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.

火山和火山活动是重大的自然灾害，但人们对它们知之甚少。 该项目的主要目标是限制地球表面火山活动的时间，位置和数量的过程，特别是在大陆裂谷内，但更广泛地说，在任何经历构造扩张的地区。 在大陆裂谷（如东非裂谷）的观察发现，火山活动的风格发生了变化，从广泛的，不规则分布的火山中心，在少量的延伸区域，到令人惊讶的规则分布，在显著延伸的区域，均匀的火山。 我们建议，火山风格的变化可能是由地表附近的断层和裂缝的位置和地壳下的岩浆生产的可变性之间的平衡控制，在地球的地幔。为了确定这两个过程的作用以及这些作用如何随着延伸而变化，威尔将使用数值模拟和模拟实验室模型来开发数学工具，这些工具将为我们了解这些地区火山活动的驱动因素提供信息。随着大陆裂谷的演变，裂谷内的火山中心通常会发展出一个特征性的间距，或波长，如在红海裂谷和阿法尔凹陷、埃塞俄比亚主裂谷（MER）和东非裂谷系（EARS）的肯尼亚（格雷戈里）裂谷中观察到的。令人惊讶的规则间隔的火山中心内的EARS是由于岩石圈厚度，预先存在的断层系统，和地幔过程。然而，这些假设很少进行定量评估，很少有研究试图包括岩石圈的粘弹塑性流变学。这项工作的主要目标是使用耦合的数值和实验室实验沿着从东非裂谷系（EARS）的观测数据，以定量评估的贡献，熔体生产和熔体提取过程的火山活动分布沿着的三个主要分支的积极传播的EARS。我们将进行两组耦合实验室和数值实验;第一组将模拟部分熔融地幔（熔体生产）内的瑞利-泰勒型不稳定性，第二组将模拟预先存在的裂缝和火山负荷对地表火山作用（熔体提取）的重要性。在数值上，我们将使用3D标记单元，有限差分代码来初始匹配实验室实验，然后将参数范围扩展到实验室中可能的范围之外。这两组实验将改变裂谷的打开速度，岩石圈厚度，预先存在的裂缝，和火山负荷。最后，我们将开发预测的比例尺定律，火山的间距和体积与上述参数。这些比例定律将允许使用表面观测来估计在EARS和其他大陆裂谷中岩石圈以下的熔体生产与通过岩石圈的熔体提取的相对重要性。