26Al/10Be埋藏测年及其在洞穴沉积年代学研究中的应用

长期暴露于地表的石英砂被快速搬入洞穴或埋藏,不再接受宇宙射线辐射,埋藏前所积累的陆地宇生核素26 Al 和10 Be 随时间指数衰减。据此用加速器质谱计测定沉积物中石英样品现存的26 Al /10 Be可计算其埋藏年代。用此方法本文对周口店第一地点的下部地层年代作了初探。此次研究表明自第10层以下的沉积物其年代很可能≥ 1 Ma。      

IN SITU COSMOGENIC NUCLIDE BURIAL DATING:RECENT PROGRESSES AND PROSPECTS IN CHRONOLOGICAL STUDIES OF EARLY HOMININ SITES IN CHINA

本文介绍26Al/10Be埋藏测年的基本原理和最新进展,并分析了其数据误差的主要来源:仪器测量引起的计数统计误差和相关物理常数引起的系统误差.该法最重要的假设前提为“简单恒态侵蚀模式”,同一层位多个石英质砾石26Al-10Be等时线和21Ne-26Al-10Be三核素埋藏测年法有可能揭示样品是否符合这一假设前提.取自周口店第1地点第8～9层的3件石英质石制品和1个石英砂样的29Al-10Be等时线过坐标原点,且其斜率给出的年代与单个样品年代的加权平均值在误差范围内吻合,为这些样品没有系统显著偏老倾向的有力证据.宇生核素埋藏测年法理化基础坚实,独立于其他测年技术,应用范围正值我国年代研究的“盲段”,样品为广泛分布的石英矿物,应可为我国早更新世人类遗址年代系列的建立作出重要贡献.     

陨石中宇宙成因核素10Be和26Al的化学分离纯化

陨石离开其小行星母体直至降到地球表面期间,受到宇宙射线的照射,产生一系列包括10Be和26Al等的放射性核素.10Be和26Al的含量及其比值记录了宇宙射线辐照历史,而陨石降落到地球表面后,它们的衰变又提供了测定其降落时间,即居地年龄的方法.10Be和拍26Al由加速器质谱测定,样品需分离纯化.为此,开展了陨石样品Be和Al的分离纯化实验.通过模拟样品的条件实验,建立了Be和Al分离纯化的化学流程,其回收率分别达到89%和70%.在此基础上,分离并测定了一个降落型普通球粒陨石(吉林陨石)非磁性部分的10Be和26Al的含量.结果显示,吉林陨石26Al/10Be的比值为5.005,远大于两者的饱和比值(2.72),说明吉林陨石经历了短期的暴露辐射,这一结果与吉林陨石第二阶段的暴露年龄0.4 Ma一致.整个化学流程的10Be/9Be和26Al/27Al空白分别为(4.33±0.46)×10-14和(6.59 ±4.66)×10-15,其中前者接近于该仪器的空白测量值,而后者则接近于仪器的检测限2.3×10-15.     

贵州荔波黑洞碎屑沉积物宇宙成因核素26Al/10Be埋藏年龄

河流下切在岩溶区形成的多级层状洞穴,记录了地体隆升和地貌演化历史,但由于测年手段的限制,国内在这方面的研究一直进展不大.近年来,运用宇宙成因核素得到洞穴碎屑沉积物埋藏年龄的方法,已成为反演山地区域构造-地貌演化的新途径.本文尝试运用宇宙成因核素26AL/10Be埋藏测年技术,对属于贵州荔波地区4层洞穴系统的黑洞(第二层)碎屑沉积物进行年龄测定,假设样品进洞前无埋藏史,测年结果显示黑洞年龄至少有1.06±0.23Ma,并且该地区三岔河流域的侵蚀速率为55.1±2.3m/Ma.这是对该地区洞穴测年的一次新探索,体现出洞穴沉积物宇宙成因核素埋藏测年技术在我国晚新生代地质地貌演化研究方面具有良好的应用前景.     

中国西南天山西域砾岩的磁性地层年代与地质意义*

西域组是我国西部一重要并广泛引用的晚新生代地层,关于其年代和成因至今尚存争议。在西南天山喀什远源盆地喀什-阿图什褶皱带不同构造部位选择有代表性的5~6个晚新生代地层剖面开展了详细的沉积学、磁性地层年代学对比研究,据此限定了不同构造的起始变形时间以及西域砾岩的沉积年代。西域砾岩并非一年代地层单位,作为一岩石地层单位,其底界具有穿时特征,从山体(北)向喀什前陆盆地(南)逐渐变新。其底界年龄在盆地北部近源区约为15.5Ma^[1],在盆地中部中源区约为8.6Ma^[1],在盆地南部远源区的阿图什背斜为1.9Ma,喀什背斜为1.6~0.7Ma。这一穿时的砾岩沉积楔体的起始堆积起因于盆地北部边界逆冲断层(KBT)的活动。构造变形是由北南脉冲式迁移扩展的,其速率是非均匀的,在约15.5Ma至4.0Ma期间为1.4~3.4mm/a,在约4.0Ma以来剧增至>10mm/a。西域砾岩沉积前缘向南进积速率与构造变形前缘迁移速率有很好的一致性,但在时间上较构造变形可能滞后2.0Ma。这表明构造变形前缘向南的脉冲式扩展是西域砾岩进积并发生侧向和垂向上岩相突变的主因。     

陨石中宇宙成因核素~(10)Be和~(26)Al的化学分离纯化

陨石离开其小行星母体直至降到地球表面期间,受到宇宙射线的照射,产生一系列包括10Be和26Al等的放射性核素。10Be和26Al的含量及其比值记录了宇宙射线辐照历史,而陨石降落到地球表面后,它们的衰变又提供了测定其降落时间,即居地年龄的方法。10Be和26Al由加速器质谱测定,样品需分离纯化。为此,开展了陨石样品Be和Al的分离纯化实验。通过模拟样品的条件实验,建立了Be和Al分离纯化的化学流程,其回收率分别达到89%和70%。在此基础上,分离并测定了一个降落型普通球粒陨石(吉林陨石)非磁性部分的10Be和26Al的含量。结果显示,吉林陨石26Al/10Be的比值为5.005,远大于两者的饱和比值(2.72),说明吉林陨石经历了短期的暴露辐射,这一结果与吉林陨石第二阶段的暴露年龄0.4Ma一致。整个化学流程的10Be/9Be和26Al/27Al空白分别为(4.33±0.46)×10-14和(6.59±4.66)×10-15,其中前者接近于该仪器的空白测量值,而后者则接近于仪器的检测限2.3×10-15。     

富钴结壳的10Be、26Al定年方法初步研究北大核心CSCD

大洋富钴结壳的生长速率及其定年测量在研究古大洋环流、古环境及古气候变迁等方面具有重要意义,而宇宙成因核素10Be、26Al因为其测量时间尺度长、精度高,而被视为富钴结壳年代测定的最有效手段之一。本文在前人研究的基础上,对富钴结壳中10Be、26Al定年新方法进行了探究。对采自太平洋的2块富钴结壳样品进行连续的淋滤实验,并对其中1个样品CXD08-1自生相中的10Be和26Al进行分离、纯化及AMS(Accelerator Mass Spectrometry)测量分析。利用10Be浓度和10Be/9Be值计算得到CXD08-1在5~10 mm间的平均生长速率分别为(10.23-0.47^+0.52)mm/Ma和(14.25-0.89^+1.02)mm/Ma。而26Al因为大量衰变及27Al载体的加入而未得到可靠的分析结果,因此,26Al定年须进一步探索。     

宇宙成因核素在地质年代学研究中的新进展

根据地表暴露岩石或埋藏物中宇宙成因核素浓度可计算样品的暴露年龄或埋藏年龄,从而估算出研究区域的侵蚀速率和抬升速率等重要地质信息,该方法现已成为晚新生代地质和地貌变化研究的重要手段。概述了近5年来国内外宇宙成因核素在地质年代学研究中的最新进展,主要包括以下几个方面:①10Be研究进展,26Al/10Be双核素测年计算模型的改进和完善,以及21Ne的加入对26Al-10Be测年方法的拓展;②宇宙成因36Cl在碳酸盐岩中的研究和应用进展;③53Mn、41Ca等新核素的研究和应用;④宇宙成因核素测年技术在国内的应用进展。最后,分析了宇宙成因核素测年存在的主要问题及下一步重点研究方向。     

新疆天山地区早更新世沉积及其下限

经过对新疆天山地区第四纪地层的广泛、综合研究，提出该区早更新世由两套沉积组成：下部西域砾岩层，为随青藏高原隆升而发生的山前磨拉石堆积，后受盐水沟运动影响，岩层褶皱，组成山前成排的背斜构造，并受剥蚀。上部为五梁司砾石层，按岩性分为两层：下层为山麓冰川前缘冰水堆积；上层为经长途搬运的间冰期冰水沉积物。五梁司层与西域岩层呈不整合接触，并构成天山山前最高台地顶部。根据对安集海和独山子两剖面的地层岩性、古地磁、孢粉、重矿物等的综合对比研究，确定新疆第四系下限应依西域砾岩层底界年龄而定。本文指出西域砾岩层底界特征，并根据古地磁测试确定其底界位于古地磁柱高斯正极性时凯恩纳负极性亚时的顶面，年龄为２．９２ＭａＢ．Ｐ。本文还分析了新疆早更新世的构造背景和沉积环境。     

鄂尔多斯盆地西南缘崆峒山组砾岩中的碎屑锆石LA-ICP-MS U-Pb定年及其构造意义

甘肃省平凉崆峒山地区是崆峒山组地层命名所在地,该套地层主要由大套红色砾岩层组成,通常称为崆峒山组砾岩。长期以来,对崆峒山组砾岩的成因、形成时代和物源存在争议。本文选取崆峒山组砾岩层中的3块砾石为研究对象,运用LA-ICP-MS方法对砾石样品中的碎屑锆石进行了年代学研究。结果表明,崆峒山组砾岩碎屑锆石年龄谱可分为380~479Ma、561~1198Ma、1285~1982Ma、2319~2612Ma和2714~2764Ma共5个年龄区间。依据崆峒山组砾岩碎屑锆石年龄谱分布特征,以及前人研究成果,认为崆峒山组砾岩的主要物源来源于秦祁造山带,少量来源于阿拉善地块和鄂尔多斯地块。崆峒山组砾岩的沉积时代为中三叠世至晚三叠世,崆峒山组砾岩是秦祁造山带造山过程的沉积响应,而非板内造山带的产物。     

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)

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.     

The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts

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.     

Quaternary stresses revealed by calcite twinning inversion: insights from observations in the Savonnières underground quarry (eastern France)

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).     

HYDROGEOLOGY

正20141756 Chen Ruige(Mathematical College,China University of Geosciences,Beijing100083,China);Zhou Xun Numerical Simulation of Groundwater Level Fluctuation in a Coastal Confined Aquifer with Sloping Initial Groundwater Level Induced by the Tide(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.1099-1104,6 illus.,16 refs.) Key words:confined water,groundwater level     

METAMORPHIC PETROLOGY

正20141408 Cai Jia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China);Liu Fulai Petrogenesis and Metamorphic P-T Conditions of Garnet-Spinel-Biotitebearing Paragneiss in Danangou Area,Daqingshan-Wulashan Metamorphic Complex Belt(Acta Petrologica Sinica,ISSN1000-0569,CN11-1922/P,29(7),     

SERIALS

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GEOPHYSICAL EXPLORATION

正20142386An Guoying(China Aero Geophysical Survey and Remote Sensing Center for Land and Resources,Beijing 100083,China)Application of Satellite Remote Sensing in Regional Hydrogeological Investigation:Taking Cenozoic Strata in Wenquan Sheet(1∶250 000)of Karakoram Range as an Example(Geosci-     

QUATERNARY GEOLOGY & GEOMORPHOLOGY

正20141016An Chengbang(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,Lanzhou University,Lanzhou 730000,China);Zhao Yongtao Lake Records during the Last Glacial Maximum from Xinjiang,NW China and Their Climatic Impli-     

PETROLEUM GEOLOGY

正20141538 Cao Qing(School of Earth Sciences and Engineering,Xi’an Petroleum University,Xi’an 710065,China);Zhao Jingzhou Characteristics and Significance of Fluid Inclusions from Majiagou Formation,Yichuan Huangling Area,Ordos Basin(Advances in Earth Science,ISSN1001-8166,CN62-1091/P,28(7),2013,p.819-828,7 illus.,3 tables,43 refs.)     

GEOCHEMISTRY

正20142002 Wei Hualing(Institute of Geophysical and Geochemical Exploration,Chinese Academy of Geological Sciences,Langfang065000,China);Zhou Guohua Element Content and Mineral Compositions in Different Sizes of Soil in Tongling Area,Anhui Province(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(11),2013,p.1861