Magma Beneath Yellowstone National Park

Abstract

The Yellowstone plateau volcanic field is less than 2 million years old, lies in a region of intense tectonic and hydrothermal activity, and probably has the potential for further volcanic activity. The youngest of three volcanic cycles in the field climaxed 600,000 years ago with a voluminous ashflow eruption and the collapse of two contiguous cauldron blocks. Doming 150,000 years ago, followed by voluminous rhyolitic extrusions as recently as 70,000 years ago, and high convective heat flow at present indicate that the latest phase of volcanism may represent a new magmatic insurgence. These observations, coupled with (i) localized postglacial arcuate faulting beyond the northeast margin of the Yellowstone caldera, (ii) a major gravity low with steep bounding gradients and an amplitude regionally atypical for the elevation of the plateau, (iii) an aeromagnetic low reflecting extensive hydrothermal alteration and possibly indicating the presence of shallow material above its Curie temperature, (iv) only minor shallow seismicity within the caldera (in contrast to a high level of activity in some areas immediately outside), (v) attenuation and change of character of seismic waves crossing the caldera area, and (vi) a strong azimuthal pattern of teleseismic P-wave delays, strongly suggest that a body composed at least partly of magma underlies the region of the rhyolite plateau, including the Tertiary volcanics immediately to its northeast. The Yellowstone field represents the active end of a system of similar volcanic foci that has migrated progressively northeastward for 15 million years along the trace of the eastern Snake River Plain (8). Regional aeromagnetic patterns suggest that this course was guided by the structure of the Precambrian basement. If, as suggested by several investigators (24), the Yellowstone magma body marks a contemporary deep mantle plume, this plume, in its motion relative to the North American plate, would appear to be "navigating" along a fundamental structure in the relatively shallow and brittle lithosphere overhead. The concept that a northeastwardpropagating major crustal fracture controls the migration path of the major foci of volcanisim is at least equally favored by existing data, as Smith et al. (19) noted.

Effect of Reduced Spatial Resolution on Mineral Mapping Using Imaging Spectrometry—Examples Using Hyperspectral Infrared Imager (HyspIRI)-Simulated Data

“…Yellowstone has been the site of extensive volcanism throughout the Cenozoic [51], with the geyser basins underlain entirely by Quaternary-age rhyolitic rocks [52]. Regional fault systems and the Yellowstone Caldera control the distribution of thermal features [53,54]. The entire area has been extensively glaciated, and many of the springs and geysers issue from stream and glacial sediments derived from the rhyolites [55].…”

Accessory mineral U–Th–Pb ages and 40Ar/39Ar eruption chronology, and their bearing on rhyolitic magma evolution in the Pleistocene Coso volcanic field, California

“…8). Geophysical methods that have claimed to have successfully detect extensive bodies of shallow magma elsewhere (e.g., Eaton et al 1975) have not demonstrated the existence of shallow magma bodies at Coso, but frequent seismicity (Walter and Weaver 1980), as well as teleseismic P-delay tomography studies (Reasenberg et al 1980;Wilson et al 2003), show evidence for a low-velocity body in the middle crust (top of the body at *5 km below the surface). Given that the volume of intrusive silicic magma at Coso may be as much as 100 times greater than the erupted volume ) the magma reservoir(s) may have been larger at certain times in the past.…”

Geologic field-trip guide to the volcanic and hydrothermal landscape of the Yellowstone Plateau

“…Geochronology by Gansecki and others (1996) using fig. 41) with a well cemented diamicton overlying a bedded lacustrine unit (Christiansen and Blank, 1975;Richmond, 1976 fig. 41).…”