磷灰石ID-TIMS高精度U-Pb定年方法OA北大核心CSTPCD
A High-Precision ID-TIMS U-Pb Dating Method of Apatite
磷灰石晶体结构呈六方晶系,具有相对高的封闭温度(350~550℃),能够容纳多种元素置换进入晶格内部,是火成岩、沉积岩、变质岩和矿床研究的重要定年矿物.然而,由于磷灰石通常具有较低铀含量和高普通铅含量,精准测定其年龄仍是当前U-Pb测年技术的一大挑战.本文基于208Pb-235U混合稀释剂,通过优化样品清洗、溶解以及柱色谱分离纯化U和Pb等化学前处理流程,建立了磷灰石同位素稀释-热电离质谱(ID-TIMS)高精度U-Pb定年方法,并准确测定了磷灰石标样MAD2和MAP-3的年龄,其206Pb/238U年龄加权平均值分别为474.6±1.7Ma和800.7±1.2Ma,单点定年精度优于0.4%,为磷灰石微区原位标样研发以及样品年龄精准测定提供技术支撑.采用MAP-3作为微区原位校正标样,对磷灰石Durango和Otter Lake进行LA-ICP-MS U-Pb测年分析,通过Tera-Wasserburg谐和图图解法扣除普通铅,获得下交点年龄分别为32.1±0.6Ma(MSWD=1.3,n=36)和910±13Ma(MSWD=1.6,n=36),与前人研究结果在误差范围内一致,进一步证实普通铅含量极低的MAP-3,是一个理想的磷灰石微区原位测年标样.与高普通铅的磷灰石标样相比,使用MAP-3作为外标能直接在数据处理软件中进行数据校正,有效地简化了数据处理过程,提高磷灰石微区原位U-Pb测年结果的可靠性.
ABSTRACT:Apatite belongs to the hexagonal crystal system and has a relatively high(350-550℃)closure temperature,which can accommodate multiple element substitutions into the crystal lattice.It is an important dating mineral for the study of igneous rocks,sedimentary rocks,metamorphic rocks and ore deposits.However,due to the low uranium content and high common lead content of apatite,accurate age determination remains a major challenge for current U-Pb dating techniques.Based on the208Pb-235U mixed spike,a high-precision isotope dilution-thermal ionization mass spectrometry(ID-TIMS)U-Pb dating method of apatite was established by optimizing the chemical pre-treatment process of sample cleaning,dissolution,and column chromatography separation and purification of U and Pb.The proposed method accurately determined the ages of apatite MAD2 and MAP-3,with 206Pb/238U weighted average ages of 474.6±1.7Ma and 800.7±1.2Ma,respectively.The precision of single-point analysis was better than 0.4%,providing technical support for accurately and precisely dating apatite and development of apatite standards.Moreover,taking MAP-3 as a calibration standard,LA-ICP-MS U-Pb dating was performed on apatite in Durango and Otter Lake,resulting in lower intercept ages of 32.1±0.6Ma(MSWD=1.3,n=36)and 910±13Ma(MSWD=1.6,n=36)in a Tera-Wasserburg diagram,which were consistent with the previous research results within error.This gives further evidence that MAP-3,with extremely low common lead content,is an ideal apatite in situ U-Pb dating standard.Compared with high common lead apatite standards,MAP-3 as an external standard can directly calibrate the isotopic data,effectively simplifying the data analysis process and improving the reliability of in situ apatite U-Pb dating results.
涂家润;周红英;崔玉荣;李国占;耿建珍;张健
中国地质调查局天津地质调查中心,天津 300170||中国地质调查局华北地质科技创新中心,天津 300170中国地质调查局自然资源综合调查指挥中心,北京 100055
地质学
同位素稀释-热电离质谱法U-Pb定年稀释剂普通铅标样
isotope dilution-thermal ionization-mass spectrometryU-Pb datingspikecommon leadstandards
《岩矿测试》 2024 (004)
533-545 / 13
国家自然科学基金项目(42103025,42073055,41873066)
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