[论文解读] Geochemistry of U and Th and its Influence on the Origin and Evolution of the Crust of Earth and the Biological Evolution

Xuezhao Bao, Ali Zhang|ArXiv.org|Jun 7, 2007

Geological and Geochemical Analysis参考文献 3被引用 5

一句话总结

该论文提出，铀（U）和钍（Th）独特的地球化学特性——特别是其通过氧化性挥发分和水的迁移——使得地球地幔中形成了一个富集区（EZ），从而驱动了板块构造和大陆地壳的形成。这一过程在水星、金星和火星上均不存在，原因在于这些行星缺乏水和氧化剂，而该过程所提供的持续内部热量则影响了地球上生命起源与演化的进程。

ABSTRACT

We have investigated the migration behaviors of uranium (U) and thorium (Th) in Earth and other terrestrial planets. Theoretical models of U and Th migration have been proposed. These models suggest that the unique features of Earth are closely connected with its unique U and Th migration models and distribution patterns. In the Earth, U and Th can combine with oxidative volatile components and water, migrate up to the asthenosphere position to form an enrichment zone (EZ) of U and Th first, and then migrate up further to the crusts through magmatism and metamorphism. We emphasize that the formation of an EZ of U, Th and other heat-producing elements is a prerequisite for the formation of a plate tectonic system. The heat-producing elements, currently mainly U and Th, in the EZ are also the energy sources that drive the formation and evolution of the crust of Earth and create special granitic continental crusts. In other terrestrial planets, including Mercury, Venus, and Mars, an EZ can not be formed because of a lack of oxidative volatile components and water. For this reason, a plate tectonic system can not been developed in these planets. We also emphasize the influence of U and Th in EZ on the development and evolution of life on Earth. We propose that since the Earth and planets were born in a united solar system, there should be some common mechanisms to create the similarities and differences between them. We have tried to develop an integrated view to explain some problems in the tectonics of Earth and evolution, bio-evolution, and planetary dynamics through U and Th geochemistry. We believe that a comprehensive exploration on energy sources and their evolution is a good way to build bridges between different disciplines of science in order to better understand the Earth and planets.

研究动机与目标

• 理解铀和钍地球化学在塑造地球地壳和构造演化中的作用。
• 解释为何板块构造仅在地球而非其他类地行星中发展。
• 探讨地球地幔中生热元素与生命起源之间的联系。
• 通过统一的地球化学框架整合地球物理学、行星科学与进化生物学。
• 建立一个将铀和钍迁移与行星分异及地壳演化相联系的机制模型。

提出的方法

• 对行星内部铀和钍迁移路径进行理论建模。
• 分析铀和钍在不同氧化还原及挥发性条件下的地球化学行为。
• 对比地球与水星、金星和火星的地球化学环境。
• 模拟由铀和钍富集引发的地幔上涌与地壳形成过程。
• 利用质量平衡与热力学约束，模拟岩石圈软流圈与地壳中元素的迁移性。
• 整合地质学、地球化学与生物学数据，评估内热与生物圈演化之间的反馈关系。

实验结果

研究问题

• RQ1 铀和钍在地球与其他类地行星之间的迁移模式有何不同？
• RQ2 水和氧化性挥发分的存在在行星地幔中形成铀和钍富集区的过程中起什么作用？
• RQ3 为何板块构造仅在地球上发展，而未在水星、金星或火星上出现？
• RQ4 地球地幔中铀和钍富集区的形成如何促进地壳形成与构造活动？
• RQ5 地球内部铀和钍释放的热量与生命演化之间存在何种联系？

主要发现

• 地球独特的水和氧化性挥发分组合使铀和钍能够向上迁移，并在岩石圈软流圈中形成一个产热富集区（EZ）。
• 该EZ的形成是地球发展板块构造系统的先决条件。
• 相比之下，水星、金星和火星缺乏足够的水和氧化剂，无法形成EZ，因而抑制了板块构造的发展。
• EZ中铀和钍释放的热量驱动地幔对流、地壳上涌以及花岗质大陆地壳的形成。
• 铀和钍提供的持续内部热量被提出为长期地质活动和生命演化有利条件的关键因素。
• 该研究提出了一种统一的地球化学机制，将太阳系内侧行星的分异、构造活动与生物圈发展联系起来。