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Our understanding of the present‐day state and evolution of the Canadian and Alaskan mantle is hindered by a lack of absolute P‐wavespeed constraints that provide complementary sensitivity to composition in conjunction with existing S‐wavespeed models. Consequently, cratonic modification, orogenic history of western North America and complexities within the Alaskan Proto‐Pacific subduction system remain enigmatic. One challenge concerns the difficulties in extracting absolute arrival‐time measurements from often‐noisy data recorded by temporary seismograph networks required to fill gaps in continental and global databases. Using the Absolute Arrival‐time Recovery Method (AARM), we extract >180,000 new absolute arrival‐time residuals from seismograph stations across Canada and Alaska and combine these data with USArray and global arrival‐time data from the contiguous US and Alaska. We develop a new absolute P‐wavespeed tomographic model, CAP22, spanning North America that significantly improves resolution in Canada and Alaska over previous models. Slow wavespeeds below the Canadian Cordillera sharply abut fast wavespeeds of the continental interior at the Rocky Mountain Trench in southwest Canada. Slow wavespeeds below the Mackenzie Mountains continue farther inland in northwest Canada, indicating Proterozoic‐Archean metasomatism of the Slave craton. Inherited tectonic lineaments colocated with this north‐south wavespeed boundary suggest that both the crust and mantle may control Cordilleran orogenic processes. In Alaska, fast upper mantle wavespeeds below the Wrangell Volcanic Field favor a conventional subduction related mechanism for volcanism. Finally, seismic evidence for the subducted Kula and Yukon slabs indicate tectonic reconstructions of western North America may require revision.

Mineral phase transitions cause abrupt jumps in local velocity and density structure of the mantle. The seismically observable impedance contrasts resulting from these transitions are termed seismic discontinuities. Due to estimated pressure-temperature dependence of discontinuity depth, the uplift or depression of some global seismic discontinuities can be studied as a thermometer for local mantle structure (e.g., Helffrich, 2000Helffrich, , 2002. On the other hand, nonglobal, localized seismic discontinuities can map the local enrichment of chemical heterogeneity, such that the impedance contrast of the seismic discontinuity renders it seismically observable. One such nonglobal discontinuity at 230-350 km depth is the X-discontinuity (X; e.g., Deuss & Woodhouse, 2004;Revenaugh & Jordan, 1991;Schmerr, 2015) that may be used as a tracer for upper mantle chemical heterogeneity, the distribution of which may shed important insights into mantle dynamics and the extent of chemical equilibration.

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