Geophysical and Geochemical Constraints on Neogene‐Recent Volcanism in the North American Cordillera

Abstract

In this study, we discuss the origin and distribution of the widespread Neogene-Recent volcanism in the North American Cordillera (Figure 1). Although much work has been done on volcanics from the western United States, especially the extensional Basin and Range, current and recent backarc volcanics extend in the Cordillera from Mexico to Alaska, and widely in other global backarcs. We build on previous work that addressed the origin of these volcanic rocks in the Cordillera inland of current and recent Cenozoic subduction (e.g.,

The Structure and Dynamics of the Uppermost Mantle of Southwestern Canada From a Joint Analysis of Geophysical Observations

“…Our results with the Q F correction suggest a relatively hydrated cordilleran mantle at depths greater than 75 km, in agreement with Hyndman and Canil (2021) and Canil et al. (2021).…”

“…As noted above, there is a trade‐off between temperature and water content in fitting the observed V S and resistivity. Vertical variations in temperature and water content are small, as may be expected for asthenospheric mantle that is undergoing rapid convection; this may also arise from vertical smoothing of geophysical observations (Hyndman & Canil, 2021; Hyndman et al., 2009). Along the ABC_N profile, the mantle temperatures are similar to those of ABC_S but water content is more variable owing to changes in resistivity along this profile relative to ABC_S (Figure 7).…”

“…Water content has also been inferred from the chemical analysis of igneous rocks (Figure 9b). Hyndman and Canil (2021) and Canil et al. (2021) argue that the source region of alkaline lavas contains 150–300 ppm H 2 O (∼1,000–2,000 ppm H/Si in olivine), based on similarities to basaltic magmas from the western United States.…”

“…Water content has also been inferred from the chemical analysis of igneous rocks (Figure 9b). Hyndman and Canil (2021) and Canil et al (2021) argue that the source region of alkaline lavas contains 150-300 ppm H 2 O (∼1,000-2,000 ppm H/Si in olivine), based on similarities to basaltic magmas from the western United States. In contrast, mantle xenoliths suggest a much drier mantle lithosphere (<660 ppm H/Si in olivine; depths <65 km), which may reflect the lower storage capacity of olivine in the spinel stability field (Canil et al, 2021;.…”

Cu‐Isotope Evidence for Subduction Modification of Lithospheric Mantle

“…The fluids/melts derived from this recycled crustal component permeate the overlying mantle wedge, carrying with them their low δ 65 Cu (and high δ 34 S) isotope compositions while simultaneously lowering the mantle solidus, facilitating partial melting. The absence of basaltic volcanism in the southern Basin and Range during the compressional phase of Farallon slab subduction suggests that the partial melts generated at this time probably percolated upward and ponded at the lithosphere‐asthenosphere boundary (LAB) (Hyndman & Canil, 2021). For the GVF basalts, advancing beyond the LAB was likely the result of lithospheric thinning and passive mantle upwelling during Basin and Range extension.…”