Hot high-nitrogen gas in a metal mine

Abstract

Strain is an important component of the total displacement field in the emplacement of a thrust sheet. The finite strain tensor in a penetratively deformed thrust sheet is a spatial variable. I describe a method for quantitative estimation of the finite strain variation in thrust sheets by applying spatial statistics analysis on strain data collected from a part of the Sheeprock thrust sheet, in the southern Sheeprock Mountains and the West Tintic Mountains, north-central Utah. Strain was measured in the quartzites of the Sheeprock thrust sheet and the spatial statistics method is illustrated using the XZ strain axial ratios.The Sheeprock thrust sheet was penetratively deformed during Sevier-age fault propagation folding. I quantified finite strain from quartzites using the modified normalized Fry method and calculated the three-dimensional strain ellipsoid from the quartzites using three orthogonal thin-sections from each oriented field sample. The variation of finite strain in the Sheeprock thrust sheet was best represented by an exponential semivariogram model, which I used to predict values of strain from unsampled locations by ordinary kriging. Cross-validation showed that, in general, the predicted and measured values show good agreement (within 1% of each other). The sampled space was contoured using the measured and predicted strain values to obtain a detailed finite strain variation pattern in a part of the Sheeprock thrust sheet.