Lithospheric deformation in the Canadian Appalachians: evidence from shear wave splitting
2016
Plate-scale deformation is expected to impart seismic anisotropic fabrics on the lithosphere.
Determination of the fast shear wave orientation (φ) and the delay time between the fast and
slow split shear waves (δt) via SKS splitting can help place spatial and temporal constraints
on lithospheric deformation. The Canadian Appalachians experienced multiple episodes of
deformation during the Phanerozoic: accretionary collisions during the Palaeozoic prior to
the collision between Laurentia and Gondwana, and rifting related to the Mesozoic opening
of the North Atlantic. However, the extent to which extensional events have overprinted
older orogenic trends is uncertain. We address this issue through measurements of seismic
anisotropy beneath the Canadian Appalachians, computing shear wave splitting parameters
(φ, δt) for new and existing seismic stations in Nova Scotia and New Brunswick. Average δt
values of 1.2 s, relatively short length scale (≥100 km) splitting parameter variations, and a
lack of correlation with absolute plate motion direction and mantle flow models, demonstrate
that fossil lithospheric anisotropic fabrics dominate our results. Most fast directions parallel
Appalachian orogenic trends observed at the surface, while δt values point towards coherent
deformation of the crust and mantle lithosphere. Mesozoic rifting had minimal impact on our
study area, except locally within the Bay of Fundy and in southern Nova Scotia, where fast
directions are subparallel to the opening direction of Mesozoic rifting; associated δt values of
>1 s require an anisotropic layer that spans both the crust and mantle, meaning the formation
of the Bay of Fundy was not merely a thin-skinned tectonic event.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
47
References
12
Citations
NaN
KQI