Seismic Imaging of a Large Silicic System: What we Know About the Yellowstone Magmatic System

Abstract:

The Yellowstone magmatic system has been imaged from the mantle through the crust to the surface hydrothermal systems using seismic tomographic methods of local and teleseismic data. Results show that the Yellowstone crustal magmatic system consists of a lower crustal basaltic reservoir at depths of 20-40 km and an upper crustal rhyolitic reservoir at depths of 5-15 km. Based on the magnitude of the reduced P-wave velocity (V_P) from ray paths through the partial melt, the lower crustal magma reservoir, about 4.5 times larger than the upper crustal reservoir, has a melt fraction of about 2% while the upper crustal reservoir has a melt fraction of about 5-15%. The upper-most crustal reservoir in turn provides magma for the youthful rhyolitic-basaltic Yellowstone volcanic system and the extraordinarily high heat flux, up to 30 times the continental average, that drives Yellowstone’s extensive hydrothermal system. The presence and volume estimate of the lower crustal basaltic reservoir is supported by the amount of CO₂ that is released at the surface, which requires a deeper crustal basaltic magma reservoir in addition to the upper crustal rhyolitic reservoir to produce the observed quantity of CO₂ at the surface. Unlike the P-wave velocity structure, the S-wave velocity (V_S) structure for the crustal magmatic system is less well constrained because there are less S-wave arrival times identified in the Yellowstone earthquake data. However, having a better V_S model would better constrain the amount of melt in the Yellowstone magma reservoirs and allow for a V_P/V_S model. We show preliminary V_S results for Yellowstone data for body waves and compare that to a V_S model from surface wave ambient noise tomography.