U-Pb and Lu-Hf isotope systematics of zircons from the Mississippi River sand: Implications for reworking and growth of continental crust
U-Pb and Lu-Hf isotope systematics of zircons from the Mississippi River sand: Implications for reworking and growth of continental crust
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DOI：
10.1130/g21427.1
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发表时间：
2005-06-01
期刊：
影响因子：
5.8
通讯作者：
Maruyama, S
中科院分区：
文献类型：
--
作者：
Iizuka, T;Hirata, T;Maruyama, S
我们进行了原位U-Pb和Lu-Hf同位素分析的碎屑锆石从密西西比河，以了解地壳改造和大陆生长速度。对416个锆石的U-Pb分析表明，2.8- 2.6Ga、1.8- 0.9Ga和0.2Ga以后是地壳形成的三个高峰期。在402个测年锆石中获得了初始Hf同位素比值，只有8%的锆石Hf（T）DM值小于-2.5。这些数据对应的地壳停留时间小于1.2亿年。这一发现表明，地壳改造是大陆地壳形成过程中一个非常重要的过程。Hf（T）DM）的丰度表明，在2.5- 2.0Ga和0.9Ga以后，改造作用占主导地位，而在2.0 ~ 1.6Ga之间，新生地壳形成作用占主导地位。我们计算了地幔提取模型年龄来估计大陆的生长速率。大约有一半的颗粒模型年龄在2.0和1.3 Ga之间，表明在这段时间内地壳的快速增长。大陆的生长速率表明，源区中15%和78%的地壳分别由2.5和1.3Ga形成。
We carried out in situ U-Pb and Lu-Hf isotope analyses of detrital zircons from the Mississippi River in order to understand crustal reworking and continental growth rates. The U-Pb analyses for 416 zircons reveal three major peaks of crust formation at 2.8-2.6 Ga, 1.8-0.9 Ga, and after 0.2 Ga. Initial Hf isotope ratios were obtained for 402 of the dated zircons, and only 8% of the zircons have epsilon(Hf(T)DM) values less negative than -2.5. These data correspond to a crustal residence time of < 120 m.y. This finding indicates that crustal reworking was a very important process in continental crust formation. The epsilon(Hf(T)DM) population demonstrates that reworking was predominant at 2.5-2.0 Ga and after 0.9 Ga, whereas juvenile crust formation dominated between 2.0 and 1.6 Ga. We calculated the mantle-extraction model ages to estimate the continental growth rate. Approximately half of the grains have model ages between 2.0 and 1.3 Ga, indicating rapid crustal growth during this time. The continental growth rate suggests that 15% and 78% crust in the source region of the zircons formed by 2.5 and 1.3 Ga, respectively.