云南马关新生代地幔包体中橄榄石的显微构造及其反映的上地幔物理状态特征   总被引：4，自引：0，他引：4  

陈忠  丘学林  陆琦  颜文  吴世敏  施小斌 《热带海洋学报》2004,23(1):34-43

利用氧化缀饰法研究了云南马关新生代地幔尖晶石二辉橄榄岩包体中橄榄石的位错构造。其位错构造种类多样、形态各异,主要包括(100)和(001)位错壁、亚颗粒构造、位错网格、{100}滑动条带构造等,表明该区上地幔岩具高温高应变和低温高应变特征。包体形成的温度T为1016—1098℃,压力P为18.3×108—20.6×108Pa。马关上地幔温压状态具有大洋地幔地温特征,热流值达85mW·m-2。上地幔的流动应力σ为27.9—59.7MPa,流动速率ε为1.37×10-18—2.17×10-16s-1,等效粘滞度η为9.18×1022—6.92×1024Pa·s。该区上地幔的高流动应力、高热状态和裂谷带型的流动速率、等效粘滞度特征,可能与16MaB.P.以来区域性东西向伸展作用有关。  相似文献   

Interaction of deformation and metamorphism during subduction and exhumation of hydrated oceanic mantle: Insights from the Western Alps     

G. REBAY  M. I. SPALLA  D. ZANONI 《Journal of Metamorphic Geology》2012,30(7):687-702

Petrological investigations supported by multi‐scale structural analysis of eclogitized serpentinite in the Zermatt–Saas Zone of the Western Alps allows for the determination of mineral assemblages related to successive fabrics, upon which the P–T–d–t path of these hydrated mantle rocks can be inferred. Serpentinites of the upper Valtournanche, with lenses and dykes of metagabbro and meta‐rodingite, display an Alpine polyphase metamorphic evolution from eclogite to epidote‐amphibolite facies conditions associated with three successive foliations having different parageneses in these rocks. Serpentinite mainly consists of serpentine with minor magnetite; however, where S1 and S2 foliations are pervasive, metamorphic olivine, together with Ti‐clinohumite and clinopyroxene, are also found. The mineral assemblage associated with D1 includes serpentine1, clinopyroxene1, opaque minerals, titanite ± olivine1, Ti‐clinohumite1 and ilmenite; the D2 assemblage is the same (±chlorite) but minerals have different compositions. The assemblage associated with D3 comprises serpentine3, opaque minerals, ±chlorite3, ilmenite and amphibole3. Ti‐clinohumite is associated with veins that are older than D2 and pre‐date D3. Veins that post‐date D3 are characterized by amphibole + chlorite or by serpentine. P–T conditions for S2 parageneses evaluated using two pseudosections for different bulk compositions suggest that these rocks experienced pressures >2.5 ± 0.3 GPa at temperatures slightly higher than 600 °C. The late epidote–amphibolite facies re‐equilibration associated with D3 and D4 developed during late syn‐exhumation deformation related to folding and testifies to a small temperature decrease. These results, which were integrated in the regional framework, suggest that different portions of the Zermatt–Saas Zone registered different P–T peak conditions and underwent different exhumation paths. In addition, the inferred P–T–d–t path suggests that the Valtournanche serpentinites re‐equilibrated close to the UHP conditions registered by the Cignana meta‐cherts. These results imply that tectonic slices exhumed after UHP metamorphism might be wider than previously reported or that small‐size UHP units, tectonically sampled during the Alpine convergence, are more abundant than those that have been detected to date.  相似文献   

西藏罗布莎地幔橄榄岩变形显微构造特征及其地质意义   总被引：1，自引：0，他引：1  

徐梦婧  金振民 《地质通报》2010,29(12):1795-1803

地幔橄榄岩是罗布莎蛇绿岩的主要组成成分之一,通过显微构造特征可对其变形特征进行分析,确定流变学参数,探讨地幔橄榄岩的变形历史。以蛇纹石化程度较低的二辉橄榄岩和方辉橄榄岩为研究对象,橄榄石位错特征研究显示,本区橄榄石主要发育了低温常见的直线型自由位错,局部可见位错弓弯、位错环、位错壁等高温位错,反映罗布莎地幔橄榄岩变形以低温塑性流变为主,局部经历了高温塑性流变,主导变形机制为位错蠕变。橄榄石自由位错统计结果表明,二辉橄榄岩中的橄榄石自由位错密度为4.422×107/cm2,方辉橄榄岩中的橄榄石为9.137×107/cm2,变形过程中所受差异应力分别为65MPa和93MPa。橄榄石和斜方辉石显微组构测量采用了电子背散射衍射技术(EBSD),分析结果表明,橄榄石均发育A型组构,为浅部地幔常见的组构类型,该结果与金刚石、柯石英等超高压矿物所指示的形成深度不一致。  相似文献   

上地幔的岩石组构和各向异性   总被引：7，自引：1，他引：7  

金淑燕 《地质科技情报》1993,12(3):32-38

着重介绍了上地幔各向异性及其成因,研究内容和方法,各向异性研究的地球动力学意义,并强调指出橄榄石和辉石在塑性固态流动过程中产生的晶格优选方位或组构是导致上地幔各向异性最主要原因。  相似文献   

Experimental Petrology of the Kiglapait Intrusion: Cotectic Trace for the Lower Zone at 5 kbar in Graphite   总被引：3，自引：2，他引：1  

MORSE  S. A.; BRADY  J. B.; SPORLEDER  B. A. 《Journal of Petrology》2004,45(11):2225-2259

The inferred crystallization history of the troctolitic LowerZone of the Kiglapait Intrusion in Labrador is tested by meltingmineral mixtures from the intrusion, made to yield the observedcrystal compositions on the cotectic trace of liquid, plagioclase,and olivine. Melting experiments were made in a piston-cylinderapparatus, using graphite capsules at 5 kbar. Lower Zone assemblagescrystallized from 1245°C, 5% normative augite in the liquid,to 1203°C, 24% normative augite in the liquid at saturationwith augite crystals. This transit is consistent with modaldata and the large volume of the Lower Zone. The 1245°Ccotectic composition matches the average Inner Border Zone composition.Quenched troctolitic liquid from the Upper Border Zone, andothers from nearby Newark Island, plot on or near our experimentalcotectic, supporting a common fractionation history. Olivine–plagioclaseintergrowths from cotectic troctolitic melt show mosaic texturesreflecting the differing barriers to nucleation of these twophases. The linear partitioning of X_Ab in plagioclase–meltyields an intercept constant K_D = 0·524 for these maficmelts. Observed subsolidus exchange of Ca between plagioclaseand olivine elucidates the loss of Ca from plutonic olivines.The bulk composition of the intrusion is revised downward inFo and An. KEY WORDS: experimental; olivine; plagioclase; Kiglapait; partitioningAbbreviations: AP, MT, IL, OR, AB, AN, DI, HY, OL, FO, NE, Q, FSP, AUG: (Oxygen) Normative components; Ap, Aug, Ilm, Ol, Pl: Phases; Ab, An, Di, Fa, Fo, Or, Wo: Phase components; also ternary endmembers; BSE: Back-scattered electron; CaTs: Calcium Tschermak's component, CaAlAlSiO₆; D: Partition coefficient; f: Fugacity; F_L: Fraction of the system present as liquid = 1 – (PCS/100); FMQ: Fayalite = magnetite + quartz buffer; IBZ: Inner Border Zone; IW: Iron = wüstite buffer; kbar: kilobar, 10⁸ pascal; K_D: Exchange coefficient; KI: Kiglapait Intrusion; L: Liquid phase; LLD: Liquid line of descent; Ma: Mega-annum, age; Myr: Mega-year, time; OLHY: Normative OL + HY; OLRAT: The ratio OLHY/(OLHY + AUG); P: Pressure; P: Phosphorus; PCS: Percent solidified (volume); SMAR: South Margin average composition; T: Temperature, °C; UBZ: Upper Border Zone; WM: Wüstite = magnetite buffer; Wo: Wollastonite component of pyroxene; X: Mole fraction; X_Mg: Molar ratio Mg/(Mg + Fe²⁺); , X_Mg(0): Initial X_Mg before MT is formed in the norm calculation; X: Coordinate, horizontal axis; Y: Coordinate, vertical axis  相似文献   

Melt Inclusions in Primitive Olivine Phenocrysts: the Role of Localized Reaction Processes in the Origin of Anomalous Compositions   总被引：9，自引：1，他引：8  

DANYUSHEVSKY  LEONID V.; LESLIE  ROMAN A. J.; CRAWFORD  ANTHONY J.; DURANCE  PATRICIA 《Journal of Petrology》2004,45(12):2531-2553

Melt inclusions are small portions of liquid trapped by growingcrystals during magma evolution. Recent studies of melt inclusionshave revealed a large range of unusual major and trace elementcompositions in phenocrysts from primitive mantle-derived magmaticrocks [e.g. in high-Fo olivine (Fo > 85 mol %), spinel, high-Anplagioclase]. Inclusions in phenocrysts crystallized from moreevolved magmas (e.g. olivine Fo < 85 mol %), are usuallycompositionally similar to the host lavas. This paper reviewsthe chemistry of melt inclusions in high-Fo olivine phenocrystsfocusing on those with anomalous major and trace element contentsfrom mid-ocean ridge and subduction-related basalts. We suggestthat a significant portion of the anomalous inclusion compositionsreflects localized, grain-scale dissolution–reaction–mixing(DRM) processes within the magmatic plumbing system. The DRMprocesses occur at the margins of primitive magma bodies, wheremagma is in contact with cooler wall rocks and/or pre-existingsemi-solidified crystal mush zones (depending on the specificenvironment). Injection of hotter, more primitive magma causespartial dissolution (incongruent melting) of the mush-zone phases,which are not in equilibrium with the primitive melt, and mixingof the reaction products with the primitive magma. Localizedrapid crystallization of high-Fo olivines from the primitivemagma may lead to entrapment of numerous large melt inclusions,which record the DRM processes in progress. In some magmaticsuites melt inclusions in primitive phenocrysts may be naturallybiased towards the anomalous compositions. The occurrence ofmelt inclusions with unusual compositions does not necessarilyimply the existence of new geologically significant magma typesand/or melt-generation processes, and caution should be exercisedin their interpretation. KEY WORDS: melt inclusions; olivine; geochemistry; mush zones; MORB; subduction-related magmas  相似文献   

云南鸡街碱性超基性岩杂岩体中橄榄石的化学成分分带现象     

吴静  黄智龙  A.McCaig  E.Condliffe  颜以彬 《矿物学报》2004,24(1):7-13

云南鸡街碱性超基性岩杂岩体的主体岩石为岩浆结晶分异作用的产物，形成顺序为霞霓钠辉岩→霓霞岩→磷霞岩。在杂岩体的霓霞岩中发现了1粒具分带现象的橄榄石，从中心到边缘，SiO2、MgO和NiO逐渐降低，而FeO和MnO逐渐升高。MgO与SiO2和NiO之间呈正相关关系，与FeO和MnO之间呈负相关关系，中心的Fo值(最高为86．91)略高于霞霓钠辉岩中斑晶橄榄石(Fo值：85．66～86．02)，而边缘的Fo值(最低为73．82)与霓霞岩中无分带现象橄榄石(Fo值：72．18～74．72)相近。各种证据表明，发现的具分带现象橄榄石可能不是霓霞岩熔体结晶分异作用的产物，而可能是霓霞岩熔体捕获的Fo值相对较高(高于霓霞岩橄榄石的Fo值)的橄榄石晶体内部MgO和FeO等成分扩散作用的结果。  相似文献   

Cotectic Proportions of Olivine and Spinel in Olivine-Tholeiitic Basalt and Evaluation of Pre-Eruptive Processes   总被引：1，自引：1，他引：1  

ROEDER  PETER; GOFTON  EMMA; THORNBER  CARL 《Journal of Petrology》2006,47(5):883-900

The volume %, distribution, texture and composition of coexistingolivine, Cr-spinel and glass has been determined in quenchedlava samples from Hawaii, Iceland and mid-oceanic ridges. Thevolume ratio of olivine to spinel varies from 60 to 2800 andsamples with >0·02% spinel have a volume ratio ofolivine to spinel of approximately 100. A plot of wt % MgO vsppm Cr for natural and experimental basaltic glasses suggeststhat the general trend of the glasses can be explained by thecrystallization of a cotectic ratio of olivine to spinel ofabout 100. One group of samples has an olivine to spinel ratioof approximately 100, with skeletal olivine phenocrysts andsmall (<50 µm) spinel crystals that tend to be spatiallyassociated with the olivine phenocrysts. The large number ofspinel crystals included within olivine phenocrysts is thoughtto be due to skeletal olivine phenocrysts coming into physicalcontact with spinel by synneusis during the chaotic conditionsof ascent and extrusion. A second group of samples tend to havelarge olivine phenocrysts relatively free of included spinel,a few large (>100 µm) spinel crystals that show evidenceof two stages of growth, and a volume ratio of olivine to spinelof 100 to well over 1000. The olivine and spinel in this grouphave crystallized more slowly with little physical interaction,and show evidence that they have accumulated in a magma chamber. KEY WORDS: olivine; spinel; basalt glass; volume %; cotectic  相似文献   

Middle Miocene to Quaternary primary basalt and high magnesian andesite magmas of North Hokkaido, Japan: Source mantle characteristics and degrees of partial melting   总被引：1，自引：0，他引：1  

Hiroyuki  Ishimoto  Kenji  Shuto  Yoshihiko  Goto 《Island Arc》2006,15(2):251-268

Abstract   Middle Miocene to Quaternary primitive basalts and high magnesian andesite (HMA) in North Hokkaido resulted from three periods of intense volcanism; early-stage (12–10 Ma), middle-stage (9–7 Ma) and late-stage (3–0 Ma). Based on the chemical compositions of olivines and chromian spinels and bulk chemistry of the primitive rocks, we examined depths of segregation of the calculated primary magmas and the degrees of partial melting of the source mantle. In the context of asthenospheric mantle upwelling, petrological data from the present study can be accounted for by the secular change in the depth of magma segregation from the upwelled asthenospheric mantle, which is composed of fertile peridotite. Thus, the early-stage primary magmas were generated by higher degrees of partial melting of the shallower part of hot asthenospheric mantle, whereas the middle- and late-stage primary magmas resulted from lower degrees of partial melting of a deeper part of the asthenospheric mantle. The early-stage HMA magma was generated by partial melting of the remnant subcontinental lithospheric mantle composed of refractory peridotite. This melting might have resulted from an increased geothermal gradient caused by upwelling of hot asthenosphere.  相似文献   

橄榄石热解氢释放过程的分析   总被引：14，自引：0，他引：14  

李立武  张铭杰 《地球化学》1998,27(5):514-516

采用分步法热法分析了不同粒度的橄榄石的Ｈ２的质量体系,实验表明,不同粒度的橄榄石释放出的Ｈ２的质量体积不同,随着温度或粒度的变化,Ｈ２的质量体积呈现出规律性的变化,进一步探讨了氢在橄榄石中的赋存状态。  相似文献