Heat and Tectonics of the Canadian Cordillera From the Seismically Constrained Inversion of Gravity Data

Abstract An updated approach to seismically constrained modeling of gravity data reveals two broad, NW‐trending low‐density zones in the mantle lithosphere beneath the Canadian Cordillera. The low‐density zones coincide with a shallow lithosphere‐asthenosphere boundary (LAB), a shallow Curie‐point depth, and the location of Quaternary volcanoes. The low‐density zones are primarily attributed to thermal expansion of peridotite minerals, with potential contributions from lower density gabbro intrusions and metasomatic veins. The low‐density zones may represent persistent Early Tertiary and Miocene slab windows associated with subduction of the Farallon/Kula ridge and Miocene rifting of the Queen Charlotte basin, and/or thin, possibly delaminated, lithosphere and proximity to hotter asthenosphere below. The low beneath the Southern Canadian Cordillera (SCC), shows a steep density gradient beneath the Rocky Mountain trench and the edge of the Canadian craton. Density contrasts are less pronounced beneath central BC, corresponding to the gap in Quaternary volcanoes. A broad zone of low density lies beneath northern BC and southeastern YT. A lower density gradient across the Cordillera to craton transition, from the Tintina Fault to Selwyn Basin, corresponds to increasing depths of the LAB and Curie‐point that are shallower and less abrupt when compared to the SCC‐craton boundary. The absence of volcanoes in Selwyn Basin, east of the Tintina Fault, likely corresponds to the increased depth to the asthenosphere and a thicker lithospheric filter to impede or trap magmas. Within the craton, lithospheric mantle density contrasts highlight old domains including the Mackenzie craton and structures like the Liard line.