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U–Pb geochronology of calcite carbonatites and jacupirangite from the Guli alkaline complex, Polar Siberia, Russia
Mineralogical Magazine ( IF 2.7 ) Pub Date : 2021-06-09 , DOI: 10.1180/mgm.2021.53
Ekaterina P. Reguir , Ekaterina B. Salnikova , Panseok Yang , Anton R. Chakhmouradian , Maria V. Stifeeva , Irina T. Rass , Aleksandr B. Kotov

This work is the first in situ U–Pb geochronological study of perovskite and calcic garnet (andradite) from the Guli complex in the Maimecha–Kotuy alkaline province (Polar Siberia, Russia). The U–Pb isotopic compositions of perovskite from contact zones of the two carbonatite stocks (Southern and Northern) and from jacupirangite separating the stocks were determined by laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICPMS) and isotope-dilution thermal-ionisation mass-spectrometry (ID-TIMS). The LA-ICPMS and ID-TIMS data for perovskite from the Northern carbonatite stock are in good agreement, yielding 206Pb/238U ages of 250.4 ± 1.1 Ma and 249 ± 2 Ma, respectively. These ages are also within the analytical uncertainty from the ID-TIMS results for perovskite from jacupirangites (250 ± 1 Ma). The LA-ICPMS results for perovskite from the Southern carbonatite stock indicate its somewhat older age (255.3 ± 2.4 Ma), implying the possibility of small-volume mantle magmatism predating the eruption of the Siberian flood basalts at ca. 252–251 Ma. This interpretation is supported by reports of pre-flood magmatism elsewhere in eastern Siberia. Andradite crystals from the contact between the Southern stock and metasomatised melilitolite were analysed by ID-TIMS. These measurements are inconclusive (247 ± 6 Ma) and could not be used to constrain further the timing of carbonatitic magmatism in the southern part of the complex. The present contribution also presents a refined methodology for LA-ICPMS geochronological studies of perovskite with elevated levels of common lead, and addresses some of the problems with previously proposed calibration standards.



中文翻译:

俄罗斯极地西伯利亚古里碱性杂岩中方解石碳酸岩和水杨花辉石的 U-Pb 年代学

这项工作是对来自 Maimecha-Kotuy 碱性省(极地西伯利亚,俄罗斯)古力复合体的钙钛矿和钙钛矿(红长石)的首次原位U-Pb 年代学研究。通过激光烧蚀电感耦合等离子体质谱 (LA-ICPMS) 和同位素稀释法测定来自两种碳酸盐岩储层(南部和北部)接触区的钙钛矿的 U-Pb 同位素组成以及分离储层的jacupirangite热电离质谱 (ID-TIMS)。来自北部碳酸盐岩储量的钙钛矿的 LA-ICPMS 和 ID-TIMS 数据非常一致,产生206 Pb/ 238U 年龄分别为 250.4 ± 1.1 Ma 和 249 ± 2 Ma。这些年龄也在来自 jacupirangites (250 ± 1 Ma) 的钙钛矿的 ID-TIMS 结果的分析不确定性之内。来自南部碳酸岩储量的钙钛矿的 LA-ICPMS 结果表明其年龄稍大(255.3 ± 2.4 Ma),这意味着小体积地幔岩浆作用可能早于西伯利亚洪水玄武岩喷发。252–251 马。这一解释得到了西伯利亚东部其他地方洪水前岩浆作用的报告的支持。通过 ID-TIMS 分析来自 Southern 原料和交代黄黄沸石之间接触的红霞石晶体。这些测量结果是不确定的 (247 ± 6 Ma),不能用于进一步限制复合体南部碳酸盐岩岩浆作用的时间。

更新日期:2021-08-13
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