Net tectonic rotation, apparent tectonic rotation, and the structural tilt correction in paleomagnetic studies

Abstract

The conventional tilt correction in paleomagnetic studies is intended to correct for bedding tilt. It is assumed that tilt took place about the line of strike of bedding. The basic assumption is incorrect where tectonic rotations have taken place about nonhorizontal, inclined axes. In such cases the conventional tilt correction produces declination anomalies in paleomagnetic vectors. These resemble the effects of tectonic rotation but are more aptly interpreted as apparent tectonic rotation. The challenge of paleomagnetic studies in orogenic zones is to distinguish between plate tectonic rotation, local structural rotation about vertical axes, and apparent tectonic rotation. Some criteria for recognizing apparent tectonic rotation are given, with examples. Methods for determining axes of net tectonic rotation and of relative tectonic rotation are developed by combining rotations. These have many potential applications to structural and tectonic analyses.