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1.
西藏过铝花岗岩副矿物特征及岩石成因意义 总被引：6，自引：1，他引：5
副矿物的行为可以更直接地用来指示岩浆体系的地球化学过程,为了探讨过铝花岗岩的成因,对西藏过铝花岗岩体中的岩性、矿物组成、副矿物特征和锆石含量、晶体形态分布特征进行了研究,矿物岩石特征表明西藏过铝花岗岩富含白云母、电气石和钠质斜长石,属典型的含白云母过铝质花岗岩(MPG)。副矿物见有26种,副矿物组合主要有6种类型,其中主要为锆石 磷灰石 钛铁矿型,尤以锆石 磷灰石最为常见。结果表明,可明显分出5种锆石晶体形态;阴极发光图像中,锆石具有较好的晶形,并显示出清晰的岩浆锆石韵律环带结构。离子探针分析表明锆石具有高的Th/U值。西藏过铝花岗岩为岩浆成因,岩浆主要是由地壳物质部分熔融而成。副矿物组合曲线图的曲线形态可分为3种成因类型:壳源高铝型、壳源型和壳幔混合源型(壳幔同熔型),主要为壳源高铝型。不同构造岩浆带副矿物特征反映的成因信息不同,喜马拉雅带为壳源成因,而冈底斯带除了壳源成因之外,还有幔源成分的加入,反映了青藏高原岩石圈组成和演化的不均一性。 相似文献
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云南富碱斑岩由地壳深部的源岩分离熔融形成，该源岩则由早期侵入陆壳的幔源超基性岩与陆壳组分混合而成。斑岩成矿作用的成矿物质主要来源于岩浆，铅同位素资料表明它们有深部流体相、早期陆壳和幔源岩浆三种来源，但归根结底可能本区存在异常上地幔。地质地球化学综合分析认为，铜金等元素主要来源于幔源组分，铅锌等元素来源于陆壳组分，源岩重熔和岩浆演化使成矿元素得到进一步的富集。在不同的构造单元中，源岩的壳幔组分比、重熔程度等存在差异，因而富碱斑岩特征及成矿作用有别，出现两个成矿亚系列。 相似文献
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济阳凹陷火山岩的岩石学与地球化学 总被引：3，自引：1，他引：3
对济阳凹陷的第三系火山岩、基性侵入岩进行了岩石学和地球化学研究,分别总结了火山岩、基性侵入岩岩石类型及其特征。碱性系列玄武岩主要为钠质系列,具上地幔来源的特征。从古新统到渐新统,玄武岩熔融程度降低,岩浆地幔源深度增加。微量元素和同位素的数据表明,第三纪火山岩源区存在不协调现象。稀土元素分析表明,本区玄武岩为大陆裂谷成因。钐-钕、铷-锶及铅同位素的数据表明,火山岩与侵入岩同源,都来自上地幔。玄武岩浆在形成过程中有过不同程度的混合作用,Rb/Sr相关性表明早、晚第三纪的幔源类型上存在差别。第三纪火山岩数据点分布于DMM,EMIH和EMII三个端元之间,反映第三纪火山岩成因与这三个端元不同程度混合有关。本区火山岩成因与幔源有关,地幔不相容成分的特征表明有沉积物混入的可能,不排除是陆壳物质混入,不同深度岩浆的混合也是一种解释。 相似文献
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详细研究了七段、约130km长的近垂直反射地震剖面所揭示的松辽盆地下的壳一幔结构。松辽盆地之下壳一幔之间为相对厚的Moho过渡带。可分为薄Moho和透镜状Moho以及过渡型Moho，与之对应的壳一幔结构也有差异。松辽盆地的发育阶段明显地可分为断陷期、拗陷期以及夭折期，不同的壳一幔结构可能与松辽盆地不同的发育期存在密切联系。此外，通过对比，认为裂谷盆地区具有类似的特殊壳一幔结构。在裂谷区，壳一幔之间强烈相互作用，不同的地壳组成和裂谷形成的不同阶段是形成不同壳一幔结构的主要原因，而且它们之间具有成因上的联系，并与裂谷的形成阶段相一致。 相似文献
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利用地震台阵观测资料研究大庆地区深部构造 总被引：1，自引：0，他引：1
利用绥芬河-满洲里地学断面上布设的流动地震台阵,并结合固定地震台记录到的2009年6月-2011年5月间的远震资料,通过有限频方法开展体波走时层析成像研究,获取研究区上地幔三维P波速度结构;采用瑞利面波双台相速度和背景噪声相速度层析成像方法,反演研究区的三维S波速度结构。应用两种方法最终得到大庆地区三维速度分布特征。结果显示：松辽盆地地壳厚度较薄,盆地周边的大、小兴安岭隆起区厚度变厚,松辽盆地地壳内部多存在低速异常,壳幔及上地幔与周边相比呈现高速异常,分析上地幔物质上升会造成局部高速异常结构。速度结构异常多是南北向或北北东向,可能与区域性断裂对上、中地壳影响有关。 相似文献
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太行山南段中生代侵入体微量元素地球化学及岩浆源区性质探讨 总被引：3，自引：0，他引：3
本文对在行山南中生代侵入岩体微量元素地球化学进行了系统研究,成果表明各类侵入岩的稀土配分模式均呈轻稀土富重稀土与亏损,且没有铕异常,认为这是由于岩石中副矿物中的负铕异常与主要矿物长石类矿物中高的正铕异常低消的结果,本文还探讨了岩浆源区的特点,认为为本区岩石多具幔壳混合来源（ＭＣ型）部分来自幔源（ＭＣ型）。 相似文献
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交代岩石圈地幔与大型金矿床之间的成因联系受到越来越多的关注.研究成矿金属在地幔源区的富集程度和幔源岩浆中的金含量,以及金从地幔源区释放、迁移并大规模富集成矿的机制和过程可以帮助我们更好地认识交代岩石圈地幔对金富集成矿的重要作用.金是高度亲铜元素,同时还具有流体活动性,在地幔岩浆作用、岩浆热液演化和富集成矿等诸多过程中的行为较为复杂.主要从金的地球化学行为出发,通过梳理金在各类地幔岩石和幔源岩浆中的分布,以及岩浆热液中金的主要行为及其受控因素,探讨交代岩石圈地幔对巨量金成矿的关键控制机制.主要认识包括:（1）交代岩石圈地幔可能是形成大规模热液型金矿床的重要源区,但金在源区的异常富集可能并不是成矿的必要条件;（2）地幔交代组分（特别是挥发分）有助于金从地幔源区中有效释放、并通过跨岩石圈尺度的深大断裂迁移富集;（3）富挥发分的岩浆热液中金的富集沉淀过程远比一个富金的地幔源区对大规模金成矿作用的贡献更大.因此,深刻理解岩石圈地幔长期演化过程中金在地幔交代和岩浆-热液演化过程中的行为与富集机制是解析大型金矿床成因的关键. 相似文献
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利用胶东及其邻区1∶2 0万重力异常和1∶10万航磁异常探测资料, 结合地震各向异性研究成果, 解析其三维岩石圈结构.在此基础上, 综合深部结构和矿床地质特征, 探讨深部作用与成矿动力学, 深化矿床成因认识, 为科学找矿提供决策依据.研究表明, 壳幔结构的不均一性制约着成矿系统物质和能量的交换, 反映在其结构、构造和演化等多个方面.矿集区为地幔隆起带的坳陷区, 幔坳与幔隆接触部位成矿强度大, 幔隆区的局部隆起部位成矿强度小; 金矿床主要分布于花岗岩变薄部位与变质岩的接触带上; 印支中晚期郯庐断裂带深切上地幔, 通过壳-幔相互作用, 将含矿流体系统输运到更高的层位, 发生蚀变、矿化作用.艾山岩体所处构造部位的特殊性, 反映了它可能是壳幔岩浆对流侵位中心. 相似文献
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《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(2):219-223
Present-day physical theories suggest that the mantle was partially or completely molten about 4.5 billion years ago. As is expected, the phase separation could result in the stratification of the initially homogeneous mantle into reservoirs of different chemical composition. Because of the poor knowledge of the physical phenomena connected with the multiphase system differentiation, many aspects of the evolution of partially molten zones remain disputable. In this study the simulation of liquid and crystal separation in a high- temperature centrifuge was carried out. Experimental simulation with the pyroxene + olivine + plagioclase + magnetite + melt mixture demonstrates the gravitational instability of the polycrystalline framework of partially molten zones. The melt motion in partially molten rocks is thought to be a multiphase flow involving both the melt and individual crystals. A high mobility of plagioclase crystals in the multiphase flow was ascertained. It is revealed as the formation of a monomineral plagioclase cumulate overlying the accumulated molten layer. The separation and motion of sulfides in the intercrystalline space is shown to be in an intimate relationship with the degree of melting of a silicate material. 相似文献
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《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(6-7):591-595
Present-day physical theories suggest that the mantle was partially or completely molten about 4.5 billion years ago. As is expected, the phase separation could result in the stratification of the initially homogeneous mantle into reservoirs of different chemical composition. Because of the poor knowledge of the physical phenomena connected with the multiphase system differentiation, many aspects of the evolution of partially molten zones remain disputable. In this study the simulation of liquid and crystal separation in a hightemperature centrifuge was carried out. Experimental simulation with the pyroxene + olivine + plagioclase + magnetite + melt mixture demonstrates the gravitational instability of the polycrystalline framework of partially molten zones. The melt motion in partially molten rocks is though to be a multiphase flow involving both the melt and individual crystals. A high mobility of plagioclase crystals in the multiphase flow was ascertained. It is revealed as the formation of a monomineral plagioclase cumulate overlying the accumulated molten layer. The separation and motion of sulfides in the intercrystalline space is shown to be in an intimate relationship with the degree of melting of a silicate material. 相似文献
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Only fine-grained rocks are present in the Luna 20 samples, and coarser grained rocks are represented by fragments of single crystals. A petrologic study has been made of 47 fine-grained crystalline rocks, microbreccias, and glassy aggregates. In addition, a total of 33 single crystals of pyroxene, plagioclase, olivine and spinel, in the size range 125 to 500 μ, have been examined using electron microprobe and single crystal X-ray diffraction techniques.The most abundant fine-grained crystalline rocks in the samples we have examined are recrystallized anorthositic norite and anorthositic troctolite. Gabbroic rocks, anorthosite, and KREEP basalt are present but not common. Most of the single crystals of pyroxene and plagioclase could have been derived from coarser grained noritic, troctolitic and anorthositic rocks. However, three of the 14 pyroxene crystals, and 2 of the 5 olivine crystals have contents greater than 0.45 and are believed to have been derived from mare basalts or related rocks. Two relatively sodic crystals of plagioclase were found. One is a crystal zoned at least over the range An85 to An63, and the second is a homogeneous crystal of albite (~An3). 相似文献
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火成岩中可以包含多种晶体群这一发现具有重要意义,使得成因矿物学重新成为揭示岩浆系统演化的基本指导思想。但是,这种重要性在许多文献中都没有得到反映,其典型实例就是镁铁质层状侵入体中堆晶岩的成因。争论在于堆晶矿物是循环晶还是母岩浆的液相线相。因此,本文致力于探讨四川攀西地区镁铁质层状侵入体中堆晶岩的形成过程,重申成因矿物学的重要意义。显微镜观察表明,堆晶单斜辉石富含Fe-Ti氧化物出溶叶片(含叶片辉石),表明其形成环境明显不同于与斜长石呈共结关系的单斜辉石(无叶片辉石);无叶片辉石和斜长石中的橄榄石包裹体呈浑圆状,表明了橄榄石与结晶环境间的热力学不平衡。橄榄石与熔体间Fe-Mg分配关系分析表明,根据母岩浆成分推测的橄榄石Fo值远低于岩体中观测橄榄石化学成分变化范围(Fo61-Fo81)的高限,表明至少部分橄榄石不是寄主侵入体的液相线相。橄榄石的Mg#值(100×Mg/(Mg+Fe))与微量元素(特别是Ni)的相关关系表明存在多种橄榄石晶体群,它们形成于不同的热力学环境中。晶体沉降过程分析表明,寄主岩浆析出的晶体几乎不可能发生快速重力沉降来形成堆晶岩。所有这些证据都表明,形成堆晶岩的矿物主要来自岩浆系统深部不同的岩浆房中,是被岩浆携带输运到终端岩浆房的循环晶。 相似文献
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《International Geology Review》2012,54(8):694-705
Determination of the growth rate of crystals may be based on knowledge of the linear rate, the volume rate, and duration of crystallization. Direct measurements are possible where crystals are in process of growth as in the laboratory, saline waters, and at volcanic gaseous exhalations. Indirect but absolute measurements are possible by relating crystal zones with known occurrences in time examples include calcite growth in belemnites, cave stalactites with smoke layers, and seasonally varied saline waters. Relative growth rates may be inferred from the nature of the intergrowth surface between different mineral crystals. Data is given on growth rates of gypsum, halite, calcite, fluorspar, quartz, hematite, pyrite, nepheline, bronzite, olivine, plagioclase, pyroxene, argentite, and corundum. — M. Russell 相似文献
16.
A numerical approach to boundary layer fractionation: application to differentiation in natural magma systems 总被引：1，自引：1，他引：0
With few exceptions, geochemical models of igneous differentiation have assumed that crystals form homogeneously throughout the cooling magma chamber. This is in spite of field evidence and physical models suggesting for natural systems, that heat loss, and thus most crystallization, occurs primarily along the walls and roof of magma chambers. Such systems would produce aphyric, evolved composition lavas. Existing models of boundary layer crystal fractionation suggest that the products of such a process are significantly different from the products of homogeneous crystallization. To investigate this process further, we have developed a model using a numerical approach to boundary layer crystal fractionation based on new phase equilibria and trace element constraints. In addition to olivine, augite and plagioclase, this new model includes the ability to calculate the effects of oxide (magnetite and ilmenite), apatite and low-Ca pyroxene fractionation. This is critical if we are to effectively evaluate the geochemical signature of boundary layer fractionation. This is because the products of boundary layer fractionation are most different from homogeneous fractionation for high degrees of crystallization in the solidification zone. These are the same conditions where oxides, low-Ca pyroxene and apatite are saturated in most natural, differentiated mafic systems. The results of this model suggest that boundary layer fractionation can help to explain such phenomena as phantom crystallization, variation in incompatible element ratios, and the decoupling of major and trace element systematics. In addition, many of the geochemical patterns that we use to distinguish between the products of low pressure and high pressure differentiation are obscured by the fact that the liquid line of descent can be controlled by the removal of phases not in equilibrium with the entire magma chamber. 相似文献
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The xenolithic Tertiary ultrabasic dykes of south-west Skyeare composed principally of forsteritic olivine, plagioclase,and clinopyroxene with accessory chrome spinel and magnetite.The plagioclase: pyroxene ratios are relatively constant withineach dyke but the absolute amounts of these minerals are dependenton the olivine content which varies, often considerably, acrossthe dykes. Five main types of olivine distribution are recordedfrom the dykes and in all five there is a concentration of olivinecrystals towards the centre of the dyke. The average size ofthe olivine crystals also varies across the dykes with increasesin size generally corresponding to increases in the olivinecontent. The petrogenetic hypothesis of composite intrusion previouslyproposed for these dykes by Bowen (1928) is re-examined andfound to be inadequate. It is suggested that the dykes, whichwere intruded as magmatic suspensions of olivine crystals androck fragments, are unlikely to have been differentiated intheir present positions and the possibility that the differentiationoccurred during their emplacement is examined. It is shown thatthe mineral distributions and crystal size variations occurringin the dykes are, on the whole, analogous to those expectedto arise during laminar flow in vertical conduits, and it isconcluded that flow differentiation occurred during the intrusionof the ultrabasic dykes of south-west Skye.
1Present address:Department of Geology,University of Toronto,Toronto5,Ontario,Canada. 相似文献
18.
准噶尔盆地老山沟火山岩晶体粒度分布及其结晶动力学意义 总被引：1，自引：0，他引：1
摘 要 阐述了火山岩晶体粒度分布的基本原理和研究方法分析了老山沟火山岩斜长石、
辉石、橄榄石、铁钛氧化物的晶体粒度分布。前3种矿物在中间粒度处发生了有意义的弯折
原因是岩浆上升时过冷度增大。估算了岩浆房中斜长石、橄榄石的成核速率、结晶时间及上
升过程中处于结晶带的时间。研究表明在岩浆的演化过程中晶体的分离和累积作用及岩
浆的混合和对围岩的同化作用可以忽略。 相似文献
19.
I. H. Campbell P. L. Roeder J. M. Dixon 《Contributions to Mineralogy and Petrology》1978,67(4):369-377
Plagioclase buoyancy experiments have been carried out in a high-temperature centrifuge furnace using seventeen basaltic liquids and plagioclase crystals of three compositions: An89, An76 and An55. The results show that the floating tendency of plagioclase in basaltic liquids is at least 0.03 g/cm3 greater than indicated by the calculations. If this correction factor is applied to calculations of plagioclase buoyancy in the Skaergaard Intrusion, it is found that the plagioclase crystals in the lower and middle zones were less dense than the coexisting liquids.Other phenomena relevant to crystal transport in basaltic liquids were observed in the centrifuge experiments. These included crystal flotation by rising bubbles, plagioclase sinking because of the formation of plagioclase-magnetite composite grains, graded bedding of olivine and magnetite, and more than 60% intercumulus basaltic liquid between settled olivine crystals. 相似文献
20.
本文用Mg－Cr2+做榄石、辉石、尖晶石的粉晶X射线衍射数据，采取“整体图谱最小二乘Rietveld”方法计算了上述矿物的晶胞参数和摩尔体积，并对Cr2+在各晶体结构中的占位情况进行了研究。结果显示，各矿物的晶胞参数随含Cr2+量的增大而增大。据Vegard定律，推算出各端元组分铬橄榄石（Cr2SiO1）、铬辉石（Cr2SiO2O6）及立方铬尖晶石（Cr3O4）的摩尔体积分别为47．7，68．0，44．9cm3。精化结构参数指示，在橄榄石中，Cr2+随机分配在两个八面体（M1，M2）位置；在辉石中，Cr2+优先选择八面体M2位置；在尖晶石中，Cr2+占置四面体位置。这种晶体内离子分配可从离子半径差别或晶体场稳定能大小得到解释。 相似文献