Towards a Lithospheric History of North America

地球的岩石圈代表了地球深处的对流过程和定义地壳历史的构造过程之间的边界层。了解地表板块构造与深层地幔动力学之间的关系，以及这种关系如何随时间变化，需要了解与主要地壳构造块相当的详细水平的岩石圈结构。我的计划是通过地震方法绘制大陆岩石圈地图，将岩石圈特征与已知年龄的地壳体联系起来，并发展贯穿板块整个厚度的岩石圈过程的历史。 该计划最大规模的方面是利用表面波的两站分析来制作加拿大岩石圈的新层析成像模型。在这种方法中，检查沿着到源的公共路径对齐的两个仪器之间的波形变化，产生与沿着仪器之间的路径的横向平均结构相关的色散曲线。给定大量仪器，我们可以构建一个相交路径的网格，其平均结构是已知的；通过断层扫描反演组合路径可产生结构的 3D 图像。我建议结合现有的和新的色散曲线数据来形成加拿大各地岩石圈的 3D 图像。现有的北美模型主要基于单站方法，这种方法很难适应加拿大地盾等低地震活动环境；因此，该技术产生的模型将为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约束。我进一步建议在苏必利尔河以西的跨哈德逊造山带上安装仪器，以填补加拿大仪器覆盖范围的最大空白。 这里还根据中大陆裂谷的数据提出了更有针对性的研究，中大陆裂谷是一个蜿蜒穿过五大湖的十亿年前的裂谷结构。自 2013 年起，通过国际 SPREE 项目即可获得该地区的新数据集。我提出了两个学生项目来研究裂谷轴和邻近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增生过程对岩石圈结构的影响；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（埃塞俄比亚主要裂谷）的类似数据集，以便比较化石和活动裂谷结构。   通过更好地了解岩石圈参与构造事件，对加拿大岩石圈结构的更好约束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.