中亚造山带南缘中—新元古代地壳的揭示——来自北山—阿拉善北部钻遇碱性花岗岩的年代学和Hf同位素示踪研究

前寒武纪微陆块是北山—阿拉善北部增生造山带的重要组分,旱山、雅干和珠斯楞—杭乌拉地区的前寒武纪基底是否存在学界尚存争议.居延海介于北山造山带北部和阿拉善地块北缘的构造衔接部位,受限于巴丹吉林沙漠覆盖,岩石露头极少,我们通过钻井工程,钻遇一套晚石炭世碱性花岗岩,锆石U-Pb年龄和Hf同位素特征揭示,该花岗质岩浆锆石结晶年龄为(312±1)Ma(MSDW=0.46,n=18)和(315±2)Ma(MSWD=0.93,n=15),具有正的εHf(t)值,介于+0.8～+4.4之间,平均值为+2.2,对应二阶段模式年龄TDM2为1048～1267 Ma,平均值为1183 Ma,具有古老地壳的源区属性.通过与旱山构造带、雀儿山构造带、雅干构造带和珠斯楞—杭乌拉构造带的晚石炭世花岗质岩浆对比分析,结合旱山构造带、雅干构造带和珠斯楞—杭乌拉构造带0.9 Ga花岗质岩石的出露以及区域上的重磁资料解译,我们认为旱山、雅干和珠斯楞—杭乌拉构造带存在中—新元古代地壳,且可开展进一步的衔接关系研究.     

Integration of zircon and apatite U–Pb geochronology and geochemical mapping of the Wude basalts(Emeishan large igneous province):A tool for a better understanding of the tectonothermal and geodynamic evolution of the Emeishan LIP

Radiogenic isotopic dating and Lu–Hf isotopic composition using laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)of the Wude basalt in Yunnan province from the Emeishan large igneous province(ELIP)yielded timing of formation and post-eruption tectonothermal event.Holistic lithogeochemistry and elements mapping of basaltic rocks were further reevaluated to provide insights into crustal contamination and formation of the ELIP.A zircon U–Pb age of 251.3±2.0 Ma of the Wude basalt recorded the youngest volcanic eruption event and was consistent with the age span of 251-263 Ma for the emplacement of the ELIP.Such zircons hadε_Hf(t)values ranging from7.3 to+2.2,identical to those of magmatic zircons from the intrusive rocks of the ELIP,suggesting that crust-mantle interaction occurred during magmatic emplacement,or crust-mantle mixing existed in the deep source region prior to deep melting.The apatite U–Pb age at 53.6±3.4 Ma recorded an early Eocene magmatic superimposition of a regional tectonothermal event,corresponding to the Indian–Eurasian plate collision.Negative Nb,Ta,Ti and P anomalies of the Emeishan basalt may reflect crustal contamination.The uneven Nb/La and Th/Ta values distribution throughout the ELIP supported a mantle plume model origin.Therefore,the ELIP was formed as a result of a mantle plume which was later superimposed by a regional tectonothermal event attributed to the Indian–Eurasian plate collision during early Eocene.     

北部湾涠洲岛南湾火山砂岩捕虏体光释光(OSL)测年结果

涠洲岛是北部湾内的一座火山岛,火山活动初步可以分为早-中更新世和晚更新世2期。晚期南湾火山是典型的射气岩浆喷发成因的火山,文中报道了南湾火山的上、下2层火山碎屑岩中砂岩捕虏体的光释光(OSL)测年结果,提出南湾火山喷发时代为距今约3万年左右的晚更新世末期     

Mesozoic Bimodal Volcanic Suite in Zhalantun of the Da Hinggan Range and Its Geological Significance： Zircon U-Pb Age and Hf Isotopic Constraints

1 Introduction Mesozoic volcano-intrusive rocks are widely distributed in the Da Hinggan Range of northeastern China, and are considered as one of the most spectacular geological sights in eastern Asia. Recently, studies on granites with high εNd(t) values and Phanerozoic crustal growth in the Centra Asian Orogenic Belt have greatly promoted fundamental research into the geology of this area (Jahn et al., 2000, 2001, 2004; Wu et al., 2000, 2002, 2003). However, work on the eruption time,…     

断层泥中石英碎砾溶蚀形貌的测年研究

考虑到同一条断层的同一个位置所取的断层泥中,不同碎砾的溶蚀形貌并不相同,即使是同一个碎砾,其不同的表面,溶蚀形貌也可能不同,将统计学参数估计的方法引入结果处理中,并把在金川水电站坝区F1断层一次所取得断层泥样品碎砾的各个表面的总体当作一个整体进行处理,得出此断层的活动时间可能为早更新世的结果。与ESR法测得的结果基本一致。     

矿床同位素定年方法的应用现状评析

高质量的年代学数据是矿床研究和对比的基础.针对近二十几年来在具体矿床同位素定年研究中,不同学者对同一矿床采用不同的定年方法常常得出相差十分悬殊的结论,甚至出现与地质事实截然相悖年龄数据的现象,文章对最常用的锆石U-Pb法、自生伊利石K-Ar法、金属硫化物Re-0s和Sm-Nd法、石英流体包裹体40Ar/39Ar法和Rb-Sr等时线法以及释光测年进行了评析.强调一套合理的矿床同位素年龄数据的获得,必须加强对地质背景的研究;明确测年矿物与矿化的成因联系,选择合适的定年方法.综合地质背景及可靠准确的年代学数据,对地质事件与成矿事件的联系做出合理的解释.     

贵州北部马鬃岭铝土矿床中富锂铝质粘土岩碎屑锆石U-Pb年龄、Lu-Hf同位素特征及其对锂源的制约

为研究贵州北部马鬃岭铝土矿床中富锂铝质粘土岩的物源体系及其锂的来源,对出露于大竹园组顶部的该类岩石进行了锆石U-Pb定年、Lu-Hf同位素及锆石微量元素分析。分析结果表明富锂铝质粘土岩中碎屑锆石普遍发育岩浆振荡环带,为造山作用/弧作用相关的岩浆岩类锆石。碎屑锆石U-Pb年龄从早泥盆世到太古宙（411~3001 Ma）均有分布,具627~879 Ma和925~1018 Ma两个主峰及539~602 Ma一个次峰。εHf(t)值为-27.61~7.03之间,二阶段模式年龄（tDM2）分布在1242~3387 Ma之间。结合碎屑锆石U-Pb-Hf同位素、微量元素特征及区域地质对比,认为富锂铝质粘土岩中碎屑锆石最主要的初始物源区为南岭-云开地体、江南造山带西段新元古代岩浆岩,其锂可能来源于江南造山带西段桂北-黔东地区860~750 Ma的基性岩。     

南极长城站附近企鹅栖息地粪土沉积地层放射性核素210Pb定年

用γ谱方法测定了南极长城站附近特有生物群落栖息地沉积物中放射性核素含量,地表沉积物中40K,137Cs,210Pb,226Ra,228Ra,228Th.和238U平均比活度,分别为143,7.56,24.1,3.65,5.36,4.15和6.5Bq/kg.同时测试了阿德雷岛企鹅栖息地粪土沉积地层中放射性核素含量,利用其中的210Pb比活度,210Pb_ex垂向变化特征,推演沉积物的沉积速率和地质历史年代:其中AD1-a柱样时间跨度约为74a(1928~2002年),据此计算了沉积速率为0.063mm/a(r=0.794),并讨论了在南极特定条件下,放射性核素示踪对定年影响以及与区域现代气候环境变化的内在联系.     

LEADAT: a MATLAB-based program for lead-210 data analysis of sediment cores

1Introduction Tracking the history of man s impact on the en-vironment, it is clear that in many places the periodof greatest impact and most dramatic transformationlies within the last 150 a (Oldfield and Appleby,1984). Many aspects of this impact can be…     

Sedimentary facies and paleoenvironmental interpretation of a Holocene marsh in the Gironde Estuary in France

1Introduction Since the last glacial maximum, the Holocenehas been marked by a rapid rise in sea level. After6 000 a BP, the present-day level was reached andthe rate of sea-level rise (SLR) decreased rapidly(Morzadec -Kerfourn, 1974; Kidson, 1986 ).These…