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

This paper estimates mantle mass transfer to the crust along the Yellowstone-Snake River Plain (YSRP) hotspot track by applying a simple mass-balance analysis to rhyolite petrogenesis. Mass-balances are based primarily upon distinctive Nd- and Sr-isotopic characteristics of rhyolite, basalt, and pre-existing crust. We present new Nd- and Sr-isotopic data for basalts that are coeval with hotspot volcanism. Many of these basalts exhibit moderate to strong crustal interaction having e(Nd) as low as -18 and Sr-87/Sr-86(i) of 0.715, while others overlap petrographically, compositionally and isotopically with primitive post-hotspot olivine tholeiites (epsilon(Nd) = -4.4 +/- 1.3; Sr-87/Sr-86(i) = 0.7067 +/- 0.001). we also present new Nd- and Sr-isotopic, petrologic, and U-Pb zircon geochronologic data for YSRP rhyolites associated with Picabo and Heise volcanic fields, some of which occur in 3.2 and 1.6-km-deep boreholes. Rhyolites of the central and eastern YSRP have clustered and primitive ranges of epsilon(Nd) (-8 +/- 2) and Sr-87/Sr-86(i) (0.712 +/- 0.003) composition, in contrast to heterogeneous Archean country rocks (epsilon(Nd) = -23 to -52 and Sr-87/Sr-86(m) = 0.702 to 0.893). Using these values for country rock and basalt, we calculate a conservative Neodymium Crustal Index of similar to 0.4 for YSRP rhyolite. We present a simple mass-balance model of rhyolite petrogenesis which budgets sequentially for mantle-derived mass within erupted rhyolites, and cogenetic pluton and restite masses. Our mass-balance estimates indicate that the amount of mantle-derived mass added to the crust between 11 and 4 Ma is equivalent to a layer of gabbro similar to 14-km-thick or similar to 340,000 km(3). The corresponding average mass flux of 0.05 km(3)/yr is comparable to many other global hotspot systems. (C) 2009 Elsevier B.V. All rights reserved.