COMPARISON OF WAVELET ANALYSIS AND OTHER FABRIC ANALYSIS TECHNIQUES, ROSY FINCH SHEAR ZONE, SIERRA NEVADA, CALIFORNIA

Rock fabric, typically quantified through analysis of the size, shape, and orientation of individual clasts in a population, is often used by structural geologists to infer finite strain and strain history information. These approaches ignore the spatial distribution of and interactions between clasts. Clast interactions are significant to rock fabric, as observed in nature and predicted by modeling. Wavelet analysis is a mathematical technique applicable to the analysis of rock fabric at multiple scales. By using different size and shape filters, wavelet analysis can quantify the orientation and distribution of individual clasts within a population. Unlike other image analysis techniques (e.g., shape-preferred orientation, autocorrelation function), wavelet analysis of rock fabric also allows for the simultaneous characterization of the size, shape, and orientation of interacting groups of clasts (both touching and non-touching).

We apply this technique to a large data set that contains strain gradients. The data set consists of samples from the Rosy Finch shear zone (RFSZ), a transpressional ductile shear zone in the Mono Creek Granite, east-central Sierra Nevada, California. Wavelet analysis of K-feldspar megacryst/porphyroclast tracings was conducted along several strain gradient transects within the RFSZ. Quartz elongation data was also collected at each station.

We present here results from quartz elongation analysis, SPO analysis, and wavelet analysis of K-feldspar porphyroclasts within the Mono Creek Granite. Our results indicate significant differences between the magnitude of strain recorded by quartz aggregates and fabric development recorded by K-feldspar megacrysts in the Mono Creek Granite. Strain across the RFSZ is heterogeneous and varies non-systematically, both within and between the different mineral phases. At the scale of individual clasts, the results from wavelet analysis agree well with the SPO results. More interesting patterns are apparent in the results at the scale of imbricated clasts, where objects tend to align with either C-bands or S-bands, depending on the degree of strain. Our results from wavelet analysis demonstrate that large-scale clast groupings (e.g., trains, clusters) appear to be transient within the RFSZ.