The reliability of thermoluminescence dating: A pilot experiment

The accuracy of thermoluminescence dating of pottery was tested by utilizing dendro-chronologically dated provenances in the northern part of the American Southwest. Fairly accurate determinations were achieved for potsherds recovered from sedimentary rock soil, while much younger dates were obtained for potsherds recovered from volcanic rock soil. The reduction of accumulated dose through radon escape might be responsible for the much younger dates of the sherds buried in volcanic soil. The application of the technique to samples recovered from soil matrices in volcanic materials, to burnt volcanic rocks, or to sherds containing ample volcanic rocks should be avoided for reliable determinations.     

Stratigraphy and thermoluminescence dating of Late Glacial cover sand in Denmark

In western Jutland deposits with a texture and structure similar to Dutch cover sands have been found. Investigations have been carried out on the lithology and the lithostratigraphic sequences. Pollen analysis is used for biostratigraphic correlation, and ages have been obtained by the radiocarbon method as well as by thermoluminescence techniques using both quartz and eldspar. The five sites are presented separately and the data are integrated into a general stratigraphic outline of the Late Glacial cover-sand sequence in Jutland. During the latest part of the Upper Pleniglacial and the earliest Late Glacial, older cover-sand type was deposited. Locally this sediment was also deposited during the later parts of the Late Glacial. Younger cover-sand type was deposited primarily during the Early Dryas and Late Dryas, but some sand of this type was also laid down during the Allerød and the earliest Holocene. The palaeobotanical records are discontinuous, but plant growth was probably present throughout the Late Glacial; only during the Altered did the deposition of sand decrease long enough to allow a relatively stable vegetational development. The investigation shows that the sequence of events in Jutland is similar to the Dutch record.     

Some thermoluminescence properties and dating of eolian sands from the Netherlands

Bleaching characteristics of Late Glacial and Holocene eolian sands from The Netherlands confirm the suitability for TL dating of these sediments. A solar simulator has been used for both quartz and potassium feldspar separates. A number of bleaching times and dose rate determinations have been used to establish the best plateau for the ED determination and a suitable dose rate respectively, in order to date a Late Glacial cover sand sample.     

Aeolian stratigraphy and thermoluminescence dating of sediments of late Holocene age from Sola, southwest Norway

Thermoluminescence age determinations were performed on four aeolian sand samples of late Holocene scenceagesediments from Stavanger airport, Sola, in southwest Norway. The locality is well suited for testing thermoluminescence dating because of a good agreement between radiocarbon ages and age information based on archaeological typology and sea level changes. The conclusion from a comparison of thermoluminescence and archaeologicaltypologyradiocarbon dates is that it is possible to date well bleached sediments as young as 1600 years with thermoluminescence (TL). The TL dates for the aeolian deposits are in accord with expected ages. Six formal, diachronous aeolian/non-aeolian phases are defined and grouped together as the Sola Episode. The first phase onousaeolian/non-aeolianof aeolian activity was short-lasting and took place in the middle Subboreal chronozone. A second and lianactivitywaslong-lasting period, dominated by aeolian activity, took place from the transition between the Subboreal and Subatlantic chronozones until the present. We conclude that human activities were the releasing factor for the aeolian activity recorded in sand sheets.     

内蒙巴丹吉林沙漠成因的粒度分析和热发光测年新证据

巴丹吉林沙漠位于中国内蒙古自治区的西部,是中国第三大沙漠。过去通常认为该沙漠中沙丘的可能沙源来自附近的各种沉积物和岩石,包括弱水河扇的沉积物,弱固结的二叠纪页岩、白垩纪砂岩和砾岩以及戈壁阿尔泰的古老岩石。根据对风成砂的粒度观测,有证据表明在沙漠内部的风成砂沉积朝东南方向具有较弱的但又确实的变细趋势。这与沙丘横脊线的SW-NE向排列以及坡面的南东指向是一致的。因此,可以认为西北部的弱水河冲积扇是巴丹吉林沙漠风成砂的最可能的沙源。在西北部风成床沙覆盖了较老弱水河扇起源的冲积物。这种沉积物的热发光测年范围在190～100 ka BP之间。由于测量中对沉积物漂白可能不完全以及对其中平均古水含量估算均存在不确定性,同时由于对沙漠该地区风成作用开始之前堆积的沉积物进行了测年,这一数据范围代表了最大的年龄。另外三个风成砂测年结果分别接近133.66和22 ka,代表有关巴丹吉林沙漠西北部风成作用开始的最小年龄。沙漠的沙丘高度平均为200～300m,但在东南部偶尔可达450m。一些学者曾提出风成床沙覆盖了一个陡峭岛山突起的假说,来解释这些异常的空间。本次研究发现,在研究区之下是一个产状水平的白垩纪扇砾岩和砂岩的台地,可以断定在沙漠东南部呈现台地地貌,但进一步向北该台地明显延伸到这些沙丘之下。因此现在可以认为巴丹吉林沙漠中高的沙丘是不同区域气候和地貌因素相互作用的结果,而不是覆盖一个陡峭的岛山突起。对弱水河冲积扇作为巴丹吉林沙漠的主要源区的证实强调区域环境的重要性。在全新世,沿河流的绿洲植被在某种程度上阻碍了冲积扇提供沙源。现在,河西走廊的农业用水量极大地危及沿河森林,因此沿着作为天然拦沙阱的弱水河,维持足够的河水流量来保护区域性密集的沙丘植被,一定会避免具有重大威胁的沙的活动性增加。     

Quartz thermoluminescence (TL) in gold exploration; some applications

The possible uses of thermoluminescence in mineral exploration are summarised. The methodology is described and some applications for gold exploration are developed with regard to the district of St-Yrieix (Limousin, France), the district of Salsigne (Herault, France) and some occurrences in the Ardenne massif (Belgium). From these cases, different possibilities may be mentioned: the distinction of various types of mineralized structures (St-Yrieix); the evaluation of the potential of mineralized districts from samples collected in the old mining works or in the superficial formations, etc. (St-Yrieix; Ardenne massif), and the determination of a genetic affiliation between different types of mineralizations (e.g. between stratiform deposits and vein-type deposits: the comparison between the districts of St-Yrieix and Salsigne). Finally new possibilities using the TL sensitivity and the equation of the straight lines NTL (natural TL) and ATL (induced TL) are evaluated.     

辉钼矿Re-Os同位素定年方法的改进与应用

公认的Re-Os同位素定年代表物辉钼矿,目前已在金属硫化物矿床年代学研究领域获得了广泛的应用。本研究采用浓HNO₃分解辉钼矿样品,大大地简化了Re和Os的化学制备过程,并根据辉钼矿中正常Os含量水平相对放射成因¹⁸⁷Os可以忽略的特点,以正常Os标准为稀释剂,实现了仪器测量过程中Os同位素质量分馏的在线校正,改善了分析数据的质量。该方法经辉钼矿国家标准物质进行验证,获得了满意的Re、Os含量及Re-Os年龄数据,并且在南岭地区与连阳复式岩体相关的姓坪夕卡岩型钼矿床成矿年龄研究中获得了成功应用。在实际应用中,为了获得有意义的能反映真实地质事件的年龄数据,辉钼矿样品不仅要有足够的取样量,而且还要保证粒度细、混合均匀。     

沥青铀矿(GBW04420)的微区原位U-Pb定年分析

GBW04420是沥青铀矿铀铅同位素年龄国家标准物质,是TIMS法分析铀矿物铀铅含量和年龄的标准,最近在国内被大量应用于微区原位U-Pb定年分析.本文分别利用电子探针化学定年法(EPMA CHIME)、电子探针与质谱仪联用法(EMPA&SIMS/LA-MC-ICPMS)、二次离子质谱法(SIMS)、激光剥蚀电感耦合等离子体质谱法(ns/fsLA-MC/HR/Q-ICP-MS)、同位素稀释热电离质谱法(ID-TIMS),对GBW04420进行了U-Pb定年分析;发现GBW04420的沥青铀矿颗粒之间年龄是不均一的.甚至,在加拿大曼尼托巴大学SIMS实验室两次分析得到的结果不同.由此,作者认为对于沥青铀矿标准物质GBW04420作为基体匹配标准物质来进行分馏校正,需谨慎对待.     

New geochronometer for the direct isotopic dating of native platinum minerals (190Pt-4He method)

A new method of isotope geochronology was proposed for dating native platinum minerals on the basis of the ??-decay of the natural isotope ¹⁹⁰Pt. The analysis of the thermal desorption of helium in the crystal lattice of native metals, including platinum, allowed us to predict a very high thermal stability (retentivity) of radiogenic ⁴He in native platinum minerals up to their melting temperatures. In order to validate the proposed ¹⁹⁰Pt-⁴He method, direct isotopic dating was performed for isoferroplatinum from the Galmoenan dunite-clinopyroxenite and Kondyor alkaline ultramafic massifs. The results of dating obtained by this method for primary ore platinum from the Galmoenan Massif (70 ± 5 Ma) are consistent with geological observations and mean Sm-Nd and Rb-Sr isotopic age estimates. The ¹⁹⁰Pt-⁴He age obtained for placer isoferroplatinum from the Kondyor Massif (112 ± 7 Ma) also agrees with geological observations and is close to the K-Ar and Rb-Sr ages of koswites (phlogopite-magnetite pyroxenites, gabbros, nepheline syenites, and metasomatic rocks after dunites). Our experimental data demonstrated that the ¹⁹⁰Pt-⁴He method is a promising tool for dating native platinum minerals.     

铼-锇同位素测年法研究综述

Re-Os同位素测年的最合适的对象为辉钼矿,定年是基于放射性的187Re通过β衰变成为187Os而引起锇同位素异常来计算地质年代的。在目前的测试研究中,较常用的方案为Carius管溶样法-蒸馏分离Os-萃取分离Re-TJA PQ ExCell ICPMS测定同位素比值。在我国有许多成功用Re-Os同位素测定钼矿床成矿年龄的范例,对认识矿床特征及成因、总结区域的成矿演化规律、解决相关地质问题具有重要的理论意义,而且对于指导矿床的预测和勘查具有很高科学价值。     

Optical and thermoluminescence dating of Middle Stone Age and Kintampo bearing sediments at Birimi,a multi-component archaeological site in Ghana

We report the first luminescence ages for the archeological and geological sediments forming the substrate of the Birimi archaeological site in the Northern Region of Ghana. The site's significance rests on the fact that it contains a rich collection of artifact assemblages representative of three distinct cultures, and that, on the basis of artifact typology, the earliest assemblage is diagnostic of the Middle Stone Age (MSA). In situ occurrences of MSA artifacts are found at over 1 m below today's surface. They are overlain by a ceramic-rich complex of a sedentary or semi-sendentary Later Stone Age culture known as the Kintampo. The western half of the site is dominated by the industrial remains of Iron Age smelting activity.Elemental, mineralogical, and sedimentological analysis of the cultural and sub-cultural sedimentary horizons at the site revealed at least three distinct lithostratigraphic units. The quartz sediments are derived from the sandstone of the Gambaga escarpment, mass wasted and accreted fluvially at a rate of 3.2 cm/ka, forming a wide terrace at Birimi. Silts and finer fractions derive from windblown dust, likely from White Volta River and granitic sources to the north. Soil forming processes and wide fluctuations in moisture have progressively reduced the sediments at depth to the resistant quartz and kaolinite, with rich iron oxide coatings, and created two ironstone horizons composed of goethite-cemented quartz nodules.Multiple aliquot green-light stimulated optical ages for 125–150 μm quartz grains yielded ages of 23.6±2.9 and 40.8±11.8 ka for the MSA-bearing sediments, and 58.4±15.3 ka for the base of the terrace. Radiocarbon ages on charcoal from Kintampo-bearing units are 3.36–3.83 ka cal BP, and are supported by thermoluminescence (TL) ages on pottery sherds and burnt house daub fragments of this cultural complex. A 0.4 ka age on sediment from the site's surface confirms that the quartz zeroes well when exposed to natural light. Sediments bearing the Kintampo artifacts, however, yielded ages of 7.8–16.9 ka. These ages were obtained on sediments from large pits, some over 50 cm deep, and they deviate only slightly from the ages expected for naturally aggraded sediments at these depths. We conclude, therefore, that extensive digging of pits by the Kintampo dwellers was followed by rapid refilling, and that the bulk mobilization of the matrix did not permit the sedimentary quartz grains to experience any appreciable zeroing at that time.     

About possibility of isotope dating of native gold by the (U-Th)/He method

For investigation of helium in native gold, a new measuring complex was created and used: the high sensitivity mass spectrometer MSU-G (ZAO SKB “SPECTRON”). The sensitivity of measuring ⁴He was 5.3 × 10^?13 cm³/g per impulse. Experiments in stepwise heating of samples have been carried out, and the kinetics of radiogenic ⁴He emanation from native gold was investigated. Migration parameters (activation energy and frequency factor) were determined. Model calculations of stability (closure temperature) of radiogenic ⁴He in the native gold structure with a given time and temperature of thermal influences were made using the data received. The concentration of ⁴He in native gold from the original deposit Nesterovskoe is (4.7 ± 0.1) × 10^?5 cm³/g in the sample from the placer; from Chudnoe deposit, it is (3.8 ± 0.1) × 10^?5 cm³/g; from sulfide deposits of Kitoiskii knot of Eastern Sayani, it is (1.9 ± 0.1) × 10^?5 cm³/g; and from the South Muiskii ore region it is (8.7 ± 0.5) × 10^?7 cm³/g. The received curve lines of kinetics of ⁴He emanation from native gold show that radiogenic helium is well bonded in the native gold structure: in all the examined samples, most ⁴He emanates only by reaching the temperature of 950–1000°C. A specific feature of the kinetics of radiogenic ⁴He emanation in all examined samples is an outburstlike emanation in the form of a peak of large amplitude in the area of temperatures near the melting temperature point of gold. This is stipulated by the existence of helium bubbles released by metals only while they melt. The spectrum of helium thermal desorption from native gold has a complicated form and is a result of superposition of several peaks. This proves the migration of groups of atoms located in the gold structure in different energy states. Very large values of the activation energy of helium migration from native gold were received: up to 161–176 kcal/mol. Extremely large values of the frequency factor, from 2 × 10¹⁸ to 3 × 10³², correspond to such values of activation energies. This is caused probably by helium migration in the form of gas bubbles. The received data indicate the very high stability of the (U-Th)/He isotope system in native gold. Using the (U-Th)/He method of isotope geochronology seems to be very promising for isotope dating of these strategic raw materials.     

Assessment of sandstone deterioration at Ta Keo temple (Angkor): first results and future prospects

A first application of geomorphological methods to the assessment of sandstone deterioration at Angkor is presented. Damage diagnosis was carried out on the first eastern tier of the central pyramid of the 1,000 year-old Ta Keo temple. Methods combine field observations and measurements at 230 sampling points, high-resolution lasergrammetry and stereophotogrammetry on a 2-m² test zone, and SEM observations. The first results indicate that decay operates through a synergistic combination of weathering phenomena dominated by scaling and solution, and exhibits a high spatial variability. Percentages of deteriorated surfaces vary from 17.6 to 93.8%, and average stone recession values from 0.00 to 2.71 cm (minimum) and 0.34 to 5.49 cm (maximum). On the test-zone, stereophotogrammetry and 3D-mapping of the present and reconstructed initial states using lasergrammetry indicate that erosion scars up to 6 cm deep have formed since 1963. On the whole, the amount of deteriorated surfaces more than tripled between 1963 and 2008. The degree of implication of salts in stone decay remains unclear for most efflorescences are composed of calcite (CaCO3), with secondary importance of barite (BaSO4) and gypsum (CaSO₄·2H₂O). Future prospects aim to evaluate the impact on stone decay of the clearing out of the temple from the forest in the 1920s.     

The CO2 absorption method as an alternative to benzene synthesis method forC dating

A fast and economical routine sample preparation system is described for direct counting of¹⁴C for hydrological purposes. The method employs commercially available CO₂ absorbers, such as Carbosorb, and liquid scintillation counters. The maximum error involved individual analyses is about ±4pmc (1 δ) on the Beckman counter and about ±2 pmc on the Quantulus counter with a resulting detection limit of 21,000–29,000 a for the Beckman LS7500 and 1220 Quantulus, respectively for a counting time of 1000 min. To avoid physical weighing procedures, an indirect method is presented to determine the grams of C absorbed in the counting solution by using the H-# quench monitor technique available in the Beckman liquid scintillation counters. On one sample preparation system at least five samples can be prepared per normal working day. The applicability of the CO₂-absorption method is discussed with reference to two field sites and with reference to comparisons with data obtained on the same samples measured with conventional techniques.     

The problem of inherited Ar* in dating impact glass by the Ar/Ar method: Evidence from the Tswaing impact crater (South Africa)

The Tswaing meteorite impact crater is a 1.13 km diameter structure located in the 2.05 Ga Nebo granite of the Bushveld Complex. The impact age had previously been determined by fission track dating to 220 ± 104 ka. ⁴⁰Ar/³⁹Ar step-heating and total fusion experiments performed on single- and multi-grain impact glass aliquots gave apparent ages ranging from 1.0 ± 0.3 Ma to 204 ± 6 Ma. These “ages” indicate that the radiogenic Ar derived from the target rocks has not been completely degassed as a result of the impact process, despite fusion of the target material. Results of step-heating experiments imply that the trapped within the glass is located in two distinct reservoirs thought to be the glass matrix and fluid/vapor inclusions (or un-melted residual clasts). Calculations assuming an age of 0.2 ± 0.1 Ma for Tswaing (fission track data) reveal that the amount of inherited ⁴⁰Ar*() relative to the pre-impact concentration varies from 0.015% to 4.15%. The spread defined by likely reflects the various quench rates experienced by the glass, most certainly due to the pre-impact position of the sample relative to the center of the crater. We compare the influence of on the apparent ⁴⁰Ar/³⁹Ar age determination of five impact structures. Our calculations show that the main characteristic controlling the age offset (for a given proportion of ) is the age difference between the impact and the target rocks (i.e., the ⁴⁰Ar* concentration in the target rock). The buffer effect for a given crater structure can be predicted knowing the age of the basement and having a rough estimation of the age of the crater structure itself. The occurrence of is likely influenced by (1) the degree of polymerization (i.e., silicate structure complexity) of the target rock and presumably related to the diffusivity of Ar in the melt and glass, (2) the Ar partial pressure at the grain boundary, (3) the quantity of energy involved in the impact, and (4) the porosity of the target rocks. For glass that inevitably suffers inherited and/or excess ⁴⁰Ar*, the use of the inverse isochron technique can be appropriate but should be applied with careful statistical treatment.     

TL dating of partially bleached sediments by the regeneration method

Thermoluminescence dating of sediments in the Warsaw laboratory is based on blue-to-green emission. The ‘partial bleach + regeneration’ method is proposed for dating sediments which have not been completely bleached at the time of burial. Correct TL ages are reported for sediments covering organic deposits of the Eemian Interglacial and also for glacial sediments of Würm and Riss age. We obtained good results for dating till using the partial bleach + regeneration method. The TL zeroing in till is explained by the ‘rubbing’ or compression of grains beneath the glacier and by the freeze-thaw activity occurring during glacial transport and deglaciation.     

The first results of U-Pb dating of zircons from gneissic granites of the Kharbei Complex (Polar Urals)

Data on the age of gneissic granites from the Precambrian Kharbei Complex (Polar Urals) have been obtained for the first time. Local U-Pb dating was carried out using a SHRIMP-II ion microprobe. Zircons were taken from three granitic bodies close in petrographic and petrochemical parameters. The formation of gneissic granites was implemented in two stages: during the Late Ediacarian (556 ± 2.2 Ma) and in the Late Cambrian (497 ± 3 and 487.1 ± 2.1 Ma). The rocks formed owing to rheomorphic flow of granitic material, caused by tectonic events related to Timanian (Baikalian) tectogenesis and epicontinental riftogenesis, which occurred prior to the appearance of the Paleouralian Ocean.     

标准生长曲线法在华南沿海老红砂石英光释光测年中的适用性*

如何快速准确地建立老红砂剖面年代学标尺或区域年代学框架,是在实践中有待解决的问题。而标准生长曲线法(SGC)在减少样品测试时间、提高测年仪器的测试效率方面具有独特的优势,因此在内陆黄土及沙漠沉积年代测定中得到了广泛应用。在福建和海南海岸带老红砂分布区采集了4个剖面的测年样品共计20个,应用单片再生剂量法(SAR)及SGC法进行定年研究。结果表明: (1)福建和海南海岸带老红砂样品释光(OSL)信号均以快组分为主,在信号积分通道前0.64 s 快组分的信号占据总体信号的80%以上,适合使用SAR及SGC方法测年;其快、中组分光电离截面分别为: 福建老红砂2.62×10^-17 cm²和3.24×10^-18 cm²,海南老红砂2.66×10^-17 cm²和3.51×10^-18 cm²; 2个区域样品的IRSL(红外激发释光信号)/OSL信号比值表明,较老样品的红外释光信号明显高于较年轻的样品,这可能是受到长石包裹体的影响,但其比值均小于10%,符合SAR与SGC测试要求。 (2)SGC法在华南海岸地区老红砂OSL年代学研究中具有较好的适用性,不同样品之间的剂量生长曲线存在着相似的增长模式,可以建立标准生长曲线; 但福建与海南老红砂样品之间的标准生长曲线具有较大的差异,因此在较大区域范围内运用标准生曲线法应当谨慎小心。