Emergence of modern continental crust about 3 billion years ago
Emergence of modern continental crust about 3 billion years ago
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DOI：
10.1038/ngeo2466
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发表时间：
2015-07-01
影响因子：
18.3
通讯作者：
Hawkesworth, Chris J.
中科院分区：
文献类型：
--
作者：
Dhuime, Bruno;Wuestefeld, Andreas;Hawkesworth, Chris J.
大陆地壳是过去44亿年地球状况的主要记录(1，2)。然而，大陆地壳如何随着时间的推移形成和演化仍然存在极大的争议(3，4)。特别是，年轻大陆地壳的成分和厚度尚不清楚。这里我们表明，Rb/Sr比值可以作为反映陆壳二氧化硅含量和厚度的指标。我们计算了13,000多个样品的年轻地壳的Rb/Sr比值，其模式年龄范围从海甸到显生宙。这些比值是根据从T-DM-ND模式年龄到分析样品结晶之间的锶同位素演化来计算的。我们发现，在地球演化的前15亿年里，年轻地壳的二氧化硅含量很低，大部分成分是镁铁质的，这与板块前构造行星上的岩浆作用一致。大约30亿年前，年轻陆壳的Rb/Sr比值增加，表明新形成的地壳变得更富硅，可能更厚。这种转变反过来又与板块构造的开始(5)和大陆碎屑进入海洋的增加(6)有关。
The continental crust is the principal record of conditions on the Earth during the past 4.4 billion years(1,2). However, how the continental crust formed and evolved through time remains highly controversial(3,4). In particular, the composition and thickness of juvenile continental crust are unknown. Here we show that Rb/Sr ratios can be used as a proxy for both the silica content and the thickness of the continental crust. We calculate Rb/Sr ratios of the juvenile crust for over 13,000 samples, with Nd model ages ranging from the Hadean to Phanerozoic. The ratios were calculated based on the evolution of Sr isotopes in the period between the T-DM Nd model age and the crystallization of the samples analysed. We find that the juvenile crust had a low silica content and was largely mafic in composition during the first 1.5 billion years of Earth's evolution, consistent with magmatism on a pre-plate tectonics planet. About 3 billion years ago, the Rb/Sr ratios of the juvenile continental crust increased, indicating that the newly formed crust became more silica-rich and probably thicker. This transition is in turn linked to the onset of plate tectonics(5) and an increase of continental detritus into the oceans(6).