Modification of lithospheric structure via subduction, terrane accretion, and rifting: A case study beneath Connecticut

美国东部的基岩地质因其复杂性而非同寻常。这种复杂性反映了一系列板块构造过程，这些过程在地质时期内影响了北美东部。这些过程包括超大陆的形成和分裂，新大陆在大陆边缘的吸积，以及由于俯冲和大陆裂谷而引起的广泛的火山活动。康涅狄格州虽然面积相对较小，但却是研究这一系列基本地球过程的绝佳机会。这是因为康涅狄格州的地质反映了阿巴拉契亚山脉和盘古超级大陆形成期间的几个阶段的造山和地体吸积，以及后来的盘古裂解和大西洋盆地的形成。该项目将使用部署在康涅狄格州北部的15个地震台阵列的数据，利用远距离地震的地震波记录，研究该州下方地壳和地幔的深部结构。该团队将利用这种深层结构的图像来回答有关超大陆是如何形成和分裂的基本问题，以及板块构造过程(如俯冲、裂谷和地体吸积)如何影响地壳和上地幔的演化。该项目包括与高中科学教师的接触，使教师能够花一周的时间在实地收集数据，学习康涅狄格州的地质学知识，并利用该项目的地震数据进行课堂练习。调查人员将分析康涅狄格州地下成像结构地震实验(SEISConn)的数据，该实验在康涅狄格州北部部署了15台宽带地震仪，组成密集的线性阵列。该阵列占据了阿巴拉契亚造山带的一个区域，该区域包括各种吸积的地体结构，以及哈特福德盆地，哈特福德盆地是盘古大陆解体产生的中生代裂谷结构。他们将对SEISConn数据应用一套成像技术，重点是地壳和岩石圈地幔内的不连续结构、地震速度结构和地震各向异性的成像。该项目的动机是三个主要的科学问题：1)阿巴拉契亚成矿过程中的俯冲和地体增生事件如何影响地壳和地幔的岩石圈结构，以及现代深部结构如何与地表地质相对应？2)中生代(失败的)裂谷对地壳和地幔的结构有什么影响，哈特福德裂谷盆地下的结构与北美东部(最终成功的)裂谷边缘的结构相比如何？3)地壳和地幔在俯冲、地体增生和裂谷过程中如何变形？该项目将对地震资料应用一系列分析技术，包括P-to-S和S-P接收函数分析、环境噪声层析、波场偏移成像和横波分裂。该项目的最后阶段将涉及对根据地质观察提出的关于过去构造过程的具体假设进行测试。该项目将支持耶鲁大学成功的科学教师野外体验(FEST)计划的继续，该计划为康涅狄格州的高中科学教师提供为期一周的野外地震学经验。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The bedrock geology of the eastern United States is extraordinary in its complexity. This complexity reflects a range of plate tectonic processes that have affected eastern North America over geologic time. These processes include the formation and breakup of supercontinents, the accretion of new landmasses onto the continental edge, and widespread volcanic activity due to subduction and continental rifting. The state of Connecticut, though relatively compact in area, represents a prime opportunity to study this range of fundamental Earth processes. This is because Connecticut's geology reflects several phases of mountain building and terrane accretion during the formation of the Appalachian Mountains and the Pangea supercontinent, as well as the later breakup of Pangea and the formation of the Atlantic Ocean basin. This project will use data from an array of 15 seismic stations deployed across northern Connecticut to study the deep structure of the crust and mantle beneath the state, using recordings of seismic waves from distant earthquakes. The team will use images of this deep structure to answer fundamental questions about how supercontinents are formed and break up, as well as how plate tectonic processes such as subduction, rifting, and terrane accretion affect the evolution of the crust and upper mantle. The project includes a component of outreach to high school science teachers, enabling teachers to spend one week in the field collecting data and learning about Connecticut geology, as well as developing a classroom exercise that uses seismic data from the project.The investigators will analyze data from the Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn), a deployment of 15 broadband seismometers in a dense linear array across northern Connecticut. The array occupies a region of the Appalachian Orogen that encompasses a striking variety of accreted terrane structures, as well as the Hartford Basin, a Mesozoic rift structure resulting from the breakup of Pangea. They will apply a suite of imaging techniques to SEISConn data, focusing on the imaging of discontinuity structure, seismic velocity structure, and seismic anisotropy within the crust and lithospheric mantle. The project is motivated by three major science questions: 1) How did episodes of subduction and terrane accretion during Appalachian oogenesis affect crustal and mantle lithospheric structure, and how does present-day deep structure correspond to surface geology? 2) How was the structure of the crust and mantle lithosphere affected by (failed) rifting during the Mesozoic, and how does the structure beneath the Hartford Rift Basin compare to structure across the (ultimately successful) rifted margin of eastern North America? 3) How was the crust and mantle deformed during subduction, terrane accretion, and rifting? This project will apply a range of analysis techniques to SEISConn data, including P-to-S and S-to-P receiver function analysis, ambient noise tomography, wavefield migration imaging, and shear wave splitting. The final phase of the project will involve the testing of specific hypotheses about past tectonic processes that were formulated based on geologic observations. This project will support the continuation of the successful Field Experiences for Science Teachers (FEST) program at Yale, which provides one week of field seismology experience to Connecticut-based high school science teachers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.