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1.
Primitive olivine-mica-K-feldspar lamprophyre dykes, dated at 1831 ± 6 Ma, intrude lower greenschist facies rocks of the Early Proterozoic Pine Creek Inlier, of northern Australia. They are spatially, temporally and probably genetically associated with a post-tectonic composite granite-syenite pluton (Mt. Bundey pluton). The dykes have unusually high contents of large-ion-lithophile (LILE) and LREE elements (e.g. Ba up to 10,000 ppm, Ce up to 550 ppm, K2O up to 7.5 wt. %) that resemble the concentrations found in the West Kimberley olivine and leucite lamproites. However, mineralogically the Mt. Bundey lamprophyres resemble shoshonitic lamprophyres and lack any minerals diagnostic of lamproites; leucite or leucite-pseudomorphs are absent. Mineral compositions are also unlike those in lamproites: micas contain higher Al2O3 than lamproitic mica; amphiboles are secondary actinolites after diopside; and oxides consist of zincian-chromian magnetite and groundmass magnetite. Heavy mineral concentrates contain mantle-derived xenocrysts of magnesiochromite, pyrope, Cr-diopside and rutile indicating a depth of sampling > 70 km. The Mt. Bundey lamprophyres are non-peralkaline to borderline peralkaline (molar (K + Na)/Al = 0.8 − 1.0) and potassic rather than ultrapotassic (molar K/Na < 2.5). They have distinctive major element compositions (≈46−49 wt. % SiO2, ≈1.5−2 wt. % MgO, ≈7 wt. % CaO), and element ratios (e.g. molar Al/Ti ≈10, K/Na ≈2) that indicate they are best classified amongst transitional lamproites, i.e. potassic rocks such as cocites, jumillites and Navajominettes, that have geochemical characteristics transitional between Groups I and III. (Foley et al., 1987). The Mt. Bundey lamprophyres have LILE enrichment patterns that resemble the W. Kimberley pamproites but have moderate negative Ta---Nb---Ti anomalies and HREE abundances that are closely similar to the jumillites of southeastern Spain and Mediterranean-type lamproites. Single-stage modelling of Rb---Sr data is consistent with enrichment of the source-region of the Mt. Bundey lamprophyres ≈ 120–170 Ma before partial melting; i.e. at 1.95–2.10 Ga. Source enrichment does not appear to be associated with subduction processes, but may instead relate to incipient rifting of the Archaean basement. Negative Ta---Nb---Ti anomalies in the Mt. Bundey dykes may, therefore, relate to stability of residual titanate minerals in an oxidized subcontinental mantle source. This view is supported by high Fe3+/ΣFe ratios of mantle-derived magnesiochromite xenocrysts which indicate oxidized mantle conditions (ƒo2 ≈ FMQ + 1 long units), and by the presence of xenocrystic Cr-bearing rutile. Although the Mt. Bundey dykes have sampled upper mantle material, the oxidized nature of the magma source-region, and of the magma itself, suggests that conditions may not be favourable for diamond survival at depth nor for diamond transport in transitional lamproite magmas of this kind.  相似文献   

2.
华北西部贺兰山中段黄旗口花岗岩成因及地质意义   总被引：1，自引：0，他引：1       下载免费PDF全文
华北克拉通孔兹岩带内发育类型复杂的各类岩石,是记录和反演华北西部早期块体拼合以及岩浆作用、变质演化的重要对象,而其中段发育的出露面积广阔、岩性复杂的黄旗口花岗岩体的研究还较为薄弱.在野外地质和岩相学研究基础上,主要报道了贺兰山中段黄旗口花岗岩的主、微量元素和Sr-Nd同位素组成,对岩体的源区特征、成因及地质意义进行了探讨.黄旗口复式花岗岩体主要由早期正长花岗岩、二长花岗岩和晚期英云闪长岩组成.两期岩体具有高K2O（2.97%~6.71%）含量,A/CNK均大于1.1,但晚期侵入单元较早期岩石更贫硅、富铝.两期岩体都表现为轻稀土富集、Eu负异常的特点,且强烈富集K、Rb、Th等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素.岩石87Sr/86Sr初始比值变化范围较大,可能是后期改造的结果;εNd（t）变化在+1.81~+4.90,对应的Nd同位素模式年龄TDM1为2.10~2.37 Ga,TDM2为2.10~2.35 Ga.这些特征表明黄旗口岩体为S型花岗岩,可能来自该区归属于孔兹岩的赵池沟组岩系的部分熔融,并可能有地幔岩浆的参与.结合区域变质、岩浆事件的综合研究成果,认为黄旗口不同期次的花岗岩具有造山带花岗岩的特征,分别形成于阴山地块和鄂尔多斯地块碰撞拼合以及造山后伸展的不同阶段.   相似文献   

3.
E. Hegner  M. Klbl-Ebert  J. Loeschke 《Lithos》1998,45(1-4):395-411
Subsequent to high-pressure and temperature metamorphism of the axial zone of the Variscan foldbelt in central Europe at ca. 340 to 330 Ma, formation of lamprophyre dikes during transtensional tectonics may be viewed as the beginning of the post-collisional stage of the orogeny. We report the results of 40Ar/39Ar mica dating, major and trace element data, and isotope compositions for lamprophyre and rhyodacite samples from the southern Black Forest. The chemical compositions of these rocks shed light on the upper mantle and crust at the end of the Variscan orogeny. 40Ar/39Ar plateau ages for four phlogopite–biotite separates from lamprophyres indicate emplacement at 332 to 314 Ma. This event coincides with melting of the crust as indicated by 40Ar/39Ar biotite plateau ages of ca. 332 Ma for rhyodacite dikes which are probably related to coeval undeformed granites. Incompatible trace element patterns of the lamprophyre samples reveal the characteristics of evolved continental crust and are interpreted as evidence for melting of sediment in a subduction-modified mantle. Nd, Sr, and Pb isotope compositions indicate an enriched mantle source with Nd-values of −1.5 to −6.8 which is similar to Variscan crust. Significant contamination of the lamprophyric melts by Variscan crust can be ruled out as mantle-derived phlogopite phenocrysts have similar Nd-values as in the whole-rock samples. We propose that the isotope compositions and incompatible trace element characteristics of the lamprophyres were predominantly inherited from melted sediment. The isotope compositions of Variscan lamprophyres from western Europe suggest that enriched upper mantle was only partly delaminated when ascending hot mantle triggered melting of the lower crust, as has been invoked for the origin of post-collisional granites. The isotope compositions of Tertiary basalts and mantle xenoliths indicate a depleted upper mantle under western Europe, implying that the enriched Variscan material was efficiently removed and mixed into the convecting mantle.  相似文献   

4.
The magmatic arc of the Fuegian Andes is composed mostly of Upper Mesozoic to Cenozoic calc-alkaline plutons and subordinated lavas. To the rear arc, however, isolated mid-Cretaceous monzonitic plutons and small calc-alkaline dykes and sills crop out. This calc-alkaline unit (the Ushuaia Peninsula Andesites, UPA) includes hornblende-rich, porphyritic quartz meladiorites, granodiorites, andesites, dacites and lamprophyres. Radiometric dating and cross-cutting relationships indicate that UPA is younger than the monzonitic suite. The geochemistry of UPA is medium to high K, with high LILE (Ba 500–2000 ppm, Sr 800–1400 ppm), HFSE (Th 7–23 ppm, Nb 7–13 ppm, Ta 0.5–1.1 ppm) and LREE (La 16–51 ppm) contents, along with relatively low HREE (Yb 1.7–1.3 ppm) and Y (9–19 ppm). The similar mineralogy and geochemistry of all UPA rocks suggest they evolved from a common parental magma, by low pressure crystal fractionation, without significant crustal assimilation. A pure Rayleigh fractionation model indicates that 60–65% of crystal fractionation of 60% hornblende + 34% plagioclase + 4% clinopyroxene + 1% Fe-Ti oxide, apatite and sphene (a paragenesis similar of UPA mafic rocks) can explain evolution from lamprophyres to dacites. The UPA has higher LILE, HFSE and LREE, and lower HREE and Y than the calc-alkaline plutons and lavas of the volcanic front. The HREE and Y are lower than in the potassic plutons as well. High concentrations of Th, Nb, Ta, Zr, Hf, LREE and Ce/Pb, and low U/Th, Ba/Th ratios in UPA, even in the least differentiated samples, suggest contributions from subducted sediments to the mantle source. On the other hand, relatively low HREE and Y, high LREE/HREE (La/Yb 11–38) ratios and Nb-Ta contents can be interpreted as mantle metasomatism by partial melts of either subducted garnetiferous oceanic sediment or basalt as well. Additionally, high LILE content in UPA, similar to the potassic plutons, suggests also a mantle wedge previously metasomatized by potassic parental magmas in their route to crustal levels. Therefore, UPA represents a unique suite in the Fuegian arc generated in a multiple hybridized source. UPA generation is related to a transition from normal to flat subduction which additionally caused the widening and landward migration of the magmatic arc, as well as crustal deformation. Rear-arc magmatism endured ca. 22 m.y.; afterwards, calc-alkaline magmatism remained at the volcanic front.  相似文献   

5.
贺娟  王启宇  闫国川 《地球科学》2018,43(8):2586-2599
前人对金沙江-红河构造带上的煌斑岩研究工作主要集中在南段哀牢山地区.对构造带中段鲁甸地区新发现的煌斑岩脉进行了锆石U-Pb年代学和全岩地球化学研究.结果表明,煌斑岩形成时代为始新世末期,与滇西新生代富碱斑岩高峰期一致.鲁甸煌斑岩具有高钾、富碱、高Mg#,富集大离子亲石元素（LILE）和轻稀土元素（LREE）,亏损高场强元素（HFSE,尤其是Ta-Nb-Ti）的特征.其岩浆源区为受俯冲流体和熔体交代的岩石圈地幔,源区组分为含金云母的尖晶石相方辉橄榄岩.结合同期的镁铁质火山岩和富碱斑岩研究成果,滇西区域的岩石圈地幔富集过程可能为元古宙时期与罗迪尼亚超大陆聚合相关的俯冲作用.始新世时期,在印度和亚洲大陆碰撞过程中,金沙江-红河构造带的富集岩石圈地幔发生拆沉或对流减薄,软流圈物质上涌,引发富集的岩石圈地幔部分熔融,形成本期煌斑岩岩浆作用.   相似文献   

6.
New data from a geochemical, geochronological and isotopic study of the Late Precambrian Timna igneous complex suggest the formation of alkali granites from a LIL-enriched, mantle derived, sanukitoid-type monzodiorite (a silica oversaturated rock with Mg# >60). These data also provide new insights into the petrology, timing and regional tectonic control of the transition from the calc-alkaline to the alkaline magmatic activity in the northern Arabian-Nubian Shield (ANS) during the Late Precambrian.

The Timna alkali granite was formed by fractional crystallization from the monzodioritic magma in a quasi-stratified magmatic cell which formed 610 Ma ago in the 625 Ma old calc-alkaline, porphyritic granite crust. These monzodiorites are mantle-derived, as demonstrated by their high Mg# (63), Cr (230 ppm), and Ni (120 ppm). They are characterized by initial 87Sr/86Sr of 0.7034, ε-Nd (610 Ma) = +3.4, and are enriched in K2O (2.9%), Sr (840 ppm), Ba (1290 ppm) and LREE [(La/Lu)n= 10–25]. The chemical characteristics and REE patterns of the monzodiorites and andesitic dykes of Timna are very similar to Dokhan andesites from northeastern Egypt and the Archean sanukitoids from Canada. The isotopic, geochemical and geochronologic data all indicate that Timna monzodiorites are comagmatic with the alkali granite. The alkali granite is a typical post-orogenic, borderline A-type granite. It is enriched in potassium (K2O=4.68–6.64%), has a negative europium anomaly (Eu/Eu*=0.058–0.38) and ε-Nd (610 Ma) of +3.9. The calc-alkaline granite is a typical I-type granite with a small positive europium anomaly (Eu/Eu*=1.02–1.16). Its age and the Sr, Nd and Pb isotopic characteristics with ε-Nd (625 Ma) of +5.6 to +5.9 are significantly different from these of the alkali granite and monzodiorites, and indicate little interaction with the monzodiorite during the formation of the alkali granite.

The alkali granites are correlative with the post-collisional extensional granites in Jordan and Egypt while the porphyritic granites can be correlated with the late orogenic types. Crustal thickening associated with orogenic compression resulted in crustal anatexis to form the I-type granitic rocks, whereas crustal thinning associated with extension allowed LIL-enriched mantle melts to rise very near to the surface, where space was available for these to pond and fractionate to alkali granite.  相似文献   


7.
A series of granitoids from Proterozoic to Cenozoic age occurred in the western Kunlun orogenic belt, Xinjiang, northwestern China. Several intrusions such as the West Datong (Middle Caledonian age), North Kuda (Late Caledonian age) and Kuzigan, Karibasheng, Zankan (Himalayan age) plutons have shoshonitic affinity. Their rock assemblages include (quartz) monzodiorite–(quartz) monzonite–quartz syenite (Middle Caledonian) or monzonitic granite–granite (Late Caledonian) or biotite (monzonitic) granite–diopside granite–diopside syenite (Himalayan). Generally, biotite is iron–phlogopite, with some eastonite and high Mg/(Mg+FeT) and Fe3+/Fe2+ ratio. Amphibole is mainly edenitic hornblende and magnesian hastingsitic hornblende, with some edenite and higher Mg/(Mg+FeT) and Fe3+/Fe2+ ratio. The rocks show SiO2 contents of 52.77–71.85% and high K2O+Na2O (mostly >8%, average 9.14%), K2O/Na2O (mostly >1, average 1.50) and Fe2O3/FeO (0.85–1.51, average 1.01) and low TiO2 contents (0.15–1.12%, average 0.57%). Al2O3 contents (13.01–19.20%) are high but variable. The granitoids are prominently enriched in LILE, LREE and volatiles such as F. However, the studied shoshonitic granitoids among the three intrusive periods also show differences in isotopic compositions and trace element concentrations, suggesting their different geneses: the origin of the West Datong pluton is probably related to the involvement of subducted oceanic crust sediments into the mantle source; the North Kuda and Himalayan plutons could have been generated by partial melting of subducted oceanic crust sediments or metasediments of thickened continental lower crust in the process of late-orogenic slab break-off or lithospheric thinning.  相似文献   

8.
The Paleoproterozoic terrane of the state of Bahia, Brazil, is characterized by an important mag-matic event that resulted in the generation of large and numerous syenite complexes; the terrane constitutes one of the largest syenite provinces in the world. It includes the Itiuba (1,800km2), Santanápolis (180 km2), São Felix (32 km2), and Anuri (70 km2) complexes. These syenitic bodies of shoshonitic affiliation are silica saturated, metaluminous, and exhibit: (1) moderate to high K2O/Na2O ratios, (2) relatively high MgO contents (up to 3.0%); (3) high incompatible-element contents, particularly LILE and LREE; (4) high HREE/LREE fractionations; and (5) small Eu negative anomalies. Among these syenites, Santanápolis exhibits the greatest lithological diversity, with a porphyritic and a heterogranular facies, and diverse lithotypes that vary from leucosyenites to melanocratic syenites of cumulate origin, as well as enclaves and dikes. It intruded syntectonically at 2.1 Ga and shows magmatic flow structures and subsolidus recrystallization of quartz and alkali feldspars. The mineralogical assemblage is perthitic feldspar, diopside, hornblende, phlogopite-biotite, apatite, zircon, titanite, calcite, and monazite. Differentiation of the Santanópolis Syenite was controlled by flow segregation processes in an intermediate trachytic magma, with fractionation of early crystallized diopside, apatite, and plagioclase. The parental intermediate shoshonitic magma was extracted directly from an enriched, subduction-modified mantle characterized by anomalous concentrations of LREE and LILE elements, and isotopic parameters similar to the EMI-type.  相似文献   

9.
秦岭造山带早中生代花岗岩成因及其构造环境   总被引：47，自引：1，他引：46  
秦岭早中生代花岗岩以准铝到过铝质中钾—高钾钙碱性岩石为主。它们具有相对富集LILE,LREE,贫化HFSE和Nb,Ta不同程度亏损的后碰撞花岗岩的地球化学特征,部分花岗岩显示了埃达克质（或高Sr、低Y）花岗岩和I-A型过渡的环斑结构花岗岩的特征。综合分析这些花岗岩体的构造和岩石地球化学特征,并结合与其同时代煌斑岩和基性岩脉构成的双峰式岩浆作用特点,认为秦岭早中生代花岗岩主要形成于后碰撞环境。其中,埃达克质花岗岩形成较早,与后碰撞早期环境的地壳增厚紧密相关,其后产出的大量正常块状花岗结构的花岗岩类主要形成于后碰撞阶段拆沉作用发生的伸展阶段,最终侵位的高分异富钾花岗岩和环斑花岗岩标志着秦岭已进入后碰撞晚期阶段。  相似文献   

10.
《International Geology Review》2012,54(14):1622-1683
Whole-rock and isotope geochemistry of six ～1.8 Ga post-kinematic intrusions, emplaced along the ～1.9 Ga Southern Svecofennian Arc Complex (SSAC) and in the SW part of the Karelian Domain in Finland, was studied. The intrusive age [U–Pb secondary ion mass spectrometer (SIMS)] of one of these, the Petravaara Pluton, was determined as 1811 ± 6 Ma.

Basic-intermediate rocks are alkali-rich (K2O?+?Na2O > 4 wt.%) and typically shoshonitic, strongly enriched in large ion lithophile elements and light rare earth elements, but relatively depleted in high field strength elements and heavy rare earth elements. The enrichment is much higher than can be accounted for by crustal contamination and requires previously melt-depleted mantle sources, subjected to variable metasomatism by carbonate-rich fluids and sediment-derived melts. These sources are inferred to consist of phlogopite ± amphibole-bearing peridotites from depths below the spinel–garnet transition, as shown by the high Ce/Yb ratios. 87Sr/86Sr(1.8 Ga) ratios in the range 0.7027–0.7031 and ‘mildly depleted’ ?Nd(1.8 Ga) values (+0.1 to?+1.4), with T DM values <2.1 Ga, suggest that mantle enrichment was associated with the previous Svecofennian subduction–accretion process, when enriched sub-Svecofennian mantle sections developed, dominantly characterized by 147Sm/144Nd ratios of 0.14–0.17.

The associated granitoids are diversified. One group is marginally peraluminous, transitional between I (volcanic-arc) and S (syn-collisional) types, and was derived from mixed igneous and sedimentary, but juvenile Svecofennian source rocks, as supported by near-chondritic ?Nd(1.8 Ga) and somewhat elevated 87Sr/86Sr(1.8 Ga). The other group is transitional between I and A (within-plate) types in character and had dominantly igneous protoliths. The whole-rock geochemistry and isotopes suggest that the compositional variation between ～50 and 70 wt.% SiO2 may be explained by hybridization between strongly enriched mantle-derived magmas and anatectic granitic magmas from the juvenile Svecofennian crust. One intrusion in the east contains a significant portion of Archaean, mostly igneous protolithic material (?Nd(1.8 Ga)?=?–2.8 and ?Hf(t) for zircons between?+2.8 and??11.9, with an average of??4.9).

The ～1.8 Ga post-kinematic intrusions were emplaced within the SSAC subsequent to the continental collision with the Volgo-Sarmatia craton from the SE, during a shift from contraction to extension, that is, in a post-collisional setting.  相似文献   

11.
为确定东昆仑祁漫塔格乌兰乌珠尔地区片麻状黑云母花岗岩和二长花岗岩的形成时代、岩石成因、源区性质和构造背景,对该岩石样品进行了锆石U-Pb年代学、地球化学和锆石Hf同位素研究.结果显示:片麻状黑云母花岗岩加权平均年龄为457.5±2.3 Ma,铝饱和指数A/CNK介于0.98~1.02,属准铝质岩石,Na2O/K2O比值为0.440~0.625,属于高钾钙碱性系列.二长花岗岩加权平均年龄为422.5±1.6 Ma,铝饱和指数A/CNK介于1.03~1.05,属弱过铝质岩石.二者均具有高硅(SiO2介于68.93%~74.72%)、高碱(全碱ALK介于6.83%~9.40%)、低磷(P2O5小于0.12%)等特征.富集轻稀土元素,亏损重稀土元素,δEu值为0.29~0.70,显示Eu中度负异常.富集Rb、K等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素,属于I型花岗岩.二长花岗岩样品的εHf(t)值为-2.2~+1.4,二阶段模式年龄为1 320~1 546 Ma.结合岩石成岩年龄、地球化学特征及区域构造演化认为片麻状黑云母花岗岩(457.5±2.3 Ma)为下地壳部分熔融产物,形成于原特提斯洋向北俯冲导致的局部拉张环境.二长花岗岩(422.5±1.6 Ma)岩浆来源于中元古代新增生的下部地壳熔融产物,形成于碰撞拼贴后的伸展构造环境.   相似文献   

12.
胶东蓬家夼金矿区钾玄质煌斑岩的元素地球化学研究   总被引：29，自引：5，他引：24  
程小久  程景平 《地球化学》1998,27(1):91-100
胶东蓬家夼金矿区钾玄质煌斑岩的元素地球化学研究表明,其成分上具有高碱富钾,高铝低钛,大离子亲石元素和轻稀土元素强烈富集及相容元素（Ｃｒ,Ｃｏ,Ｎｉ）明显亏损等特点,钾玄质岩浆是由富集地幔通过批式部分熔融作用产生的,而且其原始岩浆在上升和侵位过程中存在橄榄石和辉石等矿物相分离结晶,并伴有陆壳物质的混染,本区煌斑岩具有与陆弧有关的钾质火成岩类似的地球化学特征,可能与燕山期伊泽奈崎洋向中国东部大陆下的俯  相似文献   

13.
侵入于巴颜喀拉沉积盆地中的扎加岩体，主要由高钾钙碱性的黑云母花岗岩组成，并出现有具岩浆结构的暗色微粒包体。花岗岩富集轻稀土（LREE）及大离子亲石元素（LILE），相对亏损重稀土（HREE）和高场强元素（HFSE），具Eu负异常（0．5～0．7）、较低的εNd（t）值（-3．5～-6．2）和中等的（^87Sr／^86Sr）初始比值（0．7088～0．7090），它们的亏损地幔Nd模式年龄tDM在1．1～1．3Ga之间。与寄主花岗岩相比，闪长质暗色微粒包体具有较低的SiO2，更低的Eu负异常（0．2～0．4）和εNd（t）值（-4．7～-6．1），更高的（^87Sr／^86Sr）初始比（0．7084～0．7124），以及稍老的tDM（1．4Ga）。岩石的地球化学资料表明，扎加花岗岩是在碰撞后构造环境下幔源岩浆上涌诱发下地壳岩石部分熔融的产物，其物源可能是苦海杂岩和万宝沟岩群的混合物。巴颜喀拉沉积盆地下面存在中元古代的基底，属于扬子地台西缘的一部分  相似文献   

14.
The Atesina Volcanic District, the Monte Luco volcanics, and the Cima d'Asta, Bressanone-Chiusa, Ivigna, Monte Croce and Monte Sabion intrusions, in the central-eastern Southern Alps, form a wide calc-alkaline association of Permian age (ca. 280–260 Ma). The magmatism originated during a period of post-orogenic extensional/transtensional faulting which controlled the magma ascent and emplacement. The magmatic products are represented by a continuum spectrum of rock types ranging from basaltic andesites to rhyolites, and from gabbros to monzogranites, with preponderance of the acidic terms. They constitute a metaluminous to weakly peraluminous series showing mineralogical, petrographic and chemical characteristics distinctive of the high-K calc-alkaline suites. In the MORB-normalized trace element diagrams, the most primitive volcanic and plutonic rocks (basaltic andesites and gabbros with Mg No.=66 to 70; Ni=25 to 83 ppm; Cr=248 to 679 ppm) show LILE and LREE enriched patterns with troughs at Nb–Ta and Ti, a distinctive feature of subduction-related magmas. Field, petrographic, geochemical and isotopic evidence (initial 87Sr/86Sr ratios from 0.7057 to 0.7114; εNd values from −2.7 to −7.4; ∂18O values between 7.6 and 9.5‰) support a hybrid nature for both volcanic and plutonic rocks, originating through complex interactions between mantle-derived magmas and crustal materials. Only the scanty andalusite–cordierite and orthopyroxene–cordierite bearing peraluminous granites in the Cima d'Asta and Bressanone-Chiusa intrusive complexes can be interpreted as purely crustal melts (initial 87Sr/86Sr=0.7143–0.7167; initial εNd values between −7.9 and −9.6, close to average composition of the granulitic metasedimentary crust from the Ivrea Zone in the western Southern Alps). Although the Permian magmatism shows geochemical characteristics similar to those of arc-related suites, palaeogeographic restorations, and geological and tectonic evidence, seem not to support any spatial and/or temporal connection with subduction processes. The magmatism is post-collisional and post-orogenic, and originated in a regime of lithospheric extension and attenuation affecting the whole domain of the European Hercynian belt. A change in the convergence direction between Gondwana and Laurasia, combined with the effects of gravitational collapse of the Hercynian chain, could have been the driving mechanism for lithosphere extension and thinning, as well as for upwelling of hot asthenosphere that caused thermal perturbation and magma generation. In the above context, the calc-alkaline affinity and the orogenic-like signature of the Permian magmatism might result from extensive contamination of basaltic magmas, likely derived from enriched lithospheric mantle source(s), with felsic crustal melts.  相似文献   

15.
相山铀矿田钾玄质岩石与铀成矿   总被引：4，自引：2，他引：2  
岩石学、元素地球化学研究表明,相山铀矿田的英安斑岩属于板内型钾玄质岩类,为钾玄质英安斑岩。其主要地球化学特征是:SiO2含量变化小(66.73%～69.88%),高碱(K2O+Na2O=6.06%～8.41%),高K2O/Na2O比值(1.53～3.49),高Al2O3(13.24%～15.96%),强烈富集大离子亲石元素(LILE)和轻稀土元素(LREE),P、Sr、Ti显著负异常,无明显的Nb和Ta负异常,Th/Yb>5,U和Th异常偏高。相山钾玄质英安斑岩的形成是源于地幔玄武岩浆的底侵作用,其中较基性的包体应为地幔岩浆残留产物。相山铀矿化在时空上与钾玄质英安斑岩关系密切,其形成应该与钾玄质岩有关,幔源流体在铀成矿过程中扮演了重要角色。  相似文献   

16.
X射线衍射分析和化学成分研究表明,磷灰石为氟磷灰石,榍石成分中存在着的主要类质同象替代是(Fe~(3+)、Al)+(F,OH)~-=Ti~(4+)+O~(2-)。磷灰石和榍石是碱性辉长岩的REE、Ba、Zr等微量元素的主要载体;它们是在较高氧逸度的条件下结晶的。磷灰石的Sr同位素特征说明形成双龙桥碱性辉长杂岩的物质来源于上地幔。  相似文献   

17.
东天山阿拉塔格花岗岩体地球化学特征及其构造意义   总被引：2，自引：0，他引：2  
位于中天山地块南缘大黑山地区的阿拉塔格花岗岩体,岩性主要由花岗闪长岩、二长花岗岩、似斑状花岗岩组成,岩石具有高硅(w（SiO2）为66.29%~77.47%)、富碱(w（Na2O+K2O）为6.75%~9.93%)、高铝(w（Al2O3）为10.97%~14.40%)、低Sr(w（Sr）为（28.78~153.00）×10-6,平均为99.23×10-6)、低Ti（w（TiO2）为0.09％~0.77％）的特征。岩石的A/CNK值为1.19~1.50,为钙碱性过铝质岩石;岩石Eu亏损（δEu＝0.19~0.51）、LREE富集(LREE/HREE= 6.80~8.45,(La/Yb)N= 6.06~9.03),明显富集Rb、Th、K、Hf(Zr) 等大离子亲石元素(LILE),亏损Nb、Ta、P、Ti等高场强元素(HFSE);岩石的Ba含量较低,并具有明显的Sr负异常。结合区域地质特征,通过岩石的地球化学和Sr、Nd同位素综合分析,认为该花岗岩形成于后碰撞环境,且为壳幔混源的岩浆多期次侵位的复合岩体。  相似文献   

18.
Mesozoic alkaline intrusive complexes are widespread in the southern portion of the North China Craton and can provide some important constraints on the evolution of the Mesozoic lithosphere beneath the region. Three selected intrusive complexes (Tongshi, Hongshan, and Longbaoshan) are generally high in alkalis (K2O+Na2O=913 wt.%) and Al2O3 (1421.6 wt.%) and low in CaO and TiO2 (<0.6 wt.%), with high and variable SiO2 contents. Rocks from these complexes are all enriched in LREE and LILE (Cs, Rb, Ba, U, Th), depleted in Nb and Ti, have a highly positive Pb anomaly, and are characterized by lack of a clear Eu anomaly despite trace element abundances and isotopic ratios that vary greatly between complexes. The Tongshi complex has high Cs (2.68.5 ppm) and REE abundances (∑REE=112.6297 ppm, (La/Yb)N=13.130.9) and MORB-like Sr–Nd–Pb isotopic ratios ((87Sr/86Sr)i<0.704; εNd>0; (206Pb/204Pb)i>18). The Hongshan complex has low REE concentrations (∑REE=28.2118.7 ppm, (La/Yb)N=4.614.7) and is moderately enriched as demonstrated by their Sr–Nd isotopic ratios ((87Sr/86Sr)i>0.706; εNd<−7). The Longbaoshan complex is extremely REE enriched (∑REE=211.3392.6 ppm, (La/Yb)N=32.460.9) and has an EM2-like Sr–Nd isotopic character ((87Sr/86Sr)i>0.7078; εNd<−11). We suggest that the Tongshi complex originated from the asthenosphere and the Hongshan complex and the Longbaoshan complex were derived from the partial melting of previously subduction-modified lithospheric mantle, in response to post-collisional lithospheric extension and asthenospheric upwelling. The occurrence of these alkaline intrusive complexes demonstrates that the lithosphere beneath the region must have been considerably thinned at the time of intrusion of these complexes. This study also shed light on the temporal evolution of the Mesozoic lithosphere and the timing of the lithospheric thinning.  相似文献   

19.
Eslamy peninsula in NW of Iran is formed by a strato-volcano with collapsed calderon, which is intruded by lamprophyric dykes with minette composition. Also trachytic and microsyenitic dykes have intruded the volcanic rocks. The oldest volcanic activity includes eruption of leucite basanite, leucite tephrite, basanite and tephrite, which are associated with pyroclastic rocks. Lamprophyric dykes are distinguishable with large mica phenocrysts. Mica-clinopyroxenite xenoliths can be found in the rocks. The source magma of the rocks had a ultrapotassic to shoshonitic nature, rich in LREE and LILE. Eslamy peninsula lamprophyres are between alkaline and calc-alkaline lamprophyres in terms of REE patterns and spider diagrams for trace elements, but are closer to clac-alkaline lamprophyres. The behaviour of trace elements studied by the means of spider diagrams show that the magma, producing the lamprophyres, is generated from deep-mantle probably from a garnet-bearing source (garnet lherzolite) with high CO2/H2O content. The resulted magma had interacted with crustal materials and had formed Eslamy peninsula lamprophyres in a post-collisional tectonic setting. Geochemistry of rare elements indicate an extensive rutile-rich metasomatism in the source magma of the lamprophyres.  相似文献   

20.
湘东南中生代花岗闪长质小岩体的岩石地球化学特征   总被引：58，自引：15，他引：58  
湘东南花岗闪长质岩石以高K2O/Na2O,K2O+Na2O>6.0%为特征,属高钾钙碱性系列岩石,其形成主要受部分熔融作用制约;岩石稀土元素富集,铕负异常不明显,δEu=0.71～0.89;富集大离子亲石元素,Nb-Ta亏损,P、Ti或亏损或不亏损,具岛弧型岩浆作用微量元素分配模式,属板内钾质岩石,源区可能存在早期俯冲组分改造的岩石圈富集地幔组分,或是源于软流圈的岩浆与中下地壳混合作用的产物;其形成与该带中生代早期岩石圈的伸展-减薄作用有关。  相似文献   

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