Preservation and reactivation of ancient lithospheric-scale structures in Alaska inferred from receiver function imaging and geologic constraints
Abstract
We present receiver function images of crustal and lithospheric architecture based on broadband seismic data across the region that are now constrained by new data from the EarthScope Transportable Array (TA) and temporary deployments across Alaska. The resulting receiver functions (Ps and Sp) reproduce many of the Moho depth variations previously modeled by both more concentrated arrays, primarily in south-central Alaska, using receiver functions and tomographic imaging. However, these new results provide significantly more detailed images of the broader region that further illustrate the tectonic history of the continental lithosphere in the region, ancient terrane boundaries and active faulting.
Although only southern Alaska and westernmost Yukon contain a plate boundary, much of the region is undergoing active deformation, both distributed and highly localized along faults 100s of kms inboard from the active margin. The variable thickness of the crust and lithosphere primarily reflects inherited structure from Mesozoic to early Cenozoic convergent and extension events although in some areas with Proterozoic basement (SW AK, easternmost AK) the thickness may indicate old continental crustal blocks entrained in much younger orogens. Steep gradients in the Moho depth often occur across known active and/or ancient strike-slip faults which supports previous interpretations that the crustal structure of the northern Cordillera is extensively modified by large-displacement strike-slip faults. Active crustal shortening in the northernmost part of the state is difficult to link to southernmost AK convergence by detachments located within a crustal layer because strike-slip faults offset the Moho depth directly below the surface trace. The active southern portion of the region continues to be modified by subduction, collision, and strike-slip processes and in this area determining the role of inherited crustal structure from modern is not always straightforward. Combining three different receiver function methodologies for both Ps and Sp - Common Conversion Point (CCP) stacking, receiver function stacks, receiver gathers, along with geodynamic models, geologic field observations, and geochronologic constraints allows for an interpretation of Alaskan crustal structure that spans multiple temporal-spatial scales.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T13C..02M
- Keywords:
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- 7208 Mantle;
- SEISMOLOGY;
- 7218 Lithosphere;
- SEISMOLOGY;
- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS;
- 8149 Planetary tectonics;
- TECTONOPHYSICS