The coupled Hf-Nd isotope record of the early Earth in the Pilbara Craton
The coupled Hf-Nd isotope record of the early Earth in the Pilbara Craton
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皮尔巴拉克拉通早期地球的 Hf-Nd 耦合同位素记录
DOI：
10.1016/j.epsl.2021.117139
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发表时间：
2021
影响因子：
5.3
通讯作者：
Roberts, N.
中科院分区：
文献类型：
--
作者：
Salerno, R.;Vervoort, J.;Fisher, C.;Kemp, A.;Roberts, N.
地球最古老岩石的初始Hf和Nd同位素组成提供了地球在其早期历史中分化为富集地壳和亏损地幔储层的重要信息。然而，全球大多数的始新世-古太古代岩石的同位素组成似乎是解耦的：初始Hf同位素组成，确定的锆石，是广泛的变质，变化不大;初始Nd同位素的散装岩石，相反，是高度可变的超和亚变质组成。大多数这些研究是从多变质岩石的同位素系统的干扰的潜力是高的。这是特别真实的Sm-Nd系统，更容易改变稀土丰富的副相是这些元素的主要repositorses. To更好地了解壳幔演化在太古代，并解决Hf和Nd同位素的问题，我们研究了一套保存完好的古太古代花岗岩从皮尔巴拉盆地。该方法综合了锆石的初始Hf同位素组成和U-Pb年龄、钛铁矿和磷灰石的初始Nd同位素组成以及钛铁矿的激光烧蚀劈流（LASS）U-Pb年龄。锆石和钛铁矿的U-Pb数据产生的结晶年龄为3.47至3.28 Ga，在很好的协议，结合磷灰石-钛铁矿-WR Sm-Nd等时线年龄的每个样品，表明U-Pb和Sm-Nd系统没有被修改，因为岩浆结晶。所有样品中锆石的初始Hf同位素组成均为广泛的蓝绿色，εHf（i）值为−0.3 ~+0.8，与块体岩石Hf一致。钛铁矿和磷灰石的初始Nd同位素组成也是广泛的钙钛矿（εNd（i）钛铁矿，−1.0 - +2.0;磷灰石，-0.6- +0.9），并与块体岩石的Nd同位素组成（εNd（i）= +0.2 ~+1.2）和由钛磷灰石WR等时线确定的初始143 Nd/144 Nd比值（εNd（i）-0.9 ~+1.3）一致从这些数据中，我们得出两个基本的观察结果。首先，在这项研究中的花岗岩是来自于一个源，这是相对于Hf和Nd同位素从3.47至3.28 Ga，无论是系统支持存在一个强烈的亏损地幔或富集地壳源。第二，皮尔巴拉样品中的Lu-Hf和Sm-Nd同位素体系完全一致。这与高变质级别的始新世-古太古代岩石的记录形成鲜明对比，在那里Hf和Nd同位素组成已经“解耦”。这进一步强调了认识高级变质作用对Sm-Nd大块岩石记录的潜在影响的重要性。这里采取的综合年龄同位素的方法说明了一种方法来评估整体岩石Nd同位素数据的完整性，通过检查的Sm-Nd同位素系统的LREE丰富的副矿物在岩石中。
Initial Hf and Nd isotope compositions of Earth's oldest rocks provide essential information on the differentiation of the Earth into enriched crustal and depleted mantle reservoirs in its early history. The majority of Eo-Paleoarchean rocks worldwide, however, have isotope compositions that appear to be decoupled: initial Hf isotope compositions, determined on zircon, are broadly chondritic with little variation; initial Nd isotopes on bulk rocks, in contrast are highly variable with both supra- and sub-chondritic compositions. Most of these studies are from polymetamorphic terranes where the potential for disturbance of the isotope system is high. This is particularly true for the Sm-Nd system where more easily altered REE-rich accessory phases are the major repositories for these elements.In order to better understand crust-mantle evolution during the Archean—and to address the issue of Hf and Nd isotope decoupling—we examine a suite of well-preserved Paleoarchean granites from the Pilbara Craton. Our approach integrates the initial Hf isotope composition and U-Pb ages of zircon, the initial Nd isotope compositions of titanite and apatite, and U-Pb ages of titanite by laser ablation split stream (LASS) analysis. The zircon and titanite U-Pb data yield crystallization ages of 3.47 to 3.28 Ga, in good agreement with the combined apatite-titanite-WR Sm-Nd isochron ages of each sample, demonstrating that both the U-Pb and Sm-Nd systems have not been modified since igneous crystallization. The initial Hf isotope compositions of zircon from all samples are broadly chondritic withεHf(i)values of −0.3 to +0.8, in agreement with the bulk-rock Hf. The initial Nd isotope compositions of the titanite and apatite are also broadly chondritic (εNd(i)titanite, −1.0 – +2.0; apatite, −0.6 – +0.9) and agree with the Nd isotope composition of the bulk-rock (εNd(i)= +0.2 to +1.2) and the initial143Nd/144Nd ratios determined from the titanite-apatite-WR isochrons (εNd(i)−0.9 to +1.3).From these data, we make two fundamental observations. First, the granites in this study were derived from a source that was chondritic with respect to both Hf and Nd isotopes from 3.47 to 3.28 Ga; neither system supports the presence of either a strongly depleted mantle or enriched crustal source. Second, the Lu-Hf and Sm-Nd isotope systems in the Pilbara samples are in full agreement. This stands in stark contrast to the record of rocks from Eo-Paleoarchean terranes of higher metamorphic grade, where the Hf and Nd isotope compositions have been “decoupled”. This further underscores the importance of recognizing potential effects of high-grade metamorphism on the Sm-Nd bulk-rock record. The integrated age-isotope approach taken here illustrates a way to assess the integrity of bulk-rock Nd isotope data through examination of the Sm-Nd isotope systematics of the LREE-rich accessory minerals in rocks.
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影响因子：
5.3
作者：
Hasenstab, E.;Tusch, J.;Muenker, C.
通讯作者：
Muenker, C.
西澳大利亚皮尔巴拉克拉通太古代北皮尔巴拉地形的地质和构造演化
DOI：
--
发表时间：
2002
期刊：
影响因子：
--
作者：
M. V. Kranendonk;A. Hickman;R. H. Smithies;D. Nelson;G. Pike
通讯作者：
G. Pike
影响因子：
5
作者：
J. Elis Hoffmann;C. Münker;A. Polat;S. König;K. Mezger;M. Rosing
通讯作者：
J. Elis Hoffmann;C. Münker;A. Polat;S. König;K. Mezger;M. Rosing
西澳大利亚皮尔巴拉地块太古宙 Talga-Talga 亚群的年龄和地幔的早期演化：新的 SmNd 同位素证据
影响因子：
5.3
作者：
G. Gruau;B. Jahn;A. Glikson;R. Davy;A. Hickman;C. Chauvel
通讯作者：
C. Chauvel
影响因子：
3.8
作者：
Gardiner, Nicholas J.;Hickman, Arthur H.;Zhao, Jian-Xin
通讯作者：
Zhao, Jian-Xin