T050-01
Tomotectonic Reconstruction of Cordilleran North America and the Eastern Proto-Pacific

Tuesday, 15 December 2020: 08:30
Virtual
Karin Sigloch1, Edward Clennett1, Mitchell G. Mihalynuk2, Maria Seton3, Martha A. Henderson4, Kasra Hosseini1, Afsaneh Mohammadzaheri1, Stephen T Johnston5 and Dietmar Müller3, (1)University of Oxford, Department of Earth Sciences, Oxford, United Kingdom, (2)British Columbia Geological Survey, Victoria, BC, V8W 9N3, BC, Canada, (3)University of Sydney, EarthByte Group, School of Geosciences, Sydney, NSW, Australia, (4)University of Victoria, Victoria, Canada, (5)University of Alberta, Edmonton, AB, Canada
Abstract:
Tomotectonic analysis tightly integrates surface and subsurface data in order to reconstruct paleo-oceanic areas. We discuss its application to the assembly of the Alaskan and Canadian Cordillera since Jurassic times.

Quantitative plate reconstructions of the past 200 m.y. are mostly based on the spreading records of oceanic lithosphere. North America's paleo-position over time can be reconstructed from the completely preserved isochrons of the Atlantic basin. By contrast, the paleo-environments of destructive plate margins (which formed the North American Cordillera) are difficult to constrain from surface observations because much of the evidence has been subducted or is heavily overprinted.

Seismic mantle tomography can image this subducted lithosphere in situ, revealing paleo-trench geometries and lithospheric volumes (which relate to subduction rate and duration). Continental-scale experiments (USArray) and method advances have greatly improved seismic imaging under North America, where tomography now resolves a near-complete slab inventory on the spatial scale of individual arc segments.

Every slab must have been overlain by a paleo-trench and volcanic arc. North America's reconstructed motion relative to these arcs and shows that several intra‐oceanic arcs existed between the Farallon oceanic plate and North America during late Mesozoic times. This contrasts with existing models that typically extend the Farallon plate to the continental margin. We present a continuously closing plate model for the eastern proto-Pacific basin from 170 Ma to present, consistent with both mantle evidence and the geologic record of Cordilleran accreted terranes.

References:

Clennett, E. J., Sigloch, K., Mihalynuk, M.G., Seton, M., Henderson, M.A., Hosseini, K., Mohammadzaheri, A., Johnston, S.T. & Müller, R. D. (2020). A Quantitative Tomotectonic Plate Reconstruction of Western North America and the Eastern Pacific Basin. Geochemistry Geophysics Geosystems. https://doi.org/10.1029/2020GC009117

Sigloch, K. & Mihalynuk, M.G. (2020). Comment on GSA article by Pavlis et al., 2019: “Subduction Polarity in Ancient Arcs: A Call to Integrate Geology and Geophysics to Decipher the Mesozoic Tectonic History of the Northern Cordillera of North America”. GSA Today. https://doi.org/10.1130/GSATG431C.1

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