A legacy of Hadean silicate differentiation inferred from Hf isotopes in Eoarchean rocks of the Nuvvuagittuq supracrustal belt (Quebec, Canada)
A legacy of Hadean silicate differentiation inferred from Hf isotopes in Eoarchean rocks of the Nuvvuagittuq supracrustal belt (Quebec, Canada)
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DOI：
10.1016/j.epsl.2012.11.055
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发表时间：
2013-01
影响因子：
5.3
通讯作者：
M. Guitreau;J. Blichert‐Toft;S. Mojzsis;Antoine S. G. Roth;B. Bourdon
中科院分区：
文献类型：
--
作者：
M. Guitreau;J. Blichert‐Toft;S. Mojzsis;Antoine S. G. Roth;B. Bourdon
加拿大魁北克省北方Nuvvuagittuq表壳带（NSB）镁铁质和长英质岩石的Lu-Hf同位素年龄为3864± 70 Ma，与锆石U-Pb和全岩147 Sm-143 Nd年代学结果一致，但与约1000 Ma的年龄不一致。根据146 Sm-142 Nd计时器推断的4400 Ma年龄（O 'Neil et al.，2008年，2012年）。Lu-Hf结果被解释为NSB不同原地单元的平均侵位年龄。观测到的数据沿沿着Lu-Hf“散射时线”排列排除了NSB的冥古宙年龄，因为其同位素特征似乎受长期放射性向内生长的控制。NSB在Hadean的安置（例如，4362−54+ 35 Ma，如果使用Kinoshita等人（2012）的146 Sm衰变常数和O 'Neil等人的衰变常数，2008年的数据）应该会导致数亿年的年龄差异，表现为与Lu-Hf散射时的强烈偏差。在相同的NSB斜长角闪岩样品（贫钙斜长角闪岩和角闪石轴承）的组合Lu-Hf和Sm-Nd数据定义了一个混合双曲线在约。3800 Ma，端元组成代表了这些岩性的组成群（O 'Neil等人，2011年）。异常低的142 Nd/144 Nd值相对于散装硅酸盐地球是特有的一组岩石在NSB称为“低TiO 2”斜长角闪岩，这是由于一个古老的多阶段历史的地幔源。模拟结果表明，142 Nd/144 Nd亏损可能是在4510 Ma时，在一个先前分离的地幔区域内，由于再受精作用而产生的。
New Lu–Hf isotopic data for mafic and felsic rocks from the Nuvvuagittuq supracrustal belt (NSB) in northern Québec (Canada) yield an Eoarchean age of 3864±70Ma consistent with both zircon U–Pb and whole-rock147Sm–143Nd chronology, but in disagreement with ca. 4400Ma ages inferred from the146Sm–142Nd chronometer (O'Neil et al., 2008, 2012). The Lu–Hf result is interpreted as the mean emplacement age of the different autochthonous units of the NSB. An observed alignment of the data along a Lu–Hf “scatterchron” precludes a Hadean age for the NSB because its isotopic characteristics appear to be controlled by long-term radiogenic ingrowth. Emplacement of the NSB in the Hadean (e.g., 4362−54+35Ma if the decay constant of146Sm of Kinoshita et al. (2012) is used with the O'Neil et al., 2008 data) should instead have caused age differences of hundreds of millions of years to manifest as strong deviations from the Lu–Hf scatterchron. Combined Lu–Hf and Sm–Nd data on the same NSB amphibolite samples (Ca-poor cummingtonite- and hornblende-bearing) define a mixing hyperbola at ca. 3800Ma with end-member compositions representative of the compositional groups identified for these lithologies (O'Neil et al., 2011). Anomalously low142Nd/144Nd values relative to Bulk Silicate Earth are endemic to a group of rocks in the NSB termed “low-TiO2” amphibolites; this is attributable to an ancient multi-stage history of their mantle source. Modeling shows that the142Nd/144Nd deficits could have developed in response to a re-fertilization episode within a previously fractionated mantle domain at 4510Ma.