Andean Back Arc Processes in Argentina

阿根廷安第斯山后弧过程

• 批准号: 0739116
• 负责人: John Booker
• 金额: $ 19.5万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-01 至 2010-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0739116&HistoricalAwards=false
• 关键词: Andean; Back; Arc; Processes; Argentina

The overall goal of this work is to understand one of the main types of tectonic activity that has shaped Earth's surface: subduction of an ocean plate under the edge of a continent. The more immediate focus is the poorly understood back-arc between the volcanoes that form near the edge of the continent and the stable continental interior. This zone becomes especially active when the ocean plate is unusually buoyant and does not immediately descend into the deep interior. This circumstance produced much of the U.S. Rocky Mountains about 80 million years ago and is active in South America today.The Nazca Plate flattens out under Chile at about 100 km depth and descends steeply under Argentina 600 km to the east. Prior work has imaged electrical conductivity to depths of up to 600 km associated with this Nazca flat-slab using an electromagnetic technique for sensing sub-surface electrical conductivity called the magnetotelluric (MT) method. Surprising implications include evidence that partial melt can be generated when the down-going slab enters the seismic transition zone at a depth of 400 km; that the southern edge of the flat-slab is torn rather than warping continuously back to a more normal dipping geometry as commonly argued by seismologists; that water in the flat slab is controlling its seismicity and that this water is leaking upward where it may result in a massive volcanic flare-up if the slab steepens in the geologic future.These preliminary interpretations rely on two-dimensional (2D) structure assumptions. However the data and structural inferences made argue that the reality is not 2D. In a new project funded by the Geophysics Program and the Office of International Science and Engineering, all the data will be re-examined using three-dimensional (3D) and anisotropic 2D inversion algorithms and collecting about 20 additional MT sites to enhance 3D coverage. 3D inversion is being carried out using a 72-node computer cluster and software provided by an exploration company. This work involves close collaboration between scientists and graduate students from both the U.S. and Argentina. Broader impact of this work is related to understanding the chemical differentiation of Earth, formation of mountain belts, the generation of mineral deposits, and earthquake and volcanic risk. Furthermore, the technical advances required to solve the geological problems being addressed can be directly applied to improving mineral, energy and water resource exploration and assessment.

这项工作的总体目标是了解塑造地球表面的主要构造活动类型之一：大陆边缘下的海洋板块俯冲。更直接的焦点是在大陆边缘附近形成的火山和稳定的大陆内部之间的鲜为人知的弧后。当海洋板块具有异常的浮力并且没有立即沉入内部深处时，这个区域变得特别活跃。这种环境在大约8000万年前产生了美国落基山脉的大部分地区，今天在南美洲也很活跃。纳斯卡板块在智利下方约100公里深的地方向外延伸，在阿根廷以东600公里处急剧下降。先前的工作已经使用称为大地电磁（MT）方法的电磁技术对与纳斯卡平板相关的高达600公里的深度的电导率进行了成像。令人惊讶的影响包括：有证据表明，当下行板块进入深度为400公里的地震过渡带时，可以产生部分熔融;平板的南部边缘被撕裂，而不是像地震学家通常认为的那样，不断弯曲回到更正常的倾斜几何形状;平板中的水控制着它的地震活动，这些水向上泄漏，可能导致大规模的火山爆发-这些初步解释依赖于二维（2D）结构假设。然而，数据和结构推断认为，现实不是二维的。在地球物理计划和国际科学与工程办公室资助的一个新项目中，所有数据将使用三维（3D）和各向异性二维反演算法重新检查，并收集大约20个额外的MT站点以增强3D覆盖范围。目前正在利用一家勘探公司提供的72节点计算机集群和软件进行三维反演。这项工作涉及来自美国和阿根廷的科学家和研究生之间的密切合作。这项工作的更广泛影响涉及了解地球的化学差异、山脉的形成、矿床的生成以及地震和火山风险。此外，解决正在处理的地质问题所需的技术进步可以直接用于改进矿物、能源和水资源的勘探和评估。