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1.
在柴北缘东段识别出早古生代埃达克岩-富Nb玄武岩的火山岩组合。埃达克岩富Na2O、贫K2O,K2O/Na2O比值介于0.14~0.43之间;高Sr(614×10-6~1043×10-6),但亏损Y(3.26×10-6~14.1×10-6)和Yb(0.33×10-6~1.46×10-6),具有高的Sr/Y比值(44~282);富集Sr、Ba等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素及Cr、Ni、Co、V等相容元素。富Nb玄武岩富Na2O、贫K2O、高TiO2,其Nb含量较高,介于16.9×10-6~17.9×10-6之间,具有高的Nb/Ta、Nb/U、(Nb/La)N比值,同时富集高场强元素。埃达克岩锆石U-Pb定年得到453±4Ma和457±4Ma的结晶年龄。锆石εHft)范围较大,介于3.40~13.23之间,对应的二阶段模式年龄tDM2介于1059~566Ma之间,显示以新生物质为主的特征。综合研究表明柴北缘东段埃达克岩可能为岛弧环境下俯冲的南祁连大洋板片部分熔融的产物。板片来源的埃达克质熔体交代或与上覆地幔楔橄榄岩反应,导致被交代的地幔橄榄岩部分熔融而形成富Nb玄武质岩浆。柴北缘东段埃达克岩-富Nb玄武岩火山岩组合的厘定表明南祁连洋可能直到~455Ma之前并未完全闭合,同时表明俯冲大洋板片的部分熔融可能是柴北缘早古生代地壳增生的一种重要方式。  相似文献   

2.
昌都微陆块内部发育一套晚三叠世粗安岩.本文基于系统的野外踏勘,对具有代表性的火山岩进行岩石学、地球化学等研究.结果显示该区火山岩的SiO2含量为51.36%~58.04%,全碱含量(Na2O+K2O)为5.03%~7.84%,根据岩石K2O,MgO及K2O/Na2O比值判断,属钾质-超钾质火山岩,具高K、高Al、低Ti的特征.本区岩石强烈富集大离子亲石元素(LILE)和轻稀土元素(LREE),Nb、Ta、Ti的负异常明显,整体特征类似于弧火山岩.其稀土总量较高(270×10-6~960×10-6),轻重稀土分馏明显,重稀土分布形态较平缓.岩石具有较高的初始锶同位素比值(87Sr/86Sr)i=0.7150~0.7176和较低的初始钕同位素比值(143Nd/144Nd)i=0.51180~0.51184,εNd(t)=-10.9~-10.2,二段Nd模式年龄为t2DM=1.82~1.88Ga.本区岩石的地球化学特征显示其源区是由俯冲板片所产生的流体/熔体交代的岩石圈地幔,源区矿物组成分析结果显示,其源区以尖晶石二辉橄榄岩为主,含少量石榴石二辉橄榄岩及金云母.本区钾质-超钾质岩石虽然与西藏南部的钾质-超钾质岩石有相似的地球化学特征,但却产于碰撞后的构造背景之下.结合其所具有的弧火山岩特征及时代构造背景判断其为一种"滞后型"弧火山岩,其形成过程可以概括为三个阶段.  相似文献   

3.
西准噶尔巴音达拉地区发育一套酸性火山岩,被称为卡拉岗组,岩石组合以流纹岩、英安岩、流纹质熔结凝灰岩等酸性火山岩为主。本文对卡拉岗组火山岩进行高精度锆石LA-ICP-MS U-Pb测年,获得英安岩和流纹岩的加权平均206Pb/238U年龄分别为(294.4±1.3)Ma(n=9,MSWD=0.8)和(298.4±2.5)Ma(n=9,MSWD=3.4),其形成于早二叠世。岩石地球化学特征表明,卡拉岗组火山岩岩具有高硅(66.69%~75.21%),富碱(Na2O+K2O:6.98%~8.35%),低MgO(0.18%~1.32%),贫钙(0.24%~2.49%)的特征,均属过铝质(A/CNK:1.14~1.33)及高钾钙碱性系列。微量元素数据显示,稀土总量为∑REE为83.82×10-6~197.61×10-6,(La/Yb)N=3.15~12.50,轻、重稀土元素分馏比较明显,轻稀土元素(LREE)较为富集,重稀土元素分布相对平坦,球粒陨石标准化配分模式为右倾型。微量元素富集大离子亲石元素(LILE)Rb、Th、U、K,并亏损高场强元素(HFSE)Nb、Ta、P、Ti。综合最新区域资料及本文研究成果,文章认为研究区早二叠世卡拉岗组火山岩岩浆来源于壳源物质不同程度的部分熔融,残留相中有少量斜长石和角闪石,为后碰撞伸展阶段的产物。  相似文献   

4.
陈石  张元元  郭召杰 《岩石学报》2009,25(3):527-538
新疆三塘湖盆地广泛出露哈尔加乌组地层,主要为陆相中性喷发岩夹火山碎屑岩。火山岩锆石SHRIMP U-Pb年龄为319.6±9.8Ma(MSWD=4.8)。地球化学分析表明,哈尔加乌组火山岩高钾富碱,属于高钾钙碱性系列;LREE强烈富集、大离子亲石元素(LILE)强烈富集、大多数高场强元素(HFSE)明显高于MORB,没有Ti的负异常和P的正异常,Nb、Ta负异常明显,基本没有Eu、Ce的异常,Ti/Y(467~494)、Nb/Y(0.41~0.43)值高。判别图解投入板内火山岩和岛弧火山岩区域,整体显示板内火山岩的特征又携带岛弧火山岩的地球化学痕迹。εNd (t)值(+5.90~+6.31)为正值、Mg#较高(0.54~0.57),显示与亏损地幔相关的源区特点,(87Sr/86Sr) i值(0.70397~0.70464)相对于亏损地幔高、La/Nb(3.12~3.39)、Nb/U(5.86~9.80)比值显示源区有陆壳组分的参与。综合区域地质特征和前人研究资料表明,三塘湖盆地哈尔加乌组火山岩是碰撞造山中增厚的岩石圈根部拆沉作用致使软流圈地幔上涌底侵,致使早期的陆壳组分和弧组分部分熔融而形成的火山喷发,形成于后碰撞伸展转换背景。  相似文献   

5.
形成于弧前背景的岩浆岩可能记录了俯冲起始的重要证据。本文以北祁连走廊南山蛇绿混杂岩带新识别出的富铌辉长岩和斜长花岗岩为研究对象,在野外观察的基础上,结合岩石学、地球化学、同位素地球化学和年代学的综合研究,对原特提斯洋初始俯冲的时间进行约束,并探讨其形成过程及构造意义。锆石U-Pb定年结果显示富铌辉长岩样品锆石加权平均206Pb/238U年龄为512±4 Ma;两个斜长花岗岩样品的锆石加权平均206Pb/238U年龄分别为522±3 Ma和519±1 Ma。全岩地球化学结果显示富铌辉长岩的Nb含量为7.49×10-6~10.80×10-6,TiO2含量为1.50%~2.08%,Nb/U值为11.9~13.4,(Nb/La)N>0.5,明显高于岛弧玄武岩,其εNd(t)值介于+4.38~+5.78之间。斜长花岗岩样品K2O含量(0.31%~1.66%)和K2O/Na2O值(0.05~0.43)较低,稀土元素分布模式较为平缓,具有轻微的Eu正或负异常,相对富集Ba、Sr、U等大离子亲石元素,亏损Nb、Ta等高场强元素,结合其正的εNd(t)值(+3.35)和高、正的锆石εHf(t)值(主要在6.2~12.9之间),类似于弧前大洋斜长花岗岩。综合这些研究资料和区域地质,我们认为百经寺斜长花岗岩可能形成于俯冲初始阶段高温环境下俯冲洋壳部分熔融,随着俯冲继续,俯冲板片在更深部的部分熔融形成埃达克质熔体,并交代地幔楔形成富铌辉长岩。这些研究资料表明北祁连所代表的原特提斯洋的初始俯冲发生在早寒武世。  相似文献   

6.
北山柳园地区中志留世埃达克质花岗岩类及其地质意义   总被引:7,自引:3,他引:4  
北山柳园地区发育的埃达克质片麻状花岗闪长岩为钙碱性岩浆系列,具有较高SiO2 (>56%),Al2O3 (>15%)和较低的MgO (<3%)含量,Na2O>K2O; 并且具有高的Sr含量(>400×10-6)和Sr/Y比值; 样品轻重稀土强烈分异(La/Yb)N =18~86,强烈亏损重稀土Yb与Y,具有不明显的Eu异常(δEu=0.90~0.95); 富集LREE和大离子亲石元素(LILE),而亏损HREE、高场强元素(HFSE: Nb、Ta),与世界上典型的俯冲洋壳熔融形成的埃达克岩相似。然而样品具有相对高的(87Sr/86Sr)I (0.70635~0.70636)和相对低的εNd(t) (-0.8~-0.9),以及锆石具有相对较低的εHf (t) (-0.8~+2.7)同位素特征,比典型的俯冲洋壳熔融形成埃达克岩具有更多的放射成因,推测可能是源区加入了地壳物质/沉积物/或特殊的洋壳(OIB/E-MORB)熔融,以及侵位过程中地壳物质的混染所造成的。埃达克质片麻状黑云母花岗岩锆石LA-ICPMS年龄为424±4Ma,代表了花岗岩埃达克花岗岩的结晶年龄。花牛山岛弧带在中晚志留世时期具有较高的地热梯度,发育了大面积高εNd(t)钙碱性花岗岩和区域围岩发生了高温变质作用。因此,柳园埃达克岩是由于热的洋壳向花牛山岛弧地体俯冲过程中熔融形成的,俯冲洋壳熔融是本地区早古生代大规模地壳增生的重要方式之一。  相似文献   

7.
曲林岩体位于冈底斯带中段的南缘,为渐新世-中新世复合岩体,主体为粗粒花岗斑岩,被后期煌斑质、花岗闪长质和花岗质岩脉切割,是多期岩浆作用的产物,出露面积约8km2。花岗斑岩两组样品(T0849-PG和T0849-G)的锆石U-Pb定年结果分别为29.7±0.1Ma和30.0±0.2Ma。花岗斑岩为高钾,准铝质,低MgO,高度富集轻稀土元素(LREE)和大离子亲石元素(LILE),亏损重稀土元素(HREE)和高场强元素(HFSE)。此外具有高Sr、Sr/Y、(La/Yb)N;低Y和Yb,弱Eu负异常等特征。岩体内发育一系列近南北向展布的花岗闪长玢岩脉,其中两组样品的锆石U-Pb定年结果分别为15.5±0.1Ma(T0848-PY)和14.4±0.1Ma(T0850)。两条花岗闪长玢岩脉具有与岩体主体相似的稀土和微量元素分布模式,同样富集轻稀土及大离子亲石元素,亏损重稀土及高场强元素。花岗斑岩的87Sr/86Sr(i)=0.706102~0.706202,εNdt)=-0.6~+0.6,锆石εHft)=+4.9~+7.9;花岗闪长玢岩脉的87Sr/86Sr(i)=0.705429~0.705474,εNdt)=-1.4~-0.2,锆石εHft)=+2.6~+7.6。本文数据和文献数据结果表明:曲林花岗斑岩与花岗闪长玢岩脉均来源于加厚南拉萨下地壳的部分熔融,很可能与增厚的深部岩石圈的拆沉或俯冲印度岩石圈的撕裂诱发软流圈上涌有关。  相似文献   

8.
松林口岩体位于松潘—甘孜造山带中东部,为确定岩体的侵位时代和地球化学特征,通过镜下薄片观察、主微量元素分析以及锆石U-Pb测年,对松林口岩体进行了研究。结果表明,松林口岩体由二长花岗岩体和花岗闪长岩体组成,花岗闪长岩锆石206Pb/238U年龄加权平均值为(212.4±0.9) Ma (MSWD=0.66),二长花岗岩锆石206Pb/238U年龄加权平均值为(222.4±1.1) Ma (MSWD=0.39),形成于晚三叠世,由两期次岩浆作用形成;岩石的SiO2含量56.56%~61.97%;铝饱和指数A/CNK=0.93~1.05,全碱含量3.78~5.38,K2O/Na2O=1.02~1.68,里特曼指数σ=1.194~1.612,样品属于准铝质中—高钾钙碱性岩系列。岩石轻重稀土比值LREE/HREE=5.22~7.13,LaN/YbN比值为6.93~8.96,轻、重稀土分异较明显,具较强的负Eu异常。岩石Mg#值较高(50.97~61.27),w(Rb)/w(Sr)为0.12~0.25,Rb-(Y+Nb)图解显示为后碰撞环境。因此,松林口二长花岗岩—花岗闪长岩属后碰撞准铝质中—高钾钙碱性I型花岗岩类。  相似文献   

9.
闫慧慧  朱光有  陈志勇  张纯  侯政  孙琦森 《岩石学报》2020,36(11):3414-3426
塔里木板块广泛发育新元古代岩浆岩,它们对研究塔里木新元古代构造演化及塔里木对Rodinia超大陆汇聚和裂解的响应具有重要意义。本文报道了塔里木板块东北缘I型花岗岩的U-Pb年代学、原位Hf同位素以及全岩地球化学研究结果。该花岗岩具有较高的SiO2含量(平均值为71.61%),低的镁铁质含量(FeOT和MgO平均值为1.52%和0.72%);Na2O/K2O比值介于0.51~3.76,平均值为1.12;铝饱和度(A/CNK)介于0.69~1.16,属于碱性-钙碱性过渡型花岗岩。花岗岩表现为高场强元素(HFSE,如:Nb、Ta、Ti、Th等)的亏损以及大离子亲石元素(LILE,如:Rb、Sr、Ba、U等)的相对富集。样品Nb/Ta、Zr/Hf平均值分别为10.93、36.86,说明该花岗岩形成时有流体的参与。受斜长石的影响,花岗岩表现出明显的Eu正异常,Eu/Eu*平均值1.39。该花岗岩206Pb/238U加权平均年龄为748.8±6.1Ma,其原位Hf同位素εHft)值范围在-16.5~-9.7之间,对应两阶段模式年龄tDM2介于2.30~2.74Ga,指示该期花岗岩可能为古元古代地壳的部分熔融,可能形成于古洋壳向南俯冲塔里木板块产生的大陆弧后环境。结合之前在塔北缘的研究工作,提出了塔里木板块北缘新元古代弧后伸展体系,并且认为该体系主要受控于Rodinia超大陆的裂解。  相似文献   

10.
乌图布拉克岩体位于准噶尔北东缘,额尔齐斯-玛因鄂博构造带南侧。岩体主要由花岗闪长岩和二长花岗岩组成,有少量石英闪长岩和钾长花岗岩。岩体的锆石SHRIMP U-Pb年龄为360.1±3.6Ma。岩石的K2O+Na2O=7.05%~9.48%,A/NKC=0.91~1.04,属准铝-过铝质“I”型花岗岩。岩石稀土总量低,∑REE为72×10-6~184×10-6,轻稀土富集,(La/Yb)N=5~13。石英闪长岩、花岗闪长岩、二长花岗岩具弱的铕负异常或无明显异常(δEu=0.72~0.98);钾长花岗岩铕负异常明显(δEu=0.15~0.21)。在微量元素配分模式中,具有Sr、Ba、P、Ti的亏损,而Nb、Ta亏损不明显。岩石有低的Sr初始值(0.70165~0.70462)和高的εNd(t)u(+4.7~+6.9)。2个样品的Nd模式年龄分别为758Ma和551Ma。上述特征表明,岩浆可能具有较复杂的来源,推测该岩体岩浆可能来源于年轻的玄武质地壳,并有幔源物质的加入。综合本文资料及区域地质特征分析,阿尔泰造山带后碰撞时限可能为360~290Ma,即泥盆纪末-石炭纪末。  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.
Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ1 roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003).  相似文献   

15.
Well investigated platforms have been selected in each continent, and the history of Cretaceous transgressions and regressions there is concisely reviewed from the available evidence. The factual records have been summarized into a diagram and the timing of the events correlated between distant as well as adjoining areas.On a global scale, major transgressions were stepwise enlarged in space and time from the Neocomian, via Aptian-Albian, to the Late Cretaceous, and the post-Cretaceous regression was very remarkable. Minor cycles of transgression-regression were not always synchronous between different areas. Some of them were, however, nearly synchronous between the areas facing the same ocean.Tectono-eustasy may have been the main cause of the phenomena of transgression-regression, but certain kinds of other tectonic movements which affected even the so-called stable platforms were also responsible for the phenomena. The combined effects of various causes may have been unusual in the Cretaceous, since it was a period of global tectonic activity. The slowing down of this activity followed by readjustments may have been the cause of the global regression at the end of the Cretaceous.  相似文献   

16.
《地学前缘(英文版)》2014,(3):I0001-I0003
正1 AIM AND SCOPE GEOSCIENCE FRONTIERS(GSF) is a bi-monthly international journal that publishes in English high quality original research articles and timely reviews in interdisciplinary fields of Earth and Planetary Sciences.GSF aims to bridge innovative,provocative and challenging concepts and models related to various fields of research including petrology and geochemistry in understanding lithospheric architecture  相似文献   

17.
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   

18.
正20141430 Chen Ji(Key Laboratory of Petroleum Resources,Chinese Academy of Sciences,Lanzhou 730000,China);Shi Ji’an Sedimentary Facies and Models for the Palaeogene-Neogene Deposits on the Northern Margin of the Qaidam Basin,Qinghai Province(Sedimentary Geology and Tethyan Geology,ISSN1009-3850,CN51-1593/P,33(3),2013,p.16-26,14 illus.,16 refs.)  相似文献   

19.
SEISMIC GEOLOGY     
正20141967An Zhanghui(Lanzhou Base of Institute of Earthquake Prediction,CEA,Lanzhou 730000,China);Du Xuebin Study onthe Geo-Electric Field Variation of Sichuan Lushan MS7.0and Wenchuan MS8.0Earthquake(Chinese Journal of Geophysics,ISSN0001-5733,CN11-2074/P,56(11),  相似文献   

20.
GEOCHEMISTRY     
正20141357 Guo Tao(School of Mathematics and Science,Shijiazhuang University of Economics,Shijiazhuang 050031,China);Hu Jiawen Assessment on the New Pressure-Volume-Temperature(PVT) Data of Supercritical Water(Geological Journal of China Universities,ISSN1006-7493,CN32-1440/P,19(3),2013,p.447-455,9 illus.,3 tables,32 refs.)Key words:supercritical fluids  相似文献   

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