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1.
经历反复埋藏暴露演化过程的河流阶地样品,难以用常规方法将原生宇宙核素10Be、26Al有效分离。本文在前人实验方法基础上,使用人工挑选、磁选仪分选及酸洗方法,分离样品中碳酸盐、含铁矿物及大气生成的10Be,进一步优化了石英提纯实验流程。结果表明:长度为9 cm、内径为1 cm的阴离子交换树脂装置匹配4 mol/L氢氟酸淋滤液,可将B、Mg、Ca、Cr、Fe、Mn、Ni、Ti和Be、Al有效分离,Be、Al回收率分别可达95.7%、85.7%。阳离子交换树脂能有效分离Be、Al,两元素回收率均达到85%。获得10Be/9Be和26Al/27Al流程空白分别为2.19×10-15和1.63×10-15。优化后的实验方法显著提高了河流阶地样品中原生宇宙核素10Be、26Al的纯化效率,且10Be/9Be和26Al/27Al流程空白数值与国内外实验室具有可比性。采用本方法获得了成都平原冲积物10Be、26Al暴露年龄分别是76.36±9.51 ka和69.44±14.13 ka,为评价龙门山前缘隐伏断裂构造特征和活动性提供了年代学依据。 相似文献
2.
《地球化学》2008,(2)
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。 相似文献
3.
陨石中宇宙成因核素10Be和26Al的化学分离纯化 总被引：1，自引：0，他引：1
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. 相似文献
4.
暴露测年样品中26Al和10Be分离及其加速器质谱测定 总被引：4，自引：4，他引：0
在已有实验流程基础上,建立并优化了石英样品中Be和Al提取、纯化等实验流程,设计的流程条件实验包括实验试剂、器皿和离子交换柱选择、离子交换树脂分离Be和Al时酸浓度选择等。结果表明,选择钢铁研究总院研制的9Be标准溶液作为10Be样品制备的载体;使用一次性实验器皿;选用4 cm规格的离子交换柱;用0.05 mol/L草酸和0.75 mol/L盐酸混合溶液洗脱吸附于阴离子树脂上的Al,可有效提取、纯化样品中的Be和Al。加速器质谱(AMS)测量结果显示,13组化学空白的10Be/9Be和26Al/27Al比值平均值分别为7.48×10-15和1.96×10-15,与国内已有宇宙成因核素实验室的结果(5×10-15~8×10-15)具有可比性。电感耦合等离子体发射光谱(ICP-AES)的测量结果表明,Be、Al回收率分别达90%和60%。基于新建立的实验流程分析了祁连山北侧金佛寺的一个岩石样品,获得了10Be和26Al的暴露年代分别为(10.7±1.0) ka和(10.0±1.2) ka,与前人研究结果一致。 相似文献
5.
宇生核素暴露测年过程中,通常假设在样品最后一次暴露前,样品中的宇生核素（继承性宇生核素）浓度为0。然而,大量的测年数据研究发现,样品的暴露年代结果会受到继承性核素的影响从而高估地貌的真实年代。因此,如何降低继承性核素对暴露年代结果的影响或者定量分析继承性核素的影响程度不仅可为地貌演化提供准确的年代数据,而且对宇生核素暴露测年技术的研究具有重要意义。因此,本文以宇生核素暴露测年技术在冰川地貌中应用为例,通过分析继承性核素的研究概况,并结合宇生核素暴露测年原理,探讨继承性核素对测年结果影响的定量分析方法。研究结果表明： ① 通过样品中 n ( 26 Al)/ n ( 10 Be) 值\[即同一样品中宇生核素Al 26 与Be 10 浓度（单位为atom/g）的比值\]以及同一地貌位置多个的样品年代数据分布情况可初步判断测年结果是否受到继承性核素的影响;② 通过现代冰川冰碛物中宇生核素的浓度可以定量分析继承性核素对暴露测年结果的影响; ③ 通过计算冰碛垄顶部和一定深度（＞2~3 m）样品的宇生核素浓度差,可以减少继承性核素的影响。本研究内容对冰川地貌宇生核素暴露测年具有重要意义。 相似文献
6.
Shen Guanjun 《第四纪研究》2012,32(3)
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. 相似文献
7.
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。 相似文献
8.
原地生成宇宙成因核素^10Be和^26Al样品采集及处理 总被引：4，自引：3，他引：4
着重介绍原地生成宇宙成因核素^10Be和^26Al理想样品的特点、野外采集注意事项、实验室分离与纯化以及加速器质谱测量用靶样制备等。 相似文献
9.
西域砾岩是分布于青藏高原北缘天山、昆仑山一带的一套晚新生代砾石堆积地层,获知其可靠的年代信息对于理解高原隆升及地貌演化过程尤为关键.宇宙成因核素26Al/10Be埋藏测年是近年来发展起来的同位素测年新技术.本文对帕米尔高原西昆仑山山前的两个西域砾岩剖面采集的砾石样品进行了26Al/10Be埋藏测年分析.简单快速埋藏模式计算获得亚马勒剖面西域砾岩下部混合砾石样品的埋藏年龄＞3.5Ma,对该剖面西域砾岩上部5个样品加权平均得到的年龄为2.11+0.60/-0.46Ma;另一处奥依塔克西域砾岩生长地层底部砾石样品的埋藏年龄在0.46 ～ 7.12Ma.研究表明,研究区的西域砾岩堆积具有穿时性.本文是26Al/10Be埋藏测年方法应用于西域砾岩年代学研究的一次有益探索和尝试,并对在西域砾岩26Al/10Be埋藏测年中存在的问题进行了探讨. 相似文献
10.
宇生核素26Al/10Be埋藏测年法铝化学分析程序的改进 总被引：1，自引：1，他引：0
原地宇生核素26Al/10Be埋藏测年法是最近十多年涌现的测年新技术之一,广泛应用于地貌演化、古人类等研究领域,Al回收率及其纯度很大程度上决定着年代结果的精度.美国Purdue大学现用Al分离纯化程序有一些步骤尚待完善.本文通过条件实验,对该程序提出如下修改建议:①用38 ～ 75 μm阴离子交换树脂取代原用的75 ～ 150 μm树脂,以减少淋洗液(0.05 mol/L草酸-0.5 mol/L盐酸)体积并实现Al与主要干扰元素Fe、Ti的定量分离;②用阳离子交换法从草酸-盐酸中提取Al,以规避较为冗长的化学法破坏草酸.模拟样品的分析结果表明,经改进的两步骤可实现Al近于定量的回收,全流程Al回收率达91％-+5％,纯度为98％. 相似文献
11.
Cosmogenic nuclide concentrations measured on abandoned fan surfaces along the Mojave section of the San Andreas Fault suggest that sediment is generated, transported, and removed from the fans on the order of 30-40 kyr. We measured in situ produced cosmogenic 10Be, and in some cases 26Al, in boulders (n = 15), surface sediment (n = 15), and one depth profile (n = 9). Nuclide concentrations in surface sediments and boulders underestimate fan ages, suggesting that 10Be accumulation is largely controlled by the geomorphic processes that operate on the surfaces of the fans and not by their ages.Field observations, grain-size distribution, and cosmogenic nuclide data suggest that over time, boulders weather into grus and the bar sediments diffuse into the adjacent swales. As fans grow older the relief between bars and swales decreases, the sediment transport rate from bars to swales decreases, and the surface processes that erode the fan become uniform over the entire fan surface. The nuclide data therefore suggest that, over time, the difference in 10Be concentration between bars and swales increases to a maximum until the topographic relief between bars and swales is minimized, resulting in a common surface lowering rate and common 10Be concentrations across the fan. During this phase, the entire fan is lowered homogeneously at a rate of 10-15 mm kyr−1. 相似文献
12.
琼北火山岩激光40Ar/39Ar定年研究 总被引：1，自引：1，他引：0
新生代以来,雷琼地区多次、大量地喷发了一系列火山岩。前人主要基于K-Ar法对此划分了期次。本文采用激光40Ar/39Ar年代学方法,对琼北火山岩区进行了精细定年研究。低本底激光40Ar/39Ar法能够对低钾含量,极少量样品(毫克级)进行精细测定,非常适合极年轻火山岩的定年工作。结果显示的火山岩激光40Ar/39Ar法高质量数据表明琼北火山喷发活动时限跨越1.3～0.052Ma。在比较了表观年龄与等时线年龄差异之后,本文给出了年龄推荐值。正如测试数据所显示,本地区新生代火山岩普遍存在40Ar和36Ar过剩的问题,此时只有等时线年龄才代表喷发的真实年龄。 相似文献
13.
Constraints from strontium and neodymium isotopic ratios and trace elements on the sources of the sediments in Lake Huguang Maar 总被引：4，自引：0，他引：4
Houyun Zhou Bo-Shian Wang Huazheng Guan Yi-Jen Lai Chen-Feng You Jinlian Wang Huai-Jen Yang 《Quaternary Research》2009,72(2):289-300
The sediments in Lake Huguang Maar in coastal South China were previously thought to originate mainly from wind-blown dust transported from North China, such that the lake sediments recorded the varying strength of the Asian winter monsoon. An alternative explanation was that the local pyroclastic rocks supplied the lake sediments, but the actual contributions from the different sources remained unclear. Geochemical analyses including 87Sr/86Sr and 143Nd/144Nd and trace elements support the local pyroclastic rock as the dominant source: < 22% of the total Sr in the lake sediments and 17% of the Nd arises from the distant source. Nb/Ta and Zr/Hf for the lake sediments are identical to those for the local rock but differ from the ratios for the wind-blown dust, and chondrite-normalized rare earth element patterns for the lake sediments are similar to those for the local rock and soil, but differ from those for the distant source. The sediments in Lake Huguang Maar are probably input into the lake through runoff and thus controlled by the hydrology of the lake. Wind-blown dust transported by the Asian winter monsoon from arid North China is only a minor contribution to the sediments. 相似文献
14.
对具有不同地质历史背景的3类40Ar/39Ar法样品中的40Ar和39Ar释出特征进行对比,研究结果表明,40Ar/39Ar法样品中的40Ar、39Ar释气曲线主要表现为以下3种形式:完全重合型、过剩氩型和不规则型。当40Ar与39Ar释气曲线呈完全重合型时,40Ar/39Ar法全熔年龄代表了岩体的形成年龄;当40Ar、39Ar释气曲线是过剩氩型时,40Ar/39Ar法全熔年龄则大于岩体的形成年龄;当40Ar与39Ar释气曲线呈不规则型时,表明样品中的放射成固氩(40Ar*)发生了丢失,其全熔年龄一般较岩体的形成年龄小。对于40Ar、39Ar释气曲线呈过剩氩型的样品,40Ar/39Ar法年龄谱通常呈马鞍形,且马鞍形年龄谱的底部年龄一般都具有地质意义,代表了岩体的形成年龄。对于40Ar、39Ar释气曲线呈不规则型的样品,对其年龄谱的解释应持谨慎态度。 相似文献
15.
16.
H. Knicker G. Almendros F. J. Gonzlez-Vila H. -D. Lüdemann F. Martin 《Organic Geochemistry》1995,23(11-12)
A variety of fungal melanins with natural 15N abundance are characterized by solid-state 13C and 15N NMR spectroscopy and are compared to solid-state 13C and 15N NMR spectra of organic matter from representative soils. In all solid-state 15N NMR spectra the peptide/amide region (−220 to −285 ppm) dominates with more than 70% of the total intensity. The region between −285 and −375 ppm, assigned to amino and ammonium groups, always contains more than half of the remaining intensity. The area in the region from −30 to −220 ppm, where aromatic heterocycles would show signals, makes up less than 10% of the total intensity. These findings call into question common structural models for melanins. The solid-state 13C NMR spectra, on the other hand, reveal large differences when the melanins are compared to each other, and to composts and soils. The concentration of the aromatic carbon varies from 5 to 40% in the melanin series. The ratio Caro/Ntot and Cali/Ntot were calculated, and confirm that nitrogen in these samples is bound in Ca-groups rather than in aromatic heterocyclic structures. 相似文献
17.
18.
The ^190Pt-^186Os system should be a unique tracer for mantle processes be-cause both Pt and Os are concentrated in the mantle.The ^190Pt-^186Os system will also be a good supplement to the ^187Re-^187Os system for dating and tracing mantle pro-cesses because the ^190Pt-^186Os system is not so easily contaminated by crustal materials as the ^187Re-^187Os system.In turn,the application of the ^187Re-^187Os system to Pt-enriched materials uncontaminated by crustal materials will indirectly refine the half life of ^190Pt.The ^190Pt is refined.In the coupled ^187Re-^187Os and ^190Pt-^186Os sys-tematics,an ^186Os*/^190Pt-^187Os*/^187Re Concordia diagram similar to the ^206Pb*/^238U-^208Pb*/^232Th Concordia can be constructed.In such a Concordia diagram,a date will be obtained so long as the ^190Pt-^186Os system remains closed even if the ^187Re-^187Os sys -tem is contaminated by crustal materials.In addition ,for the coupled ^190Pt-^186Os and ^187Re-^187Os systematics,the mantle processes and the interactions between the mantle and the crust will be described by two ratios:^186Os/^188Os and ^187Os/^188Os .The coupled ^187Re-^187Os and ^190Pt-^186Os systematics will be a powerful tool in the investigation of the geodynamic history of the Earth because the ^187Re-^187Os system is sensitive to the interactions between the mantle and the crust,while the ^190Pt-^186Os system is a good tracer for mantle processes. 相似文献
19.
Mark Quigley Yu Liangjun Liu Xiaohan Christopher J.L. Wilson Mike Sandiford David Phillips 《Tectonophysics》2006,421(3-4):269-297
Structural and thermochronological studies of the Kampa Dome provide constraints on timing and mechanisms of gneiss dome formation in southern Tibet. The core of Kampa Dome contains the Kampa Granite, a Cambrian orthogneiss that was deformed under high temperature (sub-solidus) conditions during Himalayan orogenesis. The Kampa Granite is intruded by syn-tectonic leucogranite dikes and sills of probable Oligocene to Miocene age. Overlying Paleozoic to Mesozoic metasedimentary rocks decrease in peak metamorphic grade from kyanite + staurolite grade at the base of the sequence to unmetamorphosed at the top. The Kampa Shear Zone traverses the Kampa Granite — metasediment contact and contains evidence for high-temperature to low-temperature ductile deformation and brittle faulting. The shear zone is interpreted to represent an exhumed portion of the South Tibetan Detachment System. Biotite and muscovite 40Ar/39Ar thermochronology from the metasedimentary sequence yields disturbed spectra with 14.22 ± 0.18 to 15.54 ± 0.39 Ma cooling ages and concordant spectra with 14.64 ± 0.15 to 14.68 ± 0.07 Ma cooling ages. Petrographic investigations suggest disturbed samples are associated with excess argon, intracrystalline deformation, mineral and fluid inclusions and/or chloritization that led to variations in argon systematics. We conclude that the entire metasedimentary sequence cooled rapidly through mica closure temperatures at 14.6 Ma. The Kampa Granite yields the youngest biotite 40Ar/39Ar ages of 13.7 Ma immediately below the granite–metasediment contact. We suggest that this age variation reflects either varying mica closure temperatures, re-heating of the Kampa Granite biotites above closure temperatures between 14.6 Ma and 13.7 Ma, or juxtaposition of rocks with different thermal histories. Our data do not corroborate the “inverse” mica cooling gradient observed in adjacent North Himalayan gneiss domes. Instead, we infer that mica cooling occurred in response to exhumation and conduction related to top-to-north normal faulting in the overlying sequence, top-to-south thrusting at depth, and coeval surface denudation. 相似文献
20.
由于较低的钾元素含量以及过剩氩的存在,长期以来对硅质岩的40Ar/39Ar定年一直存在较大难度。近年来,由于仪器水平的不断提高,新实验技术和方法的应用,特别是激光全熔40Ar/39Ar定年技术的应用,40Ar/39Ar定年方法具有了足够高的测试精度和稳定的低本底水平,可以满足测试极低钾元素含量的硅质岩样品的要求。利用多组矿物颗粒测试数据计算等时线年龄的方法可以很好地去除过剩氩对硅质岩年龄的影响。本文利用激光全熔40Ar/39Ar定年方法对新疆准噶尔盆地边缘的两个硅质岩样品进行了定年研究。采自白碱滩地区的08BJT-3样品的年龄测试结果为294±14Ma,该年龄结果与硅质岩样品所处的晚石炭世地层沉积年代基本一致。采自卡拉麦里地区的KML-2样品的年龄测试结果为266±14Ma,该年龄结果与强烈变形改造硅质岩样品的卡拉麦里构造变形带活动年代十分一致,表明激光全熔40Ar/39Ar定年方法可以准确地对硅质岩进行定年。 相似文献