(U⁃Th)/He定年及影响因素研究进展

The Research Advances of(U-Th)/He Dating and Influencing Factors

(U-Th)/He同位素定年以其低温敏感性(70℃)为造山带隆升‒剥蚀速率的时空格架构建、油气成藏时间约束、沉积盆地埋藏历史恢复、矿床剥蚀保存研究及古地形地貌重塑等提供了精确的时间‒温度演变模型,应用前景广阔.理解矿物封闭温度、内部结构、4He扩散机制、铀‒钍分带效应等是(U-Th)/He数据解释的核心所在.本文详尽论述了(U-Th)/He技术研究,包括测年适宜对象及在不同地质领域的应用、测试方法的发展及标准矿物结果、着重归纳了造成年龄偏差的因素,并简述了主要矿物的辐射损伤机制.研究表明,我国(U-Th)/He定年技术从非稀释剂法测定发展至单颗粒激光熔融技术,再延续到准分子激光剥蚀系统RESOlution下的原位微区双定年技术,FCT锆石、Durango磷灰石及蓬莱锆石的测定结果与国际标定年龄在误差范围内一致,并自主开发了MK-1磷灰石标样,目前该技术已相对成熟.能有效保存4He的多数铀‒钍副矿物均可成为适宜定年对象,本文总结了有效规避矿物包裹体、矿物粒径、α粒子射出及植入效应、成分环带等影响因素的策略,可为国内学者在(U-Th)/He数据解释中提供帮助和参考.

(U-Th)/He isotopic dating with its low-temperature sensitivity(70℃),provides an accurate time-temperature evolution model for the construction of temporal-spatial framework of uplift and denudation rates in orogenic belts,temporal constraints on hydrocarbon formation,recovery of burial history in sedimentary basins,the study of denudation and preservation of mineral deposits,and reconstruction of paleotopography and geomorphology,with promising applications.Understanding mineral closure temperatures,internal structure,4He diffusion mechanisms,and uranium-thorium zoning effects are keys to interpreting(U-Th)/He data.A detailed discussion of(U-Th)/He technical studies is presented,including the appropriate target minerals and different geological applications for dating,the development of test methods and standard references,a focus on the factors that contribute to age bias,and a brief description of the radiation damage mechanisms for the major minerals.Research has shown that China’s(U-Th)/He dating technology has advanced significantly,progressing from the non-dilution method to the single-particle laser fusion technique,and subsequently to the in-situ micro-area dual dating method using the RESOlution excimer laser ablation system.Measurement results from FCT zircon,Durango apatite,and Penglai zircon align closely with international calibration ages,falling within the expected margin of error.Moreover,an MK-1 apatite standard sample has been developed independently,indicating the maturity of the technology.Most of the uranium-thorium bearing minerals that have effectively preserved 4He can be suitable objects for dating.A summary of strategies to effectively avoid the effects of mineral inclusions,mineral grain size,α-particle ejection and implantation effects,and compositional ring-banding can help Chinese scholars interpret(U-Th)/He data.Key words:(U⁃Th)/He;influencing factors;apatite;zircon;geochemistry;isotopes.