鲁西纯橄岩捕虏体中富硅质熔（流）体的交代作用：对中生代岩石圈地幔减薄的意义

鲁西中生代辉长-闪长质岩石中纯橄岩捕虏体的岩石学、矿物化学及微量元素地球化学研究表明,纯橄岩捕虏体代表了古老岩石圈地幔的残留;地幔纯橄岩捕虏体中存在两种类型的交代作用,一是以填隙型金云母为代表的早期富含CO_2和H_2O的不活动流体的交代作用;二是以斜方辉石交代脉和网络状斜方辉石为代表的晚期富硅质熔(流)体的交代作用。后者代表了起源于软流圈的富硅质熔(流)体对古老岩石圈地幔的一种化学侵蚀。这对认识华北地块东部中生代岩石圈地幔的性质以及岩石圈减薄机制具有重要意义。     

地幔捕虏体中的流体-熔体包裹体

地幔流体的研究现已成为国内外前沿课题。地幔岩捕虏体中的流体-熔体包裹体是地幔流体的直接证据,通过对它们的研究可以直接获取地授流体的信息。包裹体按相态特征主要有三类：二氧化碳流体包裹体、二氧化碳-硅酸盐熔体包裹体、硫化物-熔体流体包裹体。本总结了地幔岩中流体-熔体包裹体的基本特征、微量元素地球化学、硫化物-熔体包裹体和二氧化碳流体包裹体稳定同位素特征的研究进展状况。讨论认为：地幔流体是由C、H、O、S等元素的挥发份和硅酸盐熔体组成;上地幔流体在化学成分上明显富含CO2、硫化物、LILE和BEE,它引起地幔交代作用和地授部分熔融;上地授流体的分布存在不均匀性,其组成也存在地区性差异。     

海南岛陆缘扩张带形成及新生代岩石圈动力学机制:来自幔源包体的地球化学证据

海南岛陆缘扩张带蓬莱地区新生代玄武岩中捕获大量尖晶石二辉橄榄岩和方辉橄榄岩幔源包体。激光剥蚀等离子体质谱(LA-ICP-MS)分析结果表明,蓬莱地幔橄榄岩含有三种不同地球化学特征的单斜辉石(Cpx):(1)a类单斜辉石Mg~#=92.3~93.4,来自富集Cpx的二辉橄榄岩,具有极低的LREE和不相容元素含量,HREE平坦,Th、U、La、Sr正异常,经历了7%~10%的尖晶石相部分熔融,仅受到极低程度强不相容元素(Th、U、La、Sr)初期富集交代作用;(2)b类单斜辉石Mg~#=89.9~90.3,来自较富集Cpx的二辉橄榄岩,具有中等的LREE和LILE含量,HREE平坦,微量元素蛛网图上显示Th、U正异常,Rb、Ba、Nb、Ta、Sr、Ti负异常,经历4%~5%的尖晶石相部分熔融,可能受到了含LREE和Th、U等不相容元素的硅酸盐熔体交代;(3)c类单斜辉石Mg~#=91.4~92.8,来自贫Cpx的二辉橄榄岩和方辉橄榄岩,具有富集的LREE和LILE含量,HREE弱分异,微量元素蛛网图上显示Th、U正异常及强烈的Nb、Ta、Ti负异常,经历了8%~20%的尖晶石相部分熔融,其交代熔体可能是来自源区有石榴子石残留的碳酸盐熔体。全岩主、微量元素及模拟计算结果表明,这些幔源包体的主量元素主要受部分熔融程度影响,并且方辉橄榄岩经历的部分熔融程度大于二辉橄榄岩。地幔橄榄岩的Sr-Nd同位素组成表明该区具有MORB-OIB型亏损地幔特征。此外,蓬莱部分地幔橄榄岩包体显示正斜率的HREE分异特征((Gd/Yb)_N=0.4~0.7),暗示该区地幔经历了源自石榴子石稳定区的变压熔融,总体熔融程度为18%以上,指示了较高的地幔潜能温度。综合前人对海南岛新生代玄武岩最新研究成果,我们认为海南地幔柱可能为该区软流圈地幔置换古老岩石圈地幔提供了热源,导致了区域岩石圈地幔的破坏,从而引起包括地幔柱本身、软流圈和富集岩石圈的熔融。岩石圈地幔性质的改变和不均一性可能是海南岛陆缘扩张带新生代岩石圈减薄的主要动力学机制。     

熔体再富集作用对大陆岩石圈地幔的影响

         二辉橄榄岩通常被认为是低程度部分熔融的残留,但熔体再富集作用为其成因提供了一种新的解释。熔体再富集作 用通常是指软流圈来源的玄武质熔体加入到难熔的方辉橄榄岩或纯橄岩形成更为饱满的二辉橄榄岩的过程。除了使主量元 素富集之外,熔体再富集作用还可以使微量元素与Sr-Nd 同位素从方辉橄榄岩中的富集特征转变为二辉橄榄岩所呈现的亏 损特征。对于熔体再富集作用是否改变橄榄岩的Os 同位素组成还存在较大的争议,它主要取决于加入熔体的比例,熔体中 硫的饱和程度以及熔体再富集作用发生的时间等因素。对于以低熔/岩比例为主的大陆岩石圈地幔来说,熔体再富集作用对 橄榄岩的Os 同位素组成的影响可能较为有限。除了化学成分上的影响之外,熔体的加入也会改变大陆岩石圈地幔的物理特 征。这一过程使得岩石圈地幔的渗透率增大和黏滞度降低,从而会破坏大陆岩石圈地幔的稳定性。虽然熔体再富集作用可 以影响和改变岩石圈地幔的性质,但它是否导致克拉通地幔的减薄以及克拉通破坏尚有疑问。     

Geochemistry and Evolution of Subcontinental Lithospheric Mantle in Central Europe: Evidence from Peridotite Xenoliths of the Kozakov Volcano, Czech Republic

Neogene basanite lavas of Kozákov volcano, located alongthe Lusatian fault in the northeastern Czech Republic, containabundant anhydrous spinel lherzolite xenoliths that providean exceptionally continuous sampling of the upper two-thirdsof central European lithospheric mantle. The xenoliths yielda range of two-pyroxene equilibration temperatures from 680°Cto 1070°C, and are estimated to originate from depths of32–70 km, based on a tectonothermal model for basalticunderplating associated with Neogene rifting. The sub-Kozákovmantle is layered, consisting of an equigranular upper layer(32–43 km), a protogranular intermediate layer that containsspinel–pyroxene symplectites after garnet (43–67km), and an equigranular lower layer (67–70 km). Negativecorrelations of wt % TiO₂, Al₂O₃, and CaO with MgO and clinopyroxenemode with Cr-number in the lherzolites record the effects ofpartial fusion and melt extraction; Y and Yb contents of clinopyroxeneand the Cr-number in spinel indicate 5 to 15% partial melting.Subsequent metasomatism of a depleted lherzolite protolith,probably by a silicate melt, produced enrichments in the largeion lithophile elements, light rare earth elements and highfield strength elements, and positive anomalies in primitivemantle normalized trace element patterns for P, Zr, and Hf.Although there are slight geochemical discontinuities at theboundaries between the three textural layers of mantle, theretends to be an overall decrease in the degree of depletion withdepth, accompanied by a decrease in the magnitude of metasomatism.Clinopyroxene separates from the intermediate protogranularlayer and the lower equigranular layer yield ¹⁴³Nd/¹⁴⁴Nd valuesof 0·51287–0·51307 (_Nd = +4·6 to+8·4) and ⁸⁷Sr/⁸⁶Sr values of 0·70328–0·70339.Such values are intermediate with respect to the Nd–Srisotopic array defined by anhydrous spinel peridotite xenolithsfrom central Europe and are similar to those associated withthe present-day low-velocity anomaly in the upper mantle beneathEurope. The geochemical characteristics of the central Europeanlithospheric mantle reflect a complex evolution related to Devonianto Early Carboniferous plate convergence, accretion, and crustalthickening, Late Carboniferous to Permian extension and gravitationalcollapse, and Neogene rifting, lithospheric thinning, and magmatism. KEY WORDS: xenoliths; lithospheric mantle; REE–LILE–HFSE; Sr–Nd isotopes; Bohemian Massif     

Petrography and Geochemistry of Peridotite Xenoliths from Hannuoba and Significance for Lithospheric Mantle Evolution

Mantle-derived xenoliths and xenocrysts in Pale-ozoic diamondiferous ki mberlites in Mengyin (Shan-dong Province) and Fuxian (Liaoning Province) showthe presence of a cold,thick lithospheric mantle be-neath the North China craton ( NCC) in the MiddleOrdovician ( Griffin et al ., 1998 ; Menzies et al .,1993 ;Fan and Menzies ,1992) . However ,studies onmantle peridotites captured in the Tertiary to Neo-gene basalts of the NCC have revealed the existenceof a thin, hot and fertile lithosph…     

Insights into Petrological Characteristics of the Lithosphere of Mantle Wedge beneath Arcs through Peridotite Xenoliths: a Review

The petrological characteristics of peridotite xenoliths exhumedfrom the lithospheric mantle below the Western Pacific arcs(Kamchatka, NE Japan, SW Japan, Luzon–Taiwan, New Irelandand Vanuatu) are reviewed to obtain an overview of the supra-subductionzone mantle in mature subduction systems. These data are thencompared with those for peridotite xenoliths from recent orolder arcs described in the literature (e.g. New Britain, WesternCanada to USA, Central Mexico, Patagonia, Lesser Antilles andPannonian Basin) to establish a petrological model of the lithosphericmantle beneath the arc. In currently active volcanic arcs, thedegree of partial melting recorded in the peridotites appearsto decrease away from the fore-arc towards the back-arc region.Highly depleted harzburgites, more depleted than abyssal harzburgites,occur only in the frontal arc to fore-arc region. The degreeof depletion increases again to a degree similar to that ofthe most depleted abyssal harzburgites within the back-arc extensionalregion, whether or not a back-arc basin is developed. Metasomatismis most prominent beneath the volcanic front, where the magmaproduction rate is highest; silica enrichment, involving themetasomatic formation of secondary orthopyroxene at the expenseof olivine, is important in this region because of the additionof slab-derived siliceous fluids. Some apparently primary orthopyroxenes,such as those in harzburgites from the Lesser Antilles arc,could possibly be of this secondary paragenesis but have beenrecrystallized such that the replacement texture is lost. TheTi content of hydrous minerals is relatively low in the sub-arclithospheric mantle peridotites. The K/Na ratio of the metasomatichydrous minerals decreases rearward from the fore-arc mantleas well as downward within the lithospheric mantle. The lithosphericmantle wedge peridotites, especially metasomatized ones frombelow the volcanic front, are highly oxidized. Shearing of themantle wedge is expected beneath the volcanic front, and isrepresented by fine-grained peridotite xenoliths. KEY WORDS: mantle wedge; lithospheric mantle; peridotite xenoliths; melting; metasomatism     

浙江新昌地幔岩捕虏体中的硫化物包裹体初步研究

浙江新昌一带晚第三纪碱性玄武岩中地幔岩（二辉橄榄岩）捕虏体内存在大量硫化物熔体包裹体。电子探针分析表明,硫化物相成分主要为镍黄铁矿,次为磁共铁矿。硫化物包裹体的Ｎｉ／Ｆｅ值与寄主地幔岩的橄榄石含量呈正相关。同一包裹体的硫化物相成分不均一,自中心至边缘硫化物的Ｎｉ／Ｆｅ、（Ｆｅ＋Ｎｉ）／Ｓ值和Ｎｉ呈均呈增加趋势。通过与中国汉诺坝、德国ＷｅｓｔＥｉｆｅｌ东欧Ｎｏｇｒａｄ－Ｇｏｍｏｒ地区资料的综合分析,     

汉诺坝橄榄岩捕虏体的单斜辉石LAM-ICPMS分析及其岩石圈地幔演化意义

橄榄岩成分及其中矿物(如单斜辉石)微量元素组成可以很好地揭示岩石圈地幔性质．在对汉诺坝新生代玄武岩中橄榄岩捕虏体做详细岩相学和岩石化学研究基础上,重点分析了单斜辉石的激光原位微量元素,并探讨了新生代华北克拉通北缘岩石圈地幔特征及地幔演化．汉诺坝地区岩石圈地幔是相当于原始地幔经过不同程度的部分熔融抽取形成的,除个别样品的部分熔融程度为15％-20％外,多数样品<5％．全岩主元素、单斜辉石成分体现出新生代汉诺坝地区的岩石圈地幔是很不均一的:在主体饱满型中有亏损型地幔的残留．这种共存现象可能是软流圈物质对古老地幔进行侵蚀、混合和改造置换的结果．单斜辉石微量元素组成所体现的碳酸岩岩浆交代作用和硅酸盐熔／流体的交代作用也支持这一认识．     

山东蓬莱新生代岩石圈地幔的异常锂同位素组成：橄榄岩包体的离子探针分析

应用离子探针技术对山东蓬莱新生代玄武岩中橄榄岩包体的主要组成矿物进行了原位测定,结果显示了强烈偏离正 常地幔矿物组成和平衡的Li 含量和同位素比值。橄榄石、斜方辉石和单斜辉石的Li 含量和δ7Li 分别为（2.0~10.4）×10-6, （2.8~23.8）×10-6 和（3.3~59.7）×10-6;-28.6‰ ~+0.5‰,-12.7‰ ~+12.8‰和-41.5‰ ~+22.6‰。这种强烈的非平衡体系反 映了最近强烈和复杂的地幔交代作用。辉石的高Li（~ 60×10-6）和δ7Li（~ +20‰）反映了最近富Li地幔熔体/ 流体的特征, 而橄榄石的中等Li 富集（<5×10-6）和强烈的δ7Li 亏损（~ -20‰）则可能记录了更早一期低δ7Li 的地幔交代。同位素剖面 的扩散反演以及Li 强烈富集与LREE 相对亏损之间的解耦显示了两期地幔交代作用的短暂性和近期性。因此,我们认为华 北东部克拉通上地幔中存在与再循环有关的锂同位素异常组分,它们的形成应该与中生代以来太平洋板块向东亚大陆下的 俯冲有关. 这些组分能够在地幔中较长的保存直至最近被热扰动所释放,并被橄榄岩包体所记录。     

济南辉长岩岩浆演化过程:来自熔体包裹体的证据

本研究首次报道了早白垩世济南辉长岩中橄榄石斑晶捕获的熔体包裹体的研究结果。济南辉长岩中橄榄石的Fo(60.3~74.6),Mn(2500~3500μg/g),Ni(70~1349μg/g),Fe/Mn比值(61.2~83.5),与源区母岩为纯的橄榄岩形成的熔体结晶出的橄榄石性质不同,可能与源区存在辉石岩的贡献有关。橄榄石中熔体包裹体主量元素具有较大的变化范围。熔体包裹体成分的标准矿物计算(CIPW)表明,MgO10%的熔体包裹体为含有霞石和橄榄石标准矿物分子的硅不饱和熔体,Mg O10%时为含石英标准矿物分子的硅饱和熔体。橄榄石中包裹有辉石和斜长石,说明岩浆演化过程应该处于开放环境。熔体包裹体的(~208Pb/~206Pb)i和(~207Pb/~206Pb)i与MgO具有良好的负相关关系,与SiO_2具有良好的正相关关系,以及熔体包裹体具有较高的SiO_2特征表明岩浆演化过程中可能有下地壳长英质组分的加入。熔体包裹体的Pb同位素落在EMI附近并向EMII延伸,其源区可能有EMI和EMII的贡献,熔体包裹体的主量元素成分说明其源区母岩可能有橄榄岩和辉石岩的贡献。     

Transformation of Archaean Lithospheric Mantle by Refertilization: Evidence from Exposed Peridotites in the Western Gneiss Region, Norway

Orogenic peridotites occur enclosed in Proterozoic gneissesat several localities in the Western Gneiss Region (WGR) ofwestern Norway; garnet peridotites typically occur as discretezones within larger bodies of garnet-free, chromite-bearingdunite and are commonly closely associated with pyroxenitesand eclogites. The dunites of the large Almklovdalen peridotitebody have extremely depleted compositions (Mg-number 92–93·6);the garnet peridotites have lower Mg-number (90·6–91·7)and higher whole-rock Ca and Al contents. Post-depletion metasomatismof both rock types is indicated by variable enrichment in thelight rare earth elements, Th, Ba and Sr. The dunites can bemodelled as residues after very high degrees (>60%) of meltextraction at high pressure (5–7 GPa), inconsistent withthe preservation of lower degrees of melting in the garnet peridotites.The garnet peridotites are, therefore, interpreted as zonesof melt percolation, which resulted in refertilization of thedunites by a silicate melt rich in Fe, Ca, Al and Na, but notTi. Previous Re–Os dating gives Archaean model ages forthe dunites, but mixed Archaean and Proterozoic ages for thegarnet peridotites, suggesting that refertilization occurredin Proterozoic time. At least some Proterozoic lithosphere mayrepresent reworked and transformed Archaean lithospheric mantle. KEY WORDS: Archaean mantle; Proterozoic mantle; Western Gneiss Region, Norway; mantle metasomatism; garnet peridotite     

华北克拉通中生代拆沉陆壳物质对岩石圈地幔的改造:来自橄榄岩捕虏体中角闪石的成分制约

对鲁西和太行山南段早白垩世高镁闪长岩中橄榄岩捕虏体中的角闪石进行了主量元素和痕量元素分析,并讨论了角闪石成分与改造岩石圈地幔熔体的性质与来源之间的关系。研究结果表明,橄榄岩类捕虏体中的角闪石主要为交代成因。在化学上,它们属于钙质角闪石。太行山南段符山橄榄岩捕虏体中的角闪石属于镁质普通角闪石和浅闪石或浅闪石质普通角闪石;鲁西铁铜沟橄榄岩捕虏体中的角闪石为韭闪石质普通角闪石、浅闪石质普通角闪石和镁绿钙闪石质普通角闪石。与板内橄榄岩捕虏体中的角闪石相比,鲁西和太行山南段早白垩世高镁闪长岩橄榄岩捕虏体中的角闪石具有相对高的Mg#(鲁西:86.0~90.8;太行山:90.7~94.2)和SiO2(鲁西:44.04%~46.98%;太行山:47.09%~49.79%)以及相对低的Na2O(1.92%~2.51%)、TiO2(0.01%~1.46%)、Nb(0.29×10-6~1.98×10-6)和Zr(1.61×10-6~5.34×10-6),这与来自俯冲带之上地幔楔橄榄岩捕虏体中的角闪石相类似。综合橄榄岩捕虏体的地球化学特征,可以判定华北克拉通早白垩世岩石圈地幔遭受了起源于拆沉陆壳物质熔融熔体的改造。     

河北阳原新生代玄武岩中橄榄岩捕虏体矿物化学:华北岩石圈地幔演化

橄榄岩及其中矿物的组成, 特别是单斜辉石的微量元素, 可以很好的揭示岩石圈地幔性质.在对河北阳原新生代玄武岩中橄榄岩捕虏体详细岩相学和矿物化学研究基础上, 重点分析了单斜辉石的激光原位微量元素, 讨论了新生代华北内部山带岩石圈地幔特征及其演化机制.阳原地区陆下岩石圈, 除个别样品的部分熔融程度为15%~20%外, 多数样品<5%, 显示该区的地幔演化是不均一的, 并表现为饱满与难熔-过渡型地幔的交叉并存.这种共存现象可以用软流圈物质对古老地幔进行不均匀侵蚀、改造和置换作用来解释.      

中国东部早第三纪玄武岩中幔源包体的变形特征及其上地幔流变学意义

中国东部含幔源包体的早第三纪玄武岩已发现的有吉林双辽、河北阳原和山西繁峙。本文详细研究了这三个地点幔源包体的变形特征，结果表明，这些地点的幔源包体以尖晶石二辉橄榄岩为主，其结构主要为残斑结构。包体中橄榄石显示明显的优选方位，发育有反映高温位错蠕变机制的位错亚构造。包体的平衡温度在８００一１１００℃之间，压力为０．７一１．７ＣＰａ。来源深度为２８一５２ｋｍ。采用显微构造应力计计算的差异应力在１７一２４ＭＰａ之间，由橄榄岩高温流变律计算的应变速率为１０￣（－１５）－１０￣（－１８）ｓ￣（－１）等效粘滞度为１０￣（２１）一１０￣（２５）ｓｐａ．Ｓ之间。中国东部早第三纪与晚第三纪以后的幔源包体具有基本相同的特征，表明晚第三纪以后的上地幔继承和发展了早第三纪时的特征。中国东部早第三纪以来的上地幔符合大陆拉张带和裂谷上地幔的流变特征。     

中国东部早第三纪玄武岩中幔源包体的变形特征及其上地幔流变学意义

中国东部含幔源包体的早第三纪玄武岩已发现的有吉林双辽、河北阳原和山西繁峙。本文详细研究了这三个地点幔源包体的变形特征，结果表明，这些地点的幔源包体以尖晶石二辉橄榄岩为主，其结构主要为残斑结构。     

大兴安岭北段新林区塔木兰沟组火山岩成因及地幔富集作用

本文报道了大兴安岭北段新林区塔木兰沟组玄武岩样品锆石U-Pb定年结果和岩石地球化学分析,探讨了塔木兰沟组玄武岩的成因及中生代岩石圈地幔的性质。锆石U-Pb定年结果显示,塔木兰沟组玄武岩形成于晚侏罗世(~153Ma),该玄武岩样品的SiO_2含量介于49.96%~59.06%之间,全碱含量介于5.21%~7.44%之间,Mg~#{100×n(Mg~(2+))/[(n(Mg~(2+))+n(Fe~(2+))]}值介于50~94之间。该玄武岩相对富集轻稀土元素(LREEs)、亏损重稀土元素(HREEs),La_N/Yb_N值介于10.7~20.0之间,具有轻微的Eu异常(δEu=0.80~1.09),结合区域研究成果,认为塔木兰沟组玄武岩形成于蒙古—鄂霍茨克洋闭合造山后岩石圈伸展环境,源区岩浆起源于石榴子石相二辉橄榄岩与尖晶石相二辉橄榄岩部分熔融的混合形成,含富含挥发分的金云母和角闪石等,暗示岩石圈地幔经历了交代作用的改造,交代类型以俯冲板片流体/熔体交代为主。结合区域已有研究表明,本区地幔交代富集作用来源于蒙古—鄂霍茨克洋的向南俯冲,塔木兰沟组火山岩形成于蒙古~鄂霍茨克洋闭合造山后岩石圈伸展背景。     

山东省第四纪玄武岩中幔源包体的变形特征及其上地幔流变学意义

山东省第四纪玄武岩中含有数量、大小不等的幔源包体。这些包体主要为尖晶石二辉橄榄岩，以原生粒状和残斑结构为特征。包体中橄榄石的位错亚构造反映了上地幔高温蠕变机制。包体的平衡温度在８００—１１００℃之间，压力为０．８—２．０ＧＰａ，相应的来源深度为２８—６５ｋｍ。在该深度范围内，上地幔的流动应力为１３—２６ＭＰａ，应变速率为１０－１４—１０－２０ｓ－１，等效粘滞度为１０２０—１０２５Ｐａ·ｓ，符合大陆拉张带上地幔的特征。作者认为，中国东部上地幔在早第三纪或之前开始有底辟上涌，它导致岩石圈的减薄以及地壳的拉张，造成中国东部的拉张环境和裂谷的发育。上地幔的这种运动可能在新第三纪达到高峰，而在第四纪已减弱     

扬子克拉通东北缘岩石圈地幔的Re-Os同位素地球化学:大陆岩石圈地幔的形成和演化的制约

苏皖地区新生代碱性玄武岩中有丰富的地幔橄榄岩捕虏体 ,测定了 2 0多个样品的Re Os元素丰度和锇同位素组成 ,结果 :Re =0 .0 2 7× 10 - 9～ 0 .375×10 - 9,Os=0 .112×10 - 9～ 3.35× 10 - 9,1 87Os 1 88Os=0 .117～ 0 .134。由代理等时线法1 87Os 1 88Os Yb获得该区岩石圈地幔早期熔体亏损事件的年龄为 1.7Ga(中元古代 )。苏皖地区岩石圈地幔的古老性表明它是元古代后岩石圈拆沉 减薄作用的残余地幔部分。岩石圈地幔经过了亏损 富集多阶段演化。     

The Evolution of the Upper Mantle beneath the Canary Islands: Information from Trace Elements and Sr isotope Ratios in Minerals in Mantle Xenoliths

Laser ablation microprobe data are presented for olivine, orthopyroxeneand clinopyroxene in spinel harzburgite and lherzolite xenolithsfrom La Palma, Hierro, and Lanzarote, and new whole-rock trace-elementdata for xenoliths from Hierro and Lanzarote. The xenolithsshow evidence of strong major, trace element and Sr isotopedepletion (⁸⁷Sr/⁸⁶Sr 0·7027 in clinopyroxene in themost refractory harzburgites) overprinted by metasomatism. Thelow Sr isotope ratios are not compatible with the former suggestionof a mantle plume in the area during opening of the AtlanticOcean. Estimates suggest that the composition of the originaloceanic lithospheric mantle beneath the Canary Islands correspondsto the residues after 25–30% fractional melting of primordialmantle material; it is thus significantly more refractory than‘normal’ mid-ocean ridge basalt (MORB) mantle. Thetrace element compositions and Sr isotopic ratios of the mineralsleast affected by metasomatization indicate that the upper mantlebeneath the Canary Islands originally formed as highly refractoryoceanic lithosphere during the opening of the Atlantic Oceanin the area. During the Canarian intraplate event the uppermantle was metasomatized; the metasomatic processes includecryptic metasomatism, resetting of the Sr–Nd isotopicratios to values within the range of Canary Islands basalts,formation of minor amounts of phlogopite, and melt–wall-rockreactions. The upper mantle beneath Tenerife and La Palma isstrongly metasomatized by carbonatitic or carbonaceous meltshighly enriched in light rare earth elements (REE) relativeto heavy REE, and depleted in Zr–Hf and Ti relative toREE. In the lithospheric mantle beneath Hierro and Lanzarote,metasomatism has been relatively weak, and appears to be causedby high-Si melts producing concave-upwards trace element patternsin clinopyroxene with weak negative Zr and Ti anomalies. Ti–Al–Fe-richharzburgites/lherzolites, dunites, wehrlites and clinopyroxenitesformed from mildly alkaline basaltic melts (similar to thosethat dominate the exposed parts of the islands), and appearto be mainly restricted to magma conduits; the alkali basaltmelts have caused only local metasomatism in the mantle wall-rocksof such conduits. The various metasomatic fluids formed as theresults of immiscible separations, melt–wall-rock reactionsand chromatographic fractionation either from a CO₂-rich basalticprimary melt, or, alternatively, from a basaltic and a siliceouscarbonatite or carbonaceous silicate melt. KEY WORDS: mantle xenoliths; mantle minerals; trace elements; depletion; carbonatite metasomatism