共查询到19条相似文献，搜索用时 906 毫秒
1.
《地学前缘》2017,(3):79-93
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。 相似文献
2.
国际标样Durango磷灰石(U-Th)/He年龄测定 总被引：2，自引：1，他引：1
人们认识到可以用放射性成因4He对矿物进行定年已经有一百年的历史,但是利用富含U、Th的矿物进行(U-Th)/He定年是近三十年来快速发展的一种低温(热)年代学方法。由于U-Th-He同位素体系的封闭温度低(磷灰石4He的封闭温度为~75℃),该方法极大的拓展了中低温热年代学研究(如40Ar/39Ar,裂变径迹等)的温度范围下限,已经被广泛应用于浅表地质过程的研究中。Durango磷灰石是国际上广泛使用的磷灰石(U-Th)/He定年的标准样品,准确测定其年龄可以对实验方法及流程的可靠性进行验证。中国科学院地质与地球物理研究所(U-Th)/He定年实验室建立于2013年,经过一年多的实验与摸索,我们建立了完整、可行的化学分析流程和仪器测试流程,并采用Durango国际标样进行了流程验证。重复测定了4批共40个Durango磷灰石颗粒,40个年龄结果分布在28.95~34.11Ma之间,全部年龄的概率分布峰值为31.61±2.7Ma,与国际标定值在误差范围内一致;Th/U比范围为16.43~23.72,与国际报道值一致,表明我们所建立的实验流程准确可行,实验室已经可以稳定运行。 相似文献
3.
低温热年代学方法主要包括裂变径迹法和(U-Th)/He法,二者分别利用矿物中238U裂变产生径迹的积累和矿物中U、Th衰变产生4He的积累对矿物进行定年.由于低温热年代学方法的封闭温度低且对温度变化敏感,可用于定量确定地壳浅部所经历热事件和侵蚀事件的时间、幅度、速率及空间分布特征.目前低温热年代学方法在矿床学研究中的应用主要包括:间接或直接测定矿床的形成时代、恢复岩浆-热液成矿体系的热演化历史、约束成矿热液活动的持续时间、计算矿床的剥露速率和剥露量、估算矿床的形成深度、评价矿床的保存潜力、定量研究成矿后断层的位移、寻找古地热异常来指导找矿等.本文重点介绍这些应用的原理、方法和实例,并对部分应用的前提条件和注意事项作了说明.此外还指出低温热年代学方法还存在分析误差较大和成本较高等问题,分析技术的革新将进一步促进其在矿床学及其它领域中的应用. 相似文献
4.
同位素地质年代学是一门传统的定年学科,广泛应用于地质各个领域研究中.随着同位素地质年代学理论创新与技术进步,现在逐步发展成为地质热年代学,即将地质年代数据赋予相应封闭温度属性,使之不仅揭示地质事件年龄,而且反映该事件发生的温度条件.不同定年方法以及测试样品的不同,其对应的封闭温度不同,从而可以揭示地质体在更大温度或年龄范围的形成演化过程,定量研究矿区或矿体的隆升与剥露,评价矿床形成后的保存与变化状况,提高找矿预测效果.主要总结和论述诸如40Ar-39Ar、裂变径迹和（U-Th）/He等中-低温热年代学技术方法及其在矿床地质中的应用研究状况,分析热年代学技术与应用发展趋势,以期为成矿作用研究提供新的应用技术手段. 相似文献
5.
地质年代学发展历史的简要回顾及前景 总被引：1，自引：0，他引：1
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。 相似文献
6.
裂变径迹定年技术在构造演化研究中的应用 总被引：11，自引：0，他引：11
裂变径迹技术是一种以磷灰石和锆石等矿物为定年对象的低温热年代学方法，特别适用于研究上地壳岩石冷却剥露的时间和过程。该技术在地学中的应用早期以定年为主，随着对裂变径迹长度分布特征与裂变径迹退火特性的深入研究，这种方法得到更广泛的应用，在此基础上综述了裂变径迹技术在下列构造演化问题中的应用和进展，包括：（1）造山带隆升时代及隆升速率的研究；（2）造山带热演化历史的研究；（3）快速蚀顶或冷却事件的年代确定；（4）盆地反转时代的确认；（5）盆地基底岩系构造热历史的研究；（6）盆山耦合过程的研究。 相似文献
7.
构造-热年代学--发展与思考 总被引：18，自引：0，他引：18
构造热年代学是一门集同位素年代学、构造地质学、岩石矿物学、计算机模拟技术等为一体的综合性学科。它是在同位素年代学研究的基础上 ,结合矿物的封闭温度理论、构造事件、岩浆热事件等的研究而发展起来的。U Pb、40 Ar/ 3 9Ar、裂变径迹及 (U Th) /He等测年手段是该学科的重要支柱手段。这一学科的发展已经、并且将对传统构造地质学、年代学的应用与解释起到巨大的推动作用。而在此基础上的微区微量年代测定与应用将是对地质学特别是构造事件乃至构造运动的演化序列精细测定的一次革命。 相似文献
8.
9.
念扎金矿床是近年来最新发现的位于雅鲁藏布江缝合带南侧仁布构造混杂岩带与蚀变闪长岩接触带的大型造山型金矿床.为约束念扎矿床的冷却及剥露历史，利用锆石的U-Pb、（U-Th）/He及磷灰石裂变径迹定年对新鲜及矿化闪长岩年龄进行测定.结果表明，新鲜闪长岩锆石U-Pb年龄为（46.32±0.53）Ma，（U-Th）/He年龄介于（7.14±0.24）Ma到（9.80±0.27）Ma，矿化闪长岩锆石（U-Th）/He年龄介于（8.38±0.24）Ma到（11.19±0.31）Ma之间，两件矿化闪长岩磷灰石裂变径迹年龄分别为（5.9±0.5）Ma和（5.3±1.0）Ma.念扎金矿床自闪长岩固结以来经历了两次快速冷却过程:第一次是从46.3 Ma开始持续到43.6 Ma，温度从750℃降至350℃，冷却速率高达约148℃/Ma；第二次为8.5~2.0 Ma，温度从约200℃降至30℃，冷却速率为26℃/Ma.念扎矿床成矿深度为9.7 km；在8.5 Ma时，矿床被抬升至4.6 km处；从8.5~5.6 Ma，矿床抬升至2.8 km；从5.6~2.0 Ma，念扎矿床被剥露至地表. 相似文献
10.
11.
(U-Th)/He定年是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,而矿物中4He同位素的有效提取和含量准确测定是该技术的关键。磷灰石和锆石是(U-Th)/He定年最常用的矿物,其4He提取条件及铀钍含量测定方法都较为成熟;而其他矿物(如磁铁矿、橄榄石、针铁矿、石榴子石等)的研究则相对较少。文章介绍了当前国内外(U-Th)/He研究中采用的4He同位素提取方法———真空炉加热法和激光加热法,激光加热法因具有低4He背景值和耗时短的优点而成为主要的提取方法。以磷灰石样品测试为例,介绍了成都地质矿产研究所建立的采用激光加热法和四极杆质谱提取4He同位素及其含量测量过程、含量计算和校正方法。指出未来(U-Th)/He测试技术除继续改进现有分析方法外,应加强对更多不同矿物的测试研究。 相似文献
12.
Birk Härtel William A. Matthews Eva Enkelmann 《Geostandards and Geoanalytical Research》2023,47(3):669-681
The accuracy and validation of geo- and thermochronological dating hinges on the availability of well-characterised age reference materials. The Mesoproterozoic gabbroic anorthosite FC1 from the Duluth Complex, Minnesota is a reference material for zircon U-Pb and a suggested reference material for apatite fission-track dating. We evaluate FC1 as (U-Th)/He reference material, and determine its apatite U-Pb, and zircon and apatite (U-Th)/He age. Our dating results constrain the thermal history of FC1, showing that fast cooling occurred between ~ 1099 and 1040 Ma from ≥ 600 °C to ~ 200 °C. The zircon (U-Th)/He data from air-abraded grains give a robust isochron age of 1037 ± 25 Ma (2s) without overdispersion. The within-grain homogeneity of U and Th, the availability of FC1 zircon, and the absence of radiation-damage effects on the (U-Th)/He age support its use as reference material. Unabraded zircon grains give lower and more dispersed ages, highlighting the usefulness of air abrasion to control for α-ejection in (U-Th)/He dating. Our apatite (U-Th-Sm)/He single-grain ages vary between 180 and 300 Ma. Their wide dispersion argues against the use of FC1 apatite as (U-Th-Sm)/He reference material and makes the interpretation of their low-temperature thermal history complicated. 相似文献
13.
Lin Wu Guanghai Shi Martin Dani&#x;ík Zhiyong Zhang Yinzhi Wang Fei Wang 《Geostandards and Geoanalytical Research》2019,43(2):301-315
The (U‐Th)/He dating technique has been widely used for several decades to constrain the timing of low temperature geological processes. Recent research has shown that the commonly used reference material (the Durango apatite) often yields dispersed fragment dates that are beyond analytical uncertainties. Here, we report a new apatite (U‐Th)/He dating reference material, MK‐1, which was collected from the Mogok metamorphic belt in Burma. Electron probe microanalysis and backscattered electron images of two randomly selected fragments indicate that this apatite is chemically and structurally homogeneous. We performed single‐grain (U‐Th)/He dating on thirty randomly selected fragments of this material. (U‐Th)/He dating results from multiple laboratories show that fragments of the MK‐1 apatite megacryst yielded reproducible results, with a mean date of 18.0 ± 0.2 Ma. The Th/U ratio of this apatite is homogeneous. Nine randomly selected fragments registered a narrow range of effective uranium (eU) mass fractions (326–354 μg g?1), with a mean value of 336.6 ± 10.3 μg g?1. Twenty‐four in situ (U‐Th)/He dates yielded a mean value of 18.0 ± 0.2 Ma (MSWD = 0.41), indistinguishable from the results obtained by the conventional method. All the results suggest that this apatite has the potential to become a new reference material for (U‐Th)/He geochronology. 相似文献
14.
(U-Th)/He测年技术:α离子射出效应及其校正 总被引：1，自引：0，他引：1
(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. 相似文献
15.
《Chemical Geology》2006,225(1-2):91-120
Low temperature thermochronologic techniques (e.g. apatite fission track (AFT) thermochronology and (U–Th)/He dating) constrain near-surface T–t paths and are often applied to uplift/denudation and landscape evolution studies. Samples collected in vertical profiles from granitic walls on either side of the Ferrar Glacier, southern Victoria Land, Antarctica were analyzed using AFT thermochronology and apatite (U–Th)/He dating to further constrain the lowest temperature thermal history of this portion of the Transantarctic Mountains. AFT central ages vary systematically with elevation and together with track length information define a multi-stage cooling/denudation history in the Cretaceous and early Tertiary. Apatite (U–Th)/He single grain age variation with elevation is not as systematic with considerable intra-sample age variation. Although many complicating factors (e.g., U- and Th-rich (micro)inclusions, fluid inclusions, variation in crystal size, α-particle ejection correction, zonation and α-particle ejection correction, implantation of He into a crystal or impediment of He diffusion out of a crystal, and 147Sm-derived α-particles) may contribute to age dispersion, we found that variation in single grain ages correlated with cooling rate. Samples that cooled relatively quickly have less variation in single grain ages, whereas samples that cooled relatively slowly (< 3 °C/m.y.) or resided within an (U–Th)/He partial retention zone (HePRZ) prior to more rapid cooling have a comparatively greater variation in ages.Decay of U and Th via α-particle emission creates a 4He concentration profile dependent upon the initial parent [U,Th] within a crystal. Variation of single grain ages for samples with non-homogeneous [U,Th] distributions will be enhanced with long residence time in the partial retention zone (i.e., slow cooling) because of the relative importance of loss via volume diffusion and loss via α-particle ejection with respect to the [U,Th] zonation and the grain boundary. Correction of ages for α-particle ejection (FT correction factor) typically assumes uniform U and Th distribution within the crystal and when applied to a population of crystals with different U and Th distributions will enhance the variation in ages. Most complicating factors (listed above) for apatite (U–Th)/He ages result in ages that are “too old”. We propose that if considerable variation in (U–Th)/He single grain ages exists, that a weighted mean age is determined once outlier single crystal ages are excluded using the criterion of Chauvenet or a similar approach. We suggest that the “true age” or most representative age for that age population lies between the minimum (U–Th)/He age and the weighted mean age. We apply this approach, coupled with composite age profiles to better constrain the T–t history of the profiles along the Ferrar Glacier. Significant intra-sample variation in single crystal apatite (U–Th)/He ages and other minerals dated by the (U–Th)/He method should be expected, especially when the cooling rate is slow. The variation of (U–Th)/He single crystal ages is therefore another parameter that can be used to constrain low-temperature thermal histories. 相似文献
16.
Laser microprobe (U-Th)/He geochronology 总被引：3，自引：0，他引：3
J.W. Boyce K.V. Hodges M.J. Jercinovic P.W. Reiners 《Geochimica et cosmochimica acta》2006,70(12):3031-3039
A new analytical method had been developed to enable high-spatial-resolution (U-Th)/He dating of accessory minerals. It involves the use of a focused ArF excimer to ablate pits in a polished grain surface, with the evolved gases spiked for isotope-dilution measurement of radiogenic 4He. These data are converted to concentrations by precise measurement of each pit using an optical interferometric microscope. U, Th, and Sm concentration measurements are made using one of several alternative microanalytical techniques (e.g., wavelength-dispersive electron microprobe analysis or laser-ablation, inductively coupled plasma mass spectrometry). By way of illustration, we present both conventional and laser microprobe (U-Th)/He dating results for a Brazilian monazite sample. Laser microprobe data (28 measurements on two crystal fragments) yield a weighted mean (U-Th)/He date of 455.3 ± 3.7 Ma (2SE). This result is statistically indistinguishable from the mean conventional (U-Th)/He date for three separate grain fragments: 449.6 ± 9.8 Ma (2SE). The agreement of conventional and laser ablation dates should encourage a wide variety of applications of the technique, including: (1) detrital mineral dating for provenance and unroofing studies; (2) the dating of broken, included, highly zoned, or irregular grains which are not easily corrected for α-ejection; and (3) measuring 4He loss profiles that can be inverted to determine cooling histories. 相似文献
17.
Pieter Vermeesch Diane Seward Martin Wipf Heinrich Baur 《Geochimica et cosmochimica acta》2007,71(7):1737-1746
U-Th rich mineral inclusions in apatite are often held responsible for erroneously old (U-Th)/He ages, because they produce “parentless” He. Three aspects associated with this problem are discussed here. First, simple dimensional considerations indicate that for small mineral inclusions, the parentless helium problem might not be as serious as generally thought. For example, a mineral inclusion that is 10% the length, width and height of its host apatite needs to be a thousand times more concentrated in U and Th to produce an equal amount of He. Therefore, single isolated inclusions smaller than a few μm are unlikely to contribute significant helium. For larger or more abundant inclusions, the parentless helium problem can be solved by dissolution of the apatite and its inclusions in hot HF. Second, besides creating parentless helium, inclusions also complicate α-ejection corrections. Mathematical exploration of this latter problem for spherical geometries reveals that for randomly distributed inclusions, the probability distribution of single-grain ages is predicted to have a sharp mode at the mean age, with tails towards younger and older ages. Multiple-grain measurements will yield accurate and precise age estimates if 10 or more randomly distributed α-emitting mineral inclusions are present in a sample. Third, thermal modeling indicates that mineral inclusions have a non-trivial but minor (<5 °C) effect on the closure temperature. These predictions were tested on apatites from rapidly cooled migmatites of Naxos (Greece) which contain abundant U-rich zircon inclusions. Thirty-seven samples were subjected to two kinds of treatment. The “pooled” age (i.e., the synthetic multi-grain age computed from a number of single-grain analyses) of four inclusion-free samples (13 apatites), prepared in HNO3 is 10.9 Ma, close to apatite and zircon fission-track ages from the same rock. (U-Th)/He ages of 14 inclusion-bearing samples dissolved in HNO3 range between 9 and 45 Ma, with a pooled age of 22.6 Ma. The ages of 19 HF-treated samples range between 5 and 16 Ma, with 10 of 14 single-grain samples between 9 and 13 Ma and a pooled age of 10.9 Ma. These observations agree with the theoretical predictions and support the addition of HF-treated apatite (U-Th)/He dating to the thermochronological toolbox. 相似文献
18.
U and Th zonation in apatite observed by laser ablation ICPMS, and implications for the (U-Th)/He system 总被引：3，自引：0，他引：3
A laser-ablation inductively-coupled plasma mass spectrometry technique was developed to measure U, Th, and Ce zonation in polished sections of apatite for assessing the consequences of parent zonation for (U-Th)/He thermochronometry. The technique produces concentration maps with an averaging length-scale of ∼20 μm, comparable to the α-stopping distance, and a precision of ∼5% down to few ppm concentration levels. A model was developed to transform the measured concentration distribution into a simplified representation for use in spherical-geometry He production-diffusion models. To illustrate these methods, 30 sections of apatite from a single granite (GC863) were mapped. Every analyzed apatite from GC863 is zoned, with most grains having variable thickness rims and terminations that are enriched in U and Th by about a factor of three over the grain cores.Parent zonation has three independent effects on (U-Th)/He He ages: it influences the α ejection correction, the 4He concentration profile which governs diffusive loss, and, via radiation damage trap accumulation, spatial variability of diffusivity within the crystal. If the observed zonation is typical of the apatite population in GC863, use of the standard homogenous α ejection correction would cause He ages to be on average 3% too young, and with a large amount of grain-to-grain variability (9% too young in the most rim-enriched case to 6% too old in a core-enriched case). Independent of the ejection correction, the concentration profile modifies the effective closure temperature of the apatites by placing more (or less) 4He near the grain edge. The parent zonation in GC863 apatites causes closure temperatures to range from four degrees lower (rim-enriched case) to two degrees higher (core-enriched case) than applies in the homogenous case. Alpha ejection and concentration profile effects on He age are additive and of the same sense. In the case of typical grains in GC863 cooled between 1 and 10 °C/Ma, the two effects are roughly equal in magnitude. The effects of intracrystalline variations in radiation damage trap accumulation become apparent at slow cooling rates (1 °C/Ma). For example, in rim-enriched GC863 grains cooled at 1 °C/Ma, preferential accumulation of radiation damage traps near the grain rim almost compensates for the higher loss rate expected of 4He also located preferentially near the rim. Under some circumstances strong rim-enrichment may actually increase the effective closure temperature of an apatite. Zonation at the level observed in GC863 modifies the 4He/3He spectra substantially from that expected from a uniform distribution. Measured 4He/3He spectra are strikingly similar to predictions based on the mapped eU distributions of the very same crystals, supporting the overall validity of the analytical and interpretive approach presented here.The magnitude and style of U, Th zonation documented in GC863 is one possible source of frequently observed over-dispersion of apatite (U-Th)/He ages as well as anomalous 4He/3He spectra. 相似文献
19.
磷灰石(U-Th)/He定年方法综述 总被引：3，自引：0，他引：3
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. 相似文献