企鹅山群火山岩源自亏损地幔。在玄武岩构造环境判别图中样品均落入岛弧玄武岩范围内。通过综合该区岩石组合特征、地球化学特征、地球物理特征,认为企鹅山群为康古尔洋壳向北俯冲在大南湖岛弧南侧形成的石炭纪岛弧火山岩。 相似文献
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根据作者的发现与研究并结合国内外有关资料,综合论述了在济阳盆地(胜利油田内外找寻新类型贵金属资源的可能性。胜利油田二氧化碳气藏区火山岩中发现有高含量的金,而二氧化碳气藏经研究源自高含量金与二氧化碳流体的富集地幔,结合由盆地内向盆地外火山岩类型及其中包裹体中气体成分和含量的变化,作者认为在济阳盆地边缘二氧化碳气藏区和盆地外隆起区偏碱性和碱性火山岩分布区找寻与幔源高含量二氧化碳流体有关的地幔喷金矿床是有可能的。 相似文献
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西天山昭苏北部石炭纪火山岩的岩石地球化学特征、成因及形成环境 总被引：20，自引：20，他引：20
西天山昭苏北部早石炭纪大哈拉军山组火山岩由碱性橄榄玄武岩和少量的拉斑玄武岩组成。火山岩TiO2（1．10～1．99％）和P2O5（0．22～0．70％）含量较高，富集大离子亲石元素（Rb，Ba，K）并强烈亏损高场强元素（Nb，Ta，Ti）（（Nb／La）N=0．20～0．36），轻重稀土分异，其地球化学特征总体上与美国盆岭地区新生代（中新世中期之前）火山岩以及中美洲和南美洲的弧后“过渡型”基性火山岩相似，但与典型火山弧岩浆岩有些不同。大量元古代继承锆石的出现以及主量、微量元素和Nd同位素地球化学特征均表明火山岩经历了相当程度的结晶分异和陆壳混染（AFC）。与碱性玄武岩相比，拉斑玄武岩的SiO2含量和K2O／Na2O比值较高，而εNd（t），MgO和Mg^#值较低，可能由碱性玄武岩浆经AFC演化形成。碱性橄榄玄武岩中含富Fe，Ti贫Si的火山岩夹层（Fe-Ti玄武岩），是碱性玄武质岩浆依Fenner趋势发生较高程度结晶分异的产物。火山岩的元素地球化学特征指示岩浆源区可能为俯冲流体交代富集的岩石圈地幔，然而，Fe-Ti玄武岩的出现以及地球化学特征随时间的规律性变化均指示它们形成于拉张的构造环境。我们提出，昭苏北部大哈拉军山组火山岩可能形成于具有元古代陆壳基底的活动大陆边缘弧后拉张环境。这一认识与前人提出的大哈拉军山组火山岩为地幔柱活动影响的大陆裂谷岩浆岩的认识有所不同。 相似文献
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大兴安岭中生代玄武岩的地球化学特征：壳幔相互作用的证据 总被引：67，自引：26，他引：41
大兴安岭中生代玄武岩类由北区碱性系列岩石和南区亚碱性系列岩石组成, 主要活动时期为晚侏罗世至早白垩世, 在时间、空间上显示大体呈北北东向展布的环状 “热向斜构造”。北区碱性系列岩石高度富集轻稀土元素和大离子亲石元素, 其丰度类似于板内碱性玄武岩, 但明显亏损高场强元素这一特点又类似于火山弧钙碱性玄武岩。南区亚碱性系列岩石强烈亏损高场强元素的特征类似于火山弧钙碱性玄武岩, 但轻稀土元素和大离子亲石元素富集程度又类似于洋中脊拉斑玄武岩和岛弧拉斑玄武岩。显然, 大兴安岭中生代玄武岩系列显示地球化学双重性, 也就是既有板内特征又有火山弧特征, 既有富集特征又有亏损特征。这种地球化学双重性表明, 大兴安岭地区存在若干不同性质的地幔源： 富集性的、亏损性的、过渡性的地幔源。解释一个地区存在多元地幔源区模式的最佳方案是地幔柱。这种包含富集成分和亏损成分的地幔柱源区的形成是与古生代地质时期古亚洲域闭合过程中俯冲洋壳与亏损地幔相互作用的动力学、地球化学过程有关。 相似文献
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江山-广丰地区早白垩世晚期玄武岩的岩石地球化学及其构造意义 总被引：17，自引：0，他引：17
江山-广丰地区所在的信江红色盆地与金衢红色盆地同属于NEE向赣杭断陷盆地带的组成部分.赣杭构造带自早白垩世晚期开始强烈拉张,红色盆地形成.红层下部夹有层状玄武岩,全岩K-Ar年龄为98～105 Ma,属早白垩世晚期.岩石地球化学特征表明研究区有两类玄武岩:江山陈塘坞一带的拉斑玄武岩,礼贤、广丰一带的碱性橄榄玄武岩.Nd、Sr同位素组成分析显示,拉斑玄武岩类(87Sr/86Sr)i值为0.705 4～0.707 0,εNd(t)值为1.69～0.70(接近于0),表明源区为基本未受壳源物质混染的原始地幔,在弧后陆缘环境下快速拉张而上升,呈熔岩被形式分布于信江盆地东部;碱性橄榄玄武岩(87Sr/86Sr)i值为0.707 6～0.708 0,而εNd(t)值偏低(-6.43～-5.18),表明来源于已受壳源物质混染的富集地幔,在拉张加剧、裂陷加深的构造背景下喷发,相对集中分布于盆地中部,范围小于拉斑玄武岩.二者的差别主要是地幔源区受到不均匀混染所致.研究表明,早白垩世晚期至晚白垩世期间,太平洋板块俯冲的角度由缓变陡以及向东南方向的后退作用,对弧后陆缘的快速拉张并形成赣杭带红色断陷盆地及其玄武岩起着关键性作用. 相似文献
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西南天山托云地区白垩纪-早第三纪玄武岩地球化学及其成因机制 总被引：16，自引：0，他引：16
托云玄武岩主要分布于托云盆地东侧，按形成时代可分为白垩纪玄武岩和早第三纪玄武岩。白垩纪玄武岩包括早白垩世玄武岩和晚白垩世玄武岩，以碱玄岩和碱性橄榄玄武岩为主，碱性程度高；早第三纪玄武岩包括早第三纪玄武岩及脉岩，以碱性橄榄玄武岩、碱性橄榄辉绿岩为主，碱性程度低。所有岩石稀土元素(REE)、微量元素分布模式相似，REE均为向右陡倾型，富集不相容元素。白垩纪玄武岩的∑REE、Rb、Ba、Th、K、Sr、Nb和Ta等元素富集程度均高于早第三纪玄武岩，相容元素富集程度大体较低。微量元素和同位素特征显示，玄武岩起源于与洋岛玄武岩源区相似的富集地幔源。玄武岩中赋存有交代地幔捕虏体，这表明玄武岩浆可能是交代地幔经不同程度部分熔融的产物。微量元素的特征同时显示，早白垩世玄武岩部分熔融程度较低，早第三纪玄武岩部分熔融程度较高，且在不断的部分熔融过程中，形成的岩浆又有结晶分异作用发生。托云玄武岩形成于大陆板内拉伸环境，在形成过程中经历了较弱的壳幔相互作用。 相似文献
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白银厂矿田玄武岩地球化学特征及其形成地质环境 总被引：3，自引：0，他引：3
白银厂矿田玄武岩主要由玄武岩和碱性玄武岩组成 ,其中玄武岩属于钙碱性系列和拉斑系列 ,碱性玄武岩属于钾质碱性玄武岩系列和钠质碱性玄武岩系列。相对于N -MORB ,本区钙碱性系列和拉斑系列玄武岩明显富集Ba、Rb、Th、U ,而亏损Ti;碱性系列玄武岩高度富集K、Ba、Rb、Th、U ,而Ti、Zr、Ce相对亏损 ,表明该区玄武岩的形成与板块俯冲作用有关。钙碱性玄武岩系列和拉斑玄武岩系列玄武岩具有低的REE含量和亏损的LREE配分型式 ,表明它是由LREE亏损和HREE略有富集的地幔部分熔融形成 ;碱性系列玄武岩的REE含量和 (La/Yb) N 比值高 ,LREE和HREE的分馏程度较高 ,表明其形成于演化的岩浆 ,可能来自于富集LREE的地幔源区或地幔橄榄岩较低程度的熔融。痕量元素地球化学特征表明 ,本区玄武岩应是与板块俯冲作用有关的地幔部分熔融形成 ,成岩环境为火山弧环境 ,是岛弧向成熟岛弧转化过程中的产物。 相似文献
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琼北火山活动分期与全新世岩浆演化 总被引：12，自引：9，他引：12
琼北火山活动始于始新世以来，早第三纪火山岩以夹层隐伏于不同时期的地层中。本文新提供的琼北火山岩K-AT年龄和砂岩捕虏体热释光年龄，从年代学上确定了琼北存在全新世火山喷发活动。琼北地表火山岩从早到晚分为6期：蓬莱期(中新世)、金牛岭期(上新世)、多文岭期(早更新世)、东英期(中更新世)、道堂期(晚更新世)、雷虎岭期(全新世)。雷虎岭期又分为早晚两个亚期：雷虎岭亚期和马鞍岭亚期，它们分别属于橄榄拉斑玄武岩和石英拉斑玄武岩。火山岩稀土元素、微量元素和Sr，Nd，Pb同位素地球化学特征揭示，岩浆来自亏损地幔(DMM)和富集岩石圈或亏损地幔(DMM)与俯冲洋壳两种不同的地球化学组分混合源区。橄榄拉斑玄武岩是相对原始的地幔岩浆。橄榄拉斑玄武岩岩浆经约10％橄榄石分离结晶可以形成石英拉斑玄武岩浆。岩浆上升过程中未受明显的陆壳混染。 相似文献
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冲绳海槽中部和南部玄武岩的区域性差异及其成因研究 总被引：5，自引：0，他引：5
本文从岩石学和岩石化学角度出发 ,对冲绳海槽中部和南部玄武岩样品进行了对比研究。结果表明中部和南部玄武岩均系亚碱性玄武岩 ,其中前者兼具钙碱性系列和拉斑玄武岩系列两种性质 ,后者则主要属拉斑玄武岩系列。根据岩石化学特征命名 ,中部样品主体为石英拉斑玄武岩 ,南部样品则为橄榄拉斑玄武岩。两区海槽玄武岩岩浆均由下伏地幔岩部分熔融而成 ,但源区地幔性质不均一 ,岩浆演化程度各异。中部样品源区地幔性质为过渡型 ,结晶分异程度较高 ;南部样品源于近亏损或富集型的地幔 ,结晶分异程度较弱 ;另外两区玄武岩样品均受到了不同程度的陆壳物质混染。中、南部海槽玄武岩在岩石学、岩石化学方面的差异与源区地幔性质不均一和岩浆演化程度各异有直接关系。海槽玄武岩构造环境属于过渡洋中脊玄武岩 (张性 )与岛弧玄武岩 (压性 )之间 ,代表的仍是海槽早期的岩浆活动。 相似文献
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Geochemical and geochronological studies were conducted on basalts and laterites from the Bolaven Plateau in southern Laos in order to evaluate the mobility and mineralization of REE, Y and Sc during laterization. The basalts are classified into three categories: (i) small volumetric alkali basalt (eruption age: 15.7 Ma), large volumetric olivine tholeiite (1.2 Ma) and quartz tholeiite with olivine tholeiite (younger than 0.5 ± 0.2 Ma). Formation of REE minerals during laterization result in mobilization and fractionation of REE and Y in laterite profiles. Occurrence of florencite‐(Ce) in a laterite profile derived from alkali basalt immobilizes REE (particularly LREE) and this leads the laterites to be enriched in LREE relative to the parent basalt. Few positive Ce anomalies in this profile suggest that florencite‐(Ce) [(Ce)Al3(PO4)2(OH)2] formation was followed by CeO2 precipitation due to the change of redox condition. In tholeiite‐derived laterite profiles, florencite is not recognized and REE and Y tend to be depleted relative to the parent basalts with positive Ce anomalies. This is interpreted as scavenging REE3+ except for Ce4+ from the laterite profile in oxidizing conditions. Sc behaves similarly to Fe during laterization and it is more abundant in the tholeiitic laterite than that in the alkali basaltic laterite. Results of sequential extraction indicate that REE of the alkali basaltic laterite are contained in residual phase, which is dominantly florencite‐(Ce), but they are rarely present in ion‐adsorption phase. It is concluded that basaltic laterites have a low potential of REE resource in terms of low REE contents and a difficulty in REE extraction. 相似文献
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JIANG Changyi BAI Kaiyin HI Aizhi ZHAO Xiaoning ZHANG Hongbo Xi抋n Engineering College Xi抋n China 《Continental Dynamics》2001,(1)
1. Geological setting The terrane of Kuruktag lies in the north-eastern margin of the Tarim Basin and is a faulted marginal uplift of the basin. In the terrane, there occur extensively Dagelagebulake Group and Xinditage Group of Archaean-Paleoprotozoic metamorphic sequences overlain by Sinian-Cambrian sequences (Geological and mineral bureau of Xingjiang ulger atonomous region, 1993). The sedimentology of the Sinian-Cambrian strata have been studied (South Xinjiang petrollum exploratio… 相似文献
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The genesis of basaltic magmas 总被引：29，自引：2，他引：29
This paper reports the results of a detailed experimental investigation of fractionation of natural basaltic compositions under conditions of high pressure and high temperature. A single stage, piston-cylinder apparatus has been used in the pressure range up to 27 kb and at temperatures up to 1500° C to study the melting behaviour of several basaltic compositions. The compositions chosen are olivine-rich (20% or more normative olivine) and include olivine tholeiite (12% normative hypersthene), olivine basalt (1% normative hypersthene) alkali olivine basalt (2% normative nepheline) and picrite (3% normative hypersthene). The liquidus phases of the olivine tholeiite and olivine basalt are olivine at 1 Atmosphere, 4.5 kb and 9 kb, orthopyroxene at 13.5 and 18 kb, clinopyroxene at 22.5 kb and garnet at 27 kb. In the alkali olivine basalt composition, the liquidus phases are olivine at 1 Atmosphere and 9 kb, orthopyroxene with clinopyroxene at 13.5 kb, clinopyroxene at 18 kb and garnet at 27 kb. The sequence of appearance of phases below the liquidus has also been studied in detail. The electron probe micro-analyser has been used to make partial quantitative analyses of olivines, orthopyroxenes, clinopyroxenes and garnets which have crystallized at high pressure.These experimental and analytical results are used to determine the directions of fractionation of basaltic magmas during crystallization over a wide range of pressures. At pressures corresponding to depths of 35–70 km separation of aluminous enstatite from olivine tholeiite magma produces a direct fractionation trend from olivine tholeiites through olivine basalts to alkali olivine basalts. Co-precipitation of sub-calcic, aluminous clinopyroxene with the orthopyroxene in the more undersaturated compositions of this sequence produces derivative liquids of basanite type. Magmas of alkali olivine basalt and basanite type represent the lower temperature liquids derived by approximately 30% crystallization of olivine-rich tholeiite at 35–70 km depth. At depths of about 30 km, fractionation of olivine-rich tholeiite with separation of both olivine and low-alumina enstatite, joined at lower temperatures by sub-calcic clinopyroxene, leads to derivative liquids with relatively constant SiO2 (48 to 50%) increasingly high Al2O3 (15–17%) contents and retaining olivine + hypersthene normative chemistry (5–15% normative olivine). These have the composition of typical high-alumina olivine tholeiites. The effects of low pressure fractionation may be superimposed on magma compositions derived from various depths within the mantle. These lead to divergence of the alkali olivine basalt and tholeiitic series but convergence of both the low-alumina and high-alumina tholeiites towards quartz tholeiite derivative liquids.The general problem of derivation of basaltic magmas from a mantle of peridotitic composition is discussed in some detail. Magmas are considered to be a consequence of partial melting but the composition of a magma is determined not by the depth of partial melting but by the depth at which magma segregation from residual crystals occurs. Magma generation from parental peridotite (pyrolite) at depths up to 100 km involves liquid-crystal equilibria between basaltic liquids and olivine + aluminous pyroxenes and does not involve garnet. At 35–70 km depth, basaltic liquids segregating from a pyrolite mantle will be of alkali olivine basalt type with about 20% partial melting but with increasing degrees of partial melting, liquids will change to olivine-rich tholeiite type with about 30% melting. If the depth of magma segregation is about 30 km, then magmas produced by 20–25% partial melting will be of high-alumina olivine tholeiite type, similar to the oceanic tholeiites occurring on the sea floor along the mid-oceanic ridges.Hypotheses of magma fractionation and generation by partial melting are considered in relation to the abundances and ratios of trace elements and in relation to isotopic abundance data on natural basalts. It is shown that there is a group of elements (including K, Ti, P, U, Th, Ba, Rb, Sr, Cs, Zr, Hf and the rare-earth elements) which show enrichment factors in alkali olivine basalts and in some tholeiites, which are inconsistent with simple crystal fractionation relationships between the magma types. This group of elements has been called incompatible elements referring to their inability to substitute to any appreciable extent in the major minerals of the upper mantle (olivine, aluminous pyroxenes). Because of the lack of temperature contrast between magma and wall-rock for a body of magma near to its depth of segregation in the mantle, cooling of the magma involves complementary processes of reaction with the wall-rook, including selective melting and extraction of the lowest melting fraction. The incompatible elements are probably highly concentrated in the lowest melting fraction of the pyrolite. The production of large overall enrichments in incompatible elements in a magma by reaction with and highly selective sampling of large volumes of mantle wall-rock during slow ascent of a magma is considered to be a normal, complementary process to crystal fractionation in the mantle. This process has been called wall-rock reaction. Magma generation in the mantle is rarely a simple, closed-system partial melting process and the isotopic abundances and incompatible element abundances of a basalt as observed at the earth's surface may be largely determined by the degree of reaction with the mantle or lower crustal wall-rocks and bear little relation to the abundances and ratios of the original parental mantle material (pyrolite).Occurrences of cognate xenoliths and xenocrysts in basalts are considered in relation to the experimental data on liquid-crystal equilibria at high pressure. It is inferred that the lherzolite nodules largely represent residual material after extraction of alkali olivine basalt from mantle pyrolite or pyrolite which has been selectively depleted in incompatible elements by wall-rock reaction processes. Lherzolite nodules included in tholeiitic magmas would melt to a relatively large extent and disintegrate, but would have a largely refractory character if included in alkali olivine basalt magma. Other examples of xenocrystal material in basalts are shown to be probable liquidus crystals or accumulates at high pressure from basaltic magma and provide a useful link between the experimental study and natural processes. 相似文献
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Todd Dunn 《Geochimica et cosmochimica acta》1983,47(11):1923-1930
The diffusivity of oxygen has been measured in three basaltic liquids from 1280 to 1450°C and 4 to 21 kilobars using a solid media piston-cylinder apparatus. The measurements were done by monitoring the reduction of ferric iron in previously oxidized spheres of basalt melt. The compositions studied were olivine nephelinite, alkali basalt, and 1921 Kilauea tholeiite.The isobaric temperature dependence of oxygen diffusivity is adequately described by Arrhenius relationships for the three liquids studied. Arrhenius activation energies were determined at 12 kilobars for olivine nephelinite (62± 6 kcal/mole) and tholeiite (51 ± 4 kcal/mole) and at 4, 12, and 20 kilobars for alkali basalt (70 ± 7, 86 ± 6, and 71 ± 14 kcal/mole, respectively). The Arrhenius parameters for the three compositions define a compensation law which is indistinguishable from those for oxygen diffusion in simple silicate melts (DUNN, 1982) and for divalent cation diffusion in basaltic melts (Hofmann, 1980). These results suggest that the principal species contributing to the total diffusivity of oxygen is the oxide anion (O2?).The isothermal pressure dependence of oxygen diffusion is complex and quite different from that observed for cationic diffusion in silicate melts. All three compositions show a sharp decrease in oxygen diffusivity at approximately the same pressure as the change in the liquidus phase from olivine to pyroxene, but otherwise the pressure dependence can be described by Arrhenius type equations. The equations yield negative activation volumes for the olivine nehpelinite and the alkali basalt. The activation volumes determined for the tholeiite are near zero at low pressure and positive at high pressure. A negative activation volume represents a decrease in the average size of the principal diffusing species.The results of this study are consistent with a melt model which includes both continuous changes in the relative proportions of the various anionic species in the melt with pressure and the occurrence of anionic disproportionation reactions within narrow pressure ranges. 相似文献
19.
鲁北新生代隐伏火山岩及其石油地质意义 总被引：1，自引：0，他引：1
鲁北新生代隐伏火山岩可划分为3个喷发期6个亚期,9种火山岩岩石类型和同期侵入的辉绿岩。它们形成在近大陆边缘的板内裂谷型盆地,对于富有机质生油岩的沉积、各种储集体的形成、多种含油圈闭类型的形成以及有机质成熟向烃类转化都是非常有利的。作为储集岩主要有玄武安山岩、辉绿岩和湖底玄武质凝灰岩。储油空间主要为次生孔隙和裂缝。火山岩及其有关岩石在本区不仅形成了特殊的油气藏,而且还可作为盖层、封堵层、披复构造的基岩,因此对石油地质勘探有重要意义。 相似文献