The dynamics of dyke injection during rifting - combining geodetic and seismic methodologies

裂谷过程中堤坝注入的动力学——结合大地测量和地震方法

• 批准号: NE/E013945/1
• 负责人: Derek Keir
• 金额: $ 28.53万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE013945%2F1
• 关键词: dynamics; dyke; injection; during; rifting

The upper few hundred kilometres of the earth is comprised of a jigsaw of tectonic plates that separate, collide, or slide past each other at plate boundaries in a process called plate tectonics. Separation of a plate along a boundary located within a continent can result in the division of the continent into two or more parts and eventual formation and growth of a new ocean basin. This is achieved through the addition of new material to the plate, sourced from partially molten magma deep below the surface, and added to the upper crust as near vertical walls of frozen magma called dykes. Therefore, the process by which dykes are emplaced at separating plate boundaries is fundamental to plate tectonics. However, the majority of such plate boundaries lie at the bottom of the Earth's major oceans, and obscured by several kilometers of overlying water. Due to a lack of observations, scientists do not know accurate details of how, where and when dyking actually occurs during plate separation. A tiny proportion of the boundaries between separating plates where dykes occurs are exposed above sea-level. Examples include Iceland, and Afar (Djibouti and Ethiopia). Previous observations show that dyke intrusion does not occur on a continuous basis, but is rather restricted to week, month, or year long episodes of repeated dyke intrusions that occur every couple thousand years. Dyking is generally accompanied by violent earthquakes, fracturing of the Earth's surface, and volcanic eruptions. However, only two dyke intrusions have been observed over the last century, and none since the advent of modern scientific instrumentation. We are therefore still not sure where the source of the molten rock that feeds dykes is located, and how and when molten rock moves within the earth during the formation of a dyke. These fundamental questions can only be answered by combining accurate observations of earthquakes with high resolution measurements of actual plate movements provided by modern global positioning systems and space borne satellites. In September 2005, the intrusion of a 60 km-long basalt dyke, up to 8 metres thick, occurred in the Afar rift, Ethiopia. The event was accompanied by a volcanic eruption and swarm of violent earthquakes over two weeks. I participated in an urgent response to deploy recording equipment in Afar to accurately measure earthquakes, the expansion and contraction of magma chambers beneath the active volcanoes, and measure the movement of the tectonic plates, in the knowledge that future dykes are likely to be emplaced. The extreme effort to acquire this unique data was rewarded in June 2006 when a second dyke (15 km long, 2 metres wide) was injected beneath the rift. I thus now have access to extraordinary data from a once in a generation dyke intrusion event to accurately probe how, when and where dyking occurs at separating plate boundaries. I will be able to accurately determine where the magma came from, when the magma moved within the earth, and how much magma was frozen into the plate as a vertical dyke. The results of my proposed study are of critical importance in improving our understanding of the general process of plate separation. In collaboration with first class scientists from Ethiopia, Iceland, USA and the U.K., I will learn new skills in processing, analyzing and interpreting scientific data while solving a fundamental question on how the Earth continues to evolve. The results of my proposed research will be invaluable to the Ethiopian government in understanding the volcanic and seismic hazards, and potential sources of geothermal energy associated with the spectacular geological features in Afar.

地球的上部几百公里是由板块组成的，这些板块在板块边界上分离、碰撞或滑动，这一过程称为板块构造。板块沿着位于大陆内部的边界分离，可导致大陆分裂为两个或两个以上部分，并最终形成和生长新的洋盆。这是通过向板块添加新物质来实现的，这些新物质来自地表深处的部分熔融岩浆，并作为称为岩墙的冻结岩浆的近垂直壁添加到上地壳。因此，岩墙在分离板块边界就位的过程是板块构造的基础。然而，大多数这样的板块边界位于地球主要海洋的底部，并被几公里的上覆水所掩盖。由于缺乏观测，科学家们不知道在板块分离过程中堤坝形成的确切细节。在形成岩墙的分离板块之间，有一小部分边界暴露在海平面之上。例子包括冰岛和阿法尔（吉布提和埃塞俄比亚）。以前的观察表明，堤坝入侵并不是连续发生的，而是仅限于每两千年发生一次的几周、几个月或几年的反复堤坝入侵。筑堤通常伴随着强烈的地震，地球表面的断裂和火山爆发。然而，在上个世纪，只观察到两次堤坝入侵，自从现代科学仪器出现以来，没有一次。因此，我们仍然不能确定供给岩脉的熔融岩石的来源在哪里，以及在岩脉形成期间熔融岩石如何以及何时在地球内部移动。这些基本问题只能通过将对地震的精确观测与现代全球定位系统和空间卫星提供的对实际板块运动的高分辨率测量相结合来回答。2005年9月，埃塞俄比亚阿法尔裂谷发生了一条60公里长、厚达8米的玄武岩岩墙的侵入。这一事件伴随着火山爆发和两周多的强烈地震。我参加了在阿法尔部署记录设备的紧急反应，以准确测量地震、活火山下岩浆库的膨胀和收缩，并测量构造板块的运动，因为我知道未来可能会出现堤坝。2006年6月，为获取这一独特数据所做的巨大努力得到了回报，第二条堤坝（15公里长，2米宽）被注入裂谷下方。因此，我现在可以从一代人一次的堤坝入侵事件中获得非凡的数据，以准确地探测堤坝如何，何时以及何地发生在分离的板块边界上。我将能够准确地确定岩浆来自哪里，岩浆何时在地球内部移动，以及有多少岩浆被冻结成垂直的堤坝。我提出的研究结果是至关重要的，在提高我们的理解一般过程中的板分离。与来自埃塞俄比亚、冰岛、美国和英国的一流科学家合作，我将学习处理，分析和解释科学数据的新技能，同时解决地球如何继续进化的基本问题。我提议的研究结果将对埃塞俄比亚政府了解火山和地震危险以及与阿法尔壮观的地质特征相关的地热能的潜在来源非常宝贵。

项目成果

Volcanism and Evolution of the African Lithosphere

火山活动与非洲岩石圈的演化

• DOI: 10.1130/2011.2478(04
• 发表时间: 2011
• 作者: Bastow I

Low-Frequency Hybrid Earthquakes near a Magma Chamber in Afar: Quantifying Path Effects

• DOI: 10.1785/0120090111
• 发表时间: 2010-10-01
• 期刊: BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA
• 影响因子: 3
• 作者: Cote, Dustin M.;Belachew, Manahloh;Wright, Tim
• 通讯作者: Wright, Tim