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1.
滇中昆阳群火成碳酸岩的发现及其意义 总被引：3，自引：0，他引：3
在武定西矿带发现的已大理岩化的滇中昆阳群（Pt2k)火成碳酸岩富含钠长石、更长石、金云母、黑云母等硅酸盐矿物，发育火成结构构造，如斑状结构、隐晶结构，流纹构造、带状构造、气孔、杏仁构造等，与沉积围岩相比，岩石高Si、Al、Fe、Mg、Mn、P，富K2O Na2O，低钙，轻稀土富集，富含Nb、Zr、Hr、U、Th、Sr、Ba、稀土等不相容元素，与粗面质、粗安质等碱性硅酸盐岩共生。（铁）白云石（＞５０％）内，含有粗面南、碳酸质熔融包裹体；流体包裹体均一温度可达４５０℃以上。其发现证明滇中元古代曾有碳酸质岩浆活动。 相似文献
2.
《矿物岩石地球化学通报》2020,(1)
为探讨山东蒙阴金伯利岩的成因及其岩浆演化过程,采用SEM、EPMA和LA-ICP-MS对该区金伯利岩中金云母的微组构进行了分析研究。结果表明,该区岩浆成因金云母主要呈斑晶、显微斑晶和基质云母产出。根据主量元素(Al、Fe和Mg~#)特征将金云母分为原生金伯利岩金云母组、金云母-钡镁脆云母组、金云母-四配位铁金云母组和金云母-黑云母共生组。早期金云母结晶后,在岩浆上升过程中受源条件或矿物相在熔体中再吸收的影响,向II型基质云母、四配位铁金云母、钡镁脆云母演化。晚期通过岩浆改造或与围岩的交代变质作用形成金云母-黑云母巨晶共生组。综上认为,蒙阴金伯利岩岩浆成分受到了多种改造,其演化过程是相当复杂的。 相似文献
3.
巴楚瓦吉尔塔格金伯利岩中金云母可划分为斑晶和基质两个世代。测试结果表明,本区金云母Mg·100/Mg+(Fe)低,斑晶金云母该值变动范围大,为80.2—85.3;基质金云母该值集中在82.2—84.7,个别达91.4。斑晶往往具环带,边部较核部相对富镁低铁,表明其结晶历史漫长,而基质见不到环带,成分上较富镁,代表岩浆结晶晚期快速冷凝的产物。此外,本区金云母Al_2O_3高,为10.53—16.14％;TiO_2较高,为1.43—3.47％。据目前对金云母的研究成果,认为本区金伯利岩中金云母形成于温度较高、氧逸度偏大而压力较低的环境。 相似文献
4.
巴楚瓦吉尔塔格金伯利岩中金云母可划分为斑晶和基质两个世代。测试结果表明,本区金云母Mg·100/Mg+(Fe)低,斑晶金云母该值变动范围大,为80.2-85.3;基质金云母该值集中在82.2-84.7,个别达91.4。斑晶往往具环带,边部较核部相对富镁低铁,表明其结晶历史漫长,而基质见不到环带,成分上较富镁,代表岩浆结晶晚期快速冷凝的产物。此外,本区金云母Al_2O_3高,为10.53-16.14％;TiO_2较高,为1.43-3.47％。据目前对金云母的研究成果,认为本区金伯利岩中金云母形成于温度较高、氧逸度偏大而压力较低的环境。 相似文献
5.
岩浆(型)碳酸岩研究进展 总被引：19，自引：0，他引：19
主要从岩石学，矿物学，岩石分类，C，O，Sr同位素，碳酸岩与矿化的关系等各方面对（碱性）碳酸岩的研究进行了较为全面的总结，并结合近20年来实验岩石等，流体包裹体研究，CO2^- H2O－NaCl流体体系的性质的研究，对碳酸岩岩浆的来源及成因，岩浆－热液的演化进行了分析和探讨，碳酸岩形成至少经历了三个阶段，即岩浆阶段，岩浆期后阶段（气相碳酸岩／岩浆热液阶段），交代碳酸岩阶段，而作为与碳酸岩在空间和成因上有密切联系的基性，超基性岩，碱性岩杂岩体，则经历了碳酸岩成岩阶段以前的岩浆不混熔作用，结晶分异作用，岩浆结晶作用以及碳酸岩形成之后的围岩蚀变（霓长岩化）作用。 相似文献
6.
《地学前缘》2017,(5):265-282
西藏冈底斯成矿带拉抗俄斑岩铜钼矿床位于西藏特提斯构造域拉萨地块东段中南部。拉抗俄斑岩铜钼矿床黑云母分为岩浆黑云母和热液黑云母。岩浆黑云母和绢英岩化带的热液黑云母属于镁质黑云母,钾化带的热液黑云母属于镁质黑云母和金云母,具有富镁的特征,是斑岩铜多金属矿床的一个典型特征。成矿岩体花岗闪长斑岩,属于造山带钙碱性岩系,具壳幔混源的成因特点,并且其黑云母与角闪石共生。与钾化带和绢英岩化带的热液黑云母相比,岩浆黑云母具有较高的BaO和TiO2含量。与岩浆黑云母和绢英岩化带热液黑云母相比,钾化带热液黑云母具高Si和Mg(XMg),低Fe;而绢英岩化带的热液黑云母又比岩浆黑云母较高Mg(XMg)。岩浆黑云母温度为706~746℃,平均值725℃;钾化带热液黑云母温度为396~453℃,平均值422℃;绢英岩化带热液黑云母278~372℃,平均值331℃。拉抗俄矿床黑云母氧逸度较高,均为NNO,有利于铜钼矿化形成;从岩浆黑云母到钾化带热液黑云母氧逸度升高,有利于铜钼成矿物质的运移,而从钾化带热液黑云母到绢英岩化带热液黑云母氧逸度降低,温度和氧逸度的变化可能是铜钼沉淀的一个原因。岩浆黑云母和绢英岩化带热液黑云母遵循"F-Fe avoidance"结晶化学规则,而钾化带热液黑云母F与XMg不遵循"F-Fe avoidance"结晶化学规则。岩浆黑云母、钾化带和绢英岩化带热液黑云母Cl与XMg均不遵循"Mg-Cl avoidance"结晶化学规则。黑云母化学成分记录了岩浆结晶过程中流体成分的变化。从岩浆黑云母到钾化带热液黑云母,再到绢英岩化热液黑云母,Ⅳ(F)和Ⅳ(F/Cl)逐渐减小,Ⅳ(Cl)逐渐增大。岩浆向热液演化过程中,F和Cl含量不断增加。岩浆-成矿热液F和Cl的含量的变化,对成矿物质运移和沉淀具有重要的作用。从岩浆黑云母到钾化带热液黑云母,再到绢英岩化带热液黑云母,lg(fHF/fHCl)逐渐减小,lg(fH2O/fHCl)和lg(fH2O/fHF)逐渐增大。岩浆熔体和热液流体存在很大差别;并且绢英岩化热液流体与钾化热液流体也不同,黑云母卤素化学也不代表一种单一的流体;绢英岩化热液流体混合大气水。本文研究结果显示,黑云母化学成分可以反映岩浆的性质和化学成分以及结晶过程中的物理化学条件。 相似文献
7.
云南老王寨金矿区煌斑岩中云母的矿物化学 总被引：2，自引：4，他引：2
云南老王寨金矿区煌斑岩中呈斑晶和基质产出的云母以金云母为主，少量富镁黑云母，环带结构发育。矿物化学表明本区云母的寄主岩石属碱性岩系列，岩石类型为钙碱性煌斑岩；同时提供了煌斑岩源于交代富集地幔和受地壳物质混染程度低等成因信息。云母多种多样的环带结构暗示其寄主的煌斑岩具复杂的岩浆结晶演化过程。 相似文献
8.
青海纳日贡玛斑岩钼(铜)矿含矿斑岩矿物学特征及成岩成矿意义 总被引：4，自引：0，他引：4
本文侧重于矿物学特征分析对纳日贡玛赋矿斑岩进行了研究,结果表明:斑岩中黑云母斑晶种属为含铁金云母和富镁黑云母,角闪石种属为镁角闪石、透闪石与阳起石。纳日贡玛含矿斑岩属于I型花岗岩类,由幔源岩浆同熔壳源物质而形成;斑岩结晶压力值为1.18×108～1.39×108Pa;闪长玢岩和黑云母花岗斑岩的结晶温度为550℃～650℃,而浅色花岗斑岩则下降为500℃～550℃。斑岩中黑云母的Mg/Fe、Ti、Al、K、Na、Ca及F、Cl等元素含量及比值可以显示纳日贡玛具有良好的含矿性。纳日贡玛结晶压力、温度都较玉龙矿带低,反映纳日贡玛结晶岩浆房更靠近地表。纳日贡玛岩浆源区向壳源区靠近,而玉龙矿带则更靠近幔源区,表明成岩源区中壳幔物质混合比例的不同。 相似文献
9.
全球范围内出露的碳酸岩大多为钙质、镁质、铁质碳酸岩,少量为钠质和硅质碳酸岩,极少有富Sr碳酸岩的报道,其岩石成因、资源意义及对碳酸岩岩浆演化的指示意义尚不清楚。本次在四川省牦牛坪稀土矿区南部包子山稀土矿床的露天采坑中发现了超级富Sr的碳酸岩,其呈不规则的脉状侵入到构造角砾岩中。岩石呈紫色-淡紫色,微晶-斑状结构,斑晶主要为萤石,基质主要为菱锶矿、方解石、氟碳铈矿、氟碳钙铈矿、金云母、重晶石并含少量的金属硫化物和氧化物。全岩的微量元素分析表明,其稀土元素总量(∑REE)达3.5%～6.1%,Sr含量达19.0%～27.7%,已超过稀土矿床和锶矿床的工业品位要求。岩石中的中、重稀土元素含量占稀土元素总量的1.14%～1.77%,一些高价值稀土元素含量较高,如Pr(939×10~(-6)～1399×10~(-6))、Nd(2783×10~(-6)～3937×10~(-6))、Gd(237×10~(-6)～320×10~(-6)),因此除轻稀土元素外,中、重稀土和锶元素也具有重要的资源意义。岩石强烈富集REE、Sr、Ba,而明显亏损P、Nb、Ta、Zr、Hf元素,可能与岩浆演化过程中锆石和其它基性矿物的结晶分离有关。全岩的Sr-Nd同位素组成与牦牛坪、里庄稀土矿床的碳酸岩相似,表明它们为同源岩浆产物。笔者认为,富Sr的碳酸岩代表了碳酸岩岩浆演化晚期的产物,REE、Sr、Ba、F和S元素均在岩浆演化晚期的碳酸岩中高度富集。碳酸岩岩浆超浅成侵位至构造角砾岩中,并与下渗的大气水相遇导致岩浆的淬冷和微晶-斑状结构的形成。早期基性矿物(如霓辉石、黑云母)及碳酸盐矿物(如方解石、白云石等)的结晶分离是造成晚期碳酸岩中稀土元素富集的重要原因。富Sr碳酸岩中石英斑晶的发现和其较低的SiO_2含量表明碳酸岩岩浆演化晚期可能是硅饱和的,且这种岩浆具有很低的SiO_2溶解能力。以菱锶矿(体积分数 50%)为主要碳酸盐矿物的稀土碳酸岩可能代表了一种新的碳酸岩类型,明显不同于已知的钙质、镁质、铁质和钠质碳酸岩。 相似文献
10.
西藏甲玛斑岩矿床系统黑云母特征及其地质意义 总被引：5，自引：3，他引：2
甲玛矿床位于西藏冈底斯成矿带东段,是公益性研究与商业性勘查结合取得的重要成果。文章以不同产状黑云母为研究对象,采用岩、矿石光薄片显微鉴定、电子探针分析等系统研究矿区黑云母特征。黑云母的成因类型可分为原生黑云母和热液黑云母,原生黑云母和热液黑云母落于黑云母分类图中富镁黑云母和金云母区域,岩体中的黑云母偏向于富镁黑云母,具有富镁特征。与原生黑云母相比,角岩中的热液黑云母具有w(Mg O)、w(Cu O)升高,w(Fe OT)降低,Fe2+和Fe3+分异程度增大的特征;岩体中的热液黑云母w(Ti O2)小于3%,w(Al2O3)大于15%,具有低钛、高铝的特征,w(Mg O)、w(Cu O)升高,w(Fe OT)降低的特点。花岗斑岩中原生黑云母的结晶温度变化在730~750℃,logf(O2)较高(变化范围-13.0~-11.5,logf(O2)Fe2O3-Fe3O4),属于造山带钙碱性岩系,具壳幔混源的成因特点。与原生黑云母相比,角岩中热液黑云母Fe2+/(Fe2++Mg2+)比值均一程度低,且Fe3+/Fe2+比值显著升高,甚至部分热液黑云母不含Fe2+,指示岩浆-热液流体体系逐渐向氧化态过渡,有利于斑岩铜矿的形成。对于热液黑云母所在的岩矿石样品,矿化作用的强度与黑云母的Cu O呈正相关,对成矿具有一定的指示意义。 相似文献
11.
High-pressure minerals in mafic microgranular enclaves: evidences for co-mingling between lamprophyric and syenitic magmas at mantle conditions 总被引：1，自引：1，他引：0
Mafic microgranular enclaves, composed of diopside and rare magnesium biotite phenocrysts in a groundmass of diopside, biotite, apatite, Fe-Ti-oxides, and alkali feldspar, are associated with Neoproterozoic Piquiri potassic syenite in southern Brazil. Co-genetic mica and clinopyroxene cumulates present inclusions of pyrope-rich garnet in diopside phenocrysts. Textural evidence, as well as the chemical and mineralogical composition, suggest that enclaves crystallized from a lamprophyric magma and co-mingled with the host syenitic magma. The contrasting temperature between both magmas and the consequent chilling was important for the preservation of some early-crystallized minerals in the mafic magma. Diopside groundmass grains contain micro-inclusions of K-rich augite and phlogopite, and some clinopyroxene phenocrysts and elongate groundmass crystals have potassium-rich cores. The pyrope-rich garnet have high #mg number (67–68), with appreciable amounts of Na2O and K2O comparable to pyrope synthesized at 5 GPa. The extremely high K2O contents of K-rich augite micro-inclusions suggest non-equilibrium with the parental magma, whereas the other K-rich clinopyroxenes are similar to K-clinopyroxenes produced at 5–6 GPa. K-clinopyroxene and garnet in mafic microgranular enclaves suggest that lamprophyric magma started its crystallization at upper mantle conditions, and chilled clinopyroxenes with measurable amounts of K2O are taken as evidence that co-mingling began still at mantle pressures. 相似文献
12.
M.Satyanarayanan D.V.Subba Rao M.L.Renjith S.P.Singh E.V.S.S.K.Babu M.M.Korakoppa 《地学前缘(英文版)》2018,9(2):531-547
Petrographic, mineral chemical and whole-rock geochemical characteristics of two newly discovered lamproitic dykes(Dyke 1 and Dyke 2) from the Sidhi Gneissic Complex(SGC), Central India are presented here. Both these dykes have almost similar sequence of mineral-textural patterns indicative of:(1) an early cumulate forming event in a deeper magma chamber where megacrystic/large size phenocrysts of phlogopites have crystallized along with subordinate amount of olivine and clinopyroxene;(2) crystallization at shallow crustal levels promoted fine-grained phlogopite, K-feldspar, calcite and Fe-Ti oxides in the groundmass;(3) dyke emplacement related quench texture(plumose K-feldspar, acicular phlogopites) and finally(4) post emplacement autometasomatism by hydrothermal fluids which percolated as micro-veins and altered the mafic phases. Phlogopite phenocrysts often display resorption textures together with growth zoning indicating that during their crystallization equilibrium at the crystal-melt interface fluctuated multiple times probably due to incremental addition or chaotic dynamic self mixing of the lamproitic magma. Carbonate aggregates as late stage melt segregation are common in both these dykes, however their micro-xenolithic forms suggest that assimilation with a plutonic carbonatite body also played a key role in enhancing the carbonatitic nature of these dykes. Geochemically both dykes are ultrapotassic(K_2 O/Na_2 O: 3.0-9.4) with low CaO, Al_2 O_3 and Na_2 O content and high SiO_2(53.3-55.6 wt.%)and K_2 O/Al_2 O_3 ratio(0.51-0.89) characterizing them as high-silica lamproites. Inspite of these similarities, many other features indicate that both these dykes have evolved independently from two distinct magmas. In dyke 1, phlogopite composition has evolved towards the minette trend(Al-enrichment) from a differentiated parental magma having low MgO, Ni and Cr content; whereas in dyke 2, phlogopite composition shows an evolutionary affinity towards the lamproite trend(Al-depletion) and crystallized from a more primitive magma having high MgO, Ni and Cr content. Whole-rock trace-elements signatures like enriched LREE, LILE, negative Nb-Ta and positive Pb anomalies; high Rb/Sr, Th/La, Ba/Nb, and low Ba/Rb, Sm/La, Nb/U ratios in both dykes indicate that their pareintal magmas were sourced from a subduction modified garnet facies mantle containing phlogopite. From various evidences it is proposed that the petrogenesis of studied lamproitic dykes stand out to be an example for the lamproite magma which attained a carbonatitic character and undergone diverse chemical evolution in response to parental melt composition, storage at deep crustal level and autometasomatism. 相似文献
13.
Subbarayudu V. Gogineni Charles E. Melton A. A. Giardini 《Contributions to Mineralogy and Petrology》1978,66(3):251-261
Based on modal and chemical composition, the rocks of the Prairie Creek diatreme situated 4 km SSE of Murfreesboro, Pike County, Arkansas, are classified as micaceous kimberlite. The K-Ar isotopic analysis of phlogopite from this diatreme yielded an age of 106 ± 3 m.y. (Albian) which is in agreement with stratigraphic relations. Electron beam probe data on minerals from kimberlite breccia, one of the three textural types, are presented. The breccia is considered as the potential source of the diamonds that have been mined at the diatreme. It contains phenocrysts of olivine (Fo90–92) and serpentine pseudomorphs after olivine embedded in a groundmass of serpentine, minor calcite, chrome-diopside, phlogopite (Mg/Mg+Fe = 84.15%), perovskite, spinels, and pentlandite. Xenoliths of shales, sandstones, and mantle-derived ultramafic material are also present. Spinels are rich in Cr, Ti, and Fe and generally low in Al. Zoned spinels show enrichments in Ti and Fe towards their rims. A positive correlation between 100(Fe3++Ti)/(Cr+Al+Fe3++Ti) and 100 Mg/(Mg+Fe2+) ratios exists in these spinels and probably reflects an oxygen fugacity increase during magma crystallization. Occluded gases in diamonds and kimberlites corroborate the hypothesis that the parent magma of the Prairie Creek kimberlite was derived by partial melting of upper-mantle garnet lherzolite under volatile-rich conditions, primarily enriched in H2O and CO2. 相似文献
14.
A. E. Moore 《Contributions to Mineralogy and Petrology》1988,99(2):238-248
Petrographic and chemical criteria indicate that the overwhelming majority of olivines in kimberlites are probably cognate phenocrysts. The implied low volume of xenocryst olivines requires that primitive kimberlite magmas are highly ultrabasic liquids. Two chemically distinctive olivine populations are present in all of the kimberlites studied. The dominant olivine population, which includes large rounded olivines and smaller euhedral crystals, is Mg-rich relative to late-stage rim compositions. It is characterized by a range in 100 Mg/(Mg + Fe) and uniform Ni concentration, reflecting Rayleigh-type crystallization during magma evolution. The most Mg-rich of these olivines are considered to be similiar to those in the mantle source rocks. The second compositional population, generally very subordinate, though markedly more abundant in the megacrystrich Monastery kimberlite, is Fe-rich relative to rim compositions. This group of olivines crystallized from evolved liquids in equilibrium with iron-rich megacrysts, both entrained by the kimberlite magma during ascent. Differences between the chemical fields of Fe-rich olivines in Group I and Group II kimberlites point to relatively deeper derivation of the latter suite. Olivine chemistry can be used to characterize kimberlite magma sub-types, and may prove to be a useful tool for evaluating the diamond potential of kimberlites. 相似文献
15.
冀西北姚家庄存在一套晚三叠世的超镁铁岩-正长岩杂岩体,岩体内发育具有环带特征的单斜辉石。辉石的环带有两种:简单环带和复杂环带。简单环带一般为正环带,辉石核部的MgO和Cr2O3含量高,Si O2、Fe O和Na2O含量低;边部的主要氧化物含量与核部刚好相反。简单正环带可以分为两类,其中核边接触带平滑、由核到边化学成分具有渐变特征的正环带辉石可能是岩浆在分离结晶或地壳混染过程中形成。而核边接触带有熔蚀结构、由核到边化学成分突变的正环带辉石可能是早期结晶的辉石颗粒受到晚期低镁岩浆的溶蚀改造而成的。复杂环带具有核-幔-边结构,其中,核部低镁高铁、幔部高镁低铁、边部与核部相似,但其Mg#更低,这些特征暗示了岩浆混合作用的存在,形成辉石核部的母岩浆可能来自富集的岩石圈地幔,幔部高Mg#的特征指示了软流圈地幔物质的贡献,其边部低Mg#的特征则指示了地壳物质的加入。具有韵律环带的复杂辉石是在岩浆多期侵入的过程中形成的。辉石环带的组成特征表明,姚家庄杂岩体是由岩浆多期侵位形成的,后期侵入的岩浆与前期就位的岩浆不断反应,形成了具有多种不同环带特征的辉石,并最终形成了空间上由外到内依次为辉石岩、辉石正长岩和正长岩的环状杂岩体。结合前人的研究成果,推测形成姚家庄岩体的岩浆主要来源于富集的岩石圈地幔,并由少量地壳组分和软流圈物质的贡献。 相似文献
16.
Akira IMAI 《Resource Geology》2000,50(1):1-23
Abstract: The Mamut deposit of Sabah, East Malaysia, is a porphyry type Cu‐Au deposit genetically related to a quartz monzonite (“adamellite”) porphyry stock associated with upper Miocene Mount Kinabalu plutonism. The genesis of the Mamut deposit is discussed based on petrology of the intrusives in the Mount Kinabalu area combined with ore– and alteration–petrography, fluid inclusion and sulfur isotope studies. Groundmass of the adamellite porphyry at Mamut is rich in K which suggests vapor transport of alkaline elements during the mineralizing magmatic process, while the groundmass of the post‐ore “granodiorite” porphyry at Mamut contains small amounts of normative corundum suggesting depletion in alkaline elements at the root zone of the magma column. Sub‐dendritic tremolitic amphibole rims on hornblende phenocrysts in the Mamut adamellite porphyry suggest interaction between the mineralizing magma and the exsolved fluids. Occurrences of clinopyroxene microphenocrysts and pseudomor‐phic aggregates of shredded biotite and clinopyroxene after hornblende phenocrysts in the barren intrusives imply lower water fugacity and decreasing in water fugacity, respectively. Compositional gap between the core of hornblende phenocrysts and the tremolitic amphibole rims and those in the groundmass of the Mamut adamellite porphyry suggests a decrease in pressure. Higher XMg (=Mg/(Mg+Fe) atomic ratio) in the tremolitic amphibole rims in the Mamut adamellite porphyry compared to those of the barren intrusions suggests high oxygen fugacity. High halogen contents of igneous hydrous minerals such as amphiboles, biotite and apatite in the Mamut adamellite porphyry suggest the existence of highly saline fluids during the intrusion and solidification of the mineralizing magma. Fluid inclusions found in quartz veinlet stockworks are characterized by abundant hypersaline polyphase inclusions associated with subordinate amounts of immiscible gaseous vapor. Both Cu and Au are dispersed in disseminated and quartz stockwork ores. Chalcopyrite and pyrrhotite as well as magnetite are the principal ore minerals in the biotitized disseminated ores. Primary assemblage of intermediate solid solution (iss) and pyrrhotite converted to the present assemblage of chalcopyrite and pyrrhotite during cooling. Subsequent to biotitization, quartz veinlet stockworks formed associated with retrograde chlorite alteration. The Cu‐Fe sul–fides associated with stockwork quartz veinlet are chalcopyrite and pyrite. Overlapping Pb and Zn and subsequent Sb mineralizations were spatially controlled by NNE‐trending fractures accompanying the phyllic and advanced argillic alteration envelope. Sulfur isotopic composition of ore sulfides are homogeneous (about +2%) throughout the mineralization stages. These are identical to those of the magmatic sulfides of Mount Kinabalu adamellitic rocks. 相似文献
17.
对西秦岭礼县新生代钾霞橄黄长岩系中的基质相含钛透辉石进行了矿物化学研究，根据透辉石中Ti和Al的含量划分出低Ti—透辉石和高Ti—铝透辉石两种基本类型，它们作为同源岩浆演化结晶的产物，结晶顺序前者先于后者。火山岩系的透辉石[Ca(Mg，Fe)Si2O6]结晶过程中广泛存在着CaTiAl2O6(钛辉石)分子替代，晚期熔体富Ti、Al贫Si、Mg。百草山岩筒是演化岩浆结晶的产物，熔体向富Ti、Al、Fe^3 、Na，贫Mg、Si趋势演化；在透辉石成分上表现为CaTiAl2O6和NaFe^3 Si2O6(锥辉石)端元分子对Ca(Mg，Fe)Si2O6的替代。本地区基质相透辉石与世界上典型地区的钾霞橄黄长岩系的透辉石具有不同程度的可比性，反映了这种特殊的岩浆熔体成分在一定程度上控制着透辉石的结晶过程和阳离子在矿物晶格中的占位。 相似文献
18.
冲绳海槽玄武岩中单斜辉石的特征及其意义 总被引：2，自引：0，他引：2
冲绳海槽海底玄武岩中存在着三种不同世代的单斜辉石,即斑晶,微晶和基质辉石,它们的平均粒径分别约为400μm,30μm和5μm。斑晶辉石在电子探针下可见到明显的核部与边部之分;微晶辉石无明显的环带构造;基质辉石粒径细小但数量较大。这三个世代的辉石在成分上差异较为明显,从斑晶辉石的核部→边部和微晶辉石→基质辉石,成分从富铁向富镁,钙方向演化,这与封闭体系的辉石成分演化趋势正好相反,辉石的形态和成分特征反映出该玄武岩浆存在岩浆混合的特征,它们也可反演该地幔岩浆的活动过程;源自上地幔的拉斑玄武岩浆,在从源区向浅部岩浆房上升,运移过程中,受到携带相对富铁单斜辉石的较酸性岩浆的注入,混合;在浅部岩浆房中,混合岩浆结晶形成斑晶的边部和微晶辉石;基质辉石则是岩浆喷出洋底后淬冷结晶的结果,冲 槽玄武岩中三个世代的单斜辉石较好的完整记录了地幔岩浆后系列活动过程。 相似文献
19.
Pre-eruption history of phyric basalts from DSDP legs 45 and 46: Evidence from morphology and zoning patterns in plagioclase 总被引：3，自引：0，他引：3
Phyric basalts recovered from DSDP Legs 45 and 46 contain abundant plagioclase phenocrysts which occur as either discrete single grains (megacrysts) or aggregates (glomerocrysts) and which are too abundant and too anorthitic to have crystallized from a liquid with the observed bulk rock composition. Almost all the plagioclase crystals are complexly zoned. In most cases two abrupt and relatively large compositional changes associated with continuous internal morphologic boundaries divide the plagioclase crystals into three parts: core, mantle and rim. The cores exhibit two major types of morphology: tabular, with a euhedral to slightly rounded outline; or a skeletal inner core wrapped by a slightly rounded homogeneous outer core. The mantle region is characterized by a zoning pattern composed of one to several spikes/plateaus superimposed on a gently zoned base line, with one large plateau always at the outside of the mantle, and by, in most cases, a rounded internal morphology. The inner rim is typically oscillatory zoned. The width of the outer rim can be correlated with the position of the individual crystal in the basalt pillow. The presence of a skeletal inner core and the concentration of glass inclusions in low-An zones in the mantle region suggest that the liquid in which these parts of the crystals were growing was undercooled some amount. The resorption features at the outer margins of low-An zones indicate superheating of the liquid with respect to the crystal.It is proposed that the plagioclase cores formed during injection of primitive magma into a previously existing magma chamber, that the mantle formed during mixing of a partially mixed magma and the remaining magma already in the chamber, and that the inner rim formed when the mixed magma was in a sheeted dike system. The large plateau at the outside of the mantle may have formed during the injection of the next batch of primitive magma into the main chamber, which may trigger an eruption. This model is consistent with fluid dynamic calculations and geochemically based magma mixing models, and is suggested to be the major mechanism for generating the disequilibrium conditions in the magma. 相似文献
20.
A.V.Kargin L.V.Sazonova A.A.Nosova N.M.Lebedeva Yu.A.Kostitsyn E.V.Kovalchuk V.V.Tretyachenko Ya.S.Tikhomirova 《地学前缘(英文版)》2019,10(5):1941-1959
We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths(garnet peridotite,eclogite and clinopyroxene-phlogopite rocks)and for megacryst,macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle(SCLM)and the origin of phlogopite in kimberlite.Based on the analysed xenoliths,phlogopite is characterized by several generations.The first generation(Phil)occurs as coarse,discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene-phlogopite xenoliths.The second phlogopite generation(Phl2)occurs as rims and outer zones that surround the Phil grains and as fine flakes within kimberlite-related veinlets filled with carbonate,serpentine,chlorite and spinel.In garnet peridotite xenoliths,phlogopite occurs as overgrowths surrounding garnet porphyroblasts,within which phlogopite is associated with Cr-spinel and minor carbonate.In eclogite xenoliths,phlogopite occasionally associates with carbonate bearing veinlet networks.Phlogopite,from the kimberlite,occurs as megacrysts,macrocrysts,microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts.Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains,which indicates that they are the disintegrated fragments of previously larger grains.Phil,within the garnet peridotite and clinopyroxene-phlogopite xenoliths,is characterised by low Ti and Cr contents(TiO_21 wt.%,Cr_2 O_31 wt.% and Mg# = 100 × Mg/(Mg+ Fe)92)typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences.They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene-phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas.One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H_2O.Rb-Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma.Compared with peridotite xenoliths,eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr_2O_3 despite a wider range of TiO_2 concentrations.The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite.Phl2 has high Ti and Cr concentrations(TiO_22 wt.%,Cr_2O_31 wt.% and Mg# = 100× Mg/(Mg + Fe)92)and compositionally overlaps with phlogopite from polymict brecc:ia xenoliths that occur in global kimberlite formations.These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phil grains or crystallized directly from stalled batches of kimberlitic magmas.Megacrysts,most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths.Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts.Based on the results of this study,we propose a schematic model of SCLM metasomatism involving phlogopite crystallization,megacryst formation,and genesis of kimberlite magmas as recorded by the Grib pipe. 相似文献