ELASTIC FLEXURE AND THE PRESENCE OF LITHOSPHERIC MANTLE AT LAKE BONNEVILLE

Thin lithosphere underlying North America’s Lake Bonneville was subjected to gravitational loading, which was accommodated through regional flexure. The thickness of lithospheric mantle in this region may help to provide constraints to the growth of mantle lithosphere and its role in the evolution and stabilization of continental lithosphere.

The lithosphere was modeled as an elastic layer. In order to determine the thickness of lithospheric mantle that is present at Lake Bonneville, elastic flexure equations were used to calculate thickness, with strength quantified by the Lamé parameters. Elastic thickness of the lithosphere was calculated based on uplift of paleoshorelines. Published seismically determined values of the Lamé parameters for lithospheric rocks at Lake Bonneville were used to calculate the thicknesses of crust and mantle layers. Flexural rigidity was analyzed to obtain a better understanding of the relationship between the strength of rocks of varying lithology and the thickness of the elastic lithosphere.

Previously published seismically determined a crustal thickness of 29km. Geothermal data that suggest the elastic thickness may be up to 50km. Adding our results of a lithospheric thickness of 37-38km to the 29km crustal thickness suggests that the mantle layer that is 8-9km thick. The resulting lithospheric thickness presented here differs from published values of thickness of the lithosphere at Lake Bonneville, which range from 25-40km. The heat flow data, however, suggests an elastic thickness that is in the upper range of the published values, and overestimates most published values as well as the values presented here. Most importantly, published studies have either not sought to quantify the mantle thickness or conclude that the crust is the only elastic layer present. This project shows that more mantle may have joined the lithosphere since the development of the basin and range than previously thought.