Tracing the plate tectonic cycle, mantle composition and convection history of the Earth using super-deep diamonds.

使用超深钻石追踪地球的板块构造循环、地幔成分和对流历史。

• 批准号: RGPIN-2020-04154
• 负责人: Pearson, David
• 金额: $ 9.32万
• 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: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=750909
• 关键词: Tracing; plate; tectonic; cycle; mantle

Whereas seismology provides an image of the gross structure of the whole Earth, the only available samples of Earth's deep interior - the asthenosphere, transition zone and lower mantle - with which to validate its composition and investigate deep plate subduction, are provided by a class of diamonds known as "super-deep diamonds", that are distinct from those that occur in the lithosphere, Earth's solid outer shell, because they sample the convecting deep mantle. The unique view of the mantle offered by super-deep diamonds allow fundamental questions about the Earth to be addressed such as: How deep do oceanic plates subduct? How far are recycled water and carbon carried into the mantle? What is the composition of the lower mantle? Is there is a signature of core extraction in Earth's mantle? These and other questions will be addressed here using the stable isotopic fingerprints of some of Earth's most abundant elements; Si, Mg and Fe. Stable isotope ratios - the ratios of light and heavy atoms of an element, are controlled by temperature, pressure and mineral structure/chemistry as well as fluid-rock exchange. As such they are powerful tracers of  the interaction between Earth's crust and mantle via plate tectonics. This proposal will create a new framework, verified by high pressure experiments, to be used as a roadmap to show how Si, Mg and Fe isotopes are fractionated between the different minerals that characterise the key parts of the mantle - the asthenosphere, transition zone and lower mantle.  The results will illustrate how plate tectonics and convection of the mantle have redistributed the main elements and their isotopes that comprise our solid Earth. They will yield new direct data on the lower mantle (>670 km), inaccessible other than from diamond inclusions. They will allow us to quantify the exchange between upper and lower mantle, in the search for "primordial regions" untouched by plate subduction. They will allow new, more accurate bounds to be placed on the Bulk Silicate Earth that will, in turn, allow us to quantify key details of the composition of Earth's core. They will illuminate our knowledge of how, and in what components, subducted oceanic slabs cycle volatiles to the deepest parts of the mantle. The data produced will allow new constraints to be placed on the mechanisms and depth of element cycling.  The results will be of  interest to the diamond exploration industry who currently seek methods to enable the early identification - at the exploration and evaluation phase - of deposits that contain large, high-value super-deep gem diamonds. The project will produce a diverse cohort of young researchers trained in cross-disciplinary analytical and experimental techniques with skills relevant to Canada's diamond industry.

虽然地震学提供了整个地球的总体结构的图像，但唯一可用的地球深层--软流圈、过渡带和下地幔--的样本是由一类被称为“超深钻石”的钻石提供的，这些钻石被称为“超深钻石”，不同于出现在岩石圈中的钻石，岩石圈是地球的坚固外壳，因为它们对对流的深层地幔进行采样。由超深钻石提供的地幔的独特视角使人们能够解决有关地球的基本问题，例如：海洋板块俯冲多深？回收水和碳被带到地幔中的距离有多远？下地幔的成分是什么？地幔中有没有地核提取的迹象？这些问题和其他问题将在这里使用地球上一些最丰富的元素：硅、镁和铁的稳定同位素指纹来解决。稳定同位素比率--元素中轻原子和重原子的比率，受温度、压力、矿物结构/化学以及流体-岩石交换的控制。因此，它们是地壳和地幔之间通过板块构造相互作用的强有力的示踪物。这一提议将创建一个经过高压实验验证的新框架，作为路线图，显示硅、镁和铁同位素如何在表征地幔关键部分-软流层、过渡带和下地幔的不同矿物之间进行分馏。结果将说明板块构造和地幔对流如何重新分配构成我们固体地球的主要元素及其同位素。它们将在下地幔(&gt；670公里)产生新的直接数据，除了钻石包裹体之外，无法获得这些数据。它们将使我们能够量化上地幔和下地幔之间的交换，以寻找未被板块俯冲触及的“原始区域”。它们将允许对大量硅酸盐地球施加新的、更准确的界限，进而使我们能够量化地球核心组成的关键细节。它们将阐明我们关于俯冲的大洋板块如何以及在哪些成分中循环挥发到地幔最深处的知识。产生的数据将允许对元素循环的机制和深度施加新的限制。这些结果将引起钻石勘探行业的兴趣，他们目前正在寻找方法，以便在勘探和评估阶段及早识别包含大型、高价值超深宝石钻石的矿床。该项目将培养一批接受跨学科分析和实验技术培训的年轻研究人员，并掌握与加拿大钻石业有关的技能。