Emplacement of regularly spaced volcanic centers in the East African Rift: Melt production or melt extraction?

东非大裂谷中规则分布的火山中心的位置：熔体生产还是熔体提取？

• 批准号: 1456664
• 负责人: Eric Mittelstaedt
• 金额: $ 22.59万
• 依托单位: Regents of the University of Idaho
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-05-01 至 2019-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1456664&HistoricalAwards=false
• 关键词: Emplacement; regularly; spaced; volcanic; centers

Volcanoes and volcanic activity present significant natural hazards, but they are poorly understood. The principal goal of this project is to constrain the proccess that regulate the timing, location, and volumes of volcanism at the Earth's surface, specifically within continental rifts, but more broadly in any region undergoing tectonic extension. Observations at continental rifts, such as the East African Rift, find changes in the style of volcanism from widely, irregularly spaced volcanic centers in areas with small amounts of extension to surprisingly regularly spaced, uniform volcanoes in significantly extended regions. We propose that the changes in volcanic style may be controlled by a balance between the location of faults and fractures near the surface and the variability of magma production beneath the crust, in the Earth's mantle. To determine the role of these two processes and how those roles may change with extension, will will use both numerical simulations and analogue laboratory models to develop mathematical tools that will inform our understanding of the drivers of volcanic activity in these areas.As continental rifts evolve, volcanic centers within rift valleys often develop a characteristic spacing, or wavelength, such as observed in the Red Sea Rift and within the Afar depression, the Main Ethiopian Rift (MER), and the Kenya (Gregory) Rift of the East African Rift System (EARS). The surprisingly regular spacing of the volcanic centers within the EARS is attributed to lithosphere thickness, pre-existing fault systems, and mantle processes. However, little quantitative assessment of these hypotheses has been undertaken and few studies attempt to include the visco-elastic-plastic rheology of the lithosphere. The primary goal of this work is to use data from coupled numerical and laboratory experiments along with observations from the East African Rift System (EARS) to quantitatively assess the contribution of both melt production and melt extraction processes on the distribution of volcanic activity along the three main branches of the actively spreading EARS. We will perform two groups of coupled laboratory and numerical experiments; the first will simulate Rayleigh-Taylor type instabilities within the partially molten mantle (melt production), and the second will simulate the importance of pre-existing fractures and volcano loading on surface volcanism (melt extraction). Numerically, we will use a 3D marker-in-cell, finite difference code to initially match the laboratory experiments and then expand the parameter range beyond that possible in the laboratory. Both sets of experiments will vary rift opening rate, lithospheric thickness, pre-exiting fractures, and volcanic loading. Finally, we will develop predictive scaling laws that relate volcano spacing and volume to the above parameters. These scaling laws will permit the use of surface observations to estimate the relative importance of melt production below the lithosphere versus melt extraction through the lithosphere in both the EARS and other continental rifts.

火山和火山活动带来了重大的自然灾害，但人们对其知之甚少。 该项目的主要目标是限制控制地球表面火山活动的时间、地点和数量的过程，特别是在大陆裂谷内，但更广泛地在任何经历构造扩张的区域。 对东非裂谷等大陆裂谷的观察发现，火山活动的类型发生了变化，从小范围延伸区域内广泛、不规则间隔的火山中心，到显着延伸区域中令人惊讶的规则间隔、均匀火山。 我们认为，火山类型的变化可能是由地表附近断层和裂缝的位置与地幔地壳下岩浆产生的变化之间的平衡控制的。为了确定这两个过程的作用以及这些作用如何随着扩展而变化，将使用数值模拟和模拟实验室模型来开发数学工具，帮助我们了解这些地区火山活动的驱动因素。随着大陆裂谷的演变，裂谷内的火山中心通常会形成一种特征间距或波长，例如在红海裂谷和阿法尔洼地、埃塞俄比亚主裂谷 (MER) 和东部肯尼亚 (格雷戈里) 裂谷内观察到的情况非洲裂谷系统（EARS）。 EARS 内火山中心的令人惊讶的规则间距归因于岩石圈厚度、预先存在的断层系统和地幔过程。然而，很少对这些假设进行定量评估，也很少有研究尝试纳入岩石圈的粘弹塑性流变学。这项工作的主要目标是利用耦合数值和实验室实验的数据以及东非裂谷系统 (EARS) 的观测数据来定量评估熔体生产和熔体提取过程对沿三个区域的火山活动分布的贡献。积极传播的 EARS 的主要分支。我们将进行两组耦合的实验室和数值实验；第一个将模拟部分熔融地幔内的瑞利-泰勒型不稳定性（熔体生产），第二个将模拟预先存在的裂缝和火山载荷对地表火山作用的重要性（熔体提取）。在数值上，我们将使用 3D 细胞内标记、有限差分代码来最初匹配实验室实验，然后将参数范围扩展到实验室之外。两组实验都会改变裂谷的张开速率、岩石圈厚度、预先存在的裂缝和火山载荷。最后，我们将制定将火山间距和体积与上述参数联系起来的预测缩放定律。这些比例定律将允许使用表面观测来估计岩石圈以下熔体生产与通过岩石圈提取熔体在 EARS 和其他大陆裂谷中的相对重要性。