Paleomagnetic study in a folded zone of Hsuehshan range, northeastern coast of Taiwan

Abstract

This study uses paleomagnetic methods to analyze the tectonic features in the northeastern coastal area of Taiwan. A total of 14 sites were chosen at the different locations where slightly metamorphosed and multiply deformed sedimentary strata are characterized by gently dipping folds and dense-spaced faults. The results show that the paleo-inclinations of all the sites are negative. This suggests that the characteristic paleomagnetic directions were acquired during magnetic time zones of reversed polarity. The paleo-declinations measured are very scattered. However, after the bedding of each studied site is rotated to the regional structural attitude in northeastern Taiwan, there is a consistent trend at approximately N80°E; most of the corrected paleomagnetic directions point toward the direction of N100°E-N120°E. Micro-tectonic analysis also deciphered the direction of the major compression in the area studied, which occurred in the same period as that of corrected paleomagnetic direction. This suggests that the paleomagnetic directions of the samples in the studied area were acquired before the major folding and faulting which caused great deal of horizontal rotation in both clockwise and counterclockwise senses. In addition, the corrected paleomagnetic directions do not show an expected direction in a normal or reversed polarity epoch. This implies that they may not be the primary component of NRM acquired during the deposition of the formations. Instead, they might result from regional metamorphism/deformation with a certain degree of intensity. Thus, the results reveal that the samples studied have acquired the remanent anisotropy of their magnetizations.