Abstract

Paleomagnetic analysis of 88 samples from 14 sites in four Eocene sills in the Matanuska Valley, south-central Alaska, yields a paleomagnetic pole at lat 72.9°N, long 281.1°E, precision parameter (k) =15.4. The paleolatitude of this result suggests that this part of the Alaskan crust was at or near its present position relative to North America in the middle Tertiary. This pole also indicates that the region has been rotated clockwise by approximately 50°. These results can be explained by local block rotations of fault-bounded blocks in response to regional right-lateral shear along both the Castle Mountain and Border Ranges faults.

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