Presentation on theme: "Evolution of Wedge Width Dampens the Response of Rock Uplift Rate to a Change In Fa (from linear to ~1/2 power) A Step-function change in U Is nearly impossible."— Presentation transcript:
Evolution of Wedge Width Dampens the Response of Rock Uplift Rate to a Change In Fa (from linear to ~1/2 power) A Step-function change in U Is nearly impossible Total Erosional Efflux can only change during Transients; Only Climate can Drive a Spike A Change in Erosional Efficiency Changes both Relief AND the Steady- State Rock Uplift Rate: Coupling Between Erosion and Tectonics Response Time Set by Final Erosional Efficiency (~only) Persistent U
Taiwan Central Range GTOPO30 DEM Time Since Collision Increases at ~1Ma/60 km from south
Taiwan Central Range 20 km Averaging Time Since Collision Increases at ~1Ma/60 km from south Notable Departure from Steady Self-Similar Growth
Taiwan Topography – Approach to Steady State (Willett et al) Distance = Time (Oblique convergence) 130km = 1.5-2.5 Ma
Taiwan Central Range not Consistent with Self-Similar Growth But predicted time to steady state approximately corroborated
Taiwan Central Range Parameters Time to 90% Steady- State Values much shorter for Rock Uplift and Erosion Rate T 1/e ~ 1.2 Ma 90% Steady-State Wedge Size, Erosional Flux ~3Ma During Early stages of growth, Rock Uplift and Erosion follow very distinct paths 10-100x longer if dry, harder rock
Conclusions: Frictional Orogenic Wedges Response Time Set by Erosional Efficiency T 1/e ~ order 1Ma typical for wet climate, moderate rock strength (Taiwan example) Fast response to increase K*, Moderate response to change F A, Slow response to decrease K* Implusive (nearly 1:1) transient response of rock uplift to increase K* : isostatic For growing wedge, rock uplift and erosion rate approach near steady values long before wedge attains flux steady-state
The Erosion and Rock Uplift Paradox In an isostatically compensated orogen, most (~5/6 total) rock uplift can be said to be a response to erosion At steady state, rock uplift equals erosion – the two are interchangeable Thus it makes no sense to discuss how erosion influences rock uplift – rock uplift is erosion, more or less If erosion is not driven by rock uplift, but vice versa, what does drive erosion? And how is relief generated? Did Someone Say Something about a Paradox?
Suggested Language Erosion Tectonics Erosion Rock Uplift Erosional Efficiency Rock Uplift Erosion Rock Deformation
But What Do We Really Know? Wedge Theory, Coupled Numerical Simulations, and Analog Models Suggest a Strong, Inescapable Coupling between Erosional Efficiency and Tectonics (rock deformation rates, patterns, PTt histories of exposed rocks) But: Quantitative link between Climate Parameters and “Erosional Efficiency” remains Elusive There is yet no Field Data that Convincingly Demonstrates a Strong Coupling, with Feedback, between Climate and Tectonics Many are Pursuing this Goal; much existing data is tantalizing/ suggestive. Willett: Alps Messinian Crisis?