thumbnail

Paleomagnetism of an east-west transect across the Cascade arc in southern Washington: Implications for regional tectonism

Journal of Geophysical Research B: Solid Earth

By:
, , and

Links

  • The Publications Warehouse does not have links to digital versions of this publication at this time
  • Download citation as: RIS

Abstract

Paleomagnetic data from a transect across the Cascade arc in southern Washington were collected to test models of vertical axis rotations for this part of the Pacific Northwest and to provide information on the tectonic history of the St. Helens seismic zone. The 75 site-mean directions are divided into three groups based on isotopic, fission track, and stratigraphic ages. Group 1 consists of samples from rocks deposited between 39 and 30 Ma and shows a mean clockwise vertical axis rotation of 34?? ?? 13??, group 2 consists of samples from rocks deposited be-tween 30 and 24 Ma and shows a mean clockwise rotation of 17?? ?? 11??, and group 3 consists of samples from rocks between 24 and 16 Ma and shows a mean clockwise rotation of 20?? ?? 12??. Although these three values of rotation are statistically indistinguishable at the 95% confidence level, we interpret them in combination with other data to indicate differential rotation across the St. Helens seismic zone (SHZ). The available paleomagnetic data for Eocene-Oligocene rocks west of the seismic zone show clockwise vertical axis rotations of 30?? ?? 8?? and 35?? ?? 9?? consistent with the value for group 1. The rotational values for groups 2 and 3 and the intrusive suite of Kidd Creek (13 Ma), despite their different ages, have similar values east of the SHZ. Comparing these groups of data east and west of the seismic zone indicates a differential rotation of 10?? ?? 3?? across it. In addition, the rates of rotation in southern Washington are similar to those for rocks in the western Cascades of Oregon and indicate that rotational deformation of Miocene age extends northward into southern Washington and eastward into the axis of the arc.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Paleomagnetism of an east-west transect across the Cascade arc in southern Washington: Implications for regional tectonism
Series title:
Journal of Geophysical Research B: Solid Earth
Volume
104
Issue:
B6
Year Published:
1999
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Geophysical Research B: Solid Earth
First page:
12853
Last page:
12863