Origin and Evolution of Silicate Reservoirs in the Early Earth

地球历史的前20亿年可以说是地球存在的最重要时期。在这一时期发生的过程有效地决定了宇宙中这个最初炎热而不适宜居住的地方是如何变成我们现在的宜居世界的。陆地历史通常是从地质记录中破译出来的。由于地球的动态特性，自地球诞生以来，它的表面就周期性地恢复活力。因此，在现代幔源性岩石中观测到的同位素和化学非均质性主要反映了与大陆和海洋地壳的产生和再循环有关的地质过程；这些可能与原始地幔分化过程无关。早期的地质记录，特别是4.5到2.5 Ga之间的地质记录，最有可能收集到有关地球起源和早期演化的信息。通过短寿命和长寿命核素的放射性衰变在早期硅酸盐储层中产生的同位素特征已被早期陆地岩浆（如科马岩样）取样，并保存在早期地壳岩石中。这些同位素特征可以用来限制这些现在可能已经消失的储层的形成时间和性质。它们还可以用来破译早期行星分化的历史，直到地球历史上地壳形成和再循环过程（类似于今天发生的过程）成为地球化学分化的主要驱动力的时候。室内。本研究项目旨在研究地球早期主要硅酸盐储层的成因和演化。本研究的主要目标是：(1)评估可能发生在地球历史前100 Ma的岩浆海洋过程是否记录在科马地岩系统的潜在深层地幔源中；(2)进一步验证Maier等人（2009）的假设，即在高亲铁元素（HSE）中存在可检测到的转变：(3)综合本文所研究的科马提岩系统和其他已得到充分研究的科马提岩系统的同位素和HSE丰度数据，将这些数据整合到形成这些科马提岩系统的早期陆相硅酸盐储层的起源和时间演化的可行模型中，并评估地球的混合时间。S地幔和晚期增生的时间。为了实现这些目标，将使用最先进的分析技术对全球5个科马地岩系统中的146,147Sm-142,143Nd, Lu-Hf， Pt-Re-Os和182Hf-182W同位素系统以及亲石微量元素和HSE丰度进行表征和解释，这些系统跨越了地球历史上约3.5 Ga的时间间隔。这项研究将有助于澄清地球最早的历史，因此，将与长期争论的行星如何形成和演化的问题有关，并可能最终提高我们对现代地球的理解。一些预期的科学进步将是多达三名本科生参与的结果，作为他们所要求的高级研究论文工作的一部分，因此，为这些崭露头角的科学家未来的职业生涯提供了宝贵的培训。对这项研究的支持将有助于维持同位素地球化学实验室？美国的使命是在全球范围内分享和合作。拟议工作的结果将发表在经同行评审的科学期刊上，在专业会议和特邀讲座上发表，并在部门研讨会上进行讨论。外联工作还将包括来自三大洲的科学家之间的合作。

The first two billion years of terrestrial history arguably constitute the most important period of Earth's existence. Processes acting during this period effectively determined how this initially hot and inhospitable place in the universe became our present life-accommodating world. Terrestrial history is conventionally deciphered from the geological record. Due to the dynamic nature of Earth, its surface has been periodically rejuvenated from the time the planet was born. As a result, the isotopic and chemical heterogeneities observed in modern mantle-derived rocks primarily reflect processes associated with production and recycling of continental and oceanic crust through geological time; these likely bear no relation to primordial mantle differentiation processes. It is the early geological record, particularly between 4.5 and 2.5 Ga, from which information pertaining to the origin and early evolution of the Earth is most likely to be gleaned. Isotopic signatures created in early silicate reservoirs via radioactive decay of short- and long-lived nuclides have been sampled by early terrestrial magmas, such as komatiites, and preserved in early crustal rocks. These isotopic signatures can be used to constrain the timing of formation and the nature of these, now likely vanished, reservoirs. They can also be used to decipher the history of early planetary differentiation to the point in Earth history when crust formation and recycling processes, similar to those occurring today, took over as the main driver of chemical differentiation of the Earth?s interior. This research project is aimed at constraining the origin and evolution of major silicate reservoirs in the early Earth. The primary goals of the proposed research are: (1) to assess whether magma ocean processes that likely occurred within the first 100 Ma of Earth history are recorded in the potentially deep mantle sources of komatiite systems, (2) to further test the hypothesis of Maier et al. (2009) that there was a detectable transition in highly siderophile element (HSE: Re, Os, Ir, Ru, Pt, Pd) abundances in komatiites from the early to late Archean, and (3) to synthesize the isotopic and HSE abundance data for the komatiite systems examined here and other well-studied komatiite systems, integrating these data into viable models for the origin and temporal evolution of the early terrestrial silicate reservoirs contributing to these komatiite systems, and evaluate mixing times of the Earth?s mantle and the timing of late accretion. In order to achieve these goals, the 146,147Sm-142,143Nd, Lu-Hf, Pt-Re-Os, and 182Hf-182W isotope systematics and the lithophile trace and HSE abundances in five komatiite systems from around the globe, spanning a time interval of ca. 3.5 Ga in Earth history, will be characterized using state-of-the-art analytical techniques and interpreted. This study will help clarify the earliest history of Earth, and, therefore, will have relevance to the long-debated question of how planets form and evolve, and may ultimately improve our understanding of the modern Earth. Some of the expected scientific advances will be the result of involvement of up to three undergraduate students as part of their required senior research thesis work, thus, providing valuable training for the future careers of these budding scientists. Support for this research will help sustain the Isotope Geochemistry Laboratory?s mission to share and collaborate world-wide. The results of the proposed work will be published in peer-reviewed scientific journals, presented at professional conferences and invited lectures, and discussed at Departmental seminars. The outreach efforts will also include collaborations between scientists from three continents.