TECTONICS FROM TOPOGRAPHY USING FORMAL LINEAR INVERSION: THEORY AND APPLICATION TO THE INYO MOUNTAIN RANGE, CA

The long profiles of rivers have long been used to constrain relative tectonic rock uplift rates from the relationships between the local slope and the upstream drainage area. Recently, with the aid of closed form analytic solutions, our understanding of the relations between river patches and the spatial and temporal origin of the tectonic signal that generated them has developed.

With this new understanding, we develop a formal linear inversion scheme that allows us to infer the rate of tectonic rock uplift from the long profiles of rivers. The inversion scheme is based on a closed form analytic solution of the transient linear stream power law model, and it makes use of several main trunks and their tributaries to increase the resolution of the data. A key component of the inverse model is the response time for a perturbation to propagate along a river. The response time dictates the time in the past for which a river patch preserves the rock uplift rate, and the local gradient dictates the magnitude of the uplift rate.

We apply our methodology to the Inyo Mountains, an uplifted block along the western boundary of the Basin and Range province in California. The Inyo range is bounded by an oblique fault, and we analyze the rivers that drain across the fault to Saline Valley. We thus interpret the inferred tectonic rock uplift rate as the rate of dip-slip motion along the bounding fault with respect to Saline Valley.

We present two types of inversion schemes: One that accounts only for a temporal variability of uplift rate, and the second accounts for time-space variability, where the spatial variability is parameterized using an analytical expression for the flexural response to normal faulting. Inversion results are calibrated using thermochronometric data, and reveal an increase of tectonic rock uplift rate from a value of ~0.3 mm/yr at 4 Ma to a value of ~0.65 mm/yr at the last 0.5 Myr. The increasing trend is punctuated by periods of higher uplift rates; the most recent of them is at 0.75 Ma, in correlation with documented increased tectonic activity along other faults in this part of the Basin and Range province.

The inferred tectonic rock uplift rate is used in the calculation of the paleotopography and paleo-erosion rates of the Inyo range and show an increase of relief towards the present.