STRUCTURAL GEOLOGY OF PRECAMBRIAN ROCKS SOUTH OF BANCROFT, ONTARIO

Abstract

Structural analysis of Precambrian metamorphic rocks south of Bancroft, Ontario, has disclosed fold structures in lithologic layering, which are examined on the working hypothesis that two distinct generations are present. Folds of the first system, in the southern part of the mapped area, are fairly open, nearly recumbent, and plunge gently eastward, whereas folds of the second system, found in the northern part of the area, are tighter, with steep southeast-dipping axial planes and variably oriented axes. Uniformly steep stratiform foliation and linear mineral segregations, characterizing an extensive terrain between the so-called Hastings basin and the Haliburton–Hastings highlands, seem to have evolved by progressive tightening of the second folds and transposition of the layering parallel to the axial planes. In the area studied, the distinction between the highlands and the basin is basically one of predominant rock type, with progressive changes in structural character evident between the two. As formerly reported, the distinction involved strongly contrasting structural characteristics, with intervening zones of faulting.This part of the Grenville province is structurally very complex, and considerably more data and analysis are needed to unravel the tectonic history.