Zircon U–Pb Geochronology and Geochemistry of the Early Cretaceous Volcanic Rocks from the Manitu Formation in the Hongol Area,Northeastern Inner Mongolia     

ZHANG Xiangxin  SU Zhen  GAO Yongfeng 《《地质学报》英文版》2017,91(4):1286-1304

We undertook zircon U-Pb dating and geochemical analyses of volcanic rocks from the Manitu Formation in the Hongol area,northeastern Inner Mongolia,to determine their age,petrogenesis and sources,which are important for understanding the Late Mesozoic tectonic evolution of the Great Xing'an Range.The volcanic rocks of the Manitu Formation from the Hongol area consist primarily of trachyandesite,based on their chemical compositions.The zircons from two of these trachyandesites are euhedral-subhedral in shape,display clear oscillatory growth zoning and have high Th/U ratios(0.31-1.15),indicating a magmatic origin.The results of LA-ICP-MS zircon U-Pb dating indicate that the volcanic rocks from the Manitu Formation in the Hongol area formed during the early Early Cretaceous with ages of 138.9-140.5 Ma.The volcanic rocks are high in alkali(Na_2O + K_2O = 6.22-8.26 wt%),potassium(K_2O = 2.49-4.58 wt%) and aluminium(Al_2O_3 = 14.27-15.88 wt%),whereas they are low in iron(total Fe_2O_3 = 3.76-6.53 wt%) and titanium(TiO_2 = 1.02-1.61 wt%).These volcanic rocks are obviously enriched in large ion lithophile elements,such as Rb,Ba,Th and U,and light rare earth elements,and are depleted in high field strength elements,such as Nb,Ta and Ti with pronounced negative anomalies.Their Sr-Nd-Pb isotopic compositions show positive ε_(Nd)(t)(+0.16‰ to+1.64‰) and low T_(DM)(t)(694-767 Ma).The geochemical characteristics of these volcanic rocks suggest that they belong to a shoshonitic series and were likely generated from the partial melting of an enriched lithospheric mantle that was metasomatised by fluids released from a subducted slab during the closure of the MongolOkhotsk Ocean.Elemental and isotopic features reveal that fractional crystallization with the removal of ferromagnesian minerals,plagioclase,ilmenite,magnetite and apatite played an important role during the evolution of the magma.These shoshonitic rocks were produced by the partial melting of the enriched lithospheric mantle in an extensional regime,which resulted from the gravitational collapse following the final closure of the Mongol-Okhotsk Ocean in the Middle-Late Jurassic.  相似文献   

西藏萨嘎县罗波岗日地区中新世花岗岩地球化学特征及成因          下载免费PDF全文

马涛  胡积球  黄登鹏  李进喜 《甘肃地质》2017,26(3):1-10

罗波岗日地区大地构造位置处于冈底斯花岗岩带南亚带,该区出露较大规模的二云二长花岗岩体。LA-ICP-MS U-Pb年龄结果表明,锆石~(206)Pb/~(238)U加权平均年龄为16.15±0.19 Ma,表明上述岩体形成于新近纪中新世布尔迪尔期。二云二长花岗岩的w(SiO_2)为71.77%~73.05%,组合指数δ为1.76~2.23,A/CNK的比值为1.114~1.213,A/NK的比值为1.36~1.54,属于高钾钙碱性强过铝质S型花岗岩系列。在ORG标准化蛛网图中,二云二长花岗岩微量元素总体呈右倾富集特征,相对富集Rb,Ce,Hf,Sm,而亏损Nb,Zr。球粒陨石标准化的稀土元素配分曲线呈右倾富集型,稀土元素总量变化较大,∑REE=98.92×10~(-6)~184.17×10~(-6),LREE/HREE=11.24~25.16,(La/Yb)N=14.85~56.98,轻重稀土分馏显著,Eu的负异常不明显。样品的Rb/Sr比值为0.34~0.60,大于0.32,TFeO+MgO+TiO_2含量为2.53%~3.05%,CaO/Na_2O比值为0.32~0.41,说明罗波岗日二云二长花岗岩的源岩主要为来自于上地壳的砂质岩。与该区域的浅色花岗岩对比研究表明,罗波岗日地区二云二长花岗岩的成因,是在水等流体在伸展体制背景下沿着构造薄弱带迁移、聚集,在上地壳物质重新调整过程中,使得以砂质岩为主的源岩发生"湿"深熔作用,生成过铝质岩浆,最终结晶形成二云二长花岗岩。  相似文献   

大兴安岭中段索伦地区玛尼吐组火山岩年代学、地球化学及其构造背景   总被引：2，自引：0，他引：2  

杜岳丹  和钟铧  隋振民  谭皓元  任子慧 《世界地质》2017,36(2):346-360

索伦地区玛尼吐组火山岩岩相学鉴定为安山岩、粗安岩和英安岩,化学成分显示以玄武粗面安山岩、粗安岩为主,少量流纹岩。LA-ICPMS锆石U-Pb定年结果显示其形成于130~132 Ma之间的早白垩世。地球化学特点上主要属高钾钙碱性系列。稀土总量较高(95.19~198.38)×10~(-6),轻重稀土分馏较明显(LREE/HREE=6.38~10.59),弱的负铕异常(δEu=0.68~1.01),富集大离子亲石元素(K、Rb、Th)和轻稀土元素,亏损高场强元素(Nb、Ta、P、Ti)。微量元素具高Sr(多499×10~(-6))和低Yb(最大值为2.83×10~(-6)3.6×10~(-6))、Y(多29.9×10~(-6))和高Sr/Y和低Rb/Sr比值,显示了弧火山岩的特征。正的ε_(Hf)(t)值(7.3~13.7),锆石~(176)Hf/~(177)Hf平均值为0.282964,显示玛尼吐组安山质岩浆源区主要为岩石圈地幔和新增生下地壳的部分熔融,且岩浆形成的过程中受到了流体的改造作用。玛尼吐组火山岩形成于岛弧构造环境,该岛弧构造背景的产生可能与受古太平洋板块俯冲作用有关。  相似文献   

东昆仑—西秦岭造山带对接处三叠纪花岗质岩石时空演化、物源特征对比及其大地构造意义     

任海东  王涛 《地球学报》2017,38(S1):59-63

造山带组成与演化是大地构造研究的主要课题, 造山带之间的对接关系更是造山带研究的重要节点。在两大造山带对接地带, 构造-岩浆演化的对比, 特别是深部物质组成结构和基底属性的对比, 可为完整认识造山带的物质组成和构造演化提供重要的依据。基于花岗质岩石同位素填图(Sm-Nd、Lu-Hf)在其年代学、区域性大面积展步和易于示踪等方面的优势, 区域性的同位素填图逐步成为一项重要的技术方法, 应用于探讨造山带深部组成结构, 对比造山带基底属性异同。  相似文献   

西藏东窝东矿床矿化蚀变过程元素迁移及绢云母~(40)Ar-~(39)Ar年代学及其地质意义   总被引：2，自引：2，他引：0  

侯淋  唐菊兴  林彬  宋扬  王勤  李玉彬  冯军  李彦波  陈列  唐晓倩 《岩矿测试》2017,36(4):440-449

东窝东铜多金属矿床位于羌塘地体南缘,多龙铜金矿集区东侧。该矿床尚未开展矿化蚀变时限、成矿作用中元素迁移特征等问题的研究。为确定矿床的蚀变矿化作用时限,本文对东窝东矿床的黄铁绢英岩化蚀变带中的蚀变绢云母进行了~(40)Ar-~(39)Ar年代学测试,获得~(40)Ar-~(39)Ar坪年龄为122.20±0.84 Ma,该年龄与已有的斑岩体侵位时代(122 Ma)一致,说明东窝东矿床黄铁绢英岩化蚀变与斑岩体侵位有密切联系。此外,对比分析地表弱蚀变和钻孔中强黄铁绢英岩化花岗闪长斑岩的岩石地球化学结果,运用"等浓度线(isocon)方程"及其推导方程,探讨黄铁绢英岩化蚀变过程中的不同元素的带入、带出特点及元素迁移特征。结果表明:高场强元素质量基本守恒;轻稀土元素较重稀土元素迁移量较大,但总体上稀土元素的迁移程度较弱;主要的成矿元素Cu、Pb、Zn为带入元素。东窝东矿床含矿斑岩侵位时代和热液蚀变时限均与多龙矿集区内多不杂、波龙、铁格隆南等多个超大型-大型铜金矿床一致,说明东窝东矿床和多龙矿集区内的多个矿床受控于同一构造-岩浆成矿背景,东窝东矿区具有重要的找矿潜力。  相似文献   

西天山望峰金矿床绢云母⁴⁰Ar/³⁹Ar年龄及矿床成因研究     

袁霞  陈文  张斌  孙敬博  喻顺  尹继元  张彦  刘新宇  杨莉  张岩 《矿床地质》2017,36(1):57-67

望峰金矿床位于中天山北缘冰达坂韧性剪切带内,成矿单元划分属于博罗科努多金属成矿带内天格尔-可可乃克次级成矿带,矿体主要赋存于糜棱岩化花岗岩中,主要矿石类型为石英脉型和蚀变糜棱岩型矿石。对两种类型矿石中的绢云母进行~(40)Ar/~(39)Ar测年,获得坪年龄分别为(250.9±3.0)Ma、(255.8±3.0)Ma,两个样品正反等时线年龄与坪年龄在误差范围内一致,表明坪年龄结果可信,可以代表成矿年龄,说明望峰金矿床的主成矿期时代为晚二叠世末期,且蚀变糜棱岩型矿石的形成时代比石英脉型矿石略早。结合矿区地质情况及前人的研究结果,认为望峰金矿床是剪切带型金矿床,冰达坂韧性剪切带控制了望峰金矿的成矿过程。  相似文献   

四川乐山震旦系灯影组火山碎屑岩锆石LA-ICP-MSU-Pb定年及盆地裂陷演化讨论   总被引：1，自引：0，他引：1  

资金平  贾东  魏国齐  杨振宇  张勇  胡晶  沈淑鑫 《地质论评》2017,63(4):1040-1049

四川盆地中部晚震旦(埃迪卡拉)世—早寒武世克拉通内裂陷与安岳震旦(埃迪卡拉)系—寒武系特大气田的形成关系密切,年代学研究对认识克拉通内裂陷构造意义重大。对四川盆地乐山先锋剖面灯影组三段火山碎屑岩进行锆石LA-ICP-MS U-Pb定年,研究结果表明四川盆地灯影组三段火山碎屑岩的锆石U-Pb年龄为(539.6±1.4)Ma,年代学结果表明四川盆地灯三段与灯四段属于寒武系。基于灯影组底界(551.1 Ma)、含火山碎屑岩的灯三段(539.6 Ma)、含小壳化石的麦地坪组(535.2 Ma)和下寒武统Ni—Mo多金属硫化物富集层(521.0 Ma)四个等时面构建了克拉通内裂陷演化的时间框架。在此基础上认为四川盆地中部晚震旦(埃迪卡拉)世—早寒武世隆坳构造的形成主要受边界断裂控制,断层活动使裂陷内水体加深,少量灯四段含硅质白云岩沉积后,麦地坪组与筇竹寺组开始沉积,麦地坪组与灯四段的界线在裂陷内与裂陷两侧并不等时,裂陷内麦地坪组、筇竹寺组与裂陷两侧灯影组四段为同期异相沉积。  相似文献   

Apparent conflicting Roadian–Wordian (middle Permian) CA-IDTIMS and palynology ages from the Canning Basin,Western Australia     

A. J. Mory  J. L. Crowley  J. Backhouse  R. S. Nicoll  S. E. Bryan  M. López Martínez 《Australian Journal of Earth Sciences》2017,64(7):889-901

U–Pb dating of zircons from thin middle Permian tuffs in the Canning Basin of Western Australia by chemical abrasion-isotope dilution thermal ionisation mass spectrometry reveals a conflict with the established spore-pollen zonation. Normally, the first appearance datum of Dulhuntyispora granulata across the continent lies stratigraphically above assemblages assigned to the Microbaculispora villosa Zone. However, the youngest tuffs within non-marine facies from the M. villosa Zone in Pittston SD-1, drilled in the southwest of the Canning Basin, yielded an age of 267.04 ± 0.14 Ma, which is 1.7 million years younger than tuffs associated with the D. granulata Zone in marginal-marine facies from core holes 350–400 km to the northeast. The apparent conflict in ages is possibly due to the non-marine depositional environment having wielded a strong local influence on the palynoflora along the edge of this basin. Although the present information indicates an age 2.5 million years younger than the 266.6 Ma age previously suggested for the top of the M. villosa Zone, revisions to the ages of Roadian–Wordian spore-pollen zones are not considered justifiable without further supporting evidence. Furthermore, considerable care is needed when comparing palynological assemblages from significantly differing facies. Two basaltic sills (43.5 m and 20 m thick) immediately below the tuffaceous beds in Pittston SD-1 are coincidental, as Ar–Ar dating indicates a Late Triassic age for the intrusions.  相似文献   

南秦岭铧厂沟金矿床铬云母~(40)Ar/~(39)Ar年代学及其大地构造意义     

林振文  周永章  秦艳  岳素伟 《大地构造与成矿学》2017,41(2):315-324

南秦岭铧厂沟金矿床位于勉略缝合带以南的逆冲推覆带内,矿体呈透镜体或脉状产于新元古界蚀变细碧岩及泥盆系灰岩中,受控于近EW向叠瓦状逆冲断层及韧脆性剪切带。为了准确厘定其成矿时代,对矿区蚀变细碧岩型矿石和含矿石英脉中的铬云母进行了年龄测定。2件铬云母样品的~(40)Ar/~(39)Ar坪年龄分别为209.4±2.3 Ma和211.5±2.5 Ma,相应的等时线年龄211.4±3.6 Ma和215.3±3.9 Ma,与坪年龄在误差范围内一致。因此,铧厂沟金矿床的成矿年龄为212~209 Ma。结合铧厂沟金矿床的大地构造位置、矿床地质特征及成因类型,推测铧厂沟金矿床形成于扬子板块与秦岭微板块的碰撞过程,其成矿年龄代表了两板块发生碰撞的下限。  相似文献   

哀牢山构造带两侧上志留统-下泥盆统碎屑锆石年代学:物源及其构造意义     

刘兵兵  彭头平  范蔚茗  高剑峰  方小玉  张靖祎 《大地构造与成矿学》2017,41(4):734-752

哀牢山古特提斯洋的打开时限及其缝合带的具体位置对理解哀牢山古特提斯洋构造演化具有非常重要的意义。本文采用碎屑锆石年代学方法,分析了哀牢山构造带及其两侧不同时期沉积物源的特征及其变化,解译了其物源差别所指示的哀牢山古特提斯洋盆打开时限以及缝合带的构造位置。碎屑锆石年代学显示,哀牢山构造带两侧上志留统碎屑锆石都记录一个~450 Ma的最年轻的峰值和一个格林威尔期造山事件的年龄群(1100~800 Ma),以及一个2600~2400 Ma的次峰;不同于上志留统,构造带东侧下泥盆统碎屑锆石并未出现年轻的~450 Ma峰值年龄信息,西侧U-Pb年龄分布模式与上志留统一致,记录~450 Ma峰值年龄信息,而且构造带两侧下泥盆统碎屑锆石的2600~2400 Ma的峰值明显要强于上志留统。区域上发表的碎屑锆石年代学资料,也揭示相同的年龄峰值。因此,综合区域上的其他地质资料,我们认为哀牢山古特提斯洋盆的打开时限应该在晚志留世-早泥盆世,哀牢山断裂带代表了哀牢山洋盆闭合的位置。  相似文献