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

地球的大陆地壳和海洋地壳的结合在太阳系中是独一无二的，它们在地球岩石圈、大气和生物圈的演化中发挥了核心作用。这个地壳在地球历史早期形成和稳定的机制仍然是地质科学中悬而未决的问题之一。在这个应用程序中，我提出了三条研究路线，以解决地壳演化的主题。项目一涉及实验室实验，旨在了解构成太古宙（距今25亿年前）大陆地壳大部分的花岗质组成火成岩的成因。人们普遍认为，花岗岩岩浆是由在海洋地壳中发现的硅含量较低的岩石的部分熔融产生的。迄今为止所做的实验工作主要集中在玄武岩的部分融化上，类似于现代海洋地壳中存在的玄武岩。然而，由于地球早期温度较高，太古代海洋地壳很可能富含更多的镁。因此，研究富镁玄武岩的部分熔融而不是标准玄武岩的实验，对太古宙地壳演化问题更有意义。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，我提议对加拿大地盾的40亿年前的阿卡斯塔片麻岩进行研究。该项目旨在确定这些岩石的主元素、微量元素和氧同位素组成，并利用这些数据来了解这个保存最古老的大陆地壳形成的过程。项目3与钻石的来源有关，这些钻石在13C（碳的重稳定同位素）中被严重耗尽。人们提出了各种各样的模型来解释这类钻石，其中一个模型表明，这些钻石中的碳是地壳起源的（即有机碳），这些碳是通过构造过程从地表带到深处的。为了评估这些模型，我建议进行实验，定量确定金刚石和最常见的金刚石生长介质（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.