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1.
一种改进的简单的估算原始岩浆的方法 总被引：2，自引：0，他引：2
利用橄榄石和熔浆的Fe—Mg分配系数,制作了MgO—FeO演化图解。根据MgO—FeO体系中Fo橄榄石的Fo值:Fo=n(Mg)÷n(Mg)+n(Fen(Mg)/n(Mg)+n(Fe))等值线与Fe—Mg演化曲线交点确定原始岩浆成分。该图解优点在于可以更简单、直观地判别原始岩浆成分,适用于橄榄石分离结晶体系。同时介绍了该图解的使用方法,并以峨眉山大火成岩省丽江地区的大具与仕满两个剖面的苦橄岩为例,说明如何应用该图解来恢复原始岩浆以及解释岩石的成因。研究结果表明,仕满地区原始岩浆MgO、FeO含量分别为23.5%和12.8%,部分熔融程度较高,SM-14和SM-15是由仕满原始岩浆经过轻度橄榄石分离结晶形成的,基本可以代表原始岩浆成分。大具地区原始岩浆可分为两类,一类部分熔融程度较低,MgO、FeO含量分别为19.8%和11.3%;另一类部分熔融程度较高,MgO、FeO含量分别为23%和13.3%,与仕满原始岩浆成分类似。大具地区的岩石样品成分均不能代表该地区的原始岩浆成分,而是经历了明显的橄榄石分离结晶作用。另外,峨眉山大火成岩省中绝大多数的玄武岩中CaO含量不符合橄榄石分离结晶关系,并且MgO含量一般都低于8%,以及岩石中普遍出现单斜辉石和斜长石矿物等都表明这些玄武岩不可能由地幔部分熔融形成的原始岩浆直接通过橄榄石分离结晶作用形成。 相似文献
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峨眉山大火成岩省西部苦橄岩及其共生玄武岩的地球化学：地幔柱头部熔融的证据 总被引：12，自引：12，他引：12
丽江地区的苦橄岩位于峨眉山大火成岩省的西部，其与辉斑玄武岩、无斑玄武岩和玄武质火山碎屑岩共生。苦橄岩中的斑晶主要为富镁橄榄石，其F0含量最高达91．6％，CaO含量最高达0．42％，其内含有少量玻璃包裹体，指示了橄榄石是在熔体中结晶形成的。苦橄岩中的铬尖晶石具有高的Cr#值（73-75）。计算的初始岩浆的MgO含量大约为22wt％，初始熔融的温度为1630-1680℃。研究结果表明，玄武质岩石是苦橄质岩浆通过橄榄石和单斜辉石分离结晶形成的。苦橄岩和玄武岩的Nd-Sr-Pb同位素比值差别不大，只落在一个很小的范围内（如εNd（t）=-1．3 to＋4．0）。高的εNd（t）值以及抗蚀变不相容元素的原始地幔标准化图解与洋岛玄武岩相似，并且其重稀土元素特征指示了源区有石榴子石的残余，而且是低部分熔融的产物。同位素比值与抗蚀变不相容元素比值（如Nb／La）的相关性表明，岩浆形成过程中有少量的大陆地壳物质或者相对低εNd（t）组分的大陆岩石圈地幔的混染。因此，总体上，苦橄岩的地球化学特征的研究结果支持了峨眉山大火成岩省是地幔柱头部熔融的成因模型。 相似文献
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橄榄石是基性岩浆中最早期结晶的硅酸盐矿物之一,其主量、微量元素特征可以反映出岩浆演化环境、岩浆源区岩性和再循环组分性质等重要信息.本次研究通过对峨眉山大火成岩省平川苦橄岩中橄榄石主量和微量元素分析,以及橄榄石内尖晶石包裹体分析,并与大理苦橄岩中橄榄石和尖晶石成分进行对比,来探讨不同苦橄岩母岩浆氧逸度及源区性质的异同.橄... 相似文献
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近几年来对西伯利亚、哥伦比亚河、塔里木等大火成岩省原始岩浆水含量的分析表明,其源区的显著水化是造成地
幔熔融异常的重要原因之一。峨眉山大火成岩省是全球二叠纪大火成岩省的重要组成之一,前期对其位于宾川剖面底部的
大理苦橄岩水含量的分析表明地幔的水化在峨眉山大火成岩省形成中起到了重要作用。然而大理苦橄岩只能代表峨眉山大
火成岩省初始阶段的熔融条件,而在其后的喷发历史中水是否也起到了关键作用还不清楚。定量分析后阶段喷发的苦橄岩
水含量有助于更完整评估水在大火成岩省形成中的作用。本文报道了位于峨眉山大火成岩省西部岩带宾川剖面中上部的宾
川苦橄岩的水含量,结果表明原始岩浆水含量可高达2.8 wt%,比大理苦橄岩的水含量略低,但仍显著高于MORB 和OIB,
达到了岛弧玄武岩的水含量范围。这表明水对整个大火成岩省的形成中都扮演了重要角色。 相似文献
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峨眉山大火成岩省“高钛玄武岩”和“低钛玄武岩”成因探讨 总被引：16，自引：0，他引：16
大量的岩石化学资料分析表明，峨眉山大火成岩省玄武岩的TiO2含量是连续变化的，不存在明显的间断。野外地质特征表明高钛和低钛玄武岩既不存在空间分带，也不存在时间分带。其Sr、Nd和Pb同位素组成也没有明显的区别，推测它们可能是同源岩浆分离结晶的产物。根据MgO和TiO2的相关关系，可将苦橄岩和玄武岩的演化划分为4个趋势，并采用分离结晶模式对其进行了成因模拟，表明高钛和低钛玄武岩是同—母岩浆(苦橄—玄武岩浆)通过不同矿物相分离结晶的产物。 相似文献
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本文以微量元素地球化学观点探讨四川米易白马层状岩体辉长岩及碱性粗面—碱性正长岩的成因。形成岩体的岩浆与峨眉山玄武岩同源。母岩浆分离结晶时,结晶相演化路线为:橄榄岩橄长岩 辉长岩 正长岩;岩浆演化路径为;橄榄玄武岩浆(类似Olivine basali) 中长玄武岩浆(类似Hawaiite) 更长玄武岩浆(类似Mugearite)碱性(纳质)粗面、正长岩浆,最终向粗面岩岩浆趋势演化。文中对辉长岩和粗面—正长岩微量元素、稀土元素数据进行分析、作图,提出形成辉长岩浆主要是峨眉山玄武岩母岩浆的第三代残余岩浆,即更长玄武岩浆;而粗面—正长岩浆是堆积型辉长岩结晶后所留下的残余岩浆,也是整个峨眉山玄武岩浆分离结晶的终点。 相似文献
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近年来对太古宙科马提岩和显生宙大火成岩省中苦橄岩的水含量、地幔潜热、源区成分等研究表明，这些短时间内喷出巨量岩浆的地表过程都与水化的地幔柱有关。峨眉山大火成岩省位于扬子板块西部，是我国被公认的大火成岩省之一。前人从地球化学的角度将其分为西、中、东三区；并通过对西区丽江、永胜、宾川、大理苦橄岩和中区二滩玄武岩的水含量分析，发现形成峨眉山大火成岩省的地幔柱可能自喷发初期就已普遍存在强烈的水化，且该特征持续至喷发中晚期。然而前人的研究着重于苦橄岩，对作为大火成岩省主体部分的玄武岩研究甚少。本文以位于西区的仕满、大具剖面中的高Ti/Y玄武岩为研究对象，采用单斜辉石斑晶反演原始熔体水含量的方法，得到仕满、大具玄武岩原始熔体的水含量下限分别为1. 15%和0. 83%，该水含量略低于丽江苦橄岩水含量。而计算出的源区最低水含量分别为1380×10 -6和1245×10 -6，与二滩玄武岩相当。结合前人报道的数据，本次工作的结果证明了峨眉山大火成岩省的地幔柱水化现象普遍且长期存在，地幔柱内部的热化学组成是不均一的，且其热化学结构是随着时间而发生变化的。本次工作还暗示了峨眉山大火成岩省地幔柱内部的水含量可能是由轴部南端向轴部北端，由轴部向边缘呈放射状递减的，这对于进一步认识大火成岩省的形成过程有一定的启示。 相似文献
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峨眉山大火成岩省中发现二叠纪苦橄质熔岩 总被引：21，自引：0，他引：21
峨眉山大火成岩省是当前研究的热点,尽管早有报道在峨眉山大火成岩省中存在苦橄岩,但是是否存在真正的二叠纪苦橄质熔岩一直有争论,笔者等对前人报道的“苦橄岩”产地进行了详细的野外地质调查发现,前人报道的所谓“苦橄岩”,不是喷出的熔岩,而是呈侵入状态的苦橄玢岩。这些呈侵入状态的苦橄玢岩在区内分布较多,约有数十个,出露面积一般为50×100～200×700m~2。最大可达8km~2。这些苦橄玢岩除了侵入于峨眉山玄武岩外,部分还侵入于上三叠统白云质灰岩中。由此推测部分苦橄玢岩应晚于晚三叠世。尽管目前还没有可靠的同位素年龄数据,但根据区域对比,一般认为这些苦橄玢岩形成于喜马拉雅期,与峨眉山玄武岩系无关。需要指出的是,在这些报道所谓“苦橄岩”的论文中均没 相似文献
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近期对科马提岩以及许多大火成岩省中的苦橄岩进行的水含量分析以及地幔潜能温度的研究表明,无论是太古宙还是显生宙的大火成岩省的形成都和含水的地幔柱有关。晚二叠纪的峨眉山大火成岩省（ELIP）位于扬子克拉通西缘,目前主流观点认为其是由地幔柱形成的。前人根据大量的岩石地球化学工作将ELIP分为西区、中区和东区;证明了位于西区的大理、宾川的苦橄岩和玄武岩地幔源区的水含量高于2500×10-6。然而对于其他区域玄武岩源区的含水性还不清楚。文章以位于中区的二滩剖面底部高钛型玄武岩为研究对象,采用单斜辉石斑晶反演的方法研究恢复了其原始岩浆的水含量。结果表明,单斜辉石斑晶水含量范围为76×10-6 ~424×10-6, 对应的平衡熔体水含量为3.01 wt%。在考虑分离结晶影响后,恢复的原始岩浆水含量达到2.71±0.95 wt%。该水含量略低于大理苦橄岩水含量,与宾川苦橄岩相当。而计算的地幔源区水含量最低估计为1357×10-6,该值低于大理、宾川苦橄岩的源区水含量,但仍显著高于正常洋中脊玄武岩和洋岛玄武岩源区。ELIP中不同区域的苦橄岩和玄武岩都存在高水含量,这表明在ELIP的形成和演化过程中水都扮演了很重要的角色。 相似文献
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There are two types of temporally and spatially associated intrusions within the Emeishan large igneous province (LIP); namely, small uitramafic subvolcanic sills that host magmatic Cu-Ni-Platinum Group Element (PGE)-bearing sulfide deposits and large mafic layered intrusions that host giant Ti-V magnetite deposits in the Panxi region. However, except for their coeval ages, the genetic relations between the ore-bearing intrusions and extrusive rocks are poorly understood. Phase equilibria analysis (Q-PI-OI-Opx-Cpx system) has been carried out to elucidate whether ore-bearing Panzhihua, Xinjie and Limahe intrusions are co-magmatic with the picrites and flood basalts (including high-Ti, low-Ti and alkali basalts), respectively. In this system, the parental magma can be classified as silica-undersaturated olivine basalt and silica-saturated tholeiite. The equivalents of the parental magma of the Xinjie and Limahe peridotites and picrites and iow-Ti basalts are silica-undersaturated, whereas the Limahe gabbro-diorites and high-Ti basalts are silica-saturated. In contrast, the Panzhihua intrusion appears to be alkali character. Phase equilibria relations clearly show that the magmas that formed the Panzhihua intrusion and high-Ti basalts cannot be co-magmatic as there is no way to derive one liquid from another by fractional crystallization. On the other hand, the Panzhihua intrusion appears to be related to Permian alkali intrusions in the region, but does not appear to be related to the alkali basalts recognized in the Longzhoushan lava stratigraphy. Comparably, the Limabe intrusion appears to be a genetic relation to the picrites, whereas the Xinjie intrusion may be genetically related to be low-Ti basaits. Additionally, the gabbro-diorites and peridotites of the Limahe intrusion are not co-magmatic, and the former appears to be derived liquid from high-Ti basalts. 相似文献
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全球岛弧火山岩的铂族元素数据非常少。本研究对新疆阿尔泰山南缘中泥盆世北塔山组地层中的苦橄岩的铂族元素进行了分析,结果表明:其铂族元素的含量总体变化不大,其原始地幔标准化曲线总体上和已经报道的大西洋Lesser Antilles岛弧的G renada苦橄岩相似,均以富集钯组铂族元素(PPGE)为特征,但总体含量比后者高,而比大火成岩省的苦橄岩低。一些铂族元素的特征比值指示了苦橄岩和富辉玄武岩起源于软流圈地幔,而高的w(Os)/w(Ir)比值则暗示了源区中有深海沉积物的加入。w(Pd)/w(Ir)-w(N i)/w(Cu)图解说明本区的苦橄岩不是原始岩浆,而是原始的高镁玄武岩中有过剩橄榄石的加入,而w(Pd)-w(Cu)图解则说明原始岩浆硫不饱和。IPGE在俯冲带流体中相对稳定,而PPGE在俯冲带流体中的活动性相对较高。 相似文献
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There are two types of temporally and spatially associated intrusions within the Emeishan large igneous province (LIP); namely, small ultramafic subvolcanic sills that host magmatic Cu-Ni-Platinum Group Element (PGE)-bearing sulfide deposits and large mafic layered intrusions that host giant Ti-V magnetite deposits in the Panxi region. However, except for their coeval ages, the genetic relations between the ore-bearing intrusions and extrusive rocks are poorly understood. Phase equilibria analysis (Q-Pl-Ol-Opx-Cpx system) has been carried out to elucidate whether ore-bearing Panzhihua, Xinjie and Limahe intrusions are co-magmatic with the picrites and flood basalts (including high-Ti, low-Ti and alkali basalts), respectively. In this system, the parental magma can be classified as silica-undersaturated olivine basalt and silica-saturated tholeiite. The equivalents of the parental magma of the Xinjie and Limahe peridotites and picrites and low-Ti basalts are silica-undersaturated, whereas the Limahe gabbro-diorites and high-Ti basalts are silica-saturated. In contrast, the Panzhihua intrusion appears to be alkali character. Phase equilibria relations clearly show that the magmas that formed the Panzhihua intrusion and high-Ti basalts cannot be co-magmatic as there is no way to derive one liquid from another by fractional crystallization. On the other hand, the Panzhihua intrusion appears to be related to Permian alkali intrusions in the region, but does not appear to be related to the alkali basalts recognized in the Longzhoushan lava stratigraphy. Comparably, the Limahe intrusion appears to be a genetic relation to the picrites, whereas the Xinjie intrusion may be genetically related to be low-Ti basalts. Additionally, the gabbro-diorites and peridotites of the Limahe intrusion are not co-magmatic, and the former appears to be derived liquid from high-Ti basalts. 相似文献
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峨眉山大火成岩省在形成后遭受了强烈的风化剥蚀，与右江盆地构成了独特的源- 汇沉积体系，相关的碎屑沉积记录是重建峨眉山大火成岩省晚期火山序列、揭示大火成岩省岩浆演化的关键。本文对黔西南地区右江盆地北缘下三叠统下部飞仙关组开展了详细的沉积物源研究。飞仙关组泥岩由长石、石英和黏矿物等组成，具有低SiO2、高TiO2含量和低Al2O3/TiO2值的特征，具Eu的弱负异常，微弱的Nb、Ta负异常。基于Al2O3/TiO2和La/Sm物源图解分析，研究样品的主要物源由峨眉山大火成岩省的高- Ti玄武岩和少量酸性火山岩构成，这与右江盆地晚二叠世的碎屑沉积物源组成一致。碎屑锆石具有～260 Ma 的年龄峰值，对应锆石具有较低的Th/Nb和较高的Nb/Hf值，均支持峨眉山大火成岩省作为主要的沉积物源区，而同时存在的>400 Ma的碎屑锆石则对应于峨眉山玄武质岩浆上升时所捕获的华南地壳物质。与上二叠统的碎屑锆石U- Pb年龄组成和锆石化学组成对比分析表明，峨眉山大火成岩省在晚二叠世到早三叠世早期剥蚀的火山岩构成了一定的火山序列，反映了该大火成岩省晚期从强烈地壳混染到分异结晶为主的岩浆演化过程。 相似文献
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R. H. Sutcliffe 《Contributions to Mineralogy and Petrology》1987,96(2):201-211
Mafic rocks at Lake Nipigon provide a record of rift-related continental basaltic magmatism during the Keweenawan event at 1109 Ma. The mafic rocks consist of an early, volumetrically minor suite of picritic intrusions varying in composition from olivine gabbro to peridotite and a later suite of tholeiitic diabase dikes, sheets and sills. The diabase occurs primarily as two 150 to 200 m thick sills with a textural stratigraphy indicating that the sills represent single cooling units. Compositional variation in the sills indicates that they crystallized from several magma pulses.The diabases are similar in chemistry to olivine tholeiite flood basalts of the adjacent Keweenawan rift, particularly with respect to low TiO2, K2O and P2O5. The picrites have higher TiO2, K2O and P2O5 than the diabases and are similar to, but more primitive than, high Fe-Ti basalts which erupted early in the Keweenawan volcanic sequence.All of the rocks crystallized from fractionated liquids. The picrites are cumulate rocks derived at shallow crustal depths from a magma controlled predominantly by olivine fractionation. Picritic chills are in equilibrium with olivine phenocrysts of composition Fo80 and are interpreted to represent the least evolved liquids observed. The parental magma of the picrites was probably Fe rich relative to the parental magma of the diabase. The diabase sills crystallized from an evolved basaltic liquid controlled by cotectic crystallization of plagioclase and lesser olivine and pyroxene.The emplacement of dense olivine phyric picritic magmas early in the sequence, followed by later voluminous compositionally evolved magmas of lower density suggests the development of a crustal density filter effect as the igneous event reached a peak. Delamination of the crust-mantle interface may have resulted in the transition from olivine controlled primitive magma to fractionated magma through the development of crustal underplating. 相似文献
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Ying Xia Di‐Cheng Zhu Qing Wang Zhi‐Dan Zhao Dong Liu Li‐Quan Wang Xuan‐Xue Mo 《地学学报》2014,26(6):487-494
Picritic porphyrites and associated basalts are found in Lower Cretaceous slates within the recently identified remnant Comei Large Igneous Province, SE Tibet. They provide an opportunity to explore the mantle potential temperature of this large igneous province and the genetic correlation between the picritic porphyrites and associated basalts. The high levels of MgO and CaO in olivine phenocrysts from the picritic porphyrites indicate that these olivines crystallized from high‐Mg magmas. By deducting the accumulated olivines, we determined a parental magma MgO content for the picritic porphyrites of c. 20% MgO, corresponding to a mantle potential temperature of >1550 °C for the parental magma. Such a high temperature provides solid evidence for a mantle‐plume origin of the remnant Comei Large Igneous Province. Parallel trace‐element patterns and similar εNd (T) and (177Os/178Os)T values in the picritic porphyrites and associated basalts suggest a common hot mantle source region for their generation. 相似文献