A stochastic view of lower crustal fabric based on evidence from the Ivrea Zone

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Abstract
Despite its complicated history the Ivrea Zone is considered to be a representative surface exposure of extended continental crust. We have digitized two standard 1:25,000 geological maps from this area and evaluated their structural statistics. Because of the subvertical orientation of the Ivrea Zone these maps can be considered as small‐scale cross sections through the lower continental crust. The autocorrelation functions of the digitized lithologies measured from these maps show a clear self‐similar or fractal rather than a Gaussian or deterministic trend. We found that an anisotropic von Karman correlation function with an aspect ratio around 4 and a Hurst number of 0.3, corresponding to a fractal dimension of 2.7, matches the observed data. Our results represent an explicit confirmation of previous indirect evidence for the fractal nature of lithospheric heterogeneities and provide the means to construct realistic crustal‐scale seismic models of Ivrea‐type lower continental crust.