Collaborative Research: Rifting, Magmatism, and Lithospheric Sutures; Crustal Imaging of the South Georgia Basin and Suwanee Suture

佐治亚州沿海平原下的岩石处于形成北美东部的最基本构造事件的中心：大约2.9亿年前的大陆碰撞形成了盘古大陆；大约2.3亿年前的大陆分裂导致了大西洋的形成；以及大约2亿年前地球历史上最大的岩浆事件之一--中大西洋岩浆省。格鲁吉亚南部地壳中的构造保存了这些事件的记录和它们之间可能的关系，包括两种不同类型大陆之间的缝合，北美东海岸最大的断裂裂谷盆地和来自中大西洋岩浆省的火成岩。这些研究人员和一大批研究生和本科生正在收集地震数据，这些数据可以用来成像地壳结构，以了解这些构造事件。数百台检波器正被部署在缝合线和盆地上两个约300公里长的剖面上，这些剖面记录了一系列相距约20公里的炸药所产生的声波。地震检波器也被部署在一个专注于盆地的盒子里，以记录以网格形式排列的爆炸装药。声波在岩石中传播的速度随岩石成分、孔隙度和其他岩石特性的不同而变化。研究人员正在使用旅行时间层析成像来创建速度模型，以揭示火成岩的分布、地壳厚度的变化和地壳成分的变化。除了更好地了解基本的构造过程外，这个项目的其他好处还包括对学生的培训和教育，以及对可能成为碳固存良好目标的盆地和火成岩的表征。

The rocks beneath the coastal plain of Georgia were at the center of the most fundamental tectonic events to shape eastern North America: continental collision around 290 million years ago to form the super continent of Pangea; continental breakup leading to the formation of the Atlantic Ocean beginning around 230 million years ago; and one of the biggest magmatic events in Earth's history around 200 million years ago, the Central Atlantic Magmatic Province. A record of these events and possible relationships between them is preserved by structures in the crust of southern Georgia, including a suture between two different types of continent, the largest failed rift basin along the east coast of North America and igneous rocks from the Central Atlantic Magmatic Province. These investigators and a large team of graduate and undergraduate students are collecting seismic data that can be used to image structures in the crust to understand these tectonic events. Hundreds of geophones are being deployed along two ~300-km-long profiles across the suture and the basin, which record sound waves generated by a series of explosive charges spaced ~20 km apart. Geophones are also being deployed in a box focused on the basin to record explosive charges arranged in a grid. The speed that sound waves travel through rocks varies with composition, porosity, and other rock characteristics. The investigators are using travel-time tomography to create velocity models that reveal the distribution of igneous rocks, variations in the thickness of the crust and variations in crustal composition. Besides a better understanding of fundamental tectonic processes, other benefits of this program include training and education of students, and characterization of basins and igneous rocks that might be good targets for carbon sequestration.