非稀释剂法电感耦合等离子体质谱测定磷灰石中铀钍钐同位素的含量

准确测定238U、232Th、147Sm同位素含量是磷灰石(U-Th)/He同位素定年方法的关键。本文建立了非稀释剂法电感耦合等离子体质谱测定磷灰石中238U、232Th和147Sm同位素含量的测定流程。该方法假定样品中的238 U、232 Th和147 Sm同位素丰度与其自然丰度是一致的,根据238 U、232 Th和147 Sm同位素的自然丰度和测得的样品中总的U、Th和Sm的含量得到样品中238U、232Th和147Sm同位素的含量。对国内玄武岩标准物质和(U-Th)/He定年法的年龄标准物质Durango磷灰石进行了总U、Th、Sm含量的测试,验证流程的可行性,结果表明玄武岩标准物质的测定值与标准值在误差范围内一致,经计算得到该磷灰石的(U-Th)/He年龄为30.0 Ma,与文献获得的该磷灰石(U-Th)/He年龄(31.02±1.01)Ma(1σ)在误差范围内一致,表明本文建立的238U、232Th和147Sm同位素含量的测定流程是可行的。对于没有稀释剂的实验室,该方法简单适用,值得推广应用。     

锆石(U-Th)/He定年技术研究

锆石(U-Th)/He定年是同位素热年代学体系中重要的定年手段,是记录地质体完整热历史重要的实验方法之一,在火山岩定年、造山带演化、地貌演化、沉积盆地热演化及限定矿床热液活动时代等应用方面发挥着重要的作用。中国地质科学院地质研究所同位素热年代学实验室成功建立了锆石(U-Th)/He定年的实验方法,实验主要包括三个独立的过程:样品前处理、He含量分析和U、Th含量分析。氦同位素质谱仪对锆石样品的氦同位素比值分析精度约为0.1%左右;ICP-MS对锆石的U、Th同位素比值分析精度通常情况下优于1%。对国际上普遍使用的FCT锆石和斯里兰卡锆石标样进行(U-Th)/He年龄测定。测试结果显示27粒FCT锆石(U-Th)/He年龄分布在25.81~30.72Ma之间,加权平均年龄为28.18±0.51Ma(1σ)(参考值为28.3±2.6Ma);20粒斯里兰卡锆石碎片(U-Th)/He年龄分布在445.5~489.5Ma之间,排除异常值后加权平均值为479.0±8.0Ma(1σ)(参考值为470±11Ma)。所测两个标准物质的年龄均与参考值一致,表明本实验室的实验流程准确可靠。本实验方法的建立填补了我国锆石(U-Th)/He定年实验方法的空白,为我国热年代学的发展提供了新的技术支撑。     

Fish Canyon Tuff榍石He扩散及(U- Th)/He年代学研究

榍石富含U和Th,是(U-Th)/He定年的理想矿物之一。本文以Fish Canyon Tuff榍石为例,开展了榍石He扩散行为和榍石(U-Th)/He定年实验方法研究。榍石分步加热扩散实验结果表明He扩散系数ln(D/a²)与温度倒数呈负相关,与期望的热活化扩散过程一致。测试Fish Canyon Tuff榍石(U-Th)/He年龄分布在28.3～24.6 Ma之间,平均值为26.7±1.2 Ma (1σ),Th/U分布在4.6～5.5之间,平均值为5.2±0.2,在误差范围内与国际上已出版数据一致,表明建立的榍石(U-Th)/He定年实验方法可靠。本次测试15粒榍石碎片外表层(～20μm)存在不同程度的磨蚀(即不完整晶体),且榍石表层磨蚀厚度随着等效半径的增加而增大。榍石碎片(U-Th)/He年龄介于完整晶体(U-Th)/He年龄和真实(U-Th)/He年龄之间,且随着榍石等效半径及表层磨蚀厚度(<20μm)的增大,(U-Th)/He年龄更接近真实年龄,这表明榍石(U-Th)/He年龄不确定度与等效半径大小和表层磨蚀厚度有关。     

磷灰石(U-Th)/He定年方法综述

磷灰石He封闭温度是目前已知定年体系中最低的,能够反映低温价段(40～90℃)的热历史信息,该方法现已成为低温热年代学领域研究的重要手段.本文概述了磷灰石(U-Th)/He定年方法的原理、校正、实验流程、应用以及存在的问题.其中,重点介绍了近几年国内外(U-Th)/He定年中辐射损伤研究的进展,主要包括以下几个方面:①辐射损伤的原理:捕获模型的提出及应用;②辐射损伤对磷灰石(U-Th)/He定年的影响;③新模型的提出:辐射损伤累积-退火模型;④辐射损伤的实际应用.     

磷灰石(U-Th)/He定年技术影响因素研究

磷灰石(U-Th)/He定年作为一种有效的低温热年代学定年技术,现已被广泛应用于地质研究的各个领域,而该技术测定的样品年龄会受到多方面因素的影响,其中磷灰石性状的影响尤为突出。通过归纳总结目前国内外磷灰石(U-Th)/He定年研究中,样品性状和成分、磷灰石颗粒尺寸及形貌、包裹体、147Sm含量、辐射损伤、U和Th不均匀分布等性状因素影响的研究进展,研究这些因素对测定年龄的影响及降低影响的方法。     

（U-Th）/He定年——低温热年代学研究的一种新技术

近年来（U-Th）/He定年方法在技术和低温热年代学应用上的优势吸引人们以此开展构造、地形地貌演化等的研究；与裂变径迹、K Ar、Ar Ar等定年方法的比较，该方法是有效的；人们研究了温度及矿物粒径对He扩散的影响，确定了校正方法。（U-Th）/He的封闭温度低于其它体系（磷灰石的仅为75℃±）；有质谱仪只需数十毫克样品就能获得 U、Th、He含量；有较裂变径迹法快速、省样、省力的优点；该技术虽还有待完善，但仍不失为开展低温热年代学和低温热演化研究的潜在有效方法。     

原位U-Th/He同位素定年技术研究进展及其低温矿床学应用前景

应用传统单颗粒方法对目标矿物进行定年具有较高要求(如U、Th等母体同位素均匀分布),需要耗时的酸溶过程,同时还需进行α粒子射出效应校正。原位U-Th/He同位素定年技术是近年发展起来的一种定年技术,其主要原理是采用激光加热目标矿物,并通过与激光系统连接的稀有气体质谱(Alphachron)和电感耦合等离子体质谱(ICP-MS)分别完成 ~4He和U、Th等母体同位素分析,将 ~4He和U、Th分析结果代入年龄公式计算即可获得目标矿物的U-Th/He年龄。本文阐述了原位U-Th/He同位素定年技术的主要原理、实验测试流程、适用矿物等,重点对原位U-Th/He同位素定年的技术难点和低温矿床学应用前景进行了分析。相对于传统单颗粒方法,原位测试方法解决了两个关键问题:1无需进行α粒子射出效应的校正,提高了定年结果的可靠性和准确度;2能完成母体同位素分布不均匀样品的测试,扩展了U-Th/He同位素定年的应用范围。尽管原位U-Th/He同位素定年技术在侧向加热效应、剥蚀坑体积测定以及标准矿物等方面尚存在一些亟待解决的问题,但已在硅酸盐、磷酸盐、钛铁氧化物等矿物的年代学研究方面展示了良好的应用前景。随着原位U-Th/He同位素定年技术的发展和进步,尤其是硫化物的U-Th/He同位素定年的发展,将为解决低温矿床的年代学问题提供一种新的思路。     

(U-Th)/He测年技术:α离子射出效应及其校正

(u-Th)/He测年技术是近年来低温热年代学研究领域快速发展的一个重要分支,被应用于磷灰石、锆石、榍石、石榴子石等多种矿物,并且磷灰石(U-Th)/He在目前已知的所用低温热年代学指标中具有最低的封闭温度和较强的热敏感性,此外矿物的(U-Th)/He分析还可用来反演样品所经历的热历史,因此该技术在地质学中得到了广泛的应用.随着对(U-Th)/He方法研究程度的提高,影响测年结果的各种因素也被相继发现和认识.从(U-Th)/He测年的基本原理出发,详细介绍了矿物内 α离子的射出效应及其对氦年龄计算的影响与校正,进一步说明了矿物成分环带、晶体形状、比表面积等因素对于氦年龄校正的作用,并详细阐述了已有的针对这些因素的不同校正模型的原理、特点、发展历程以及前缘研究方向.     

地质年代学发展历史的简要回顾及前景

简要介绍了基于矿物封闭温度的地质热年代学, 并对多种地质年代学方法, 包括U-Pb 法、 Sm-Nd法、Rb-Sr法、Lu-Hf法、Re-Os法、40Ar /39Ar法、裂变径迹( FT) 测年、(U-Th) /He法、 TIMS铀系法、宇宙成因核素定年(包括14C法等) 和年轻地下水测年(如3H /3He法等) 进行了综合评述。探讨了国际地质年代学百年来和中国20世纪80年代中期以来的发展趋势。根据近期使用情况分析, 认为U - Pb法、40Ar /39Ar法和14C法是目前使用较多的可靠测年方法。应用于山脉隆升和地貌形成的低温热年代学方法及地下水等年轻地质体系的测年, 将是地质年代学发展的重要方向。     

磷灰石低温热年代学技术及在塔里木盆地演化研究中的应用

随着磷灰石低温热年代学技术理论研究的不断完善和发展,它已被广泛用于地质体定年、构造-热演化、地形地貌演化等研究领域。该文首先对磷灰石裂变径迹和(U-Th)/He热定年技术近几年的研究进展进行了综述,在此基础上阐述了低温热年代学方法在塔里木盆地构造-热历史和物源分析领域的应用效果。多组分动力学退火模型的建立、激光剥蚀ICP-MS方法的提出及裂变径迹自动测试仪的开发极大地推动了磷灰石裂变径迹技术的发展。对于磷灰石(U-Th)/He热定年技术,FT-等效圆校正模型极大地降低了He年龄校正过程中产生的误差;辐射损伤捕获扩散模型首次揭示了晶格缺陷对4 He扩散的影响模式;辐射损伤积累和退火模型有效地解释了克拉通盆地部分磷灰石样品裂变径迹年龄小于He年龄的现象。塔里木盆地巴楚隆起的低温热年代学数据和热史模拟结果揭示出巴楚隆起自中生代以来曾经历过185~140Ma、140~100Ma、75~50 Ma等三期快速隆升事件,主要是由羌塘地体、拉萨地体、印度板块与欧亚板块南缘碰撞引起的。塔北隆起钻孔内浅部样品的磷灰石裂变径迹年龄和(U-Th)/He年龄都大于相应的地层年龄,记录的是物源区南天山的热信息;其热史模拟结果揭示出南天山曾经历过晚中新世—早上新世(15~5 Ma)一期快速隆升事件,并以此构建了塔里木盆地北部与南天山晚中新世—上新世构造-沉积耦合演化模式。     

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.     

Définition d'une limite multicritère ; stratigraphie du passage Campanien–Maastrichtien du site géologique de Tercis (Landes,SW France)Definition of a multi-criteria boundary; stratigraphy of the Campanian–Maastrichtian interval of the geological site at Tercis (Landes,SW France)

Lithostratigraphy, physicochemical stratigraphy, biostratigraphy, and geochronology of the 77–70 Ma old series bracketing the Campanian–Maastrichtian boundary have been investigated by 70 experts. For the first time, direct relationships between macro- and microfossils have been established, as well as direct and indirect relationships between chemo-physical and biostratigraphical tools. A combination of criteria for selecting the boundary level, duration estimates, uncertainties on durations and on the location of biohorizons have been considered; new chronostratigraphic units are proposed. The geological site at Tercis is accepted by the Commission on Stratigraphy as the international reference for the stratigraphy of the studied interval. To cite this article: G.S. Odin, C. R. Geoscience 334 (2002) 409–414.     

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.     

Late Wuchiapingian (Late Dzhulfian,early Late Permian) limestone olistolites within the Tertiary flysch of Glypia Unit (Mount Parnon,central–eastern Peloponnesus,Greece)

Some olistolites reworked in a Tertiary flysch of Mount Parnon (Peloponnesus, Greece) exhibit a Late Permian assemblage, dominated by Paradunbarula (Shindella) shindensis, Hemigordiopsis cf. luquensis and Colaniella aff. minima. This association corresponds to the Late Wuchiapingian (=Late Dzhulfian), a substage whose algae and foraminifera are generally little known. Contemporaneous limestones crop out in the middle part of the Episkopi Formation in Hydra, but they are rather commonly reworked in Mesozoic and Cainozoic sequences. The palaeobiogeographical affinities shared by the foraminiferal markers of Greece, southeastern Pamir, and southern China, are very strong (up to the specific level), and are congruent with the Pangea B reconstructions. To cite this article: E. Skourtsos et al., C. R. Geoscience 334 (2002) 925–931.     

PALEONTOLOGY

正20141596 Liu Yunhuan(School of Earth Sciences and Resources,Chang’an University,Xi’an 710054,China);Shao Tiequan Early Cambrian Quadrapyrgites Fossils of Xixiang Boita in Southern Shaanxi Province(Journal of Earth Sciences and Environment,ISSN1672-6561,CN61-1423/P,35(3),2013,p.39-43,3 illus.,20 refs.)     

GEOCHEMICAL EXPLORATION

正20141719 Chen Zhijun(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,China);Chen Jianguo Automated Batch Mapping Solution for Serial Maps:A Case Study of Exploration Geochemistry Maps(Journal of Geology,ISSN1674-3636,CN32-1796/P,37(3),2013,p.456-464,2 illus.,2 tables,10 refs.)     

MICROPALAEONTOLOGY

正20140962 Chen Fenning(Xi’an Institute of Geology and Mineral Resources,Xi’an710054,China);Chen Ruiming Late Miocene-Early Pleistocene Ostracoda Fauna of Gyirong Basin,Southern Tibet(Acta Geologica Sinica,ISSN0001-5717,CN11-1951/P,87(6),2013,p.872-886,6illus.,56refs.)     

PETROLOGY

正1.IGNEOUS PETROLOGY20142008Cai Jinhui(Wuhan Center,China Geological Survey,Wuhan 430205,China);Liu Wei Zircon U-Pb Geochronology and Mineralization Significance of Granodiorites from Fuzichong Pb-Zn Deposit,Guangxi,South China(Geology and Mineral Resources of South China,ISSN1007-3701,CN42-1417/P,29(4),2013,p.271-281,7illus.,     

ENVIRONMENTAL GEOLOGY

正20141205Cheng Weiming(State Key Laboratory of Resources and Environmental Information System,Institute of Geographic Sciences and Natural Resources Research,CAS,Beijing 100101,China);Xia Yao Regional Hazard Assessment of Disaster Environment for Debris Flows:Taking Jundu Mountain,Beijing as an