46 Structural Geology (Posters)

Sunday, 1 November 2015
9:00 AM - 5:30 PM
Exhibit Hall

MAGNETIC FABRICS IN AN EOCENE ANDESITIC DIKE, UPPER PLATE, HEART MOUNTAIN SLIDE, WY

Paper number: 46-34
Program: Technical Sessions
Time: 9:00 AM – 5:30 PM

Authors

Abstract

The Eocene Heart Mountain landslide was preceded by emplacement of widespread mafic dikes and the magnetic characteristics of these dikes can be used as a tectonic tracer for upper plate block movements. Previous work on mafic dikes that pervade the upper plate of the Heart Mountain Madison Group limestones at Cathedral Cliffs, WY preserve a vertical Kmax orientation (n=32) indicating vertical dike intrusion and that dike intrusion did not trigger horizontal upper plate motion. We have sampled a rootless andesitic dike (N90°E, 90°) that intruded into horizontal Madison Group limestone then translated southeastward to the allochthonous Paleozoic rocks of the Madison Formation overlying the ramp at Rattlesnake Mountain. AMS patterns (n=22) record Kmax perpendicular to Kmin and both with a horizontal orientation at an acute angle to the dike. AF demagnetization (n=10) was clean with linear paleo-vector plots (mean paleopole: 355°, 10°) that require a 35° rotation about a horizontal east-west axis to align with the Eocene paleopole for this latitude. These results indicate that the dike was emplaced at a shallow angle, rather than vertically, and that some upper plate Heart Mountain blocks translated with vertical motion about a horizontal axis.