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1.
汉诺坝玄武岩中熔体-捕虏体相互作用初步研究 总被引：1，自引：0，他引：1
汉诺坝新生代玄武岩捕获的地幔橄榄岩及其解体矿物橄榄石、单斜辉石、斜方辉石捕虏晶,普遍发育反应边结构,提供了玄武岩浆在上升穿越岩石圈地幔过程中橄榄岩-熔体相互作用的重要信息。橄榄石和单斜辉石捕虏晶反应边的成分变化一致,由核部富镁向边部富铁变化,趋同于玄武岩中相应斑晶的成分。斜方辉石捕虏晶反应边一般由橄榄石+单斜辉石+玻璃构成,多为双层结构,反应边矿物橄榄石、单斜辉石较相应的地幔矿物富铁,其富硅、碱的中酸性玻璃成分,为中国东部地幔矿物包裹体中存在的富硅、碱熔体的来源提供了重要信息。同时发现橄榄岩捕虏体中尖晶石颜色、成分的变化与温度的关系。地幔矿物捕虏晶反应边结构(非平衡结构)得以保存,暗示了玄武岩浆的快速上升。而大规模的熔体-捕虏体相互作用,改变着岩石圈地幔的性质。 相似文献
2.
吉林双辽地区古近纪玄武岩中一方辉橄榄岩包体记录了上地幔交代作用的信息。原生斜方辉石被交代成因的单斜辉石和橄榄石所围绕,或形成反应边结构,或斜方辉石残留在次生单斜辉石中。这些反应结构仅出现在尖晶石的周围。电子探针分析表明次生单斜辉石具有高Mg#、Cr#和CaO/Al2O3比值,次生橄榄石高Mg#、CaO和Cr2O3,被交代的尖晶石边部高Cr#、CaO。由于交代作用并未影响橄榄岩体系的Mg#,而且熔体-岩石反应结构指示Opx(斜方辉石) Sp(尖晶石) 熔体(Ⅰ)→Cpx(单斜辉石) Ol(橄榄石) 熔体(Ⅱ),结合实验以及文献资料,认为双辽地区的岩石圈地幔受到了硅酸盐熔体的交代。这种交代导致橄榄岩中斜方辉石逐渐减少,单斜辉石和橄榄石逐渐增加,从而使方辉橄榄岩渐变成易剥橄榄岩。这种交代现象可能发生在软流圈-岩石圈接触带上的熔-岩反应区,暗示了在古近纪双辽地区岩石圈减薄和软流圈上涌导致的软流圈-岩石圈的相互作用仍在继续。 相似文献
3.
山东昌乐新生代碱性玄武岩中的巨晶单斜辉石成因研究 总被引：2，自引：0，他引：2
山东昌乐新生代碱性玄武岩中除斑晶单斜辉石和基质单斜辉石外,还发育大量巨晶单斜辉石和同源斜方辉石捕掳晶。巨晶单斜辉石与玄武岩间发育复杂和简单两种类型的反应边。复杂反应边往往发育在颗粒较大的巨晶单斜辉石外围。复杂反应边可分为4个带：内部带、过渡带、外部带和边缘带,其中,内部带、过渡带和外部带均由具不同结构特征的单斜辉石＋熔体＋金属氧化物构成,边缘带为不含熔体和金属氧化物的干净的单斜辉石;内部带的单斜辉石具梳状构造,过渡带的单斜辉石具细密筛孔构造,外部带为具似砂钟构造的筛孔状单斜辉石。反应边中单斜辉石、熔体及金属氧化物的成分显示,只有内部带受到单斜辉石巨晶的影响,其余带均受玄武岩浆的制约。简单反应边往往发育在颗粒较小的巨晶单斜辉石外围。简单反应边仅发育不含熔体和金属氧化物的干净的单斜辉石。巨晶单斜辉石的反应边是巨晶与玄武岩浆间温度差造成的。在与玄武岩浆反应的过程中,大颗粒的单斜辉石巨晶需要较长的时间与玄武岩浆达到温度平衡,从而有足够的时间发育包含4个带的复杂反应边;反之,由于缺乏足够的反应时间,小颗粒单斜辉石巨晶的外围只发育不含熔体和金属氧化物的简单反应边。同源斜方辉石捕掳晶的成分与地幔二辉橄榄岩包体中的斜方辉石类似,其边部发育类似于Bowen反应（1956）形成的单斜辉石环边。在单斜辉石AlIV-AlVI图解上,巨晶单斜辉石、二辉橄榄岩包体中的单斜辉石以及部分单斜辉石斑晶的核部,均位于较高压力的“麻粒岩和玄武岩中包体”区域,反应边中单斜辉石、基质单斜辉石以及绝大部分斑晶单斜辉石位于“火成岩”区域,说明部分斑晶单斜辉石核部来源于地幔二辉橄榄岩,属于捕掳晶。结合单斜辉石结晶压力的估算,笔者认为巨晶单斜辉石的成因模式为：来自软流圈的碱质基性熔体上侵到地幔岩石圈下部,结晶形成单斜辉石巨晶,后来该熔体携带巨晶单斜辉石与来自上地幔岩石圈、夹带大量二辉橄榄岩包体以及斜方辉石（和单斜辉石）捕掳晶的玄武岩浆混合,巨晶单斜辉石随混合后的碱性玄武岩浆上升、喷出地表。 相似文献
4.
本文利用电子背散射衍射(EBSD)技术对河北张家口大麻坪汉诺坝玄武岩橄榄岩捕虏体中斜方辉石与玄武岩反应结构的显微构造进行了详细研究。研究结果表明: ① 其反应边具有复杂的多层筛状结构特征,包括玄武岩层、富橄榄石层以及橄榄石和单斜辉石交生层;② 由外至内,橄榄石的Mg值逐渐升高,而单斜辉石的Mg值变化不大;③ 反应边结构中的单斜辉石与斜方辉石残斑之间存在很好的结晶学拓扑关系,即(100)opx//(100)cpx、(010)opx//(010)cpx、(001)opx//(001)cpx;④ 橄榄石的结晶学取向无序且与斜方辉石和单斜辉石均无关。这个反应过程可以用贫硅熔体先与斜方辉石反应形成单斜辉石,并导致熔体富硅,从而橄榄石从反应熔体中结晶出来合理地解释。相对富硅熔体与橄榄岩的反应,贫硅熔体与橄榄岩的反应过程由于筛状反应边的存在可能更容易进行,筛状结构反应边可以为熔体在橄榄岩中沿颗粒边界运移提供通道,并使橄榄岩主要组成矿物发生细粒化和岩石结构变得松散,可以有效保证熔体上升过程中对橄榄岩的持续侵蚀和破坏,从而可能导致岩石圈地幔性质的迅速转变。 相似文献
5.
近年来地幔捕虏体中富硅熔体的研究受到广泛关注,富硅熔体不仅具有多种产出状态,其成因来源也具有多样性。本文选取汉诺坝地区地幔捕虏体矿物中的熔体包裹体和斜方辉石反应边中的熔体玻璃为研究对象,探索富硅熔体在岩石圈地幔演化中的作用。通过详细的岩相学观察并结合电子探针分析发现,二者成因不同。熔体包裹体玻璃成分富硅(SiO2 61%~65%),相对贫Na2O(1%~3%)、K2O(<1%),富含挥发份(约3%~6%),为地幔交代成因;斜方辉石反应边玻璃富硅(SiO2 64%~67%)、碱(Na2O 5%~7%,K2O 6%~9%),几乎不含挥发份,是地幔捕虏体被寄主玄武岩浆快速携带上升至地表的过程中两者反应的产物。地幔交代作用产生的富硅熔体包裹体深刻影响了岩石圈地幔的地球化学性质;而玄武岩浆在上升过程中与岩石圈地幔捕虏体中斜方辉石的反应,导致了岩石圈地幔由富硅向贫硅转变,为华北克拉通的破坏提供了证据。 相似文献
6.
异剥橄榄岩化是地幔橄榄岩与硅不饱和熔体发生强烈相互作用的地幔过程。这一过程通常伴随地幔物理-化学性质的显著改变,与克拉通岩石圈减薄和破坏密切相关。本文梳理了前人对异剥橄榄岩化的驱动机理、结构和成分特征及其对大陆稳定性影响等方面的定性认识,并在此基础上通过热力学模拟,刻画了不同属性地幔与熔体在不同温度压力条件下的相互作用过程,目标是为定量限定异剥橄榄岩化的发生条件、物理-化学效应及地球动力学意义。研究显示,异剥橄榄岩化通常会出现磷灰石、角闪石、金云母和碳酸盐等标志性交代矿物,并以斜方辉石被单斜辉石替换为典型特征,还可发育海绵边、熔体囊(已冷却结晶为单斜辉石、橄榄石等细粒矿物)和矿物环带等非平衡结构。热力学模拟表明,熔岩反应过程受原岩、熔体性质以及熔/岩比例的共同控制,不同属性地幔(难熔方辉橄榄岩、饱满二辉橄榄岩)与贫硅(如霞石岩)熔体反应都能生成富单斜辉石橄榄岩,且在较高压力(如2.5GPa和4.0GPa)条件下更容易形成异剥橄榄岩;相比之下,不同性质地幔与富硅(如MORB)熔体反应在任何压力条件下均不能产生异剥橄榄岩。此外,两类熔体参与的熔岩反应均能引起围岩密度逐渐增加,并在高压条件下... 相似文献
7.
南美洲南部的Pali Aike火山岩区第四纪碱性玄武岩中普遍发育含石榴石的斜方辉石岩包体。这种斜方辉石岩既作为独立的捕掳体存在又以细脉的形式穿插于橄榄岩捕掳体中。斜方辉石岩普遍含富Ti矿物,并且次生斜方辉石含橄榄石和单斜辉石残晶。与含石榴石橄榄岩中的斜方辉石相比,这种次生的斜方辉石以高TiO2、中等含量的Al2O3以及低Mg#为特征,表明它是在一种高度分异演化的富Ti熔体交代作用下通过消耗橄榄石和单斜辉石方式形成的。斜方辉石岩全岩的Co、Ni略低,Cr和铂族元素(PGE)含量与地幔橄榄岩相当,表明这些元素在交代作用过程中相对稳定,而交代介质带入的组分以碱质(K2O+Na2O)、Ti、Si、Al和S为主。交代的斜方辉石在现代活动岛弧和古克拉通的地幔橄榄岩捕掳体中多有报道。与这些环境中地幔样品的斜方辉石相比,PaliAike地区的次生斜方辉石含有相对高的Ti和Al,以及相对低的Mg。高Ti低Mg属性反映了交代介质可能来源于下伏的软流圈地幔并且经历了高度的分异和演化过程。Pali Aike地区所见到的这种交代斜方辉石和斜方辉石岩在其他被上涌软流圈影响的陆下岩石圈地幔中可能普遍存在。这些研究对了解中国华北-东北中生代以来的岩石圈地幔减薄机制有着重要的借鉴意义。 相似文献
8.
碳酸盐熔体交代作用是指在地幔碳酸盐熔体与橄榄岩之间的相互作用，是改造地幔的重要方式之一.碳酸盐熔体交代会显著改变地幔橄榄岩的岩石学和地球化学特征.首先，碳酸盐熔体交代作用会改变地幔橄榄岩中的矿物组成和比例.尽管碳酸盐熔体与橄榄岩的反应结果受控于初始反应物成分和反应的温压条件，但多数反应会导致橄榄岩中辉石的比例增加，而且有时还会出现磷灰石、独居石等副矿物.另外，在有些受碳酸盐熔体交代显著的橄榄岩的矿物中不仅可发现大量CO2流体包裹体和碳酸盐熔体包裹体，也会出现特殊的反应边结构和熔体囊.其次，碳酸盐熔体在改造地幔橄榄岩过程中，会在地幔矿物中留下明显的地球化学指纹.在主量元素特征上，受到碳酸盐熔体交代的橄榄岩中的单斜辉石往往具有偏高的Mg#和Ca/Al比值（>5）；而在微量元素组成特征上的变化更为显著，包括单斜辉石具有高的（La/Yb）N、Eu/Ti、Zr/Hf、Y/Ho比值，并显著亏损HFSE等.另外，值得注意的是，碳酸盐熔体与地幔橄榄岩反应的程度不同也会导致这些地球化学特征存在差异，因此在判别碳酸盐熔体交代作用时要采用岩石学和地球化学特征相结合，多方面对比分析.对于引起地幔碳酸盐熔体交代作用的交代介质来源的识别主要用Mg-Zn-Ca-Sr等多种同位素体系进行示踪研究，尤其是近年来微区Sr同位素分析方法的建立为地幔碳酸盐熔体交代作用研究提供了重要手段. 相似文献
9.
昌乐方山新生代玄武岩中携带有大量深源捕虏岩,其岩石类型以二辉辉石岩、二辉橄榄岩为主,方辉橄榄岩、单斜辉石岩、单辉橄榄岩少见,未见纯橄岩。二辉辉石岩、二辉橄榄岩、方辉橄榄岩的矿物岩石、地球化学特征和平衡温度压力计算显示为地幔来源,采用地质温度压力计进行计算,获取三者都源于岩石圈地幔,形成的深度范围为41~66.7 km。根据单辉橄榄岩和单斜辉石岩的矿物化学分析,单斜辉石岩和单辉橄榄岩形成深度要低于前三者,且与前三者有密切成因联系。"熔体—岩石"反应在各类深源捕虏岩中广泛存在,除方辉橄榄岩样品不存在明显的"熔体—岩石"反应外,二辉辉石岩、单斜辉石岩、二辉橄榄岩中不同的矿物边缘与玄武质熔体接触部位有着不同类型的反应边和反应矿物出现:橄榄石边部发生(Mg,Fe)_2SiO_4(镁橄榄石)+熔体(原始岩浆)=(Mg,Fe)_2SiO_4(贵橄榄石)+熔体(演化岩浆)反应,使得边部富铁贫镁;单斜辉石与玄武质熔体反应,多具有粉红色反应边,具有富Ti、Al、Fe,贫Si、Mg,较玄武岩基质中单斜辉石斑晶更低Mg~#的特征。斜方辉石与玄武质熔体反应生成复杂的反应带,存在斜方辉石+熔体=橄榄石+SiO_2(熔体)+单斜辉石的反应,反应带内新生成的矿物由内向外具有明显趋向玄武质熔体成分的变化;尖晶石与玄武质熔体反应边缘具有富Fe、Ti,贫Mg、Al,以及更高的Cr~#,趋向于形成钛铁矿的变化特征。二辉橄榄岩中熔体囊和单辉橄榄岩中筛状单斜辉石以及粉红色的反应边都暗示了二者至少经历了两个期次的熔体作用。随着岩石圈地幔的演化,熔体的再富集作用使得难熔的方辉橄榄岩逐渐转变为相对富集的二辉橄榄岩,后期二辉橄榄岩又与玄武质熔体反应,生成更加富集的单辉橄榄岩,而方山方辉橄榄岩也受到了熔体的轻度改造,已不具有难熔古老岩石圈地幔岩石的显著特征,鲁西新生代玄武岩中深源捕虏体与熔体的反应广泛存在,熔体成分以玄武质为主,这可能是华北克拉通岩石圈置换的重要方式之一,导致古老岩石圈地幔的消失。 相似文献
10.
地幔富硅交代与大陆岩石圈的演化 总被引：4，自引：0，他引：4
富硅交代是弧下地幔中熔体岩石相互作用的主要表现形式 ,是造成古老克拉通陆下岩石圈地幔富硅的主要机制。在弧下地幔捕掳体中 ,橄榄岩被来自俯冲洋壳物质部分熔融生成的含水富硅熔体交代后 ,斜方辉石含量的增加使全岩富集SiO2 ,斜方辉石显示异常低的Al2 O3和Cr2 O3,微量元素上表现为强烈富集LILE ,强烈亏损Nb ,Ta和Ti。在古老克拉通地幔岩样品中 ,方辉橄榄岩具过剩的斜方辉石 ,橄榄石的Ni含量与斜方辉石的组成含量成正比 ,而和橄榄石的x(Mg) /x(Mg +Fe2 +)值没有正比关系 ,被解释为亏损的地幔橄榄岩和来自俯冲板片的富硅熔体相互作用的结果。熔体岩石相互作用最终导致了陆下岩石圈地幔富集SiO2 ,这种被含水富硅熔体改造后的地幔岩石的部分熔融可能是造成陆壳富硅富镁的主要原因。含水富硅熔体对岩石圈地幔的影响程度也可能是大陆岩石圈增生或裂解、增厚或减薄的关键因素之一。 相似文献
11.
I.P. Solovova A.V. Girnis L.N. Kogarko N.N. Kononkova F. Stoppa G. Rosatelli 《Lithos》2005,85(1-4):113-128
This paper presents a study of melt and fluid inclusions in minerals of an olivine-leucite phonolitic nephelinite bomb from the Monticchio Lake Formation, Vulture. The rock contains 50 vol.% clinopyroxene, 12% leucite, 10% alkali feldspars, 8% hauyne/sodalite, 7.5% nepheline, 4.5% apatite, 3.2% olivine, 2% opaques, 2.6% plagioclase, and < 1% amphibole. We distinguished three generations of clinopyroxene differing in composition and morphology. All the phenocrysts bear primary and secondary melt and fluid inclusions, which recorded successive stages of melt evolution. The most primitive melts were found in the most magnesian olivine and the earliest clinopyroxene phenocrysts. The melts are near primary mantle liquids and are rich in Ca, Mg and incompatible and volatile elements. Thermometric experiments with the melt inclusions suggested that melt crystallization began at temperatures of about 1200 °C. Because of the partial leakage of all primary fluid inclusions, the pressure of crystallization is constrained only to minimum of 3.5 kbar. Combined silicate–carbonate melt inclusions were found in apatite phenocrysts. They are indicative of carbonate–silicate liquid immiscibility, which occurred during magma evolution. Large hydrous secondary melt inclusions were found in olivine and clinopyroxene. The inclusions in the phenocrysts recorded an open-system magma evolution during its rise towards the surface including crystallization, degassing, oxidation, and liquid immiscibility processes. 相似文献
12.
《International Geology Review》2012,54(4):448-472
To better understand the origin, migration, and evolution of melts in the lithospheric mantle and their roles on the destruction of the North China Craton (NCC), we conducted a petrological and geochemical study on a quartz-bearing orthopyroxene-rich websterite xenolith from Hannuoba, the NCC, and its hosted melt and fluid inclusions. Both clinopyroxene and orthopyroxene in the xenolith contain lots of primary and secondary inclusions. High-temperature microthermometry of melt inclusions combined with Raman spectroscopy analyses of coexisting fluid inclusions shows that the entrapment temperature of the densest inclusions was ~1215°C and the pressure ~11.47 kbar, corresponding to a depth of ~38 km, i.e. within the stability of the spinel lherzolite. Intermediate pressure inclusions probably reflect progressive fluid entrapment over a range of depths during ascent, whereas the low-pressure inclusions (P < 2 kbar) may represent decrepitated primary inclusions. In situ laser-ablation ICP-MS analyses of major and trace elements on individual melt inclusions show that the compositions of these silicate melt inclusions in clinopyroxene and orthopyroxene are rich in SiO2, Al2O3, and alkalis but poor in TiO2 and strongly enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), with negative anomalies of high-field strength elements (HFSEs). These characteristics suggest that the silica-rich melts could be derived from the partial melting of subducted oceanic slab. Therefore, this kind of quartz-bearing orthopyroxene-rich websterite may be produced by interaction between the slab-derived melts with the mantle peridotite. This study provides direct evidence for the origin, migration, and evolution of melts in the lithospheric mantle, which may play an important role in the destruction of the NCC. 相似文献
13.
Olivinites of the Krestovskaya Intrusion consist of predominant amount of olivine, and minor Ti-magnetite, perovskite, and clinopyroxene (from single grain to a few vol %). Primary crystallized melt inclusions were found and studied in olivine, perovskite, and diopside of the olivinites. Daughter phases in olivine-hosted melt inclusions are monticellite, perovskite, kalsilite, phlogopite, magnetite, apatite, and garnet andradite. Perovskite-hosted melt inclusions contain such daughter phases as kalsilite, pectolite, clinopyroxene, biotite, magnetite, and apatite, while daughter phases in clinopyroxene-hosted melt inclusions are represented by kalsilite, phlogopite, magnetite, and apatite. According to melt inclusion heating experiments, olivine crystallized from above 1230°C to 1180°C. It was followed by perovskite crystallizing at ≥1200°C and clinopyroxene, at 1170°C. According to analysis of quenched glass of the melt inclusions, the chemical composition of melts hosted in the minerals corresponds to the larnite-normative alkali ultramafic (kamafugite) magma significantly enriched in incompatible elements. The high incompatible element concentrations, its distribution, and geochemical indicator ratios evidenced that the magma was derived by the partial melting of garnet-bearing undepleted mantle. 相似文献
14.
Melt Generation and Movement beneath Theistareykir, NE Iceland 总被引：2，自引：5，他引：2
A detailed study of the volume and composition of all the lavasfrom the Theistareykir segment of the Northern Volcanic Zoneof Iceland was designed to study basaltic melt generation andmovement beneath a spreading ridge. The trace element compositionsof the lavas are variable, and those of melt inclusions in olivine,clinopyroxene and plagioclase phenocrysts even more so. We showthat this variability can be produced by mixing instantaneousmelts produced by isentropic decompression of mantle whose initialpotential temperature is 1480°C, and that the calculatedvolume and composition of the average melt is consistent withgeophysical and petrological observations. Pressure and temperatureestimates suggest that the phenocrysts form in the upper mantle,at depths of 30–40 km, and trap melts formed at greaterdepths. Some mixing of the instantaneous melts occurs beforethe melt is trapped, and more mixing occurs before the lavasare erupted. A similar model can account for the compositionof melt inclusions from the FAMOUS area of the Mid-AtlanticRidge, and from the Gorda and Juan de Fuca Ridges. KEY WORDS: basalt; Iceland; melt inclusions; melting; ridges 相似文献
15.
Cliff S. J. Shaw 《Contributions to Mineralogy and Petrology》1999,135(2-3):114-132
A large body of recent work has linked the origin of Si-Al-rich alkaline glass inclusions to metasomatic processes in the
upper mantle. This study examines one possible origin for these glass inclusions, i.e., the dissolution of orthopyroxene in
Si-poor alkaline (basanitic) melt. Equilibrium dissolution experiments between 0.4 and 2 GPa show that secondary glass compositions
are only slightly Si enriched and are alkali poor relative to natural glass inclusions. However, disequilibrium experiments
designed to examine dissolution of orthopyroxene by a basanitic melt under anhydrous, hydrous and CO2-bearing conditions show complex reaction zones consisting of olivine, ± clinopyroxene and Si-rich alkaline glass similar
in composition to that seen in mantle xenoliths. Dissolution rates are rapid and dependent on volatile content. Experiments
using an anhydrous solvent show time dependent dissolution rates that are related to variable diffusion rates caused by the
saturation of clinopyroxene in experiments longer than 10 minutes. The reaction zone glass shows a close compositional correspondence
with natural Si-rich alkaline glass in mantle-derived xenoliths. The most Si-and alkali-rich melts are restricted to pressures
of 1 GPa and below under anhydrous and CO2-bearing conditions. At 2 GPa glass in hydrous experiments is still Si-␣and alkali-rich whereas glass in the anhydrous and
CO2-bearing experiments is only slightly enriched in SiO2 and alkalis compared with the original solvent. In the low pressure region, anhydrous and hydrous solvent melts yield glass
of similar composition whereas the glass from CO2-bearing experiments is less SiO2 rich. The mechanism of dissolution of orthopyroxene is complex involving rapid incongruent breakdown of the orthopyroxene,
combined with olivine saturation in the reaction zone forming up to 60% olivine. Inward diffusion of CaO causes clinopyroxene
saturation and uphill diffusion of Na and K give the glasses their strongly alkaline characteristics. Addition of Na and K
also causes minor SiO2 enrichment of the reaction glass by increasing the phase volume of olivine. Olivine and clinopyroxene are transiently stable
phases within the reaction zone. Clinopyroxene is precipitated from the reaction zone melt near the orthopyroxene crystal
and redissolved in the outer part of the reaction zone. Olivine defines the thickness of the reaction zone and is progressively
dissolved in the solvent as the orthopyroxene continues to dissolve. Although there are compelling reasons for supporting
the hypothesis that Si-rich alkaline melts are produced in the mantle by orthopyroxene – melt reaction in the mantle, there
are several complications particularly regarding quenching in of disequilibrium reaction zone compositions and the mobility
of highly polymerized melts in the upper mantle. It is considered likely that formation of veins and pools of Si-rich alkaline
glass by orthopyroxene – melt reaction is a common process during the ascent of xenoliths. However, reaction in situ within
the mantle will lead to equilibration and therefore secondary melts will be only moderately siliceous and alkali poor.
Received: 24 August 1998 / Accepted: 2 December 1998 相似文献
16.
Alkaline-basic dike from the Yllymakh Massif (Central Aldan) has been studied. Its partially crystallized matrix contains
corroded phenocrysts of olivine and hypidiomorphic phenocrysts of clinopyroxene and pseudo-, epileucite. It was found that
phenocrysts of clinopyroxene contain abundant primary inclusions, Ti-magnetite and apatite bear only single inclusions, whereas
olivine is enriched in secondary inclusions, which are confined to the cleavage of host mineral (along second and third pinacoids)
and its cracks. The homogenization temperatures of the primary inclusions in clinopyroxene and secondary inclusions in olivine
are approximately equal and lie within 1260–1240°C. The compositions of melt inclusions in olivine and clinopyroxene are also
similar and corresponded to the malignite-pseudoleucite phonolite-monzonite pulaskites, which are developed at the Yllymakh
Massif. Unheated inclusions in apatite and Ti-magnetite compositionally approach monzonites and nepheline syenites—tinguaites,
respectively. It was concluded that the alkaline basaltoid magma was presumably parental magma for the entire rock complex
of the Yllymakh Massif. Its crystallization and differentiation presumably provided all observed rock variety from ultrabasics
(early derivatives located at depth) and malignites (later derivatives) to leucite phonolites, monzonites, and alkaline pulaskites,
which were obtained during subsequent stages of the melt evolution. The parental magma, and especially its derivatives, were
enriched in BaO (0.8–0.1 wt %), Cl (0.1–0.3 wt %) and trace elements (primarily, LREE and MREE), which are several times higher
than mantle values. At the same time, ion microprobe (SIMS) study showed that derivative melts were dry: contained only 0.01–1.13
wt % H2O. The trend of melts conserved in the minerals and the massif rocks corresponds to the evolution of alkalinebasaltoid magma
with increase in Si, Al, alkalis and decrease in Mg, Ca, and Fe, i.e. the Bowen trend. The considered alkaline-basic dike
was presumably formed from the derivative of leucite-phonolite melt, which during emplacement captured olivine xenocrysts
from previously fractionated ultrabasic rocks. The parental magma was presumably derived by high-degree melting of garnet-spinel-facies
depleted mantle at some influence of crustal material. 相似文献
17.
IrinaP.Solovova Theodoros Ntaflos Andrei Girnis Natalya N.Kononkova Vyacheslav V.Akinin 《岩石学报》2007,23(1):83-92
Melt and fluid inclusions were studied in the minerals of Cenozoic olivine melanephelinites from the Chukchi Peninsula, Russia.The rock contain several generations of olivine phenocrysts varying in composition at mg=0.88～0.77.The phenocrysts bear fluid and melt inclusions recording various stages of melt crystallization in volcanic conduits and shallow magma chambers.Primary fluid inclusions are CO_2-dominated with a density of up to O.93 g/cm~3.All fluid inclusions are partially leaked,which is indicated by haloes of tiny fluid bubbles around large fluid inclusions in minerals.Melt inclusions contain various daughter crystals,which were completely resorbed in thermometric experiments at about 1230℃.Assuming that this temperature corresponds to the entrapment conditions of the CO_2 fluid inclusions,the minimum pressure of the beginning of magma degassing is estimated as 800MPa.Variations in the compositions of homogenized silicate melt inclusions indicate that olivine was the earliest crystalline phase followed by clinopyroxene,nepheline and orthoclase.This sequence is in agreement with the mineralogy of the rocks.The melts are strongly enriched in incompatible trace elements and volatiles(in addition to CO_2,high C1,F,and S contents were detected).There are some differences between the compositions of melts trapped in minerals from different samples.Variations in SiO_2,FeO,and incompatible element contents are probably related to melt generations at various levels in a homogeneous mantle reservoir. 相似文献
18.
The main rock-forming minerals of pyroxenites in the Krestovskaya intrusion in the Maimecha-Kotui alkaline-ultramafic province are Al- and Ti-fassaite and low-Al high-Mg diopside. Both clinopyroxene varieties bear primary inclusions of alkaline-ultramafic melts enriched in incompatible elements, F (up to 0.3–0.4 wt %), and probably also CO2. The homogenization temperatures of the inclusions are approximately equal and lie within the range of 1200–1300° C. However, the melts preserved in the diopside are undersaturated in Si and Al and richer in Fe, Ba, Sr, Na, and incompatible elements than melt inclusions in the fassaite; they are free in H2O (no more than 0.003 wt %); and are close in composition to katungite-mafurite. Melt inclusions in the fassaite are richer in Si, Mg, and Al; contain up to 0.435 wt % H2O; and compositionally approach alkaline picritoids. Melts of such composition cannot be produced by the differentiation of a single parental magma and were most probably derived from different mantle sources. Judging from the high concentrations of incompatible elements and their distribution in the melt inclusions, these sources were localized in the undepleted mantle at various depths (the picritoid melts were derived from a deeper source) and underwent different degrees of partial melting, with garnet and plagioclase remaining in the residue. The coexistence of diopside and fassaite in a single rock can be explained by the concurrent development of magmatic chambers at different depths during rifting, when this process was repeatedly reactivated and it facilitated the arrival of primitive melts derived from different mantle sources into the same magmatic chambers, in which these melts mixed and evolved. These processes probably predetermined the origin of the alkaline-ultramafic carbonatite intrusions and perhaps also the potassic series in the East African Rift. 相似文献
19.
He Sun Yilin Xiao Yongjun Gao Jianqing Lai Zhenhui Hou Yangyang Wang 《Contributions to Mineralogy and Petrology》2013,165(5):885-901
Melt inclusions and fluid inclusions in the Fangcheng basalt were investigated to understand the magma evolution and fluid/melt-peridotite interaction. Primary silicate melt inclusions were trapped in clinopyroxene and orthopyroxene phenocrysts in the Fangcheng basalt. Three types of melt inclusions (silicate, carbonate, and sulfide) coexisting with fluid inclusions occur in clinopyroxene xenocrysts and clinopyroxene in clinopyroxenite xenoliths. In situ laser-ablation ICP-MS analyses of major and trace element compositions on individual melt inclusions suggest that the silicate melt inclusions in clinopyroxene and orthopyroxene phenocrysts were trapped from the same basaltic magma. The decoupling of major and trace elements in the melt inclusions indicates that the magma evolution was controlled by melt crystallization and contamination from entrapped ultramafic xenoliths. Trace element patterns of melt inclusions are similar to those of the average crust of North China Craton and Yangtze Craton, suggesting a considerable crustal contribution to the magma source. Calculated parental melt of the Fangcheng basalt has features of low MgO (5.96 wt%), high Al2O3 (16.81 wt%), Sr (1,670 ppm), Y (>35 ppm), and high Sr/Y (>40), implying that subducted crustal material was involved in the genesis of the Fangcheng basalt. The coexisting fluid and melt inclusions in clinopyroxene xenocrysts and in clinopyroxene of xenoliths record a rare melt-peridotite reaction, that is olivine + carbonatitic melt1 (rich in Ca) = clinopyroxene + melt2 ± CO2. The produced melt2 is enriched in LREE and CO2 and may fertilize the mantle significantly, which we consider to be the cause for the rapid replacement of lithospheric mantle during the Mesozoic in the region. 相似文献
20.
Carbon Enrichment in the Lithospheric Mantle: Evidence from the Melt Inclusions in Mantle Xenoliths from the Hainan Basalts 
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下载免费PDF全文 It is generally believed that the lithospheric mantle and the mantle transition zone are important carbon reservoirs. However, the location of carbon storage in Earth’s interior and the reasons for carbon enrichment remain unclear. In this study, we report CO2-rich olivine-hosted melt inclusions in the mantle xenoliths of late Cenozoic basalts from the Penglai area, Hainan Province, which may shed some light on the carbon enrichment process in the lithospheric mantle. We also present ... 相似文献