Collaborative Research: Understanding Lithospheric Suturing and Passive Margin Development Beneath the Southeastern U.S.

该奖项是根据2009年《美国复苏和再投资法》(公法111-5)资助的。在建造阿巴拉契亚山脉(2.5亿-3.2亿年前)的岩石圈吸积达到顶峰时，另一个大陆(冈瓦那)的岩石圈与原北美相撞。这两个岩石圈之间的缝合线是在佐治亚州南部的地壳中通过化石、岩石类型和年龄的变化以及地震反射数据成像的向南倾斜的反射层区域来描绘的。然而，地幔中缝合线的位置和几何形状尚不清楚。该项目的目标是确定地幔中岩石圈缝合线的位置和形状，并测量缝合线上地壳和地幔的任何物理化学性质的对比。85个EarthScope USArray柔性阵列宽带站将部署在两个N-S线阵中，这两个线阵横跨缝合线。一条线从北卡罗来纳州延伸到佛罗里达州狭长地带的海岸。另一条从南卡罗来纳州延伸到佛罗里达州中部。这些观测站与地球天文望远镜USArray可移动阵列的观测站一起，将记录来自全球各地的地震波。这些数据将被分析以测量各向同性和各向异性波速的三维变化，速度模型将从温度、岩石成分(包括挥发分含量)和岩石变形组构的角度进行解释。这项研究将解决一系列基本问题。地壳缝合是如何与地幔结构相连的？地幔增生是否发生在浅倾角剪切带上，或者至少部分发生在更多的垂直接触上，这意味着在很大的深度范围内水平缩短？如果存在倾角地幔界面，它们是代表残留的俯冲岩石圈，还是与先前的俯冲无关的剪切带？地震速度的各向异性意味着吸积过程中的形变分布是什么？与冈瓦那和劳伦西亚的碰撞有关的俯冲方向是什么？岩石圈碰撞之后，大陆解体，导致了大西洋的开放。大陆岩石圈是如何受到这一次伸展、裂谷和岩浆作用的影响的？有岩石圈剥离的证据吗？岩石圈之下的弱地幔软流圈中现今的流动模式是什么？该项目直接支持研究生和本科生的教育和培训。我们正在开发教育材料，利用这个研究项目来建立对大陆碰撞、造山和大陆分裂等概念的理解。实验结果将用于我们的本科生和研究生班级，以及我们在佐治亚州、北卡罗来纳州和罗德岛州的母校附近的学校。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).At the culmination of the lithospheric accretion that built the Appalachian Mountains (250-320 million years ago) the lithosphere of another continent (Gondwana) collided with proto-North America. The suture between these two lithospheres is delineated in the crust beneath southern Georgia by variations in fossils, rock types and ages, and a zone of southward dipping reflectors imaged by seismic reflection data. However, the location and geometry of the suture in the mantle is unknown.The goal of this project is to determine the position and shape of the lithospheric suture in the mantle, and to measure any contrasts in crust and mantle physical and chemical properties across the suture. 85 EarthScope USArray Flexible Array broadband stations are being deployed in two N-S linear arrays that straddle the suture. One line stretches from North Carolina to the coast of the Florida panhandle. The other extends from South Carolina into central Florida. These stations, together with the stations of the EarthScope USArray Transportable Array, will record seismic waves from around the globe. These data will be analyzed to measure three-dimensional variations in isotropic and anisotropic wave velocities, and the velocity models will be interpreted in terms of temperature, rock composition (including volatile content), and rock deformation fabrics.This research will address a series of fundamental questions. How does the crustal suture connect to mantle structures? Did mantle accretion occur on shallow dipping shear zones, or did it occur at least in part on more vertical contacts that imply horizontal shortening over a broad depth range? If dipping mantle interfaces exist, do they represent relict subducted lithosphere, or are they shear zones unrelated to prior subduction? What does anisotropy in seismic velocities imply about the distribution of deformation during accretion? What was the direction of subduction associated with the collision of Gondwana and Laurentia? Continental break-up followed the lithospheric collision, leading to the opening of the Atlantic Ocean. How was the continental lithosphere affected by this episode of extension, rifting and magmatism? Is there evidence for delamination of the lithosphere? What are the present-day patterns of flow in the weak mantle asthenosphere that underlies the lithosphere?This project is directly supporting the education and training of graduate and undergraduate students. We are developing educational materials that use this research project to build understanding of concepts such as continental collision, mountain building, and continental break-up. Experiment results will be used in our undergraduate and graduate classes, and in outreach to schools in the vicinity of our home institutions in Georgia, North Carolina, and Rhode Island.