Interior Western United States
The GSA Annual Meeting in Salt Lake City provided a large and diverse terrain for field trips—from the Basin and Range to the Rocky Mountains, from the Snake River Plain, across the Colorado Plateau, to the Mojave Desert. This volume contains 22 field trip articles, nearly all of those run at the 2005 meeting. All combine the latest research with useful road logs to spectacular and often classic geologic settings. The regional tour has a core of structure and stratigraphy-paleontology contributions, and is rounded off with volcanic, glacial, lacustrine, fluvial geomorphology, neotectonic, geologic hazard, and geoarchaeology articles.
Sheet-like emplacement of satellite laccoliths, sills, and bysmaliths of the Henry Mountains, Southern Utah
Published:January 01, 2005
Sven Morgan, Eric Horsman, Basil Tikoff, Michel de Saint-Blanquat, Guillaume Habert, 2005. "Sheet-like emplacement of satellite laccoliths, sills, and bysmaliths of the Henry Mountains, Southern Utah", Interior Western United States, Carol M. Dehler
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Small intrusions (< km2) on the margins of the Henry Mountains intrusive complex of southern Utah are exceptionally well exposed in three dimensions and have a variety of shapes. Our examination of the geometry, structures, and fabric of the Maiden Creek sill, Trachyte Mesa laccolith, and the Black Mesa bysmalith (cylindrical intrusion bounded by vertical faults) suggests that this range of intrusion geometry may reflect a continuum of igneous emplacement as volume increases through magma sheeting. Intrusions begin as thin sills and through incremental injection of additional sheets, inflate into laccoliths. Marginal wall rocks are strained and rotated upward. Further sheet emplacement leads to the formation of a fault at the margin of the inflating intrusion. This fault accommodates piston-like uplift of the intrusion’s roof and results in the formation of a bysmalith.
All three of these intrusions exhibit evidence for sheeting, although the evidence is weakest on the margins of the Black Mesa bysmalith. Solid-state shear zones exist between sheets in the Maiden Creek sill and on the margins of the Trachyte Mesa laccolith. Cataclastic zones also separate sheets within the Trachyte Mesa laccolith. Evidence for sheeting in the interior of the Trachyte Mesa laccolith is solely based on differences in weathering and jointing patterns. Evidence for sheeting on the margins of the Black Mesa bysmalith is based on the differences in lineation patterns and also on the distribution of cataclastic zones.