Tectonic patterns in the central Baltic Shield

A network of several sets of subparallel lineaments, extending over the Baltic Shield into the surrounding areas of Paleozoic and later rocks, has been identified in Nimbus satellite imagery. The observed lengths of several lineaments exceed 1 000 km. Each set is distributed all over the Shield. Ground data collected in Finland indicate the following. The strikes of foliation of the Precambrian schists and gneisses are concentrated into eight dominant trends, each parallel to a given set of the lineaments. The strike frequency maxima of the Bouguer gravity isolines and the dominant trends of the basement scarps and trenches fall in these same directions. Schist belts, tanging in age up to 2 800 m.y., as well as the boundaries of the major structural and lithologic units, are aligned with or parallel to the lineaments, which also separate blocks differing in altitude and in rate of recent land-uplift. The data suggest that the lineaments represent a permanent abyssal shear-net system, which has contributed to the evolution of the Shield since Early Precambrian times. The system possibly extends over the surrounding ocean floor.