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1.
山东西部莱芜－淄博地区的中生代雪野碳酸岩中发育有大量罕见的反环带云母，云母的电子探针分析表明，云母斑晶的核心为黑云母，过渡带和边缘是金云母，基质中云母为金云母，核心黑云母与过渡带的金云母界限清晰，成分突变以及核心黑云母的溶蚀结构表明，核心黑云母和过渡带与边缘带金云母不是同一岩浆体系结晶的产物，核心黑云母可能是碳酸岩岩浆捕获的外来黑云母，过渡带与边缘带金云母同基质中金云母具有相似的化学成分，从过渡带到边缘带，金云母的Mg(Mg Fe)逐渐降低，反映了碳酸岩岩浆的不断结晶演化过程，TiO2的不断降低，一方面是由于岩浆的分异结晶，另一方面则是岩浆上升期间去气作用导致岩浆内CO2／H2O值降低所致。云母斑晶从过渡带向边缘带Al2O3含量逐渐减少，表明碳酸岩浆自过渡带云母结晶后没有富Al的圈岩物质加入。  相似文献   

2.
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   

3.
The tuff and basanite of Rosenberg 20 km NW of Kassel are thus far unknown occurrences of megacrysts and polycrystalline aggregates of pargasitic-kaersutitic amphibole and of xenoliths of amphibole-bearing peridotite and pyroxenite. The amphiboles precipitated successively with gradually increasing Fe/Mg from the same magma from which the basanite was ultimately derived. The amphibole fractionation commenced within the upper mantle but may have continued into higher levels within the ascending melt.Amphibole and phlogopite fractionation together caused an increased Na/K ratio in the Rosenberg basanite. The crystallization of amphibole and phlogopite is genetically interrelated with the violent eruptive nature of the Rosenberg volcano. The release of vapour during the final stage of amphibole crystallization is indicated by the existence of coarsely vesicular amphibole megacrysts.  相似文献   

4.
大兴安岭北部诺敏河地幔金云母及钾质地幔熔体研究   总被引：2，自引：1，他引：1  
隋建立  李霓  樊祺诚  徐义刚 《岩石学报》2014,30(12):3587-3594
在大兴安岭北部诺敏河第四纪钾质火山岩携带的地幔捕虏体中,发现少量金云母矿物和富钾地幔熔体。金云母颗粒大小1~5mm,呈网脉状充填在橄榄石和辉石、石榴子石等地幔矿物间隙。电子探针研究表明地幔橄榄石、单斜辉石、斜方辉石和石榴石等矿物几乎不含钾质成分(K2O0.01%),而金云母矿物成分具有高钾(K2O~10%)、高钛(Ti O25.41%~7.74%)的特点,暗示区域地幔钾的富集与金云母矿物有密切关系。地幔金云母的成因往往与富钾地幔流体/熔体的交代作用有关,在地幔捕虏体矿物反应边的硅酸盐熔体(囊体)中,发现富硅、富钾的熔体,K2O 4%~8%。结合前人地幔熔体研究,认为区域地幔经历了多期、不同成分地幔熔体的富集作用,其中富钾熔体对地幔钾质成分的富集起到重要作用。诺敏钾质火山正是富钾地幔部分熔融的产物,钾质熔体成分的来源可能与俯冲再循环的壳源物质有关。  相似文献   

5.
Phlogopite has been recognized for the first time in ultramaficxenoliths from the Canadian Cordillera. The phlogopite-bearingxenoliths are hosted in post-glacial basanitoid flows and ejectaof the Kostal Lake volcanic center, British Columbia. The xenolithassemblage consists of 60% cumulate-textured wehrlites, and40% coarse-textured lherzolites, harzburgites, dunites, andolivine websterites. The phlogopite occurs: (1) as sub-euhedral grains along grainboundaries in dunite and lherzolite xenoliths; or (2) alongorthopyroxene lamellae exsolved from intercumulus clinopyroxenein the wehrlite xenoliths; or (3) as grains hosted in 10–100pm diameter fluid inclusions in clinopyroxene of all xenoliths.The phlogopites do not show any reaction relationships withother phases in any of the xenoliths studied. Phlogopites ina given xenolith have Mg/Mg + Fe2+ similar to that of coexistingolivine, clinopyroxene, and orthopyroxene. The partitioningof Fe and Mg between phlogopite and coexisting olivine and clinopyroxeneis similar to that observed in other phlogopite-bearing mantlexenoliths, and in high-pressure melting experiments on rockswith similar bulk compositions. This indicates that the phlogopitesin xenoliths from Kostal Lake have equilibrated with these coexistingphases. The occurrence of phlogopites in fluid inclusions containingNa, K, Cl, P, and S, suggests that incompatible element-enrichedhydrous fluids/melts fluxed this part of the upper mantle beneatheastern British Columbia. Metasomatism of the upper mantle beneathKostal Lake probably occurred prior to Quaternary alkaline magmatism(7550–400 B.P.) and after the initial volcanism whichformed the wehrlite cumulates (3–5 Ma). Metasomatism causedoverall oxidation of the upper mantle beneath this area butwas not responsible for the anomalously Fe-rich nature of somexenoliths from the Kostal Lake eruptive center.  相似文献   

6.
Modal mantle metasomatism, involving the re-enrichment of depletedmantle by the introduction or production of new hydrous phases,apatite and other minerals, has been proposed as a criticalprecursor to alkaline volcanism. The merits of the modal metasomatismmodel are evaluated by examining whole-rock 100 Mg/(Mg+Fe2+)ratios and the abundances of TiO2, K2O and P2O5 in mafic volcanicsspanning the mafic alkaline-subalkaline compositional spectrum.Upper mantle amphiboles and micas are also discussed becausethey would be major donors of Ti, Fe, and K to melts duringanatexis of either modally metasomatized depleted mantle orundepleted mantle. Compared with tholeiitic and calc-alkaline basalts and andesites,basanites and alkali basalts and alkali andesites are neitherdistinctive nor unique by virtue of persistant or well-definedhigher abundances of TiO2, K2O, and P2O5 or lower 100 Mg/(Mg+Fe2+)ratios, features which might reflect precursor modal metasomatismof the alkaline sources. Some basanites and alkali basalts dohave higher abundances of TiO2, K2O, and P2O5 than some tholeiitesbut these abundances may be the result of lower degrees of meltingof similar undepleted mantle sources for both magma types. The most widespread mantle phases of inferred metasomatic originare interstitial amphiboles and micas in Group I spinel peridotitexenoliths. These have high 100 Mg/(Mg+Fe) ratios ({small tilde}90) and high Cr2O3 and low TiO2 abundances, and the K2O/Na2Oratios of the amphiboles (chromian pargasites) are low, generallyless than 0?3. Interstitial amphiboles and micas developed asa result of near-isochemical hydration reactions which largelyinvolved Cr-spinel and Cr-diopside. Their formation was probablyinduced in many instances by fluids derived from crystallizingmafic magmas. Metasomatized Group I xenoliths with interstitialhydrous phases remain depleted in TiO2, K2O, and P2O5, and theyretain the high 100 Mg/(Mg+Fe) ratios characterizing depletedGroup I xenoliths. Together with the low K2O/Na2O ratios, thesefeatures preclude such peridotites as suitable sources of mostalkaline (and subalkaline) volcanics. It is suggested that modalmetasomatism plays an insignificant role in the genesis of mostmantle-derived mafic volcanics. Compared with the interstitial phases, kaersutitic amphibolesand titaniferous micas from vein, Group II inclusion and megacrystupper mantle parageneses have lower 100 Mg/(Mg+Fe) ratios andCr2O3 contents, and much higher TiO2 abundances. K2O/Na2O ratiosof the Ti-amphiboles are also much more wide-ranging (0?3 togreater than 1?0). These Fe, Ti-rich amphiboles and micas areneither widespread nor pervasive phases in metasomatized mantle.They are directly related to alkaline magmatism in the uppermantle where they may be associated with incompatible elementenrichment of peridotite wallrocks in the immediate vicinityof frozen conduits of alkaline mafic magmas. The varying K2O/Na2O ratios of mafic volcanics (MORB constitutea major exception) indicate that the principal K-bearing phasesin undepleted mantle are kaersutitic amphibole and titaniferousmica, in varying proportions. The former is probably the majorsource of Ti and K for low K/Na volcanics (K2O/Na2O < 0?5)and also many medium K/Na types (0?5 < K2O/Na2O < 1?0),whereas mica is more likely to be the major K-bearing phasein the source regions of high K/Na extrusives (K2O/Na2 >1?0). Experimental data indicate that kaersutitic amphibole,mica and apatite probably coexist in undepleted spinel- andgarnet lherzolites at pressures up to 25 kb, with mica persistingto pressures as high as 50 kb. It is proposed that undepleted asthenospheric mantle is heterogeneouswith respect to its amphibole, mica, and apatite contents (andhence TiO2, K2O, and P2O5 abundances and K2O/Na2O ratios), andalso with respect to 100 Mg/(Mg+Fe2+ ) ratios which may be significantlyless than the ratios generally assigned to undepleted mantle,namely 88–90.  相似文献   

7.
Abstract. Halogen-rich phlogopite occurs in the groundmass of andesite and dacite lavas from Late Tertiary to Quaternary volcanoes associated with native sulfur and limonite deposits (Shiretoko-Iwozan, Hachimantai, Adatara, Omeshidake, Masaki) and hydrothermal ore deposits (Harukayama, Muineyama, Hishikari) in Japan. The F contents of the halogen-rich phlogopite range from 3.6 to 5.7 wt%, corresponding to atomic F/(F+C1+OH) ratios ranging from 0.45 to 0.69. On the other hand, the Cl contents of the halogen-rich phlogopite are around 0.2 wt%. The atomic Mg/(Mg+Fe) ratios range from 0.69 to 0.83.
The fluorine intercept value [IV(F)] defined by Munoz (1984) of the phlogopites ranges from 0.79 to 3.17, and the chlorine intercept value [IV(Cl)] ranges from -7.11 to -7.77. The observed IV(F) of the phlogopites broadly overlap the range of the IV(F) for biotites from porphyry copper deposits. On the other hand, the observed IV(Cl) are significantly lower than the IV(Cl) for biotites from porphyry copper deposits. Whereas the F contents of the phlogopite appear more prominent compared to the Cl contents, the calculation of halogen intercept values revealed that the phlogopites are enriched in Cl with respect to the element distribution effect of Mg-Fe substitution. Since the degree of Cl enrichment of the phlogopite is more significant compared to that of biotite in porphyry copper deposits, the phlogopites are considered to have formed under the condition of significantly high activity of halogens. Hydrothermal ore deposits may be formed in magmatic hydrothermal system associated with volcanoes where halogen-rich phlogopite is formed by hypersaline fluid.  相似文献   

8.
Summary The chemistry of amphiboles from schists, quartzofeldspathic gneisses and migmatites ranging in metamorphic grade from greenschist to amphibolite facies has been determined by electron microprobe. Intercalated amphibolites suggest that some of the rocks retrograded from the eclogite stability field; others were never metamorphosed above greenschist facies. Rocks which contain other mineralogical evidence for an original high pressure assemblage have amphiboles with high Na/K, low Fe and relatively low Ti. Other high-grade rocks contain amphibole of broadly pargasitic composition. The pargasites from more Ca-rich bulk compositions have less substitution of Na for Ca in the M4 site than do those from Ca-poor bulk compositions. A lower grade assemblage of amphiboles ranges from hornblende through actinolitic hornblende to actinolite; this is retrograde in the gneisses and migmatites, but may be prograde in the schists. In contrast, the high-grade assemblage shows almost constant high K with variable Na and quite different trends for edenite-type substitution (IVAl variation with A site occupancy) and variation ofIVAl with Fe/(Fe + Mg) and with Ti.
Chemische Zusammensetzung von Pargasit und Hornblende in niedrig- bis hoch-gradig metamorphen Gesteinen der Rhodope-Zone, Xanthi, Griechenland
Zusammenfassung Die Chemische Zusammensetzung von Amphibolen aus Schiefern, Quarz-Feldspat-Gneisen, und Migmatiten, deren metamorpher Grad von Grünschiefer- bis zur Amphibolitfazies reicht, wurde mit der Elektronenstrahl-Mikrosonde bestimmt. Zwischengeschaltete Amphibolite legen die Vermutung nahe, daß einige der Gesteine durch retrograde Metamorphose aus dem Eklogit-Stabilitatsfeld hervorgegangen sind; andere jedoch hatten niemals in ihrer Entwicklung einen höheren Grad als den der Grünschie-ferfazies erreicht. Gesteine, die andere mineralogische Hinweise für eine ursprungliche Hochdruck-Paragenese führen, enthalten Amphibole mit hohem Na/K, niedrigen Eisen und relativ niedrigen Ti. Andere high-grade Gesteine enthalten Amphibol von pargasitischer Zusammensetzung. Die Pargasite aus mehr Kalzium-reichen Gesteinen zeigen geringere Substitution von Natrium für Kalzium an den M4 Plätzen als jene aus Kalzium-armen Gesteinen. Eine niedriger-gradige Paragenese von Amphibolen umfaßt Zusammensetzungen von Hornblende über aktinolitische Hornblende bis zu Aktinolit; diese ist in den Gneisen und Migmatiten retrograd, durfte in den Schiefern jedoch prograd sein. Im Gegensatz dazu zeigt die hochgradige Paragenese fast durchwegs konstant hohe Kalium-Gehalte mit variablem Natrium und einen anderen Trend für Edenit-artige Substitution (IVAl Variation mit Besetzung der A Plätze) und eine Variation vonIVAl mit Fe/(Fe + Mg) und mit Ti.

With 4 Figures  相似文献   

9.
The western part of the Hidaka Metamorphic Belt, Hokkaido, consistsof primary pyroxene gabbro and lesser amounts of olivine gabbrothat have been dynamically metamorphosed to metagabbro—gabbroicamphibolite-amphibolite-epidote amphibolite during uplift andshearing about 23 m.y. ago. Textures and the presence of relic and recrystallized amphiboleand plagioclase in the same rock indicate incomplete reactionand non attainment of equilibrium during recrystallization. EPMA and bulk analyses of 165 amphiboles indicate a continuousoverall compositional range from actinolite to dark green hornblende(with 100 mg/(Mg+Fe2++Fe3+Mn) ratios varying from 89.5 to 32.0)marked by increasing Al, Fe, Ti, and Na. A compositional gapis usually present between relic and recrystallized amphibolesin any one rock which becomes more prominent with increasingshearing. In addition to host rock chemical control, amphibole compositionis largely dependent on the An content of coexisting plagioclase.Locally epidote and sphene exert a strong influence on bothamphibole and plagioclase compositions. Amphibole Ti and Mncontents decrease with shearing and Fe enrichment of the hostrocks largely as a result of the incoming of rutile, sphene,and Fe-Ti oxides. Analysis of host rock oxidation ratio andamphibole compositions indicates that the rocks essentiallybehaved as closed systems to oxygen during metamorphism. Al1V-AlIV, AlIV-Fe3+, and AlIV-(Na, K)A are the main substitutionsin the amphiboles. Within any one rock the recrystallized amphibolesare enriched in Al, Fe, Ti, and Na relative to the relice amphiboles.Increasing metamorphism results in a progressive change of amphiboles(recrystallized) to more Fe and Si (rather than Al) rich compositionsreflecting the trend towards greenschist where Fe-actinolite(+Mg chlorite) would be stable. Differentiation of the amphiboles is within the limits of SiAlreplacement and the compositional limits of the early stagereaction rim and replacement amphiboles in the host olivineand pyroxene metagabbros.  相似文献   

10.
The distribution of Rb-Na and Rb-K between richterite and a 2-molal aqueous (Na, K, Rb)-chloride solution has been investigated with hydrothermal experiments at 800∘C and 200 MPa. Experiments were performed as syntheses in which amphiboles grew in the presence of an excess fluid containing the exchangeable cations Na+-Rb+ or Na+-K+-Rb+. The obtained amphiboles were large enough (up to 20 m in width) for reliable EMP analysis. They were chemically homogeneous and HRTEM investigations showed that they were structurally well ordered. The Rb, Na, K, Ca and Mg concentrations in coexisting fluids were measured by ICP-AES. According to the possible incorporation of Na, K and Rb on the A-site, solid solutions in the ternary Na(NaCa) Mg5[Si8O22/(OH)2] (richterite)-K(NaCa)Mg5[Si8O22/(OH)2] (K-richterite)-Rb(NaCa)Mg5[Si8O22/(OH)2] (Rb-richterite) were expected. However, Rb-rich richterites always had significant amounts of A-site vacancy concentrations (X □ amph=□ A /(RbA+KA +NaA+□A) of up to 0.42 in the K-free (Na,Rb)-richterites and of up to 0.67 in the (Na, K, Rb)-richterites which corresponds to the same content of tremolite+cummingtonite-component. Amphiboles containing practically only Rb besides vacancies and no Na and/or K on the A-site were also synthesized, however. The Rb-Na and Rb-K exchange coefficients between fluid and richterites are similar. Rubidium always fractionated strongly into the fluid phase. For low Rb-concentrations in richterite (X Rb amph<0.1) a linear correlation between X Rb fluid and X Rb amph exists. In this concentration range, the derived exchange coefficients K D(Rb−K) amph−fluid and K D(Rb−Na) amph−fluid were 0.08 ± 0.04 and 0.04 ± 0.02, respectively. These low exchange coefficients show that significant amounts of Rb in amphiboles require a Rb-rich fluid phase. The results indicate that K-Rb fractionation between alkali amphiboles and fluids is significantly different from K-Rb fractionation between alkali feldspar/ phlogopite and fluid, with KDs of about 0.5 and 1.2, respectively. Formation of richterites will drastically alter the K/Rb-ratios of fluids or melts. These results may have important implications for the genetical interpretation of various geological settings, e.g., MARID-type rocks. Received: 6 October 1997 / Accepted: 7 July 1998  相似文献   

11.
Previously proposed substitution mechanisms for Ti in phlogopites, based on experimental studies and crystal chemistry, have been examined using data for 81 phlogopites from mantle-derived rocks (primarily as nodules in kimberlites and also from alkali basalts, lamprophyres and carbonatites), 49 phlogopites from high-K rocks with basaltic affinities, and from 32 phlogopites crystallized in high pressure experiments mainly on high-K rock compositions. For the majority of phlogopites from the kimberlite group and for all those crystallized in the experimental studies, the substitution of Ti can be represented by a combination of the mechanisms represented by 2Mg[VI]⇌ Ti[VI]□[VI] and Mg[VI]2Si[IV]⇌Ti[VI]2Al[IV]. Some phlogopites in ultrapotassic rocks have only the former substitution mechanism. The Ti contents of phlogopites generally increase with decreasing octahedral site occupancy and decreasing Si+Al[VI]. For the phlogopites crystallized in the experiments on high-K rocks, the solubility of Ti increases with increasing fO2 and temperature, and possibly with decreasing pressure at constant fO2. The effect of the composition of the liquids used in the experimental studies from which these phlogopites have crystallized has only minor effect on either the substitution mechanism or the solubility of Ti in phlogopites. This suggests that phlogopite in high-K rocks may be a potential geothermometer and possibly a geobarometer.  相似文献   

12.
Compositional data on apatite, phlogopite, and amphibole indicatethat the high-temperature hydrothermal fluids which affectedthe lower portions of the Stillwater and Bushveld Complexeswere Cl-rich. Apatites from the platinum-group element (PGE)ore zones from both complexes are enriched in Cl relative toother cumulus and noncumulus apatites in these intrusions andto apatites from the Skaergaard and Kiglapait Intrusions andthe Great Dyke. Apatites from all five intrusions can be groupedinto three distinct compositional fields: (a) Cumulus apatitesare essentially fluorapatites with molar Cl/(Cl+OH+F) <0?03;(b) noncumulus apatites, with the exception of those from thePGE ore zones of the Stillwater and Bushveld Complexes, haveCl/(Cl+OH+F) <0?20; (c) Cl-rich apatites associated withPGE-rich zones have Cl/(Cl+OH+F) between 0?45 and 1?0. The REEcontent of noncumulus and Cl-rich apatites also show a positivecorrelation with Cl concentration. It is argued that becauseCl is less soluble in silicate melts than F and because meltswith extremely high Cl/F ratios are unknown, the Cl-rich apatitesequilibrated with Cl-rich hydrothermal fluids exsolved duringsolidification of the cumulate sequence. The Cl, F, and OH contents of phlogopites and amphiboles aremore variable. Compositional heterogeneity is due to crystal-chemicalcontrols on halogen contents, variation in the halogen contentof the original melt/fluid phase and subsolidus re-equilibrationduring cooling with both surrounding mineral phases and lowtemperature fluids. However, both the Stillwater and Bushveldphlogopites are enriched in Cl compared to those from the Skaergaardand Kiglapait Intrusions. The compositions of coexisting minerals from the platinum depositof Olivine-Bearing Subzone I of the Stillwater Complex are usedto compute a fluid composition. The fluid is rich in alkalisand iron as well as HCl, and the solution composition is consistentwith fluid compositions deduced for the PGE-bearing secondaryhortonolite pipes of the Bushveld Complex. The high (Pt+Pd)/Irratios of these deposits are also consistent with a hydrothermalorigin, as both Pt and Pd are more soluble in Cl-complexingfluids than Ir.  相似文献   

13.
A corundum-bearing mafic rock in the Horoman Peridotite Complex, Japan, was derived from upper mantle conditions to lower crustal conditions with surrounding peridotites. The amphiboles found in the rock are classified into 3 types: (1) as interstitial and/or poikilitic grains (Green amphibole), (2) as a constituent mineral of symplectitic mineral aggregates with aluminous spinel at grain boundary between olivine and plagioclase (Symplectite amphibole) and (3) as film-shaped thin grains, usually less than 10 μm in width, at grain boundary between olivine and clinopyroxene (Film-shaped amphibole). The Film-shaped amphibole is rarely associated with orthopyroxene extremely low in Al2O3, Cr2O3 and CaO (Low-Al OPX). These minerals were formed by infiltration of SiO2- and volatile-rich fluids along grain boundaries after the rock was recrystallized at olivine-plagioclase stability conditions, i.e. the late stage of the exhumation of the Horoman Complex.

Chondrite-normalized rare earth element patterns and primitive mantle-normalized trace-element patterns of the Green amphibole and clinopyroxene are characterized by LREE-depleted patterns with Eu positive and negative anomalies of Zr and Hf. These geochemical characteristics of the constituent minerals were inherited from original whole-rock compositions through a reaction involving both pre-existing clinopyroxene and plagioclase. We propose that the fluids were originally rich in a SiO2 component but depleted in trace-elements. Dehydration of the surrounding metamorphic rocks in the Hidaka metamorphic belt, probably related to intrusion of hot peridotite body into the Hidaka crust, is a plausible origin for the fluids.  相似文献   


14.
Four pairs of associated calcic and sodic amphiboles from blueschistfacies metamorphic rocks were analyzed with the electron microprobeand studied by single-crystal X-ray diffraction techniques.Except for ranges in the ratios Mg/(Mg+Fe) and Fe3+/(Fe3++Al+Ti),the sodic amphiboles are similar in chemical composition. Theamount of calcium in the M(4)-site ranges only from 0·18to 0·21 ion per formula unit. The calcic amphiboles,in addition to a range in Mg/(Mg+Fe), vary in Na/(Na+Ca) ratio(0·29–0·48). Three of the calcic amphibolescontain less than 1·5 calcium ions per formula unit,indicating a significant solid solution of sodic amphibole componentsin the calcic amphibole phase. The a and b unit-cell parametersof the calcic amphiboles decrease with increased content ofthe sodic component.  相似文献   

15.
The pre‐pilot hole (PP1) of the Chinese Continental Scientific Drilling Project (CCSD) recovered drill core samples from a 118 m‐thick section of peridotites located at Zhimafang in the southern Sulu UHP terrane, China. The peridotites consist of phlogopite‐bearing garnet lherzolite, harzburgite, wehrlite and dunite. Some peridotite layers contain magnesite and Ti‐clinohumite, and are characterized by LREE and LILE enrichment and HFSE depletion. Phlogopite (Phl) occurs in the peridotite matrix and is LILE‐enriched with low Zr/Hf ratios (0.19–0.60). Phlogopite shows a mantle signature in H and O isotopes (δ18O: +5.4‰ to +5.9‰, and δD: ?76‰ to ?91‰). Ti‐clinohumite (Ti‐Chu) is Nb and Ta‐enriched and has higher Ti and HREE concentrations than phlogopite. Magnesite (Mgs) occurs as megacrysts, as a matrix phase, and as veins (±Phl ± Ti‐Chu), and contains low REEtotal contents (<0.3 ppm) with a flat REE pattern. The δ18O values (+5.5‰ to +8.0‰) of magnesite are in the range of primary carbonatite, but the δ13C values (?2.4‰ to ?3.4‰) are slightly more positive than those of the mantle and of primary carbonatite. Petrochemical data indicate that the Zhimafang peridotite was subjected to three episodes of metasomatism, listed in succession from oldest to youngest: (1) crystallization of phlogopite in the mantle caused by infiltration of K‐rich hydrous fluid/melt; (2) formation of Mgs and Mgs ± Phl ± Ti‐Chu veins possibly caused by infiltration of mantle‐derived carbonatitic melt with a hydrous silicate component; and (3) replacement of magnesite, garnet and diopside by dolomite and secondary hydrous phases caused by a crust‐related, CO2‐bearing, aqueous fluid. Stable isotopic compositions of phlogopite and magnesite indicate metasomatic agents for events (1) and (2) are from an enriched mantle. Multiple metasomatism imposed on mantle peridotite of variable composition led to significant compositional heterogeneity at all scales within the Zhimafang peridotite.  相似文献   

16.
By applying the 40Ar/39Ar-dating method, age estimates for phlogopites of mantle xenoliths with different parageneses from the Udachnaya and Mir kimberlite pipes (Yakutia, Russia) were obtained. The oldest ages determined are 2.6–2.3 Ga, which far transcends the Paleozoic age of kimberlite entrainment. The phlogopite formation of these ages reflects ancient metasomatic events following rearrangement processes in the mantle in the Archean-Early Proterozoic, particularly during and after accretion of the Pangea-0 super-continent. A multistep age spectrum of UV162/09 was obtained from several generations of phlogopite and indicates a later multistage metasomatic process taking place in the mantle under Udachnaya pipe. Several stages of mantle metasomatism of various ages and scales are detected within the Siberian platform.  相似文献   

17.
Except forming two Cs-rich minerals like pollucite and londonite, cesium generally occurs in trace amounts in potassium-bearing minerals owing to its very low Clarke value and large ionic radius. However, in the Koktokay#3 pegmatite (Altai, NW China), lepidolite is extremely enriched in cesium (typically 21–26 wt% Cs2O). Cs-enriched lepidolite is restricted to the inner of the pegmatite, where four types of occurrence are characterized by using in situ techniques (EMP: electron microprobe, micro-XRD: micro-area X-ray diffractometer and Raman probe: micro-area Raman spectrometer) as: (1) outer zones on Cs-poor lepidolite cores; (2) fine overgrowths on muscovite veinlets; (3) veinlets in Cs-poor lepidolite and (4) veinlets in elbaite. There is an inverse correlation between K and Cs and in terms of VIAl versus Cs/(K+Cs), the Cs-dominant micas are an analog of the Li-rich mica polylithionite. Micro-XRD patterns and micro-Raman spectra indicate that Cs-dominant polylithionite structurally corresponds to minerals of the lepidolite series. According to its distribution and compositional characteristics, the Cs-dominant polylithionite seems to have formed at the magmatic to hydrothermal transition stage of pegmatitic magma evolution as a result of marginal replacement of early-formed lepidolite by Cs-rich fluids. Alternatively, it may have formed through direct precipitation from Cs-rich fluids. The results of the present study have important implications for the storage of nuclear waste in that Li mica such as polylithionite is a good candidate for immobilizing high-level radioactive cesium waste.  相似文献   

18.
The solubility of Tio2 in phlogopites has been experimentally determined in the system K2Mg6Al2Si6O20(OH)4-K2Mg4TiAl2Si6O20(OH)4-K2Mg5TiAl4Si4O20(OH)4 between 825–1300°C and 10–30 kbar under vapour absent conditions. Starting compositions lie along the join K2Mg6Al2Si6O20(OH)4-K2Mg4.5TiAl3Si5O20(OH)4 which represents a combination of the Mg[VI]2Si[IV] = Ti[VI]2Al[VI] and 2Mg[VI] = Ti[VI]□[VI] substitution mechanisms for Ti in phlogopites. The results of the experiments indicate a systematic increase in solubility of Ti with increasing temperature and decreasing pressure for given bulk Tio2 content. Under isobaric conditions high temperature Ti-saturated phlogopite breaks down to Ti-deficient phlogopite + rutile + vapour. Mass balance calculations suggest that the vapour phase may contain K2O dissolved in H2O and that the reaction is controlled by the vapour phase. Analyses of phlogopites coexisting with rutile and vapour can be represented in terms of the end-member components phlogopite [K2Mg6Al2Si6O20(OH)4], eastonite [K2Mg5Al4Si5O20(OH)4], an octahedral site deficient Ti-phlogopite (Ti-OSD) of composition K2(Mg4Ti□)Al2Si6)O20(OH)4, and Ti-eastonite [K2Mg5TiAl4Si4O20(OH)4]. With decreasing amounts of Ti in these phlogopites there is a decrease in the Ti-eastonite component and increase in the eastonite component.The general equation for the breakdown of Ti-phlogopite solid solution to Ti-free phlogopite + rutile + vapour is: 14 Ti-eastonite + 7 Ti-OSD ? 16 eastonite + 3 phlogopite + 21 rutile + 4 H2O + 2 K2O. Lack of knowledge of H2O and K2O activities in the vapour phase does not permit evaluation of thermodynamic constants for this reaction. The Ti solubility in phlogopites and hence its potential as a geothermobarometer under lower crustal to upper mantle conditions is likely controlled by common mantle minerals such as forsterite.  相似文献   

19.
New analyses of K, Rb, Sr and Ba contents and the 87Sr86Sr ratios of eight amphiboles, one phlogopite, two diopsides and one host alkalic basalt for an amphibole are reported: The samples are mostly inclusions in alkalic basalts and occur in association with peridotite inclusions. Two of the samples are from alpine-type peridotite bodies — one from the Etang de Lhers massif in the French Pyrenees and the other from the Finero massif in the Ivrea zone in northern Italy. The kaersutites come from the following localities: Hoover Dam, Arizona; Deadman Lake, California; Massif Central, France; Queensland; Spring Mountain, New South Wales.The data indicate that kaersutitic amphiboles are genetically unrelated to their host basalts. The isotopic and trace element data of these amphiboles further strengthens the suggestion of BASU and MURTHY (1977) that kaersutites play a significant role in ocean ridge basalt genesis. In addition, pargasitic amphibole with higher 87Sr86Sr ratios, if present, may be important in the source regions of alkalic basalts.The bulk amphibole lherzolite from Lherz has the KRbratio and 87Sr86Sr ratio appropriate for source material of ridge tholeiites. If the diopside and the amphibole in this rock had isotopically equilibrated under upper mantle conditions, the data show the time of last equilibration to be approximately 735 m.y., in contrast to the young emplacement age of the ultramafic massif.The coexisting phlogopite and diopside in the spinel lherzolite inclusion from Kilbourne Hole, New Mexico, show, surprisingly, isotopic equilibration under upper mantle conditions despite their drastically different RbSr ratios. The data show that the phlogopite must have formed very recently in the upper mantle. This phlogopite also has a high KRb ratio (1133), contrary to the commonly held view that mantle phlogopites have low KRb ratios. The coexisting diopside shows high K content (778 ppm) and a lower KRb ratio than the phlogopite. This phlogopite lherzolite has trace elemental and isotopic characteristics that may be adequate for the origin of alkalic basalts upon partial melting.  相似文献   

20.
岚皋金云角闪辉石岩类捕虏体：地幔交代作用的证据   总被引：6，自引：2，他引：6  
产于陕西岚皋地区碱质基性－超基性潜火山杂岩中的金云角闪辉石岩类捕虏体，主要由透辉石、富钛韭闪石、金云母、磷灰石、榍石、及钛铁矿组成。捕虏体发育三联晶、碎裂边、肯克变形等固相线下变形变质结构，矿物学特征表明，透辉石、富钛韭闪石、金云母为地幔来源，是地幔交代作用的产物；与正常地幔尖晶石二辉橄榄岩相比，捕虏体富ＴｉＯ２、Ｆｅ２Ｏ３、ＣａＯ、Ｎａ２Ｏ、Ｋ２Ｏ，贫ＭｇＯ，其稀土元素具富集特征，尤其富集ＬＲＥＥ；微量元素分配型式显示了富亲石不相容元素的特征。岩相学、矿物学及岩石化学特征表明：该类捕虏体为交代地幔捕虏体，它代表了北大巴山早古生代裂谷作用时期的异常地幔，是地幔交代作用的产物。交代营力可能源于地幔热缕的上升，交代过程推测为深处小范围的流体交代及随后硅酸岩熔体的“弥散”性交代  相似文献   

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