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1.
Rare-earth element distribution in the rocks and minerals of the olivinite-clinopyroxenitemelilitolite-melteigite-ijolite-nepheline syenite series was analyzed to study the evolution trends of the alkaline-ultrabasic series of the Kola province. The contents of REE and some other trace elements were determined in olivine, melilite, clinopyroxene, nepheline, apatite, perovskite, titanite, and magnetite. It was established that distribution of most elements in the rocks of the Kovdor, Afrikanda, Vuoriyarvi, and other massifs differ from that in the Khibiny ultrabasic-alkaline series, being controlled by perovskite crystallization. Primary olivine-melanephelinite melts of the minor ultrabasic-alkaline massifs are characterized by the early crystallization of perovskite, the main REE-Nb-Ta-Th-U depository. Precipitation of perovskite simultaneously with olivine and clinopyroxene results in the depletion of residual magma in rare-earth elements and formation of low-REE- and HFSE ijolite and nepheline syenite derivatives. In contrast, the formation of the Khibiny ultrabasic-alkaline series was complicated by mixing of olivine melanephelinite magma with small batches of phonolitic melt. This led to a change in crystallization order of REE-bearing titanates and Ti-silicates and accumulation of the most incompatible elements in the late batches of the melt. As a result, the Khibiny ijolites have the highest REE contents, which are accommodated by high-REE apatite and titanite. 相似文献
2.
Petrogenetic processes in the ultramafic, alkaline and carbonatitic magmatism in the Kola Alkaline Province: A review 总被引：1，自引：0，他引：1
Hilary Downes Elena Balaganskaya Andrew Beard Ruslan Liferovich Daniel Demaiffe 《Lithos》2005,85(1-4):48-75
Igneous rocks of the Devonian Kola Alkaline Carbonatite Province (KACP) in NW Russia and eastern Finland can be classified into four groups: (a) primitive mantle-derived silica-undersaturated silicate magmas; (b) evolved alkaline and nepheline syenites; (c) cumulate rocks; (d) carbonatites and phoscorites, some of which may also be cumulates. There is no obvious age difference between these various groups, so all of the magma-types were formed at the same time in a relatively restricted area and must therefore be petrogenetically related. Both sodic and potassic varieties of primitive silicate magmas are present. On major element variation diagrams, the cumulate rocks plot as simple mixtures of their constituent minerals (olivine, clinopyroxene, calcite, etc). There are complete compositional trends between carbonatites, phoscorites and silicate cumulates, which suggests that many carbonatites and phoscorites are also cumulates. CaO / Al2O3 ratios for ultramafic and mafic silicate rocks in dykes and pipes range up to 5, indicating a very small degree of melting of a carbonated mantle at depth. Damkjernites appear to be transitional to carbonatites. Trace element modelling indicates that all the mafic silicate magmas are related to small degrees of melting of a metasomatised garnet peridotite source. Similarities of the REE patterns and initial Sr and Nd isotope compositions for ultramafic alkaline silicate rocks and carbonatites indicate that there is a strong relationship between the two magma-types. There is also a strong petrogenetic link between carbonatites, kimberlites and alkaline ultramafic lamprophyres. Fractional crystallisation of olivine, diopside, melilite and nepheline gave rise to the evolved nepheline syenites, and formed the ultramafic cumulates. All magmas in the KACP appear to have originated in a single event, possibly triggered by the arrival of hot material (mantle plume?) beneath the Archaean/Proterozoic lithosphere of the northern Baltic Shield that had been recently metasomatised. Melting of the carbonated garnet peridotite mantle formed a spectrum of magmas including carbonatite, damkjernite, melilitite, melanephelinite and ultramafic lamprophyre. Pockets of phlogopite metasomatised lithospheric mantle also melted to form potassic magmas including kimberlite. Depth of melting, degree of melting and presence of metasomatic phases are probably the major factors controlling the precise composition of the primary melts formed. 相似文献
3.
Shaikh Azhar M. Kumar Satya P. Patel Suresh C. Thakur Satyajeet S. Ravi Subramanian Behera Duryadhan 《Mineralogy and Petrology》2018,112(2):609-624
Distinctly different groundmass mineralogy characterise the hypabyssal facies, Mesoproterozoic diamondiferous P3 and P4 intrusions from the Wajrakarur Kimberlite Field, southern India. P3 is an archetypal kimberlite with macrocrysts of olivine and phlogopite set in a groundmass dominated by phlogopite and monticellite with subordinate amounts of serpentine, spinel, perovskite, apatite, calcite and rare baddeleyite. P4 contains mega- and macrocrysts of olivine set in a groundmass dominated by clinopyroxene and phlogopite with subordinate amounts of serpentine, spinel, perovskite, apatite, and occasional gittinsite, and is mineralogically interpreted as an olivine lamproite. Three distinct populations of olivine, phlogopite and clinopyroxene are recognized based on their microtextural and compositional characteristics. The first population includes glimmerite and phlogopite–clinopyroxene nodules, and Mg-rich olivine macrocrysts (Fo 90–93) which are interpreted to be derived from disaggregated mantle xenoliths. The second population comprises macrocrysts of phlogopite and Fe-rich olivine (Fo 81–89) from P3, megacrysts and macrocrysts of Fe-rich olivine (Fo 85–87) from P4 and a rare olivine–clinopyroxene nodule from P4 which are suggested to have a genetic link with the precursor melt of the respective intrusions. The third population represents clearly magmatic minerals such as euhedral phenocrysts of Fe-rich olivine (Fo 85–90) crystallised at mantle depths, and olivine overgrowth rims formed contemporaneously with groundmass minerals at crustal levels. Close spatial association and contemporaneous emplacement of P3 kimberlite and P4 lamproite is explained by a unifying petrogenetic model which involves the interaction of a silica-poor carbonatite melt with differently metasomatised wall rocks in the lithospheric mantle. It is proposed that the metasomatised wall rock for lamproite contained abundant MARID-type and phlogopite-rich metasomatic veins, while that for kimberlite was relatively refractory in nature.
相似文献4.
铬铁矿作为蛇绿岩中的重要矿产,其成矿母岩浆性质及演化一直存在较大争议.铬铁矿的矿物包裹体同时或先于铬铁矿结晶,其成分和类别能很好地记录成矿母岩浆性质和演化过程.土耳其Pozant?-Karsant?蛇绿岩不同类型铬铁岩的铬铁矿中发现了多种类型包裹体:不含水硅酸盐矿物（如橄榄石和单斜辉石）、含水硅酸盐矿物（如角闪石和金云母）、复合型矿物包裹体（如蛇纹石、硅灰石和单斜辉石的复合型包裹体）和不常见矿物（如磷灰石、铂族元素硫化物）.含水矿物包裹体的出现以及矿物的高Mg#特征（如橄榄石Fo=95.4~97.1;单斜辉石Mg#=92.0~99.9;角闪石Mg#=88.9~99.8）表明结晶铬铁矿的母岩浆具有富水、富Mg的特征.同时,除钙铬榴石和磷灰石的包裹体外,在铬铁矿中首次发现富Ca矿物方解石和硅灰石,其中方解石和菱镁矿以复合型包裹体形式产出,硅灰石则分布于蛇纹石矿物包裹体中.这些富Ca矿物的出现以及硅酸盐矿物的高CaO含量均揭示了铬铁岩母岩浆的富Ca特征.母岩浆中的Ca组分可能来源于俯冲板块中富Ca岩石/矿物的部分熔融,Ca离子的大量出现使得Cr3+在熔体中更加稳定,同时富Ca矿物的结晶促进了岩浆中Cr的进一步富集而利于铬铁矿的大量结晶沉淀. 相似文献
5.
本文提供了不同成分的8大类主岩(偏铝质(超)基性岩、过碱性(超)基性岩、偏铝质中性岩、过碱性中性岩、偏铝质酸性岩、过碱性酸性岩、过铝质酸性岩、超酸性岩)中28个矿物(橄榄石、单斜辉石、斜方辉石、角闪石、黑云母、金云母、斜长石、钾长石、石英、磁铁矿、钛铁矿、石榴石、锆石、磷灰石、绿帘石、黄玉、榍石、堇青石、蓝方石、石榴石、霞石、白磷钙矿、镁铁钛矿、板钛矿、黄长石、钙钛矿、尖晶石、金红石)的69个化学元素(Li、Rb、Cs、K、Na、Ca、Sr、Ba、Mn、Fe、Mg、Cu、Pb、Zn、Co、Ni、Be、La、Ce、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu、Y、Sc、Cr、In、Ga、Al、B、Cd、Sb、Bi、U、Th、Zr、Hf、Si、Ti、Ge、Sn、Mo、Nb、Ta、W、V、P、F、Cl、S、N、O、C、As、Pu、Re、Os、He、Ne、Ar、Xe、Kr)和1个化学一价原子团OH的分配系数。综合分析对比表明,矿物、熔体的成分和结构是分配系数的最重要的控制因素。对前人未讨论过的矿物结构和熔体铝过饱和度这两个因素应引起重视。最后,本文分析了矿物-熔体间元素分配系数的研究现状、存在问题,指出了这一领域今后的研究方向。 相似文献
6.
The paper presents data on inclusions in minerals of the least modified potassic lamprophyres in a series of strongly carbonatized potassic alkaline ultramafic porphyritic rocks. The rocks consist of diopside, kaersutite, analcime, apatite, and rare phlogopite and titanite phenocrysts and a groundmass, which is made up, along with these minerals, of potassic feldspar and calcite. The diopside and kaersutite phenocrysts display unsystematic multiple zoning. Chemically and mineralogically, the rock is ultramafic foidite and most likely corresponds to monchiquite. Primary and secondary melt inclusions were found in diopside, kaersutite, apatite, and titanite phenocrysts and are classified into three types: sodic silicate inclusions with analcime, potassic silicate inclusions with potassic feldspar, and carbonate inclusions, which are dominated by calcite. Heating and homogenization of the inclusions show that the potassic lamprophyres crystallized from a heterogeneous magma, with consisted of mixing mafic sodic and potassic alkaline magmas enriched in a carbonatite component. The composition of the magmas was close to nepheline and leucite melanephelinite. The minerals crystallized at 1150–1090°C from the sodic melts and at 1200–1250°C from the potassic ones. The sodic mafic melts were richer in Fe than the potassic ones, were the richest in Al, Mn, SO3, Cl, and H2O and poorer in Ti and P. The potassic mafic melts were not lamproitic, as follows from the presence of albite in the crystallized primary potassic melt inclusions. The diopside, the first mineral to crystallize in the rock, started to crystallize in the magmatic chamber from sodic mafic melt and ended to crystallize from mixed sodic–potassic melts. The potassic mafic melts were multiply replenished in the chamber in relation to tectonic motions. The ascent of the melts to the surface and rapidly varying P–T parameters of the magma were favorable for multiple separations of carbonatite melts from the alkaline mafic ones and their mixing and mingling. 相似文献
7.
Based on the investigation of melt inclusions using electron and ion microprobe analysis, we estimated the composition, evolution, and formation conditions of magmas responsible for the calcite-bearing ijolites and carbonatites of the Belaya Zima alkaline carbonatite complex (eastern Sayan, Russia). Primary melt and coexisting crystalline inclusions were found in the nepheline and calcite of these rocks. Diopside, amphibole (?), perovskite, potassium feldspar, apatite, calcite, pyrrhotite, and titanomagnetite were identified among the crystalline inclusions. The melt inclusions in nepheline from the ijolites are completely crystallized. The crystalline daughter phases of these inclusions are diopside, phlogopite, apatite, calcite, magnetite, and cuspidine. During thermometric experiments with melt inclusions in nepheline, the complete homogenization of the inclusions was attained through the dissolution of a gas bubble at temperatures of 1120–1130°C. The chemical analysis of glasses from the homogenized melt inclusions in nepheline of the ijolites revealed significant variations in the content of components: from 36 to 48 wt % SiO2, from 9 to 21 wt % Al2O3, from 8 to 25 wt % CaO, and from 0.6 to 7 wt % MgO. All the melts show very high contents of alkalis, especially sodium. According to the results of ion microprobe analysis, the average content of water in the melts is no higher than a few tenths of a percent. The most salient feature of the melt inclusions is the extremely high content of Nb and Zr. The glasses of melt inclusions are also enriched in Ta, Th, and light rare earth elements but depleted in Ti and Hf. Primary melt inclusions in calcite from the carbonatites contain a colorless glass and daughter phlogopite, garnet, and diopside. The silicate glass from the melt inclusions in calcite of the carbonatite is chemically similar to the glasses of homogenized melt inclusions in nepheline from the ijolites. An important feature of melt inclusions in calcite of the carbonatites is the presence in the glass of carbonate globules corresponding to calcite in composition. The investigation of melt inclusions in minerals of the ijolites and carbonatites and the analysis of the alkaline and ore-bearing rocks of the Belaya Zima Massif provided evidence for the contribution of crystallization differentiation and silicate-carbonate liquid immiscibility to the formation of these rocks. Using the obtained trace-element compositions of glasses of homogenized melt inclusions and various alkaline rocks and carbonatites, we determined to a first approximation the compositions of mantle sources responsible for the formation of the rock association of the Belaya Zima alkaline-carbonatite complex. The alkaline rocks and carbonatites were derived from the depleted mantle affected by extensive metasomatism. It is supposed that carbonate melts enriched in sodium and calcium were the main agents of mantle metasomatism. 相似文献
8.
A suite of spinel lherzolite and wehrlite xenoliths from a Devonian kimberlite dyke near Kandalaksha, Kola Peninsula, Russia, has been studied to determine the nature of the lithospheric mantle beneath the northern Baltic Shield. Olivine modal estimates and Fo content in the spinel lherzolite xenoliths reveal that the lithosphere beneath the Archaean–Proterozoic crust has some similarities to Phanerozoic lithospheric mantle elsewhere. Modal metasomatism is indicated by the presence of Ti-rich and Ti-poor phlogopite, pargasite, apatite and picroilmenite in the xenoliths. Wehrlite xenoliths are considered to represent localised high-pressure cumulates from mafic–ultramafic melts trapped within the mantle as veins or lenses. Equilibration temperatures range from 775 to 969 °C for the spinel lherzolite xenoliths and from 817 to 904 °C for the wehrlites.
Laser ablation ICP-MS data for incompatible trace elements in primary clinopyroxenes and metasomatic amphiboles from the spinel lherzolites show moderate levels of LREE enrichment. Replacement clinopyroxenes in the wehrlites are less enriched in LREE but richer in TiO2. Fractional melt modelling for Y and Yb concentrations in clinopyroxenes from the spinel lherzolites indicates 7–8% partial melting of a primitive source. Such a volume of partial melt could be related to the 2.4–2.5 Ga intrusion of basaltic magmas (now metamorphosed to garnet granulites) in the lower crust of the northern Baltic Shield. The lithosphere beneath the Kola Peninsula has undergone several episodes of metasomatism. Both the spinel lherzolites and wehrlites were subjected to an incomplete carbonatitic metasomatic event, probably related to an early carbonatitic phase associated with the 360–380 Ma Devonian alkaline magmatism. This resulted in crystallisation of secondary clinopyroxene rims at the expense of primary orthopyroxenes, with development of secondary forsteritic olivine and apatite. Two separate metasomatic events resulted in the crystallisation of the Ti–Fe-rich amphibole, phlogopite and ilmenite in the wehrlites and the low Ti–Fe amphibole and phlogopite in the spinel lherzolites. Alternatively, a single metasomatic event with a chemically evolving melt may have produced the significant compositional differences seen in the amphibole and phlogopite between the spinel lherzolites and wehrlites. The calculated REE pattern of a melt in equilibrium with clinopyroxenes from a cpx-rich pocket is identical to that of the kimberlite host, indicating a close petrological relationship. 相似文献
9.
The investigation of rocks, minerals, and melt inclusions showed that porphyritic alkaline picrites and meimechites crystallized from different parental magmas. At a similar ultrabasic composition, the alkaline picrite melts were enriched in K2O relative to Na2O, and contained up to 0.12–0.13 wt % F and less Cr, Ni, and H2O (only 0.01–0.16 wt % H2O, versus 0.6–1.6 wt % in the meimechite melts) compared with the meimechite magmas. The crystallization of alkaline picrite melts occurred under stable conditions at relatively low temperatures without abrupt changes: olivine and clinopyroxene crystallized at 1340–1285 and 1230–1200°C, respectively, as compared with 1600–1450 and 1230–1200°C in the meimechites. The alkaline picrite melts evolved toward melanephelinite, nephelinite, tephrite, and trachydolerite; whereas the meimechite magmas gave rise to subalkaline picritic rocks. The partitioning of vanadium between olivine and melt suggests that the meimechite magma crystallized under more oxidizing conditions compared with the alkaline picrite melts: the KDV values for the meimechite melts (0.011–0.016) were three times lower than those for the alkaline picrite melts (0.045–0.052). The parental magmas of the alkaline picrites and meimechites were enriched in trace elements relative to mantle levels by factors of tens to hundreds. The alkaline picrite magma showed lower LILE and LREE contents compared with the meimechite magma. The magmas had also different indicator ratios of incompatible elements, including those immobile in aqueous fluids. It was concluded that the meimechite and alkaline picrite melts were derived from different mantle sources. The former were generated at lower degrees of melting of an undepleted mantle source, and the meimechite melts were produced by high-degree melting of a probably lherzolite-harzburgite source. 相似文献
10.
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
11.
Summary Mesozoic melilite-bearing ultramafic lamprophyres are developed as sill, dyke and plug-like intrusive bodies in the East
Antarctic Beaver Lake area. They consist of varying amounts of olivine, melilite, phlogopite, nepheline, titanomagnetite and
perovskite as major phases, accompanied by minor amounts of apatite, carbonate, spinel, glass and, rarely, monticellite. The
rocks are mineralogically and geochemically broadly similar to olivine melilitites, differing in higher CO2 and modal phlogopite and carbonate contents. The ultramafic lamprophyres are MgO-rich (13.4–20.5 wt%) and SiO2-poor (32.8–37.2 wt%), indicative of a near-primary nature. Major and trace element features are consistent with minor fractionation
of olivine and Cr-spinel from melts originating at depths of 130–140 km.
Primary melts originated by melting of upper mantle peridotite which had been veined by phlogopite + carbonate + clinopyroxene-bearing
assemblages less than 200 Ma before eruption. The presence of the veins and their time of formation is required to explain
high incompatible trace element contents and growth of 87Sr/86Sr, leaving 143Nd/144Nd unaffected. The major element, compatible trace element, and most radiogenic isotope characteristics are derived from melting
of the wall-rock peridotite. The depth of about 130 km is indicated by the presence of phlogopite rather than amphibole in
the veins, by control of the REE pattern by residual garnet, by the high MgO content of the rocks, and by the expected intersection
of the rift-flank geotherm with the solidus at this depth. The higher CO2 contents than are characteristic for olivine melilitites favoured the crystallization of melilite at crustal pressures, and
suppressed the crystallization of clinopyroxene. The Beaver Lake ultramafic lamprophyres are a distal effect of the breakup
of Gondwanaland, too distal to show a geochemical signature of the Kerguelen plume. Upward and outward movement of the asthenosphere-lithosphere
boundary beneath the Lambert-Amery rift led first to the production of phlogopite- and carbonate-rich veins, and later to
the generation of the ultramafic lamprophyres themselves.
Received March 31, 2000; revised version accepted September 3, 2001 相似文献
12.
山东五莲七宝山地区早白垩世的碱性侵入岩位于火山机构的中央部位,该岩体具有高Ba-Sr含量、高Nb/Ta和Zr/Hf比、低Ti/Eu比等特征,前人的研究指出其起源于岩石圈地幔。然而,该侵入体中的岩性与成分变化所反映的深部动力学过程尚未理清。本文对七宝山二长辉长岩和两类辉石二长岩开展了详细的矿物学和岩石地球化学研究,识别出钠质和钾质两类钾玄质岩石系列。该套碱性中基性侵入岩具有富碱、富轻稀土和富大离子亲石元素的特征,同时具有高的(La/Yb)N和(Gd/Yb)N值。碱性侵入岩中两类单斜辉石和两类斜长石作为再循环晶,记录了不同批次岩浆/熔体的混合,这些矿物组分和全岩成分共同约束了岩浆的起源与演化过程。结合前人的地球化学资料,本文指出七宝山碱性侵入岩的源区是曾受到沉积物交代的富集地幔,源区存在金云母脉体和角闪石脉体。上述脉体连同周围的地幔橄榄岩共同发生部分熔融,形成原生的碱性熔体。七宝山碱性侵入岩显示高的Nb/Ta和Zr/Hf比、低的Ti/Eu比,同时在微量元素蜘蛛图上呈现Ti*和Hf*的负异常,结合高稀土单斜辉石平衡熔体的属性,共同指示了碳酸盐熔体组分对该套碱性侵入岩的形成发挥了重要作用。钠质系列与钾质系列岩石反映了源区富碱矿物相类型相对贡献量的差异,即钠质为主的碱性岩反映源区角闪石的贡献更大,而钾质为主的碱性岩反映源区金云母的贡献占优势。此外,碱性侵入岩中的钾质系列具有异常高的Rb-Zr-Hf-U含量,很可能反映了源区在部分熔融过程中热液锆石熔解后形成的熔体加入到了钾质岩浆房内。本研究强调了碳酸盐熔体组分对高Nb/Ta碱性中基性的形成发挥着重要作用,亦强调了热液锆石的熔解加入导致岩浆具有高Zr-Hf-U含量的特征。 相似文献
13.
A peralkaline olivine-free nephelinite from Morocco containsan unusual minerological assemblage of Ti-rich garnet, nosean,clinopyroxene, nepheline, leucite, K-feldspar, and melilite.This occurrence appears to be the first report of coexistingK-feldspar and melilite in a lava. The rock bulk compositionshows unusually high SrO content (0.90%) but the calculatedCIPW norm indicates only moderate silica-undersaturation. Amongthe minerals present nosean contains minor amounts of Sr butmost of the available Sr is concentrated in melilite and largezoned crystals of xenocrystic apatite. Apatite contains up to25% SrO. Experimentally determined partition coefficients ofSr between apatite and melt indicate that it could not haveprecipitated from a nephelinite magma. Isotopic compositionof both Nd and Sr dispel any contamination by either sediments,metamorphic basement, or carbonatites. It is deduced that partialor complete dissolution of Sr-rich xenocrysts (apatite and possiblycarbonates) from an ultrabasic alkaline complex in a peralkalinenephelinite composition induces the precipitation of Sr-bearingmelilite in the presence of the normal nepheline +leucite +K-feldspar assemblage. The Moroccan nephelinite thus providesan interesting example where a minor element influences therelations and commonly observed petrological incompatibilitiesbetween phases. 相似文献
14.
Trace element abundances in megacrysts and their host basalts: Constraints on partition coefficients and megacryst genesis 总被引：1，自引：0，他引：1
In an effort to obtain information about mineral/melt trace element partitioning during the high pressure petrogenesis of basic rocks, we determined rare earth and other trace element abundances in megacrysts of clinopyroxene, orthopyroxene, amphibole, mica, anorthoclase, apatite and zircon, and in their host basalts. In general, the ranges of mineral/melt partition coefficients established from experimental partitioning studies and phenocryst/matrix measurements overlap with the ranges of megacryst/host abundance ratios. Our data for Hf, Sc, Ta and Th partitioning represent some of the only estimates available. Consideration of phase equilibria, major element partitioning and isotopic ratios indicate that most of the pyroxene and amphibole megacrysts may have been in equilibrium with their host magmas at high pressures (mostly 10–25 kb). In contrast, it is unlikely that mica, anorthoclase, apatite and zircon megacrysts formed in equilibrium with their host basalts; instead, we conclude that they were precipitated from more evolved magmas and have been mixed into their present host magmas. Consequently, the trace element abundance ratios for megacryst/host should not be interpreted as partition coefficients, but only as guides for understanding trace element partitioning during high pressure petrogenesis. With this caveat, we conclude that the megacryst/ host trace element abundance data indicate that mineral/melt partition coefficients in basaltic systems during high pressure fractionation are not drastically different from partition coefficients valid for low pressure fractionation. 相似文献
15.
The Cretaceous M?gantic intrusive complex of southern Qu?beccontains early noritic gabbrodiorites which represent cumulatesfrom crustally contaminated hawaiite to syenite magmas. Wholerock and mineral chemistry, as well as textural evidence, indicatethat post-cumulus recrystallization and reaction were important,and most of the amphibole and biotite are thought to have formedin this way. A younger plutonic quartz-syenite ringdyke maynot be cogenetic with the gabbro-diorites sice it lacks orthopyroxene.It may, however, be cogenetic with basaltic to riebeckite granitedykes. Fractionation of olivine, plagioclase, aluminous clinopyroxene,and minor Ti-magnetite from critically undersaturated alkalibasaltic magmas generated hawaiitic magmas. The developmentof quartzbearing mugearitic and syenitic residua from the hawaiitescan best be modelled by fractionation of amphibole, plagioclase,olivine, oxides, and apatite. Attempts to model fractionationusing observed phenocrysts (including clinopyroxene) were unsuccessful.Amphibole fractionation is interpreted to have taken place througha reaction with still-porous, higher-temperature cumulates onthe walls of the magma chamber. The plutonic syenites probablyrepresent alkali feldspar cumulates from the residual syeniticmelts. Magnesian calc-alkaline lamprophyres exhibit olivineto phlogopite reaction textures, are enriched in Cr, Ni, K,Rb, Nb, Y, Zr, and Si relative to the basaltic dykes, yet havesimilar incompatible element ratios. Their relation to the basaltsis problematical. The late biotite-granite core to the complexis identical to typical White Mountain granites and may haveformed as an anatectic cap on rising, fractionating, mantlederivedmagmas. 相似文献
16.
The Cayconi district of the Cordillera de Carabaya, SE Peru, exposes a remnant of an upper Oligocene–Lower Miocene (22.2–24.4 Ma) volcanic field, comprising a diverse assemblage of S-type silicic and calc-alkaline basaltic to andesitic flows, members of the Picotani Group of the Central Andean Inner Arc. Basaltic flows containing olivine, plagioclase, clinopyroxene, ilmenite and glass, and glassy rhyolitic agglutinates with phenocrystic quartz, cordierite, plagioclase, sanidine, ilmenite and apatite, respectively exhibit mineralogical and geochemical features characteristic of medium-K mafic and Lachlan S-type silicic lavas. Cordierite-bearing dacitic agglomerates and lavas, however, are characterized by dispersed, melanocratic micro-enclaves and phenocrysts set in a fine-grained quartzo-feldspathic matrix. They contain a bimodal mica population, comprising phlogopite and biotite, as well as complexly zoned, sieve-textured plagioclase grains, sector-zoned cordierite, sanidine, quartz, irregular patches of replaced olivine, clinopyroxene and orthopyroxene and accessory phases including zircon, monazite, ilmenite and chromite. The coexistence of minerals not in mutual equilibrium and the growth/dissolution textures exhibited by plagioclase are features indicative of magmatic commingling and mixing. Trachytic-textured andesite flows interlayered with olivine+plagioclase–glomerophyric, calc-alkaline basalts have a phenocrystic assemblage of resorbed orthopyroxene and plagioclase and exhibit melanocratic groundmass patches of microphenocrystic phlogopite, Ca-rich sanidine, ilmenite and aluminous spinel. The mineralogical and mineral chemical relationships in both the dacites and the trachytic-textured andesites imply subvolcanic mixing between distinct ultrapotassic mafic melts, not represented by exposed rock types, and both the S-type silicic and calc-alkaline mafic magmas. Such mixing relationships are commonly observed in the Oligo-Miocene rocks of the Cordillera de Carabaya, suggesting that the S-type rocks in this area and, by extension, elsewhere derive their unusually high K2O, Ba, Sr, Cr and Ni concentrations from commingling and mixing with diverse, mantle-derived potassic mafic magmas. 相似文献
17.
GREGOIRE M.; MOINE B. N.; O'REILLY SUZANNE Y.; COTTIN J. Y.; GIRET A. 《Journal of Petrology》2000,41(4):477-509
Mantle xenoliths in alkaline lavas of the Kerguelen Islandsconsist of: (1) protogranular, Cr-diopside-bearing harzburgite;(2) poikilitic, Mg-augite-bearing harzburgite and cpx-poor lherzolite;(3) dunite that contains clinopyroxene, spinel phlogopite, andrarely amphibole. Trace element data for rocks and mineralsidentify distinctive signatures for the different rock typesand record upper-mantle processes. The harzburgites reflectan initial partial melting event followed by metasomatism bymafic alkaline to carbonatitic melts. The dunites were firstformed by reaction of a harzburgite protolith with tholeiiticto transitional basaltic melts, and subsequently developed metasomaticassemblages of clinopyroxene + phlogopite ± amphiboleby reaction with lamprophyric or carbonatitic melts. We measuredtwo-mineral partition coefficients and calculated mineral–meltpartition coefficients for 27 trace elements. In most samples,calculated budgets indicate that trace elements reside in theconstituent minerals. Clinopyroxene is the major host for REE,Sr, Y, Zr and Th; spinel is important for V and Ti; orthopyroxenefor Ti, Zr, HREE, Y, Sc and V; and olivine for Ni, Co and Sc. KEY WORDS: mantle xenoliths; mantle metasomatism; partition coefficients; Kerguelen Islands; trace elements 相似文献
18.
One mantle xenolith from a basanite host of the Mt. Melbourne Volcanic Field (Ross Sea Rift) is extraordinary in containing
veins filled with leucite, plagioclase, clinopyroxene, nepheline, Mg-ilmenite, apatite, titaniferous mica, and the rare mineral
zirconolite. These veins show extensive reaction with the dunitic or lherzolitic host (olivine+spinel+orthopyroxene+clinopyroxene).
The reaction areas contain skeletal olivine and diopside crystals, plagioclase, phlogopite, aluminous spinel and ilmenite
in a fine grained groundmass of aluminous spinel, clinopyroxene, olivine, plagioclase and interstitial leucite. The vein composition
estimated from modal abundances and microprobe analyses is a mafic leucite-phonolite with high amounts of K, Al, Ti, Zr and
Nb but low volatile contents. The melt is unrelated to the host basanite and was probably derived by smallscale melting of
incompatible element-enriched phlogopite-bearing mantle material and must have lost most of its volatile content during migration,
crystallization and reaction with the host dunite. While the veins are completely undeformed the dunitic host shows slight
deformation. Vein minerals crystallized at high temperatures above 1000°C and pressures below 5 kbar according to the phase
assemblage including leucite, nepheline and K-feldspar. Spinel/olivine geothermometry yielded 800–920°C for the re-equilibration
of the host peridotite. Thus the xenolith must have been at shallow depth prior to and during the late veining event. Mantle
material at shallow depths is consistent with rifting and the regional extreme displacement at the transition from the rifted
Victoria Land Basin in the Ross Sea to the uplifted Trans-Antarctic Mountains. 相似文献
19.
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
20.
W. D. Birch 《Australian Journal of Earth Sciences》2013,60(7-8):369-385
Comparison of bulk chemistry confirms the comagmatic nature of the New South Wales leucitite belt and the olivine leucitite at Cosgrove, Victoria. This relationship was previously implied by general mineralogical, petrographical, and age similarities, as well as the meridional trend of the occurrences. Differences of a minor nature occur between the N.S.W. and Victorian rock types, the latter being less potassic and magnesian (poorer in leucite and olivine) and more calcic (richer in clinopyroxene). Trace‐element compositions for the Cosgrove leucitite are within the ranges recorded for the N.S.W. belt. Essentially one‐rock type—a melanocratic leucitite—characterizes the belt, with the essential minerals olivine, diopside/salite, leucite, titanomagnetite, ilmenite, nepheline, and Ti‐Ba biotite. However, a pegmatoid phase, relatively enriched in Ti, Fe, and P, is well developed at Cosgrove, with its mineralogy (salite‐titanian aegirine, sodic amphibole, K‐feldspar, nepheline, titanomagnetite, apatite, ilmenite, aenigma‐tite, sodalite, and analcite) demonstrating extreme peralkaline differentiation. Some evidence suggests that the analcite resulted from alteration of leucite. The role of volatiles such as F was significant in facilitating development of coarse textures as well as crystallization of the amphibole, apatite, and sodalite. Magmas for the southeastern Australian leucitite belt were probably generated by equilibrium fusion of phlogopite peridotites, of slightly variable mineralogy. Deep‐seated crustal fractures controlled the relatively limited appearance of the magmas at the surface. There is no regular age variation along the belt, despite the age range of from 7 to 13 m.y. 相似文献