More than one way to stretch: a tectonic model for extension along the plume track of the Yellowstone hotspot and adjacent Basin and Range Province

Abstract

Abstract.The eastern Snake River Plain of southern Idaho poses a paradoxical problem because it is nearly aseismic and unfaulted although it appears to be actively extending in a SW-NE direction continuously with the adjacent block-faulted Basin and Range Province. The plain represents the 100-kmwide track of the Yellowstone hotspot during the last -16-17 m.y., and its crust has been heavily intruded by mafic magma, some of which has erupted to the surface as extensive basalt flows. Outside the plain's distinct topographic boundaries is a transition zone 30-100 km wide that has variable expression of normal faulting and magmatic activity as compared with the surrounding Basin and Range Province. Many models for the evolution of the Snake River Plain have as an integral component the suggestion that the crust of the plain became strong enough through basaltic intrusion to resist extensional deformation. However, both the boundaries of the plain and its transition zone lack any evidence of zones of strike slip or other accommodation that would allow the plain to remain intact while the Basin and Range Province extended around it; instead, the plain is coupled to its surroundings and extending with them. We estimate strain rates for the northern Basin and Range Province from various lines of evidence and show that these strains would far exceed the elastic limit of any rocks coupled to the Basin and Range; thus, if the plain is extending along with its surroundings, as the geologic evidence indicates, it must be doing so by a nearly aseismic process. Evidence of the process is provided by volcanic rift zones, indicators of subsurface dikes, which trend across the plain perpendicular to its axis. We suggest that variable magmatic strain accommodation, by emplacement and inflation of dikes perpendicular to the least principal stress in the elastic crust, allows the crust of the plain to extend nearly aseismically. Dike injection releases accumulated elastic strain but generates only the small earthquakes associated with dike propagation. The rate of dike emplacement required to accommodate the estimated longitudinal strain rate of the plain is roughly a Copyright 1998 by the American Geophysical Union.Paper number 98TC00463. 0278-

La Revista Mexicana de Ciencias Geológicas a través de los índices de impacto del Institute for Scientific Information

“…Así, con respecto a las relaciones entre el volcanismo y el fallamiento, se pueden citar algunos ejemplos: se publicó en el Geological Society of America Bulletin un trabajo sobre la actividad volcánica en Camargo, Chih. (Aranda-Gómez et al, 2003), en Tectonophysics un modelo analógico de la relación entre el tipo de volcán y el fallamiento (Takada, 1994), en Tectonics, la explicación de porqué una zona con alta actividad volcánica no tiene la misma cantidad de fallas que las zonas aledañas con menos volcanismo (Parsons et al, 1998).…”

Development Report on the Idaho National Laboratory Sitewide Three-Dimensional Aquifer Model

“…Two uplifted and eroded basalt flows with intact feeder dikes can be seen just outboard of the eastern Snake River Plain boundary at the toe of the Beaverhead Range (Price et al 1999). Assuming the 11,700 m of dike emplacement of Parsons, Thompson, and Smith (1998) is a reasonable number, then within their 75-km-long box between Hell's Half Acre and the Great Rift, 75,000 m of extruded basalt include 11,700 m of dikes; this implies that there is 1 m of dike every 6.4 m somewhere in the subsurface. It must be noted that this is a model scenario using the assumption common to almost all eastern Snake River Plain rift models, namely that dikes take up the entire width of the plain.…”

“…For example, using such an approach, over a 4.5 Ma time interval and for the portion of the eastern Snake River Plain between Hell's Half Acre and the Great Rift, Parsons, Thompson, and Smith (1998) calculated that upwards of 11,700 1-to 2-m dikes were required if the eastern Snake River Plain were extending at the same rate as the neighboring basin and range province. When spread over the lifetime of the eastern Snake River Plain, emplacing one 1-to 6-m-wide dike every 1,000 years is sufficient to match total number of dikes required and the strain rates of the eastern Snake River Plain (Parsons, Thompson, and Smith 1998;. …”

“…The intrusion of dikes in these rifts is a proposed mechanism to accommodate the calculated NE-SW extension of the eastern Snake River Plain aseismically (Parsons, Thompson, and Smith 1998;Smith, Jackson, and Hackett 1996). Eastern Snake River Plain rifts therefore should consist of NW-SE-trending linear rift features with multiple dikes in the subsurface aligned perpendicular to the axis of the plain, where these dikes may or may not reach the surface.…”

“…This implies that approximately one-seventh of the boreholes drilled on the plain should have intersected a dike-yet the abundant documentation on drilling in the Big Lost Trough shows no such information. If the Parsons, Thompson, and Smith (1998) strain rate is used and we limit the assessment to young (last million years) and shallow basalts, then the odds of intersecting a dike in a C-5 borehole are 1 to 29. Those are still remarkable odds.…”