Evolution of earth's crust: experimental and field based studies

地球的陆壳和洋壳在太阳系中是独一无二的，在地球岩石圈、大气层和生物圈的演化中发挥了核心作用。地壳在地球历史早期形成和稳定的机制一直是地质科学中悬而未决的问题之一。在这项申请中，我提出了三条研究路线，以解决地壳演化的主题。项目1包括实验室实验，旨在了解花岗岩成分火成岩的成因，这些火成岩构成太古代(&GT；25亿年前)大陆地壳的一大部分。人们普遍认为，花岗岩浆是通过洋壳中发现的更少二氧化硅的岩石部分熔融而产生的。到目前为止所做的实验工作主要集中在玄武岩的部分熔融上，这与现代洋壳中存在的类似。然而，由于早期地球的温度较高，太古宙洋壳很可能明显更富镁。因此，研究富镁玄武岩的部分熔融而不是标准玄武岩的部分熔融，将与太古宙地壳演化问题更相关。我建议进行这样的实验，并记录其中产生的矿物和熔体的化学成分。在项目2中，我提议对加拿大盾的40亿年前的Acasta片麻岩进行研究。该项目旨在确定这些岩石的常量元素、微量元素和氧同位素组成，并利用这些数据来了解这一最古老的保存下来的大陆地壳的形成过程。项目3涉及碳的重稳定同位素13C中严重贫化的钻石的来源。人们提出了各种模型来解释这类钻石，包括一种模型，该模型表明这些钻石中的碳来自地壳(即有机碳)，它是通过构造作用从地表带到深处的。为了评估这些模型，我建议进行实验，定量地确定钻石和最常见的钻石生长介质碳酸盐熔体之间的碳同位素分配。

Earth's continental and oceanic crust, the combination of which is unique in the solar system, has played a central role in the evolution of the planet's lithosphere, atmosphere, and biosphere. The mechanisms by which this crust formed and stabilized early in Earth history remains one of the outstanding questions in the geological sciences. In this application, I propose three lines of research that address the topic of crustal evolution. Project 1 involves laboratory experiments aimed at understanding the genesis of granitic composition igneous rocks that make up a large fraction of Archean (>2.5 billion year old) continental crust. There is wide agreement that granitic magmas are produced through partial melting of the more silica-poor rocks found in oceanic crust. Experimental work done to date has focused on the partial melting of basaltic rocks, similar to those present in modern-day oceanic crust. However, because of higher temperatures in the early Earth, it is likely that Archean oceanic crust was significantly more magnesium-rich. Thus, experiments investigating the partial melting of Mg-rich basalts rather than standard basalts would be more relevant to the issue of Archean crustal evolution. I propose to conduct such experiments and document the chemical compositions of minerals and melts produced therein. In project 2, I propose to investigate the >4.0 billion year old Acasta gneisses of the Canadian Shield. The project aims to determine the major-element, trace-element and oxygen isotope composition of these rocks and use these data to understand the processes responsible for the formation of this most ancient of preserved continental crust. Project 3 relates to the origin of diamonds that are strongly depleted in 13C, the heavy stable isotope of carbon. A variety of models have been proposed to account for such diamonds, including a model suggesting that the carbon in these diamonds is of crustal origin (i.e., organic carbon), which was taken from the surface to great depth by tectonic processes. To evaluate these models, I propose to conduct experiments that will determine quantitatively the carbon isotope partitioning between diamond and the most common diamond growth medium, carbonate melt.