西藏班公湖中特提斯洋盆的打开时间:镁铁质蛇绿岩地球化学与锆石U-Pb LAICPMS定年结果   总被引：11，自引：0，他引：11       下载免费PDF全文

曲晓明  辛洪波  赵元艺  王瑞江  樊兴涛 《地学前缘》2010,17(3):53

对青藏高原西北部班公湖缝合带开展了路线剖面地质调查,在北面日土蛇绿岩带上采得2处镁铁质岩墙(辉长岩和辉绿岩),岩石地球化学分析表明这两处镁铁质岩墙具有平缓的球粒陨石标准化稀土元素分布型式,显示出洋中脊玄武岩特征,说明它们形成于洋中脊环境,其锆石U-PbLAICPMS年龄测定结果分别为(181.9±2.6)Ma(MSWD=11.5)和(184.4±4.4)Ma(MSWD=2.2),表明班公湖中特提斯洋是在早侏罗世晚期打开的。另外,在狮泉河—改则蛇绿岩带上采得橄榄辉绿岩,岩石以K2O(质量分数为1.49%～1.56%)、Al2O3(质量分数为14.76%～15.21%)含量高,Fe2O3/FeO比值高(1.73～2.49),富集大离子不相容元素(Rb、Ba、Th、Sr)和轻稀土元素(LREE)为特点,在基性岩构造环境判别图上显示出洋岛玄武岩的亲合性。该样品给出的(176.2±9.0)Ma(MSWD=3.1)的锆石U-PbLAICPMS年龄说明,班公湖中特提斯洋从早侏罗世晚期打开,经过近10Ma的扩张至中侏罗世早期已变成一个成热的洋盆。  相似文献   

青藏高原羌塘南部晚古生代地幔柱？——来自基性—超基性岩的地球化学证据     

王明  李才  翟庆国  彭帅英  解超明  吴彦旺  胡培远 《中国区域地质》2010,(12):1754-1772

羌塘南部地区大面积出露基性—超基性火成岩。基性岩墙和玄武岩沿龙木错-双湖板块缝合带的南侧呈近东西向分布,大地构造位置位于冈瓦纳大陆北缘,分布范围西起国境线,东到双湖地区,总长约800km,形成时代集中在晚石炭世—早二叠世（284～318Ma）,反映出岩浆的快速侵位-喷溢的过程。基性岩墙和玄武岩主要为碱性系列岩石,少数为亚碱性系列,Ti和Fe的含量均比较高,Mg#比较低,表明它们都是原始岩浆经不同程度分异结晶后的残余熔体。基性岩墙和玄武岩的稀土元素、微量元素、形成环境等均与板内玄武岩或典型的地幔柱成因玄武岩具有相似的特点。另外,苦橄质岩石多与基性岩墙和玄武岩一起产出,主要为单斜辉石橄榄岩和二辉橄榄岩,矿物成分贫挥发性组分,主量、稀土和微量元素的特点反映出其很可能代表了地幔柱原始岩浆结晶的产物而非岩浆捕获体,而且其源区很可能为石榴子石二辉橄榄岩。由此,初步认为羌塘南部基性岩墙和玄武岩为地幔柱的头部减压熔融的产物,而苦橄质岩石为地幔柱尾柱通道熔融的产物。  相似文献   

镁铁-超镁铁层状侵入体研究现状   总被引：1，自引：0，他引：1  

胡素芳  周新华 《矿物岩石地球化学通报》2001,20(1):52-57

本文主要探讨了镁铁 -超镁铁层状侵入体的一般特征及成因机制 ,并对世界上著名的斯开利戛德、布什维尔德、斯蒂尔沃特层状侵入体和我国攀西层状侵入体的岩石学和地球化学特征进行了总结和对比。  相似文献   

东南极拉斯曼丘陵镁铁质麻粒岩的地球化学特征及其中压变质作用          下载免费PDF全文

王彦斌  赵越  任留东  陈廷愚  刘小汉  仝来喜 《极地研究》1994,6(3):4-14

在东南极普里兹湾拉斯曼丘陵地区变泥质岩和长英质片麻岩中，定向分布着透镜状、扁豆状和香肠状镁铁质、超镁铁质麻粒岩。这些岩石主量元素、微量元素和稀土元素地球化学特征显示其原岩化学成分具镁铁质堆晶岩特征，并可能代表岩墙的构造作用残留体。在米洛半岛发现石榴子石周围有斜方辉石和斜长石的反应边，斜方辉石和斜长石由下述反应形成：石榴子石＋石英→斜方辉石＋斜长石。这个反应为减压反应，应用地质温压计确定其温度和压力分别为７４７±４８°Ｃ和６．３±０．５ｋｂａｒ，本文首次应用石榴子石－斜方辉石－斜长石－石英组合确立本区早期中压麻粒岩相事件的存在。本文还对镁铁质麻粒岩的原岩成因及矿物中的减压结构所代表的构造意义进行了探讨  相似文献   

造山岩套中镁铁质和长英质岩浆的相互作用研究进展   总被引：7，自引：0，他引：7  

马昌前 《地质科技情报》2003,22(3):1-8

结合2002年9月14—21日在意大利中部召开的“欧洲花岗岩网络”年会的会议讨论和野外考察内容,评述了镁铁质和长英质岩浆的相互作用关系以及镁铁质熔体在巨量花岗岩浆形成中的作用。在花岗岩岩基内,不仅出露有狭义的花岗岩,还可见到更富镁铁质的岩石,例如辉长岩和闪长岩。一般,这些镁铁质岩石,既可能是慢源母岩浆结晶的产物,或是岩浆混合和分异一同化作用中的端员组分,也可能代表了下地壳源区的物质,或者是导致大陆壳部分熔融的热源物质记录。对镁铁质和长英质岩浆相互作用关系的研究,有助于限定造山作用过程中地壳物质再循环和新的地慢物质加入的相对贡献。  相似文献   

Zircon geochronology and geochemistry of mafic xenoliths from Liaoning kimberlites:Track the early evolution of the lower crust,North China Craton   总被引：1，自引：0，他引：1  

ZHENG Jianping  YU Chunmei  LU Fengxiang & LI Huimin .Faculty of Earth Sciences  China University of Geosciences  Wuhan  China  .Tianjin Institute of Geology  Mineral Resources  Tianjin  China 《中国科学D辑(英文版)》2004,47(11):961-972

Since the formation of the primal nucleus at 3.8Ga[1], the North China had underwent the multi-cycle geologic processes such as arc accretion[2—4] andrift[5—7], and finally accomplished the craton[8] aroundat 1.8 Ga[2,3,9]. Paleozoic Fuxian kimberlites (LiaoningProvince) contain not only abundant peridotitic butalso mafic xenoliths. The investigation on peridotiticxenoliths indicted that the North China Craton hadcold and thick lithospheric root in the middle Ordovi-cian. The deep part o…  相似文献   

Petrogenesis of Mafic Inclusions in Rhyolitic Lavas from Narugo Volcano, Northeastern Japan   总被引：1，自引：0，他引：1  

BAN  MASAO; TAKAHASHI  KOJI; HORIE  TAKEHIRO; TOYA  NARUHISA 《Journal of Petrology》2005,46(8):1543-1563

Mafic inclusions present in the rhyolitic lavas of Narugo volcano,Japan, are vesiculated andesites with diktytaxitic texturesmainly composed of quenched acicular plagioclase, pyroxenes,and interstitial glass. When the mafic magma was incorporatedinto the silica-rich host magma, the cores of pyroxenes andplagioclase began to crystallize (>1000°C) in a boundarylayer between the mafic and felsic magmas. Phenocryst rim compositionsand interstitial glass compositions (average 78 wt % SiO₂) inthe mafic inclusions are the same as those of the phenocrystsand groundmass glass in the host rhyolite. This suggests thatthe host felsic melt infiltrated into the incompletely solidifiedmafic inclusion, and that the interstitial melt compositionin the inclusions became close to that of the host melt (c.850°C). Infiltration was enhanced by the vesiculation ofthe mafic magma. Finally, hybridized and density-reduced portionsof the mafic magma floated up from the boundary layer into thehost rhyolite. We conclude that the ascent of mafic magma triggeredthe eruption of the host rhyolitic magma. KEY WORDS: mafic inclusion; stratified magma chamber; magma mixing; mingling; Narugo volcano; Japan  相似文献   

Palaeomagnetism of 935 Ma mafic dykes in southern Sweden and implications for the Sveconorwegian Loop   总被引：1，自引：0，他引：1  

S. A. Pisarevsky  G. Bylund 《Geophysical Journal International》2006,166(3):1095-1104

New palaeomagnetic results for the 935 Ma Göteborg-Slussen mafic dykes in southern Sweden provide a well-dated high-quality palaeomagnetic pole for Early Neoproterozoic Baltica. New U-Pb geochronological data for several palaeomagnetically studied mafic intrusions yield three additional well-dated palaeopoles and one virtual geomagnetic pole. This set of dated poles suggests minimal drift of Baltica in moderate latitudes between ∼965 and 915 Ma. They also support the hypothesis of a post-900 Ma regional remagnetization event in SW Sweden and SW Norway. The positions of three distinct clusters of ∼1100 to 850 Ma palaeopoles suggest a clockwise time progression of the Baltica apparent polar wander path (the Sveconorwegian Loop) during this time interval. New well-dated palaeomagnetic poles for ∼970 to 900 Ma from Laurentia are required to verify the palaeogeographic reconstructions of Baltica and Laurentia.  相似文献   

Three-dimensional seismic reflection investigation of the upper crustal Winagami sill complex of northwestern Alberta, Canada     

J. Kim Welford  Ron M. Clowes 《Geophysical Journal International》2006,166(1):155-169

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Petrology and mineralogy of granulite-facies mafic xenoliths (Sardinia, Italy): Evidence for KCl metasomatism in the lower crust     

Alessandra Montanini  Daniel Harlov 《Lithos》2006,92(3-4):588-608

Here new mineralogical data is presented on the occurrence of K-feldspar in granulite-facies metagabbronorite xenoliths found in recent alkaline lavas from Western Sardinia, Italy. The xenoliths originated from the underplating of variably evolved subduction-related basaltic liquids, which underwent cooling and recrystallisation in the deep crust (T = 850–900 °C, P = 0.8–1.0 GPa). They consist of orthopyroxene + clinopyroxene + plagioclase porphyroclasts (An = 50–66 mol%) in a granoblastic, recrystallised, quartz-free matrix composed of pyroxene + plagioclase (An = 56–72 mol%) + Fe–Ti oxides ± K-feldspar ± biotite ± fluorapatite ± Ti-biotite. Texturally, the K-feldspar occurs in a variety of different modes. These include: (1) rods, blebs, and irregular patches in a random scattering of plagioclase grains in the form of antiperthite; (2) micro-veins along plagioclase–plagioclase and plagioclase–pyroxene grain rims; (3) myrmekite-like intergrowths with Ca-rich plagioclase along plagioclase–plagioclase grain boundaries; and (4) discrete anhedral grains (sometimes microperthitic). The composition of each type of K-feldspar is characterized by relatively high albite contents (16–33 mol%). An increasing anorthite content in the plagioclase towards the contact with the K-feldspar micro-vein and myrmekite-like intergrowths into the K-feldspar along the plagioclase–K-feldspar grain boundary are also observed. Small amounts of biotite (TiO₂ = 4.7–6.5 wt.%; F = 0.24–1.19 wt.%; Cl = 0.04–0.20 wt.%) in textural equilibrium with the granulite-facies assemblage is present in both K-feldspar-bearing and K-feldspar-free xenoliths. These K-feldspar textures suggest a likely metasomatic origin due to solid-state infiltration of KCl-rich fluids/melts. The presence of such fluids is supported by the fluorapatite in these xenoliths, which is enriched in Cl (Cl = 6–50% of the total F + Cl + OH). These lines of evidence suggest that formation of K-feldspar in the mafic xenoliths reflects metasomatic processes, requiring an external K-rich fluid source, which operated in the lower crust during and after in-situ high-T recrystallisation of relatively dry rocks.  相似文献