Plume-lithosphere interaction: Implications for magmatism associated with the Yellowstone hotspot track

The relative contributions of lithosphere vs. upwelling sub-lithospheric mantle to formation of Snake River Plain-Yellowstone (SRPY) basaltic magmas remains an ongoing debate. The association of this province with initially thick and cold Archean lithosphere (Wyoming craton) poses a problem in that this lid will probably hinder and possibly prevent melting of rising plume hot material. However, petrologic modeling indicates that SRPY primitive basalts last segregated from mantle at ~1450°C and ~100 km depth, suggesting that their source is only slightly warmer than MORB-source mantle and significantly cooler than sources of most oceanic hotspot magmas. In the light of such evidence plume melting can only occur if the lid can be substantially thinned over geologically reasonable time. We developed a series of 3D time- dependent geodynamic models to study lithospheric thinning processes and to investigate the extent and rate of lithosphere thinning assuming an initial structure representative of the Wyoming craton. Modeling results show that thermal erosion by plume impingement alone appears incapable of providing the required lithospheric thinning for initial lithosphere thicknesses exceeding 150 km, even assuming a wide rage of plume parameters (chemical buoyancy Δρ=30-50 kg/m3 and temperature contrasts ΔT=150-300°C). On the other hand, alternative models (e.g., involving low-angle Laramide subduction, delamination) are considered unlikely because they conflict with geochemical evidence that SRPY basalts contain a dominant contribution of old, isotopically evolved mantle material - presumably derived from subcontinental lithospheric mantle (SCLM). Thus, we conclude that SCLM is likely to be preserved, that the SCLM lid thickness probably prevents substantial melting of rising plume material (tomographically imaged), and SRPY basalts are predominantly derived by melting of lithospheric mantle.