Collaborative Research: Geophysical Investigation of the Mid-Continent Rift System

合作研究：中部大陆裂谷系统地球物理调查

• 批准号: 1148027
• 负责人: Lucy Flesch
• 金额: $ 11.5万
• 依托单位: Purdue University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-10-01 至 2016-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1148027&HistoricalAwards=false
• 关键词: Collaborative; Research; Geophysical; Investigation; Mid

Geophysical Investigation of the Mid-Continent Rift System Surprisingly, the Central U.S. is an ideal place to study one of the more important processes shaping our planet - the breaking apart of continents to form new oceans. Throughout earth's history, continents have split along rifts, long zones of volcanism and stretching, which become spreading centers along which new ocean basins form and can grow to the size of the Atlantic and Pacific. It even looks like similar rifting may have happened on other planets.Understanding how rifting works is important for both science and society, because rifting provides conditions for the deposition of hydrocarbons and other mineral resources. The problem is that when rifting succeeds in forming a new ocean, not much remains from its early stages so it's hard to see what happened.To get around this, researchers are studying a spectacular rift that failed, the Mid-Continent Rift System. This system evolved around 1.1 billion years ago, when North America nearly split. However, the rift failed, leaving a 2000 km long belt of volcanic and sedimentary rocks left from the early rifting stage. This fossil rift, which is similar in length to the present East African and Baikal rifts, has two major arms meeting in the Lake Superior region. One extends southwestward at least as far as Kansas, and the other extends southeastward through Michigan. These arms are identified using the large gravity and magnetic anomalies resulting from dense and highly magnetic igneous rocks. They are largely covered by younger sediments but outcrop near Lake Superior and can be followed further south in drill cores. The study combines seismic and magnetotelluric data being acquired by NSF's EarthScope program with gravity and magnetic data to develop an integrated three-dimensional image of the rift system and constrain its evolution. One of its goals is to learn whether the rift formed as a response to melting in the underlying mantle, as commonly proposed for the East African Rift, or because of stresses transmitted within the lithosphere, as appears to be the case for Asia's Baikal Rift.

中部大陆裂谷系统的地球物理调查 令人惊讶的是，美国中部是研究塑造地球的更重要过程之一——大陆分裂形成新海洋的理想场所。纵观地球历史，大陆沿着裂谷、长长的火山作用和伸展带分裂，成为扩张中心，新的海洋盆地沿着这些盆地形成，并可以发展到大西洋和太平洋的大小。甚至看起来类似的裂谷也可能发生在其他行星上。了解裂谷如何运作对于科学和社会都很重要，因为裂谷为碳氢化合物和其他矿产资源的沉积提供了条件。问题是，当裂谷成功形成新海洋时，其早期阶段留下的痕迹并不多，因此很难看到发生了什么。为了解决这个问题，研究人员正在研究一个失败的壮观裂谷，即中大陆裂谷系统。 这个系统在大约 11 亿年前演化，当时北美几乎分裂。 然而，裂谷失败了，留下了早期裂谷阶段留下的长达2000公里的火山岩和沉积岩带。 这个化石裂谷的长度与现在的东非和贝加尔裂谷相似，有两个主要的裂臂在苏必利尔湖地区相遇。一条向西南延伸至少至堪萨斯州，另一条向东南延伸穿过密歇根州。这些臂是利用致密且高磁性的火成岩产生的巨大重力和磁异常来识别的。它们大部分被较年轻的沉积物覆盖，但在苏必利尔湖附近露头，可以在钻芯中继续向南延伸。该研究将 NSF EarthScope 计划获取的地震和大地电磁数据与重力和磁力数据结合起来，开发裂谷系统的集成三维图像并限制其演化。其目标之一是了解裂谷的形成是否是由于地幔融化的反应（如东非裂谷通常提出的那样），还是由于岩石圈内传递的应力（如亚洲贝加尔裂谷的情况）。