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

地壳的演化：实验和实地研究

• 批准号: 46751-2011
• 负责人: Chacko, Thomas
• 金额: $ 2.04万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2013
• 资助国家: 加拿大
• 起止时间: 2013-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=521822
• 关键词: Evolution; earth; crust; experimental; field

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.

地球的大陆地壳和海洋地壳，在太阳系中是独一无二的，在地球的岩石圈、大气圈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，解决地壳演化的主题。项目1涉及实验室实验，旨在了解构成太古代（> 25亿年）大陆地壳很大一部分的花岗岩成分火成岩的成因。人们普遍认为，花岗质岩浆是由大洋地壳中硅含量较低的岩石部分熔融而产生的。迄今为止所做的实验工作主要集中在玄武岩的部分熔融上，类似于现代洋壳中存在的玄武岩。然而，由于早期地球的温度较高，太古代的洋壳可能更富含镁。因此，研究富镁玄武岩而不是标准玄武岩的部分熔融的实验与太古代地壳演化问题更相关。我打算进行这样的实验，并记录矿物的化学成分和其中产生的熔体。在项目2中，我建议调查加拿大地盾的> 40亿年的古陆片麻岩。该项目旨在确定这些岩石的主要元素、微量元素和氧同位素组成，并利用这些数据了解这一最古老的保存大陆地壳的形成过程。项目3涉及碳的重稳定同位素13C严重贫化的钻石的起源。已经提出了各种模型来解释这种金刚石，包括表明这些金刚石中的碳是地壳起源的模型（即，有机碳），这是从表面采取了很大的深度，由构造过程。为了评估这些模型，我建议进行实验，将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。