Experimental and natural buoyant structures
Abstract
Low-density, buoyant plumes that experience simultaneous cap expansion and vertical ascent entrain surrounding higher-density host fluid at a rate that is dependent on the vortical velocity within the plume cap. Such plumes have a viscosity contrast between the host and source fluids near unity and a cap/stem diameter ratio of about 2 to 3. Plumes that entrain host material increase in volume, change from spherical to a form with a flat base and bluntly-pointed tip, and experience a deceleration due to an increase in effective density relative to the density of the surrounding host material. The ascent of all plumes with a host/source viscosity ratio within the range 0.1-21 and a density contrast of about 1.5 can be modeled as Stokesian provided that entrainment is accounted for by use of the weighted average density of the plume and entrained host material. Regional gravity and seismic data indicate that salt deposits within the salt anticlines of the Paradox Basin, Utah consist of 10 to 40 kilometer long, 5 to 10 kilometer wide, 600-3500 meter thick salt cores with deep-level, 10 kilometer wide and shallow level, 2 to 5 kilometer wide independent, parasitic salt cells. Cache Valley, which occurs along the crest of a salt-cored anticline in the Paradox Basin, exposes numerous folds and faults resulting from salt evacuation and subsequent crestal collapse followed by localized diapirisms of salt caprock stocks. Salt evacuation produced downdropping in excess of 600 meters by folding, graben faulting, and block foundering. Diapirism resulted in divergent tilting of peripheral strata by an much as 60 degrees. Based on estimates of volumetric downdropping averaged over a presumed 20 m.y. collapse period, salt removal rates within three structurally distinct areas are, from northwest to southeast, 4.4 $\times$ 10$\sp{-2}$, 1.7 $\times$ 10$\sp{-2}$, and 0.9 $\times$ 10$\sp{-2}$ m$\sp3$/yr per unit length along the valley axis. The southeastward volumetric salt loss reduction and the corresponding decrease in downdropping is attributed to decreased dissolution rates along a southeastward constricting salt core.
Degree
Ph.D.
Advisors
Johnson, Purdue University.
Subject Area
Geology
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