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1.
塔里木地台南缘发现钾镁煌斑岩   总被引:10,自引:1,他引:9  
赵磊  杨万志 《现代地质》1998,12(4):555-558
首次在塔里木地台南缘皮山县境内找到钾镁煌斑岩,它们呈脉状产出,围岩为白云母石英片岩。该钾镁煌斑岩的岩石化学成分与亚洲钾镁煌斑岩的平均岩石化学成分接近,与澳大利亚西金伯利地区钾镁煌斑岩一致,稀土元素及其配分模式位于世界钾镁煌斑岩的范围之内,其中大多数标本具有已知世界钾镁煌斑岩的共同微量元素特征:具Ba、K、La和Ce的正异常及Ta、Nb、Sr和Ti的负异常。该钾镁煌斑岩的发现对研究区金刚石找矿和深部地质过程研究均具深远意义。  相似文献
2.
Proterozoic mafic potassic and ultrapotassic igneous rocks emplacedin the Cuddapah Basin and Dharwar Craton of the southern Indianshield are among the earliest recorded on Earth. Lamproitesintrude the basin and its NE margin, whereas kimberlites intrudethe craton to the west of the basin. Kimberlites occur in twospatially separate groups: the non-diamondiferous Mahbubnagarcluster that was emplaced at 1400 Ma and is of a similar ageto the Cuddapah lamproites, and the predominantly diamondiferousAnantapur cluster, emplaced at  相似文献
3.
塔里木南缘煌斑岩的时代及其地质意义   总被引:9,自引:2,他引:7  
郭坤一  张传林  赵宇  董永观  王爱国 《地质科学》2003,38(4):532-534,518
在塔里木南缘皮山县境内发现东西向煌斑岩带 ,它们呈脉状产出 ,围岩为前寒武纪绢云绿泥石英片岩、变质粉砂岩及石炭纪玄武岩、结晶灰岩等。岩石地球化学特征与典型地区的钾镁煌斑岩相似。从煌斑岩中挑选的金云母经Ar Ar测年 ,获得理想的坪年龄为 2 1 7.65± 0 .39Ma ,40 Ar/36Ar 39Ar/36Ar等时线年龄为 2 1 7.2 7± 1 .38Ma,与坪年龄一致。这一年龄值代表了煌斑岩的形成时代 ,与阿尔金断裂形成时代基本一致 ,它代表了塔里木南缘在这一时期重要的走滑事件。煌斑岩带的发现 ,对塔里木南缘的金刚石找矿勘查具有重要意义  相似文献
4.
Major and trace element, Sr–Nd–Pb isotope and mineralchemical data are presented for newly discovered ultrapotassiclavas in the Tangra Yumco–Xuruco graben in southern Tibet.The ultrapotassic lavas are characterized by high MgO, K2O andTiO2, low Al2O3 and Na2O contents, and also have high molarK2O/Al2O3, molar (K2O + Na2O)/Al2O3 and K2O/Na2O ratios. Theirhigh abundances of incompatible trace elements such as largeion lithophile elements (LILE) and light rare earth elements(LREE) reach the extreme levels typical of lamproites. The lamproitesshow highly radiogenic 87Sr/86Sr (0· 7166–0·7363) and unradiogenic 143Nd/144Nd (0· 511796–0·511962), low 206Pb/204Pb (18· 459–18· 931),and elevated radiogenic 207Pb/204Pb (15· 6732–15·841) and 208Pb/204Pb (39· 557–40· 058) ratios.On the basis of their geochemical and isotopic systematics,the lamproites in south Tibet have a distinct magma source thatcan be differentiated from the sources of potassic lavas inthe east Lhasa and Qiangtang blocks. Their high Nb/Ta ratios(17· 10–19· 84), extremely high Th/U ratios(5· 70–13· 74) and distinctive isotope compositionsare compatible with a veined mantle source consisting of partialmelts of subducted Tethyan oceanic sediments and sub-continentallithospheric depleted mantle. Identification of the lamproitesand the delineation of their mantle source provide new evidencerelevant for models of the uplift and extension of the Tibetanplateau following the Indo-Asia collision. Metasomatism by partialmelts from isotopically evolved, old sediment subducted on theyoung Tethyan slab is an alternative explanation for PrecambrianNd and Pb model ages. In this model, differences in isotopiccomposition along-strike are attributed to differences in thetype of sediment being subducted, thus obviating the need formultiple metasomatic events over hundreds of million years.The distribution of lamproites, restricted within a north–south-trendinggraben, indicates that the initiation of east–west extensionin south Tibet started at 25 Ma. KEY WORDS: lamproites; subducted oceanic sediment; Tibetan active continental collision belt  相似文献
5.
西昆仑北缘钾镁煌斑岩及超镁铁岩地质特征   总被引:5,自引:1,他引:4  
产于塔里木地台铁克力克隆起内的钾镁煌夺岩石化学成分与亚洲钾煌斑岩的平均岩这成分接近,与澳大利亚西后利地区钾镁煌斑岩一致。稀土元素、微量元素组成与世界已 知钾镁煌斑岩具有相同特征。铁克力克隆起南缘柯岗-塔伦深断裂南阔绰人串珠状分布的超镁铁岩体,与钾镁煌斑岩具有相同的地质背景。该深断裂与西昆仑北缘深断裂交汇处是寻找含矿钾镁煌斑岩的有利部位。  相似文献
6.
贵州省镇远地区钾镁煌斑岩岩石特征   总被引:5,自引:0,他引:5  
贵州省镇远地区的钾镁煌斑岩(Lamproite)的分布在大地构造上受地台和地台内隆起与坳陷间的深断裂控制,为浅成侵入脉岩,呈岩墙或岩床产出,规模不大,厚几厘米至数米,长数十米至千米,已见于深冲、白坟、思南塘等岩群。岩石具煌斑结构,块状构造,斑晶为钛金云母、透辉石、假像橄榄石,基质除上述矿物外,还有透长石、白榴石、角闪石、磷灰石、锆石、金红石等,还见到微量镁铝榴石和铬铁矿。其中钛金云母、铬铁矿、镁铝榴石的矿物化学成分与西澳同类岩石十分接近,投入米切尔,J·格尼有关图件中,均落入钾镁煌斑岩趋势区。岩石化学成分属钾质超基性岩,K_2O>Na_2O,K_2O/Na_2O为20.85~66.51,富含TiO_2,但MgO较西澳同类岩石略低。富含Sr、Ba、Zr、Nb、P等痕量元素。稀土总量高,富集轻稀土。稀土分配模式与西澳同类岩石一致。D_5岩体中经1987年再次选矿证实含微量金刚石。  相似文献
7.
西昆仑克里阳地区钾镁煌斑岩岩石学特征及其意义   总被引:4,自引:1,他引:3  
对西昆仑克里阳钾镁煌斑岩的岩石学特征及源区性质进行了详细研究,并同国内外钾镁煌斑岩及其他超钾质岩石作了对比。该钾镁煌斑岩富Al2O3、贫TiO2,不相容元素相对亏损,为不含金刚石类型其源区富集程度不高,交代作用较弱,且起源深度较浅(〉115km)。高的C、Sr、Pb同位素组成表明该钾镁煌斑岩可能受到壳源物质的混染。这些特征暗示西昆仑地区有其他含金刚石源岩的存在。  相似文献
8.
The Serbian province of Tertiary ultrapotassic volcanism isrelated to a post-collisional tectonic regime that followedthe closure of the Tethyan Vardar Ocean by Late Cretaceous subductionbeneath the southern European continental margin. Rocks of thisprovince form two ultrapotassic groups; one with affinitiesto lamproites, which is concentrated mostly in the central partsof the Vardar ophiolitic suture zone, and the other with affinitiesto kamafugites, which crops out in volcanoes restricted to thewestern part of Serbia. The lamproitic group is characterizedby a wide range of 87Sr/86Sri (0·70735–0·71299)and 143Nd/144Ndi (0·51251–0·51216), whereasthe kamafugitic group is isotopically more homogeneous witha limited range of 87Sr/86Sri (0·70599–0·70674)and 143Nd/144Ndi (0·51263–0·51256). ThePb isotope compositions of both groups are very similar (206Pb/204Pb18·58–18·83, 207Pb/204Pb 15·62–15·70and 208Pb/204Pb 38·74–38·99), falling withinthe pelagic sediment field and resembling Mesozoic flysch sedimentsfrom the Vardar suture zone. The Sr and Nd isotopic signaturesof the primitive lamproitic rocks correlate with rare earthelement fractionation and enrichment of most high field strengthelements (HFSE), and can be explained by melting of a heterogeneousmantle source consisting of metasomatic veins with phlogopite,clinopyroxene and F-apatite that are out of isotopic equilibriumwith the peridotite wall-rock. Decompression melting, with varyingcontributions from depleted peridotite and ultramafic veinsto the final melt, accounts for consistent HFSE enrichment andisotopic variations in the lamproitic group. Conversely, themost primitive kamafugitic rocks show relatively uniform Srand Nd isotopic compositions and trace element patterns, andsmall but regular variations of HFSE, indicating variable degreesof partial melting of a relatively homogeneously metasomatizedmantle source. Geochemical modelling supports a role for phlogopite,apatite and Ti-oxide in the source of the kamafugitic rocks.The presence of two contrasting ultrapotassic suites in a restrictedgeographical area is attributable to the complex geodynamicsituation involving recent collision of a number of microcontinentswith contrasting histories and metasomatic imprints in theirmantle lithosphere. The geochemistry of the Serbian ultrapotassicrocks suggests that the enrichment events that modified thesource of both lamproitic and kamafugitic groups were relatedto Mesozoic subduction events. The postcollisional environmentof the northern Balkan region with many extensional episodesis consistent at regional and local levels with the occurrenceof ultrapotassic rocks, providing a straightforward relationshipbetween geodynamics and volcanism. KEY WORDS: kamafugite; lamproite; Mediterranean; Serbia; mantle metasomatism; veined mantle; petrogenesis  相似文献
9.
Composite dykes consisting of leucominette and dacite as wellas discrete dykes and flows of minette and lamproite composition,occur in the Veliki Majdan area, western Serbia. This area ispart of the Serbian Tertiary magmatic province, which consistsof numerous small occurrences of ultrapotassic igneous rocks.The composite dykes have leucominette margins (up to 150 cmthick) enclosing a central part of dacite up to 100 m in width.Between these two lithologies, a decimetre-sized transitionzone may occur. Petrography, mineral chemistry and bulk-rockgeochemistry, including Sr, Nd and Pb isotopes, provide evidencethat the minettes and leucominettes formed by hybridizationbetween a felsic magma similar in composition to dacite anda mantle-derived lamproitic magma. The leucominettes and minettescontain all phenocryst types (biotite, plagioclase, quartz)present in the dacites, but in partly resorbed and reacted form.The mica displays a great diversity of resorption textures asa result of partial dissolution, incipient melting and phlogopitization,suggesting superheating of the felsic melt during hybridization;the mineral modes and mineral compositions of the leucominettesand minettes resemble those in the lamproites. A model for themodification of lamproite melt towards minette is presentedin which minette is formed by mixing of lamproite and <30%felsic magma. The lack of any significant correlation betweenPb isotopic ratios and some of the ‘mixing-indices’(SiO2, Zr, Zr/Nb, 143Nd/144Ndi) recognized in the hybridizationmodel for the Veliki Majdan dykes may be a result of similarityof the Pb-isotopic signature in the two end-members. Highlyphlogopitized biotite xenocrysts in the minettes are ascribedto the retention of volatile components after magma mixing andcrystallization of a new generation of phlogopite from the hybridizedmagma. The magma-mixing model explains the reverse zoning andresorption features of phlogopite macrocrysts commonly recognizedin calcalkaline lamprophyres elsewhere. Therefore, this mixingmechanism may be globally applicable for the origin of minettesassociated with calcalkaline granitic plutonism in post-orogenicsettings. KEY WORDS: Serbia; lamproites; micas; phlogopitization; calcalkaline lamprophyres; superheating; magma mixing  相似文献
10.
扬子地台西缘钾质煌斑岩类的岩石学研究   总被引:3,自引:0,他引:3       下载免费PDF全文
舒小辛 《岩石学报》1994,10(3):248-260
扬子地台西缘钾质煌麻岩的矿物组合中缺少钾碱镁门石、柱红石等富钾贫铝矿物,其辉石和白榴石富Al2O3,金云母贫TiO2,透长石的Na2O含量高。全岩Al2O3高,K2O/Al2O3(<0.7)低,(Gd/Yb)N低。岩体中含有二辉橄榄岩包体、镁铝榴石捕虏体晶。这些特点表明其岩浆源区的亏损程度低。此外,钾质煌斑岩明显亏损Nb、Ti,可能是与其源区经受过板块边缘活动影响有关。  相似文献
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