原地生成宇宙成因核素测年技术思考（五）： 单核素计算地表最大抬升速率方法

在以往研究中,原地生成宇宙成因核素测年技术虽然理论上可以利用两种核素（如10Be和26Al）联立方程组同时解出暴露年龄和侵蚀速率,但在实践中却常采用单种核素（常用10Be）分别解出最小暴露年龄和最大侵蚀速率,26Al数据只用于辅助判断。这主要是因为受目前误差水平限制,10Be和26Al的测试数据结果,常常并未能达到联立两个方程解出暴露年龄和侵蚀速率两个参数的精度（当然也有其他因素影响）,这在投影图上常表现为被认为只有一次性暴露历史的样品,投影结果在稳态侵蚀岛之外,只有加上误差,才能进入或靠近稳态侵蚀岛。同理,在推导出包含生成速率加速率的计算等式后,虽然理论上抬升区长期暴露的样品也能够利用两种核素（如10Be和26Al）同时解出侵蚀速率和抬升速率,但实践上10Be和26Al浓度投影结果可能并未在抬升的正常投影区（稳态侵蚀岛上曲线附近）,从而解出的侵蚀速率和抬升速率合理性存疑。对此,参考计算最大侵蚀速率的原理,提出利用长期暴露样品的10Be浓度来解出抬升区地表最大抬升速率的计算方法（,从而可以对碰撞造山抬升区的抬升速率上限进行限定。     

Pitfalls in the AMS radiocarbon-dating of terrestrial macrofossils

The AMS ¹⁴C technique has the advantage that small samples of Late Quaternary age can be dated with high accuracy, and that errors due to reservoir effects can be avoided if specifically determined terrestrial micro- and macrofossils are measured. However, to obtain such high-accuracy measurements, it is important how small samples are handled prior to treatment in the radiocarbon laboratories. Here we present a set of 51 AMS ¹⁴C measurements, of which 31 dates gave expected ages and 20 dates resulted in anomalously young ages, despite the fact that all samples consisted of clearly identified Late Weichselian terrestrial plant macrofossils. To evaluate possible sources of error, we compared these samples in respect to preparation methods, sample storage and sample weight. Our results show that the long-term storage of wet macrofossil samples appears to have a significant effect on the radiocarbon age obtained, even when the samples are kept cool. Fungi or micro-organisms may easily be incorporated into a sample during preparation and identification, and can easily contribute to the contamination of a sample, if stored cool and wet for several months. © 1998 John Wiley & Sons, Ltd.     

新疆哈尔里克山口门子韧性剪切带变形期次及年代学研究

新疆哈尔里克山口门子韧性剪切带作为东天山地区重要的构造记录之一,其变形期次及年代学研究对认识博格达?哈尔里克山乃至整个东天山的区域构造演化具有重要意义。本文基于宏观与微观变形特征、变形温压条件、同位素年代学研究,厘定了两期(脆)?韧性变形,分别是早期韧性逆冲变形和晚期左旋脆?韧性走滑变形。卷入早期韧性逆冲变形的花岗岩、火山岩年代学分析表明,该期变形发生于440.1±3.2 Ma之后;未卷入该期变形的花岗闪长岩脉和辉绿岩脉年代学分析表明,早期韧性逆冲变形发生于298.1±1.0 Ma之前。结合泥盆纪?早石炭世哈尔里克山地区呈现为稳定构造环境以及存在早、晚石炭世地层间的角度不整合,推断早期韧性逆冲变形形成于早、晚石炭世之交,与石炭纪陆内裂谷的闭合有关。晚期左旋脆?韧性走滑变形叠加使早期糜棱岩面理发生褶皱,结合前人获得的259±1 Ma的变质绢云母^40Ar-^39Ar年龄,认为该期变形是晚二叠世受西伯利亚板块向南推挤的陆内转换压缩变形产物。     

Geochemistry and zircon U-Pb ages of the Oligocene sediments in the Baiyun Sag,Zhujiang River Mouth Basin

In this study, element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin. The experimental results are discussed with respect to weathering conditions, parent rock lithologies, and provenances. The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering. Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements, "V"-shaped negative Eu anomalies, and negligible Ce anomalies. The rare earth element distribution curves are obviously right-inclined, with shapes and contents similar to those of post-Archean Australian shale and upper continental crust, indicating that the samples originated from acid rocks in the upper crust. The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area. For the samples from the upper Enping deltas, the overall age spectrum shows four major age peaks ca. 59–68 Ma, 98–136 Ma, 153–168 Ma and 239–260 Ma. For the Zhuhai Formation samples,the overall age spectrum shows three major age peaks ca. 149 Ma, 252 Ma and 380 Ma. The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation, the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances: Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift, and the former supply became stronger through time. Thus, the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.     

Study on210Po in marine organisms in North China Waters

The concentrations of natural radionuclide²¹⁰Po in various components of the marine organisms of North China coastal waters are described and its contribution to the radiation exposure of marine organisms and man are estimated. Data on its concentrations in different species show that, in general, its concentration in crustaceans and molluses is higher than that in fish, where its concentrations in liver and gut are much higher than that in bone and muscle. An estimation of the dose to marine organisms and man due to exposure to²¹⁰Po is very necessary for any assessment of the impacts of man-made radionuclides from coastal nuclear power installations.     

延安典型丹霞地貌景观特征及发育演化研究

本文是在延安典型丹霞地貌景观特征分析的基础上, 采用宇宙成因核素10Be和26Al技术获得暴露年龄和侵蚀速率, 研究“黄土覆盖型沟谷丹霞”地貌景观的演化历史。研究结果显示: 延安典型丹霞地貌的类型有狭缝式、石蘑菇式、天生桥式, 其中狭缝式丹霞的景观特征为“窄狭、多弯、韵律、多彩”, 同时也是典型的“黄土覆盖型沟谷丹霞”, 石蘑菇式丹霞造型奇特, 天生桥式丹霞地貌整体规模宏大, 这两者发育都严格受控于垂直节理和外力作用的侵蚀; 运用宇宙成因核素10Be和26Al技术, 计算获得志丹猫巷狭缝式丹霞地貌的暴露年代有两期, 分别为(0.75±18)~(0.83±0.14) ka和(1.14±13)~(1.29±0.30) ka, 安塞王家湾石蘑菇式丹霞地貌暴露年代为(1.76±0.45)~(1.77±0.15) ka, 这两处丹霞地貌暴露地表的年代都在全新世(Qh), 前者晚于后者, 地貌较年青; 运用宇宙成因核素10Be-26Al计算获得两处典型丹霞地貌侵蚀速率为(39±3.3)~(104±24.4) cm·ka–1, 与目前国内外学者研究地表和基岩得到的侵蚀速率对比, 这两处典型丹霞地貌的侵蚀速率较大, 结果还有待进一步研究; 延安典型丹霞地貌景观发育的演化始于白垩纪红层的堆积, 大致都经历了四个演化阶段, 初步揭示了地质构造、上覆黄土盖层以及流水等多种因素共同控制和影响延安典型丹霞地貌的形成, 演化阶段总体都处于青年晚期。     

Shore exposure affects mussel population structure and mediates the effect of epibiotic algae on mussel survival in SW Ireland

On rocky shores, the relative importance of abiotic and biotic processes that regulate community structure are thought to vary with levels of shore exposure. This can lead to characteristic features found on sheltered and exposed shores. This study identified differences in the population structure of mussels on exposed and sheltered rocky shores on Atlantic coasts of south-west Ireland. Direct interactions between epibiotic algae and their host mussels were also examined to test if potential effects varied with shore exposure. Mussel beds on sheltered shores were less dense and comprised larger mussels with greater rates of individual survival and growth than those on exposed shores. The results of a field experiment showed that algal epibionts had a negative effect on mussel survival on sheltered shores but not on exposed shores. Surprisingly, the presence of algal epibionts had no effect on mussel growth on either shore type. These findings contrast with those of previous studies. The effects of shore exposure and algal epibionts on mussels may be species-specific and may interact with other factors across different regions. This study shows that predictions of effects of exposure on mussel populations and their epibionts should only be based on specific experimental evidence and cannot be generalised across regions.     

我国南极橄辉无球粒陨石(GRV 024516)和H5球粒陨石(GRV 024517)宇宙射线暴露年龄和气体保存年龄

我国在南极格罗夫山陨石富集区回收的GRV024516和GRV024517陨石样品分别为橄辉无球粒陨石和H5普通球粒陨石,在矿物-岩石学研究的基础上测定和计算了这两个陨石的宇宙射线暴露年龄和气体保存年龄,其宇宙射线暴露年龄分别为33.3Ma和51.7Ma,气体保存年龄分别为1936.8Ma和3720Ma。橄辉无球粒陨石含金刚石、石墨和无定型碳,并为主要稀有气体的载体,且冲击变质效应明显,导致40Ar部分丢失。H5球粒陨石主要显示其母体内的热变质效应,其气体保存年龄落在未受严重冲击的H5球粒陨石范围(3220-4510Ma)内。