ANALYSIS OF RELATIONAL DATA FROM METAMORPHIC TECTONITES: DERIVATION OF DEFORMATION SEQUENCES FROM OVERPRINTING RELATIONS

ABSTACT The derivation of a deformation sequence from field observations of overprinting relations in metamorphic tectonites is a problem in multirelational data-base management. Adoption of sequential coding and explicit statements of relations results in a “coding syntax” or “file language”. Field notes recorded in normal English have been translated successfully into an alphanumeric file and a number of tests show that it is close to a faithful image of the field data as recorded in the notebooks. Data retrieval on the overprint relation shows that (i) it is possible to detect errors in nomenclature between an observer and himself at different times and between different observers; and (ii) inferences made by employing Occam's Razor on the file structure agree with conclusions reached by manual methods of interpretation of data from this region, and with conclusions reached independently elsewhere. Detailed consideration of the operations of the geological mapping system termed “mesoscopic structural analysis” yields a model of the operations that demonstrates why overprinting relations by themselves are an insufficient basis on which to establish a deformational sequence. The effect of progressive deformation on a rock under conditions of little or no metamorphism may be described as an increase in relational degree of overprinting textures as well as an increase in dissymmetry of fabric.