Mass transfer along the Yellowstone hotspot track II: Kinematic constraints on the volume of mantle-derived magma

This paper evaluates the Neogene kinematic evolution of the Eastern Snake River Plain (ESRP) to estimate the volume of mafic magma transferred from mantle to crust during passage over the Yellowstone hotspot. Four major kinematic processes affected the ESRP including densification due to emplacement of gabbro into the middle crust, subsidence and consequent filling of a 6–km–deep basin with volcanic and plutonic rocks, 20% extension via dike injection or faulting/ductile attenuation, and lower crustal flow from ESRP to the adjacent Basin and Range. Two kinematic models involving these processes are proposed. Overall, the two models are viable only if the initial crustal thickness were 43–47–km–thick; otherwise, the lost mass of the ESRP is not balanced by the excess mass in the Basin and Range. In the first model (densification, eruption, and extension by dike injection), the ESRP crust receives mantle-derived gabbro equivalent to a 16–km–thick layer, but would need to lose 10 km of crust via lower crustal flow. In the second model (densification, eruption, and extension by faulting and ductile attenuation), the ESRP crust receives a 9.4 km equivalent thickness of mantle-derived gabbro, and would need to lose 6 km of crust via lower crustal flow. The cumulative amount of mantle-derived gabbro in the ESRP crust derived by this kinematic analysis (equivalent to a 9.4–16–km–thick layer) is nearly identical to the amount estimated independently using a mass balance petrologic model, suggesting it is a robust result.