Towards a Lithospheric History of North America

地球岩石圈代表了地球深部对流过程和地壳构造过程之间的边界层，构造过程定义了地壳的历史。要理解地表板块构造和深层地幔动力学之间的关系，以及这种关系是如何随时间变化的，就需要对岩石圈结构的了解达到与主要地壳构造块相当的详细程度。我的计划是通过地震方法绘制大陆岩石圈图，将岩石圈特征与已知年龄的地壳体联系起来，并发展贯穿整个板块厚度的岩石圈过程的历史。******这个项目规模最大的方面是利用两站面波分析，生成一个新的加拿大岩石圈层析模型。在这种方法中，检查沿到源的公共路径排列的两台仪器之间的波形变化，产生与仪器之间沿路径的横向平均结构相关的色散曲线。给定一组大的仪器，我们可以建立一个相交路径的网格，其平均结构是已知的；通过层析反演将路径结合起来，产生三维结构图像。我建议将现有的和新的色散曲线数据结合起来，形成横跨加拿大的岩石圈的三维图像。现有的北美模式主要基于单站方法，很难适应像加拿大地盾这样的低地震活动环境；因此，这种技术产生的模型将对北美岩石圈的结构和动力学以及地壳地质和上地幔结构之间的关系提供新的限制。我进一步建议对苏必利尔河以西的跨哈德逊造山带进行仪器测量，以填补加拿大仪器覆盖范围的最大空白。******这里也提出了更多的重点研究，基于中大陆裂谷的数据，这是一个有10亿年历史的裂谷结构，穿过五大湖。截至2013年，通过国际SPREE项目，该地区的新数据集已经可用。我提出了两个学生项目来研究横跨裂谷轴和邻近的苏必利尔省的地壳和岩石圈结构，以探索裂谷过程对岩石圈的影响，岩石圈因素在裂谷过程中的作用，以及苏必利尔省增生过程对岩石圈结构的印记；将探索详细测量岩石圈结构的新技术。一项相关研究将检查来自当代裂谷（埃塞俄比亚主裂谷）的类似数据集，以比较化石和活动裂谷结构。*** ***更好地约束加拿大岩石圈结构，通过更好地了解岩石圈参与构造事件，将对加拿大地质产生大规模影响，并将有助于大规模矿产勘探

The Earth's lithosphere represents a boundary layer between the convective processes of the deep Earth and the tectonic processes that define the history of the crust. Understanding the relationship between plate tectonics at the surface and mantle dynamics at depth, and how this relationship has changed over time, requires knowledge of the structure of the lithosphere at a level of detail comparable to the major crustal tectonic blocks. My program is to map the continental lithosphere through seismic methods, relate lithospheric features to crustal bodies of known age, and develop a history of lithospheric processes that extends through the full thickness of the plate.******The largest-scale aspect of this program is production of a new tomographic model of the Canadian lithosphere using two-station analysis of surface waves. In this approach, the change in waveform between two instruments aligned along a common path to the source is examined, producing a dispersion curve related to the laterally-averaged structure along the path between the instruments. Given a large set of instruments, we can build a grid of intersecting paths on which the average structure is known; combining the paths via tomographic inversion yields 3-D images of structure. I propose to combine existing and new dispersion-curve data to form a 3-D image of the lithosphere across Canada. Existing North American models are largely based on single-station methods which are poorly adapted to low-seismicity settings like the Canadian Shield; the model produced by this technique will thus provide a novel constraints on the structure and dynamics of the North American lithosphere and the relationship between crustal geology and upper-mantle structures. I further propose to instrument the Trans-Hudson Orogen, west of the Superior, to fill in the largest gap in Canadian instrument coverage.******More focused studies are also proposed here, based on data from the Mid-Continent Rift, a billion-year-old rift structure curving through the Great Lakes. A new data set from this region has become available as of 2013, via the international SPREE project. I propose two student projects to examine crustal and lithospheric fabric across the rift axis and in the adjacent Superior Province, to explore the effect of the rifting process on the lithosphere, the role of lithospheric factors in the rifting process, and the imprint of the Superior accretionary process on lithospheric fabric; new techniques for measuring lithospheric fabric in detail will be explored. A related study will examine a similar data set from a contemporary rift -- the Main Ethiopian Rift -- in order to compare fossil and active rift structures.*** ***Better constraints on Canadian lithospheric structure will have large-scale impact on Canadian geology, through a better understanding of lithospheric participation in tectonic events, and will assist in large-scale mineral exploration.**