Dating the termination of the Palaeoproterozoic Lomagundi-Jatuli carbon isotopic event in the North Transfennoscandian Greenstone Belt
Dating the termination of the Palaeoproterozoic Lomagundi-Jatuli carbon isotopic event in the North Transfennoscandian Greenstone Belt
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DOI：
10.1016/j.precamres.2012.09.010
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发表时间：
2013
影响因子：
3.8
通讯作者：
Adam P. Martin;D. Condon;A. Prave;V. Melezhik;A. Lepland;A. Fallick
中科院分区：
文献类型：
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作者：
Adam P. Martin;D. Condon;A. Prave;V. Melezhik;A. Lepland;A. Fallick
现有的放射性同位素年龄约束表明，全球古元古代Lomagundi-Jatuli碳酸盐碳同位素大幅度正偏移（δ 13 C>+5‰）发生在2.2 ~ 2.06Ga之间。在俄罗斯西北部科拉半岛、挪威北方和芬兰的北外芬斯堪的纳维亚绿岩带，在Imandra-Varzuga和佩琴加绿岩带的Umba和Kuetsjärvi沉积组的碳酸盐岩中记录了Lomagundi-Jatuli事件。在这两个地区，厚的镁铁质火山单位（Umba和Kuetsjärvi火山组）覆盖在含碳同位素的沉积单位之上。上覆和较年轻的沉积单元含有碳酸盐岩，δ 13 C值通常介于c. -1和+3‰，标志着Lomagundi-Jatuli短途旅行的结束。两个新的U-Pb ID-TIMS（同位素稀释热电离质谱）锆石年龄限制这两个序列的终止。Il'mozero沉积地层的下部单元是一个交叉和平行层状的火山灰杂砂岩，主要来源于下层Umba火山地层的侵蚀。它产出的碎屑锆石的207 Pb/206 Pb年龄为2055.5±2.3Ma，这是沉积的最大年龄，并被推断为下伏Umba火山岩的年龄。在佩琴加，Kolosjoki沉积层被ICDP（国际大陆科学钻探计划）支持的FAR-DEEP（芬诺斯堪的纳维亚北极俄罗斯钻探早期地球项目）钻探计划获得的钻孔覆盖。该岩芯中的镁铁质细凝灰岩的锆石获得207 Pb/206 Pb年龄为2056.6±0.8Ma。这个年龄被解释为喷发年龄与沉积作用同时发生。新的年龄测定在不确定性范围内相互重叠，并且与先前发表的Kolosjoki沉积地层的碎屑锆石年龄2058± 2 Ma和Kuetsjärvi火山地层的2049± 28 Ma的误差范围内。综合起来，这表明Lomagundi-Jatuli漂移在2056.6±0.8Ma结束于芬诺斯坎迪亚，可能与芬诺斯坎迪亚和南非德兰士瓦的相似终止年龄相关。
Existing radio-isotopic age constraints indicate that the global Palaeoproterozoic Lomagundi-Jatuli large, positive carbonate carbon isotopic excursion, with δ13C values >+5‰, occurred between 2.2 and 2.06Ga. In the North Transfennoscandian Greenstone Belt of the Kola Peninsula, NW Russia, northern Norway and Finland, the Lomagundi-Jatuli Event is recorded in the carbonate rocks of the Umba and Kuetsjärvi Sedimentary Formations in the Imandra-Varzuga and Pechenga greenstone belts. In both areas, thick mafic volcanic units (Umba and Kuetsjärvi Volcanic Formations) overlie the carbon isotopic excursion-bearing sedimentary units. Overlying and younger sedimentary units contain carbonate rocks with δ13C values typically ranging between c. −1 and +3‰, signalling the termination of the Lomagundi-Jatuli excursion. Two new U–Pb ID-TIMS (isotope-dilution thermal ionisation mass spectrometry) zircon dates constrain this termination in both successions. The lower unit of the Il’mozero Sedimentary Formation is a cross- and parallel-bedded volcaniclastic greywacke derived largely from erosion of the underlying Umba Volcanic Formation. It has yielded detrital zircons with207Pb/206Pb dates as young as 2055.5±2.3Ma, which is a maximum age for deposition and is inferred to date part of the underlying Umba volcanics. In Pechenga, the Kolosjoki Sedimentary Formation was intersected by a drill hole obtained by the ICDP (International Continental Scientific Drilling Program)-supported FAR-DEEP (Fennoscandian Arctic Russia-Drilling Early Earth Project) drilling programme. Zircons from a mafic fine tuff in this drill core have yielded a207Pb/206Pb age of 2056.6±0.8Ma. This age is interpreted as an eruption age contemporaneous with sedimentation. The new age determinations overlap each other within uncertainty, and is within error of previously published detrital zircon ages of 2058±2Ma from the Kolosjoki Sedimentary Formation and 2049±28Ma from the Kuetsjärvi Volcanic Formation. Combined, these indicate that the Lomagundi-Jatuli excursion terminated across Fennoscandia by 2056.6±0.8Ma and may correlate with similar termination ages in Fennoscandia and the Transvaal, South Africa.