Landscape Evolution in Response to Laccolith Inflation on the Colorado Plateau

Abstract:

Laccoliths are shallow plutonic structures that develop by uplifting and deforming overlying horizontal and near-horizontal strata. Radial drainage patterns resulting from this uplift coupled with proposed short timescales of emplacement through several episodes of rapid magmatic intrusion (<100 yr) provide a natural laboratory for the interaction between magmatically induced uplift and bedrock erosion. To investigate the coupling between the two, we compare results from numerical models of landscape evolution with analysis of natural laccolith-influenced landscapes on the Colorado Plateau. In particular, we focus on the Mount Hillers (Henry Mountains, UT), Shay Mountains (UT), and Navajo Mountains (AZ) laccoliths. Reconstructions of the original inflated surfaces of Hillers and Navajo Mtn. are available, from which we can estimate total volume and patterns of denudation since emplacement.

We generate synthetic laccoliths to quantify landscape response through time in a simplified modeling framework. Surface deformation is modeled using the classical elastic flexure solution for laccolith emplacement (Pollard & Johnson, 1972), also exploring more recent treatments that include role of gravity. We analyze different growth curves by exploring pressure distribution and influx rates during emplacement. Landscape response to this surface uplift is then modeled numerically using the landscape evolution code of Perron et al. (2008). We quantify the dominant spectra of erosion and vary laccolith inflation rate and background erosion rates to construct a regime diagram of model landscape response to laccolith emplacement. We then asses the ability of these models to explain real laccolith topographic data, with the ultimate aim of providing constraints on the timing of laccolith dissection on the Colorado Plateau and more generally quantify the influence of intrusive magmatism on landscape evolution.