辽北开原地区房木花岗斑岩LA-ICP-MS锆石U-Pb年龄及地球化学特征     

豆世勇 《吉林大学学报(地球科学版)》2020,50(6):1752-1765

研究区位于华北克拉通北缘东段、华北克拉通与兴蒙造山带的交接部位。本文通过对辽北开原地区房木花岗斑岩的岩石学、年代学和地球化学研究，探讨了其形成时代、岩石成因和构造环境，并进一步探讨了华北克拉通东部岩石圈减薄的起始时间。用LA-ICP-MS技术测定了花岗斑岩的锆石U-Pb同位素，获得其锆石²⁰⁶Pb/²³⁸U加权平均年龄为（117±1）Ma，表明花岗斑岩形成于早白垩世。花岗斑岩具有高硅、富碱、贫镁和钙的特征，富集大离子亲石元素（K、Rb）和高场强元素（Th、Ta、Nb），亏损Sr、Ba、P、Ti元素，稀土配分曲线均呈现右倾海鸥型，具有明显的负Eu异常；显示研究区花岗斑岩为A型（A₁亚型）花岗岩，形成于古太平洋俯冲的后造山伸展环境，其岩浆源于地幔物质上涌而导致的地壳物质重熔。研究区在（156±1）Ma之前，属于挤压造山环境，表明研究区岩石圈减薄时间应处于156~117 Ma之间。  相似文献   

滇中禄丰地区中元古代早期球颗玄武岩的锆石U-Pb年龄、地球化学特征及其大地构造意义     

刘军平  孙柏东  王晓峰  刘伟  马进华  关学卿  宋冬虎  吕勃烨 《地质论评》2020,66(1):35-51

在1∶5万区域地质调查的基础上,在禄丰地区东川群黑山组新发现了球颗玄武岩及凝灰岩夹层。采用LA-ICP-MS技术测得球颗玄武岩和凝灰质板岩中锆石U-Pb加权平均年龄分别为1678±10 Ma和1572±19 Ma,表明黑山组沉积时代为中元古代早期;其中球颗玄武岩SiO_2含量介于40.83%～52.56%,δEu正异常,大离子亲石元素Rb、Ba和高场强元素Nb、Ta、Th等强不相容元素相对富集,全岩地球化学显示为大陆板内低钛拉斑海相玄武岩,形成于伸展的构造环境,可能为Columbia超大陆裂解的产物。本次的发现,为准确地标定东川群时代、层序及大地构造属性提供新的参考依据,也为重塑整个滇中前寒武纪地层格架提供时代约束。  相似文献   

华北板块北缘勃隆克A型花岗岩锆石U-Pb定年及其地质意义     

李春麟  王宗秀  陶涛 《地质通报》2020,(1):40-50

内蒙古翁牛特旗勃隆克岩体位于华北板块北缘,侵位于上侏罗系火山岩地层中。详细的岩相学研究显示,勃隆克花岗岩具有粒状结构、蠕虫结构和文像结构,块状构造,部分斜长石已绢云母化、泥化。对勃隆克花岗岩进行了LA-ICP-MS锆石U-Pb定年,获得134.0±1.8Ma和134.9±4.1Ma的侵位年龄,表明其形成于早白垩世。地球化学特征显示,花岗岩属于高钾钙碱性系列,有较高的SO2(74.1%~75.6%)、Na2O+K2O(8.98%~9.2%)、Rb(210×10-6~225×10-6)含量和10000×Ga/Al(2.69~2.80)、Rb/Sr(5.8~18.9)值,具有较低的CaO、MgO、Ba和Sr含量。铝饱和指数A/CNK=0.99~1.03,属于偏铝质或过铝质A型花岗岩。稀土元素球粒陨石标准化图解显示,轻稀土元素相对富集,负Eu异常明显;在原始地幔标准化图解上,Ba、Sr、Nb、Ta、P、T强烈亏损,富集Rb、Th、K、Hf等元素,与华北板块北缘早白垩世A型花岗岩类似。结合区域构造演化,认为勃隆克花岗岩形成于伸展构造背景。晚中生代,华北板块北缘构造体制经历了重大的转变,地壳从挤压体制转为岩石圈减薄和地壳伸展体制,软流圈物质上涌导致上覆地壳长英质物质的部分熔融形成勃隆克A型花岗岩。  相似文献   

晚第四纪MIS6以来柴达木盆地成盐作用对冰期气候的响应   总被引：2，自引：0，他引：2  

陈安东  郑绵平  宋高  王学锋  李洪普  韩光  袁文虎 《地质论评》2020,66(3):611-624

气候是控制柴达木盆地盐类沉积的主要因素之一,但是其作用机制尚待明确。作者以柴达木盆地察汗斯拉图盐湖的3个含盐剖面为研究对象,采用多接收电感耦合等离子质谱(MC-ICP-MS)铀系测年测定其沉积时代,并通过X射线粉晶衍射(XRD)分析测定其盐类矿物种类。铀系测年显示D18剖面石盐和芒硝层的沉积时代为13.1±2.0 ka BP～15.9±2.5 ka BP,其中芒硝沉积年代属于末次冰期MIS2晚期;MXK2剖面芒硝层的沉积时代分别为131.7±39.5 ka BP和158.3±10.8 ka BP,D12剖面芒硝层的沉积时代分别为166.6±20.2 ka BP和198.0±20.6 ka BP,可以对应于倒数第二次冰期MIS6。XRD分析确定了3个剖面的盐类矿物主要为芒硝、石盐和石膏。综合多个盐湖晚第四纪成盐数据,本文认为倒数第二次冰期MIS6和末次冰期MIS2是柴达木盆地晚第四纪重要的成盐期,冰期的冷干气候有利于石盐和芒硝等盐类沉积。柴达木盆地"冰期成盐"的根本原因,是由于冰期环境下盆地周边山体冰川规模的扩张以及干冷的冰期气候,共同造成了盐湖补给水量的减少。此外,晚第四纪MIS6和MIS2的冰期降温也是导致盆地中冷相盐类沉积的直接原因。  相似文献   

Sediment routing in the Zagros foreland basin: Drainage reorganization and a shift from axial to transverse sediment dispersal in the Kurdistan region of Iraq     

Renas I. Koshnaw  Brian K. Horton  Daniel F. Stockli  Douglas E. Barber  Mazin Y. Tamar-Agha 《Basin Research》2020,32(4):688-715

In the northwestern sector of the Zagros foreland basin, axial fluvial systems initially delivered fine-grained sediments from northwestern source regions into a contiguous basin, and later transverse fluvial systems delivered coarse-grained sediments from northeastern sources into a structurally partitioned basin by fold-thrust deformation. Here we integrate sedimentologic, stratigraphic, palaeomagnetic and geochronologic data from the northwestern Zagros foreland basin to define the Neogene history of deposition and sediment routing in response to progressive advance of the Zagros fold-thrust belt. This study constrains the depositional environments, timing of deposition and provenance of nonmarine clastic deposits of the Injana (Upper Fars), Mukdadiya (Lower Bakhtiari) and Bai-Hasan (Upper Bakhtiari) Formations in the Kurdistan region of Iraq. Sediments of the Injana Formation (~12.4–7.75 Ma) were transported axially (orogen-parallel) from northwest to southeast by meandering and low-sinuosity channel belt system. In contrast, during deposition of the Mukdadiya Formation (~7.75–5 Ma), sediments were delivered transversely (orogen-perpendicular) from northeast to southwest by braided and low-sinuosity channel belt system in distributive fluvial megafans. By ~5 Ma, the northwestern Zagros foreland basin became partitioned by growth of the Mountain Front Flexure and considerable gravel was introduced in localized alluvial fans derived from growing topographic highs. Foredeep accumulation rates during deposition of the Injana, Mukdadiya and Bai-Hasan Formations averaged 350, 400 and 600 m/Myr respectively, suggesting accelerated accommodation generation in a rapidly subsiding basin governed by flexural subsidence. Detrital zircon U-Pb age spectra show that in addition to sources of Mesozoic-Cenozoic cover strata, the Injana Formation was derived chiefly from Palaeozoic-Precambrian (including Carboniferous and latest Neoproterozoic) strata in an axial position to the northwest, likely from the Bitlis-Puturge Massif and broader Eastern Anatolia. In contrast, the Mukdadiya and Bai-Hasan Formations yield distinctive Palaeogene U-Pb age peaks, particularly in the southeastern sector of the study region, consistent with transverse delivery from the arc-related terranes of the Walash and Naopurdan volcano-sedimentary groups (Gaveh-Rud domain?) and Urumieh-Dokhtar magmatic arc to the northeast. These temporal and spatial variations in stratigraphic framework, depositional environments, sediment routing and compositional provenance reveal a major drainage reorganization during Neogene shortening in the Zagros fold-thrust belt. Whereas axial fluvial systems initially dominated the foreland basin during early orogenesis in the Kurdistan region of Iraq, transverse fluvial systems were subsequently established and delivered major sediment volumes to the foreland as a consequence of the abrupt deformation advance and associated topographic growth in the Zagros.  相似文献   

大兴安岭满归地区变中酸性火山岩LA-ICP-MS锆石U-Pb年龄及其地质意义     

李中会  李睿杰  李阳  沙环宇 《中国地质调查》2020,7(1):47-52

对大兴安岭满归地区新元古界—下寒武统大网子组变中酸性火山岩进行锆石U-Pb同位素年代学研究,探讨其形成时代及地质意义。大网子组由变安山岩、变英安岩、变流纹岩和少量变晶屑凝灰岩组成,缺少板岩、变砂岩、片岩等沉积岩夹层。通过对变安山岩进行锆石U-Pb同位素年龄测定,获得其锆石²⁰⁶Pb/²³⁸U加权平均年龄为(199±1) Ma,表明大网子组变中酸性火山岩形成于早侏罗世早期,非前人认为的形成于新元古代—早寒武世。额尔古纳地块早侏罗世火山岩为漠河盆地提供了物源,表明额尔古纳地块在早侏罗世处于火山-岩浆弧构造背景。该研究为蒙古—鄂霍茨克洋闭合过程中的地球动力学研究提供了新资料。  相似文献   

羌塘中部白措花岗岩岩石地球化学特征、锆石U Pb年龄和Hf同位素组成及其构造意义     

李学仁  万友利  王剑 《地质论评》2020,66(5):1172-1185

本文对羌塘中部白措花岗岩的研究表明，岩体是由花岗闪长岩和二长花岗岩同时侵位的复合岩基，锆石U Pb年龄分别为213. 8±1. 3 Ma、210. 0±1. 1 Ma和208. 1±1. 4 Ma。白措花岗岩为硅过饱和的准铝质—弱过铝质岩石，Eu负异常明显，富集大离子亲石元素，亏损高场强元素，显示典型的壳源特征。εHft)为负值，主要集中于-10～-15，对应的Hf同位素二阶段模式年龄峰值为1. 78 Ga，显示源区为古元古代古老地壳；同时，花岗岩中含有大量闪长质暗色包体，表明有壳幔岩浆混合作用，推测为同时期玄武质岩浆的底侵作用，在地壳深部诱发富硅质基底岩石重熔，快速喷发形成玄武岩—流纹岩双峰式组合，而花岗岩则是由玄武质岩浆在地壳充分熔融后，岩浆沿羌塘中部已有的构造破碎带侵入形成，并且在熔融过程中有镁铁质岩浆注入少量结晶的长英质岩浆中形成暗色包体。因此，花岗岩与双峰式火山岩是同一裂陷动力机制的产物。花岗岩的侵入预示了晚三叠世羌塘盆地构造岩浆活动的结束，之上开始了羌塘侏罗纪海相盆地的沉积。  相似文献   

The evolution of zircon during low‐P partial melting of metapelitic rocks: theoretical predictions and a case study from Mt Stafford,central Australia     

WEI‐ Wang  E. Dunkley  G. L. Clarke  N. R. Daczko 《Journal of Metamorphic Geology》2014,32(8):791-808

Palaeoproterozoic metasedimentary migmatite reflects the highest temperature parts of a regional aureole at Mt Stafford, central Australia, comprising rocks that experienced 500–800 °C at ≈3 kbar. Whole‐rock major element concentrations are correlated with Zr content, psammitic compositions having nearly twice the Zr content of pelitic compositions. Zirconium is concentrated in mesosome compared with leucosome. Zircon is largely detrital, mostly lacking any overgrowth contemporary with migmatite formation. Comparatively small proportions of micro‐zircon (<10 μm) in sub‐solidus rocks are mostly hosted by quartz and plagioclase. Much higher proportions (three to five times) of micro‐zircon in migmatite are hosted by prograde K‐feldspar, cordierite and biotite. T–X and P–T NCKFMASHTZr pseudosections constructed using thermocalc model the distribution of Zr between solid and silicate liquid phases. Half of the detrital zircon (~100 ppm Zr) is predicted to be dissolved into silicate liquid at ≈800 °C and all dissolved by 850 °C, if all zircon is involved in the equilibration volume. Melt segregation at relatively low temperature is predicted to enrich the residuum in Zr, consistent with the observed distribution of Zr between mesosome and leucosome. The limited development of metamorphic zircon rims or overgrowths at Mt Stafford is explained by three concurrent processes: (i) Zr liberated during prograde metamorphism formed micro‐zircon, rather than following the prediction that Zr will partition into silicate liquid; (ii) some detrital zircon was probably armoured by other rock‐forming minerals, reducing Zr content in the effective bulk rock composition; and (iii) small proportions of melt loss during migmatization removed Zr that otherwise would have been available to form metamorphic rims.  相似文献   

GEOCHRONOMETRY & ISOTOPE GEOLOGY     

《Abstract of Chinese Geological Literature》2014,(3)

正20141655 Gao Linzhi(Institute of Geology,CAGS,Beijing 100037,China);Ding Xiaozhong The Revision of the Chentangwu Formation in Neoproterozoic Stratigraphic Column:Constraints on Zircon U-Pb Dating of Tuff from the Mengshan Section in Pujiang County,Zhejiang Province(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.988-995,5 illus.,1 plate,2 tables,24 refs.)  相似文献   

黔西北普宜地区下三叠统嘉陵江组沉凝灰岩锆石LA-ICP-MS U-Pb年龄、微量元素特征及其地质意义     

缪宇  吴亮  肖长源  李锁明  李致伟  宋文婷  田瑜峰 《地质论评》2021,67(2):289-310

早三叠世时期频繁的火山事件是导致全球性气候和海洋环境异常的主要原因,前人对早三叠世重要界线时期的火山事件地层开展了大量研究,但对典型界线时期以外的其他火山事件地层却鲜有报道。本文以上扬子西南普宜地区嘉陵江组两件沉凝灰岩为研究对象开展了岩石学、岩相学、锆石年代学及微量元素组合特征等方面的研究。沉凝灰岩样品具有典型岩浆锆石的内部结构和微量元素组合特征,两组沉凝灰岩锆石谐和年龄分别为250.6±0.6 Ma和249.1±0.8 Ma,代表了母岩岩浆中新生锆石的结晶年龄。沉凝灰岩母岩主要以酸性花岗岩类为主,次为中性正长岩类和少量基性岩类。嘉陵江组沉凝灰岩与二叠系—三叠系界线(PTB)凝灰岩及Olenekian—Anisian界线(OAB)绿豆岩具有同源性,形成于活动大陆边缘的碰撞造山环境,源区很可能位于中越边境地区长山构造岩浆带—十万大山火山带,且在陆壳碰撞过程中源区地壳处于持续的增厚阶段,下地壳增厚部位的部分熔融形成补给岩浆上涌并使早期结晶矿物发生了部分熔蚀。本文嘉陵江组沉凝灰岩样品250.6±0.6 Ma年龄对应着Smithian—Spathian界线时期的全球性降温及短期生物复苏事件;249.1±0.8 Ma年龄的样品对应Spathian亚阶中期极端高温气候和生物再次灭绝事件,再次证明了早三叠世时期频繁的火山活动是导致气候改变和生物周而复始新生和灭绝的重要因素。其原因可能是阳伞效应和温室效应等因素综合反馈的结果,但具体证据仍需要将来更多学科综合研究成果的约束。  相似文献