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1.
安徽庐枞中生代富钾火山岩成因的地球化学制约   总被引:74,自引:7,他引:74  
庐枞中生代火山岩产于下扬子断裂坳陷带的继承式火山盆地中,主要为一套以粗面玄武岩-玄武粗安岩-安粗岩-粗面岩为主体的偏碱质中基性岩石组合。化学成分上具有富碱、富钾、富轻稀土及大离子亲石元素(如Rb、Th、Pb)和贫高场强元素(如Nb、Ti)等特点。在郯庐断裂中南段及其邻近地区的中生代火山岩中,庐枞盆地火山岩的特征最接近钾玄岩系火山岩。这套火山岩具有较高的ISr值(0.70570-0.70653)及偏低的εNd(t)值(-5.01~-9.96)。火山岩产出地质背景的全面分析及元素-同位素的综合示踪,排除了岩浆上升过程中存在强烈的地壳物质的混染,富钾火山岩的岩浆源区应为受俯冲板片析出流体交代作用所形成的富集地幔(EMI),岩石主要起源于富集型地幔的部分熔融。  相似文献   

2.
沙溪铜(金)矿床是目前长江中下游成矿带中已探明储量最大的斑岩型铜矿床。文章通过对沙溪矿区内闪长斑岩的年代学、全岩化学成分、同位素地球化学等综合研究,探讨了闪长斑岩的形成机制。闪长斑岩的LA-ICP-MS锆石U-Pb加权平均年龄为128.3±1.5 Ma,属于早白垩世岩浆活动产物。岩石具有富碱(ALK=6.12~7.53 wt%)、富钾、富镁(Mg#=38.99~51.53)、准铝质(A/CNK=0.90~0.99)等特征,属于钙碱性—高钾钙碱性系列岩石;岩石轻稀土元素富集,重稀土元素亏损(LaN/YbN=12.63~17.63),无明显的Eu异常(δEu=0.84~1.14);大离子亲石元素(Ba、Sr)和Pb等富集,高场强元素(Nb、Ta、Ti等)亏损。闪长斑岩的全岩(87Sr/86Sr)t值为0.7052~0.7056,εNd(t )值为-6.09~-3.42,(206Pb/204Pb)t值为17.51~18.16、(207Pb/204Pb)t值为15.49~15.63、(208Pb/204Pb)t值为37.57~38.45,表明成岩物质源于壳幔混合。130 Ma左右,平移的郯庐断裂的伸展引发了大规模岩浆作用,来自深部的岩浆沿着郯庐断裂带上侵,并混染了大量的地壳物质,形成了沙溪闪长斑岩及与铜矿有关的石英闪长斑岩。  相似文献   

3.
莒县早白垩世火山岩沿郯庐断裂带分布,由粗安岩、粗面岩和流纹岩组成,属高钾钙碱性-钾玄岩系列.岩石富集Rb、K、Ba等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、Ti等高场强元素和重稀土元素,Sr-Nd同位素组成((87Sr/86Sr)t=0.7082~0.7095,ENd(t)=-16.4~-19.8)与区内基性岩的相类似,而Pb同位素组成((206pb/204Pb)t=16.523~17.038,(207pb/204Pb)t=15.414~15.468,(208pb/204Pb)t=37.058~37.427)类似于EM1型富集地幔.(87Sr/86Sr)t和εNd(t)与SiO2没有明显的相关性,且较高的Th/U、Ce/Pb值和较低的Nb/La、Nb/U值均暗示岩浆在上升过程中未遭受明显的地壳混染.粗安岩具有高的Cr、Ni、MgO含量及Mg#值和古老Nd同位素模式年龄,暗示其起源于富集的岩石圈地幔.粗面岩与粗安岩的主要氧化物、微量元素与SiO2呈明显的相关性,这暗示可能为同源岩浆结晶分异而来.研究表明,莒县地区中酸性火山岩形成于岩石圈伸展减薄背景下,由曾遭受俯冲扬子陆壳熔体改造的华北岩石圈地幔部分熔融形成的岩浆分离结晶作用而成.郯庐断裂带的伸展活动控制着火山岩的分布,为岩浆的形成和运移提供了有利的场所,在华北克拉通破坏中可能起到了重要的作用.  相似文献   

4.
大别-苏鲁造山带南、北两侧广泛发育晚中生代富钾火山岩,主要岩石组合为粗面玄武岩-玄武粗安岩-粗安岩-安粗岩姐面岩,这套岩石总体具有富碱、富钾、富轻稀土和大离子亲石元素(如Rb、Th等),贫高场强元素(如Nb、Ti等),(^87Sr/^86Sr),值偏高,εNd(t)值偏低等特点,但南、北两侧富钾火山岩的地球化学特征存在较显著的差异,主要表现在造山带北侧富钾火山岩稀土总量更高,轻、重稀土分异更明显,且(^87Sr/^86Sr),值更高,eNd(t)值和^206Pb/^204Pb值显著偏低。元素-同位素综合示踪显示,区内富钾火山岩均起源于富集地幔的部分熔融,但南、北两侧源区地幔的富集机制存在差异,南侧富集地幔的形成主要与俯冲洋壳析出流体的交代作用有关,而北侧富集地幔的形成除受到俯冲洋壳析出流体的交代作用外,在更大程度上主要起因于俯冲的扬子陆壳析出流体的交代作用,即其源区遭受了多次富集事件的影响,后者是导致南、北两侧富钾火山岩地球化学特征差异的主要原因。  相似文献   

5.
上侏罗统毛坦厂组火山岩沿大别山前呈带状分布,岩性以粗安岩、粗面岩、粗面英安岩及流纹岩为主,为一套中酸性、高钾、铝过饱和、钙碱性系列的岩石。岩石中∑REE=208.06×10-6~470.57×10-6,LREE/HREE=11.99~21.75,(La/Yb)N=14.48~34.36,轻、重稀土分异程度高,轻稀土富集,重稀土亏损。La/Nb=4.37~5.91,Ba/Nb=51.16~206.09,,Rb/Sr=0.08~0.35,Eu负异常不明显,Nb负异常显著。结合区域构造背景及岩石地球化学特征分析,毛坦厂组火山岩具有板块聚敛火山弧的特点,其形成可能与扬子板块陆内俯冲有关。合肥盆地的形成与华北板块和扬子板块陆陆碰撞有关,具有挤压构造背景下的前陆盆地性质。  相似文献   

6.
北黄海盆地内多口钻井钻遇到前中生代和中生代火成岩,证实了盆地中生代经历的多期构造活动伴随着多期次火成岩的发育.对北黄海盆地X1和X2井火山岩进行了岩石学鉴定、磁化率和密度测试、主量元素、ICP-MS微量和稀土元素测试,研究表明:X1井前中生代碱玄岩和粗面玄武岩属于弱磁性((131.5~138.5)(4π×10-6))、中密度岩石,X2井中生代英安岩(下层) 和含角砾英安岩(上层) 属于微弱磁性((27.5~82.5)(4π×10-6))、中密度岩石;X1井碱玄岩属于高钾钙碱性系列,粗面玄武岩属于钙碱性系列,2种火山岩表现为ΣREE较高(108.11×10-6~208.02×10-6)、轻稀土富集(LREE/HREE=4.04~6.91)、δEu有微弱异常(0.99~1.18);X2井2层火山岩属于钙碱性系列,均表现为ΣREE较低、轻稀土富集、δEu有微弱异常,微量元素具有Ba、U、Sr富集和Nb、Ta亏损的特征,而且(Rb/Sr)N、(La/Nb)N和(Ba/Nb)N的比值均高于原始地幔值,反映岩浆源于地壳熔融.北黄海盆地前中生代火山岩形成于板内构造背景,中生代火山岩可能形成于板块俯冲的弧后伸展环境.   相似文献   

7.
卡拉麦里钾质火山岩位于准噶尔盆地的东北缘下石炭统巴塔玛依内山组内。这些火山岩以粗面玄武岩和玄武质粗面安山岩为主,SiO2含量稳定(46.29%~51.56%),具有较高的碱含量(K2O+Na2O=5.39%~6.96%)以及高K2O/Na2O比值(K2O/Na2O=0.5~1.4),TiO2含量相对稳定(0.94%~1.21%),显示钾玄质岩石特征。岩石地球化学表明,钾玄岩强烈富集LILE(如K、Rb和Sr)和LREE((La/Yb)N=4.39~6.25),Eu正异常明显(δEu=1.3~1.7),相对亏损HFSE(如Zr、Hf),Ta、Nb和Ti呈明显的"TNT"负异常,及较高Ba/Nb和Ba/Ta比值(分别为38~93,574~1470),显示典型岛弧岩浆特征,而Nd-Sr同位素显示亏损地幔源区特征。不相容元素(Nb/La)N和Ba/La比值(分别为0.33~0.41,11.07~18.82)以及高Nb含量(4.45×10-6~7.76×10-6),表明这些岩石来自一个交代作用富集的地幔源区。通过钾质火山岩环境的梯次判别图研究,发现巴塔玛依内山组钾玄岩形成于后碰撞环境,显示岛弧的岩石地球化学特征。在后碰撞期,由于陆内调整和均衡作用,东准噶尔东北缘的岩石圈伸展减薄,随着岩石圈地幔的减薄,前期交代富集的下部地幔楔(金云母和/或钾质角闪石-尖晶石相二辉橄榄岩)发生低度部分熔融形成钾玄质母岩浆,诱发了后碰撞型钾玄质岩浆活动(具有弧火山岩岩石地球化学特征),形成了卡拉麦里巴塔玛依内山组钾质玄武岩。  相似文献   

8.
通过对青藏高原碰撞后钾质-超钾质火山岩的对比分析,提出青藏高原存在羌塘-芒康-滇西(44~28Ma)和冈底斯(25~12Ma)两条高Mg^#钾质-超钾质火山岩带,而可可西里、西昆仑-东昆仑的新生代火山岩则为低Mg^#钾质火山岩.高Mg^#钾质-超钾质火山岩的化学成分均相对高镁低铁和贫钛,微量元素组成以具有类似岛弧火山岩的K/Nb、K/La、Rb/Nb、Pb/La、Ba/La等比值为特征.低Mg^#钾质-超钾质火山岩相对富铁贫镁和高钛,上述元素比值小于岛弧火山岩,大于和近似于洋岛玄武岩,指示岩浆源区富集组分有软流圈流体的贡献.羌塘-芒康的高Mg^#高钾钙碱性和高Mg^#钾玄岩系列指示高原中部受到陆内俯冲作用的影响;30Ma前俯冲板片断离,软流圈上涌,富集岩石圈地幔熔融形成羌塘低Mg^#过碱性钾质-超钾质系列.综合地球物理资料,提出青藏高原在印度大陆岩石圈的强力楔入下,高原内部软流圈物质沿欧亚岩石圈地幔俯冲板片的顶部向北东和南东挤出,使上覆岩石圈地幔发生剪切破裂,形成一系列串珠状高速体与低速体的相间分布,并随时间不断向北扩展.这也是阿尔金和滇西走滑系的深部动力源.正是软流圈与岩石圈的这种相互作用形成了可可西里和西昆仑-东昆仑低Mg^#钾玄质火山岩的软流圈-岩石圈地幔的混源特征.藏南高Mg^#超钾质岩浆源区的显著幔壳混合特征则可能来自印度大陆岩石圈俯冲作用的影响.  相似文献   

9.
沂沭断裂带内发育了大量的中生代火山岩,其成因研究对剖析断裂带活动规律具有重要意义。本文对断裂带北段潍坊、安丘、鄌郚地区中生代火山岩进行了详细的岩石学、锆石U-Pb年代学和主量元素、微量元素、Sr-Nd-Pb同位素分析。探讨了沂沭断裂带中生代火山岩成因及其形成的地球动力学过程。断裂带北段火山岩年龄集中在131~124Ma之间,喷发于早白垩世。岩石为一套高钾钙碱性火山岩,包括玄武安山岩、粗安岩、粗面岩、英安岩。火山岩富集Rb、Ba等大离子亲石元素,相对亏损Nb、Ta、Ti等高场强元素。稀土元素含量高(∑REE=140.5×10-6~433.1×10-6),富集轻稀土、亏损重稀土(∑LREE/∑HREE=9.8~31.0),无明显的Eu负异常。火山岩具有富集且变化范围较大的Sr-Nd-Pb同位素组成,(87Sr/86Sr)i=0.708054~0.711692,εNdt)值为-15.3~-7.4,(206Pb/204Pb)i=17.213~17.962,(207Pb/204Pb)i=15.425~15.590,(208Pb/204Pb)i=37.597~38.365。研究表明,高钾钙碱性火山岩的源区与区域基性岩源区一致,均为富集岩石圈地幔。玄武安山岩、粗安岩、粗面岩经基性岩浆分离结晶作用形成,英安岩则遭受了华北下地壳强烈混染。三叠纪末期,由于扬子板块向华北克拉通俯冲,扬子地壳析出的流体/熔体交代了华北古老岩石圈地幔,形成富集岩石圈地幔。早白垩世,受古太平洋板块俯冲和后撤作用,富集岩石圈地幔部分熔融形成基性岩浆,岩浆在上升过程中发生分离结晶作用,受沂沭断裂深切作用影响,部分地区遭受华北下地壳混染,最终形成区内各类高钾钙碱性火山岩。  相似文献   

10.
扎河坝钾质火山岩位于准噶尔盆地的东北缘,下泥盆统托让格库都克组内。这些火山岩以玄武岩为主,具有较高的K2O含量(1.66%~4.63%)和K2O/Na2O值(0.36~1.65),并富Sr(665×10-6~906×10-6)、Ba(680×10-6~1596×10-6)等大离子亲石元素和轻稀土(La/YbPM>8),显示出钾玄质岩石的特征。同时,这些岩石具有较高的TiO2(~1.7%),P2O5(~0.8%)和高场强元素含量,类似于高铌玄武岩。尽管具有较高的Nb含量(Nb=21×10-6~23×10-6),这些岩石仍呈现出明显的Nb~Ta亏损,显示了典型的岛弧特征。高的Nb/Yb(~5.9),Nb/Ta(19~21),Zr/Hf(46~51)值以及较高的钾含量表明这些岩石来自一个经交代作用富集的地幔源区。单纯的消减板块脱水难以造成高场强元素的富集,这些岩石较高的Ce/Th(47~50),Ce/Pb(13~19)和Ba/Th(341~777)值并缺乏明显的负铈异常等特征排除了消减沉积物熔体的加入。导致地幔富集的变质组份可能为来自消减板块的低程度熔体。扎河坝钾质玄武岩与稍早前报道的埃达克与富铌玄武岩一起,反映早泥盆世曾经出现过洋壳的消减事件。准噶尔盆地中存在的特征岛弧岩浆表明热消减机制曾经广泛地出现在准噶尔板块演化的不同历史时期,而岛弧地体在准噶尔盆地基底的组成中可能占有较大的比例。  相似文献   

11.
Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.  相似文献   

12.
Robert L. Linnen   《Lithos》2005,80(1-4):267-280
The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H2O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H2O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species.  相似文献   

13.
Lithostratigraphy, physicochemical stratigraphy, biostratigraphy, and geochronology of the 77–70 Ma old series bracketing the Campanian–Maastrichtian boundary have been investigated by 70 experts. For the first time, direct relationships between macro- and microfossils have been established, as well as direct and indirect relationships between chemo-physical and biostratigraphical tools. A combination of criteria for selecting the boundary level, duration estimates, uncertainties on durations and on the location of biohorizons have been considered; new chronostratigraphic units are proposed. The geological site at Tercis is accepted by the Commission on Stratigraphy as the international reference for the stratigraphy of the studied interval. To cite this article: G.S. Odin, C. R. Geoscience 334 (2002) 409–414.  相似文献   

14.
正The Kuqa depression deposited thick rock salt,which has a lower density than surrounding rocks.When salt bodies form a certain scale,obvious negative gravity anomalies can be detected in the surface.Therefore,gravitational method can quickly obtain the shape,plane distribution of deep-seated salt bodies and overall tectonic morphology of the basin.  相似文献   

15.
正1 Introduction The Pingluoba brine,which characterized as high concentration with sodium,potassium,boron,lithium,and rubidium,possess great development value.The main composition of the brine can be summarized to the  相似文献   

16.
正1 Introduction In the present paper,MgCl2·6H2O,FeCl3·6H2O,and CeCl3·6H2O were used as raw materials in the precipitationhydrothermal method to synthesize MgF eC e hydrotalcite.The effects of the Fe:Ce molar ratio on the composition,crystal structure,and thermal stability of hydrotalcite are examined.Energy-dispersive X-ray spectroscopy(EDS),X-  相似文献   

17.
正1 Introduction Crystallization is one of important unit operations in the chemical production process,which requires not only the crystal product with high purity and yield,but also the available particle size of the crystal products to ensure product quality.Crystallization process is affected by  相似文献   

18.
正Dear Authors and Readers:First of all,on behalf of the new Editorial Board,I would like to express our sincere appreciation for your continuing support of our journal.This journal,founded in 1922,is the oldest geological journal in China.As the flagship journal of the Geological Society of China,it has become more and more influential in earth sciences in China and beyond.The journal is now indexed by SCI,CA and more than 20 other databases,with an impact  相似文献   

19.
正20141283 Bai Daoyuan(Hunan Institute of Geological Survey,Changsha 410016,China);Zhong Xiang Nature,Origin and Tectonic Setting of Jinzhou Basin in the South Segment of Xuefeng Orogen(Geology in China,ISSN1000-3657,CN11-1167/P,40(4),2013,p.1079-1091,10 illus.,47 refs.)Key words:foreland basins,strike-slip faults,Hunan Province  相似文献   

20.
正20142093Chen Daohua(Guangzhou Marine Geological Survey,Guangzhou 510075,China);Diao Shaobo The Latest Progress of Geological Marine Testing Technology in China(Rock and Mineral Analysis,ISSN0254-5357,CN11-2131/TD,32(6),2013,p.850-859,105refs.)Key words:chemical analysis,China  相似文献   

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