Grant: Collaborative Research and Development Grants

Most minerals of economic interest form at relatively shallow depths in the Earth's crust. A major exception is diamonds, which form in high-pressure conditions only reached at mantle depths. However, diamonds are only stable at temperatures colder than found along the typical mantle geotherm. Such conditions are only achieved in the lithosphere beneath continental shields. The Earth's lithosphere - the layer beneath the crust that participates in plate motions - is inaccessible to direct sampling and can only be characterized using indirect means. The best available source of information on large-scale lithospheric structure and properties is seismic imaging, in which earthquake recordings are used to examine the propagation characteristics of seismic waves along various paths, after which these paths are combined via tomographic inversion to obtain three-dimensional images. Existing models of the Canadian lithosphere (such as model NA04, Van der Lee and Frederiksen, 2005) pre-date the major expansion of Canadian instrument coverage through addition of instruments to the Canadian National Seismograph Network (CNSN), temporary deployment of POLARIS instruments, and other temporary experiments. We propose to develop a new North American tomographic model (NA13) with greatly improved resolution of the Canadian lithosphere, using improved methods, a wider range of data types, an improved correction for crustal variability, and these additional data sources.