The K/U ratio of the silicate Earth: Insights into mantle composition, structure and thermal evolution
The K/U ratio of the silicate Earth: Insights into mantle composition, structure and thermal evolution
复制标题
DOI：
10.1016/j.epsl.2008.12.023
复制
发表时间：
2009-02-25
影响因子：
5.3
通讯作者：
Luong, Mario
中科院分区：
文献类型：
--
作者：
Arevalo, Ricardo, Jr.;McDonough, William F.;Luong, Mario
硅酸盐地球中K的丰度控制着地球内部的组成、地幔对流的主导模式、行星的热演化以及地核中Pb的浓度。由于K在吸积过程中作为挥发性物质，硅酸盐地球的K含量被确定为陆地K/U比的函数。对来自大西洋、印度洋和太平洋的MORB（包括正常型和富集型样本）的全面检查显示，复合MORB源K/U比为19，000 +/- 2600（2 sigma）。相比之下，洋岛玄武岩和平均大陆地壳的平均K/U值分别为11，900 +/- 2200和13.000 +/- 3000。这些储层的贡献率确定硅酸盐土的K/U比为13，800 +/- 2600（2 σ），相当于硅酸盐土中的280 +/- 120 μ g/g K。因此，该行星的对流Urey比被验证为近似0.34，这表明在考虑了穿过核幔边界的潜在热通量后，目前的地幔冷却速率为70-130 K Gyr（-1）。此外，地球的放射性热流和Ar-40的收支平衡需要一个富含放射性元素的下地幔储层。这里确定的整体地球Pb/U比近似于85，表明整体地球中的Pb近似于1200纳克/克，而地核中的Pb>= 3300纳克/克。(c)2008 Elsevier B. V.保留所有权利。
The abundance of K in the silicate Earth provides control on the composition of the Earth's interior, the dominant mode of mantle convection, the thermal evolution of the planet, and the concentration of Pb in the core. Because K acts as a volatile species during accretion, the K content of the silicate Earth is determined as a function of the terrestrial K/U ratio. A comprehensive examination of MORB from the Atlantic, Indian and Pacific oceans, including both normal- and enriched-type samples, reveals a composite MORB source K/U ratio of 19,000 +/- 2600 (2 sigma). In comparison, ocean island basalts and average continental crust have average K/U values of 11,900 +/- 2200 and 13.000 +/- 3000, respectively. The fractional contributions of these reservoirs establishes the K/U ratio of the silicate Earth to be 13,800 +/- 2600 (2 sigma), equating to 280 +/- 120 mu g/g K in the silicate Earth. As a result, the planet's convective Urey ratio is verified to be similar to 0.34, which indicates a current mantle cooling rate of 70-130 K Gyr(-1) after taking into account potential heat flux across the core-mantle boundary. Additionally, the Earth's balance of radiogenic heat flow and budget of Ar-40 necessitate a lower mantle reservoir enriched in radioactive elements. The bulk Earth Pb/U ratio, determined here to be similar to 85, suggests similar to 1200 ng/g Pb in the bulk Earth and >= 3300 ng/g Pb in the core. (c) 2008 Elsevier B.V. All rights reserved.