Henry Mountain Structure, Hanksville, Utah

The Henry Mountains are conventionally described as Mid-Tertiary, shallow emplacement, laccolithic structures and are more particularly described in the publication:

Geology of the Tertiary Intrusive Centers of the La Sal

Mountains, Utah—Influence of Preexisting Structural Features on Emplacement and Morphology

By

Michael L. Ross

http://pubs.usgs.gov/bul/b2158/B2158-9.pdf

The Henry Mountains are located approximately 80 miles East Southeast of Moab, Utah.

View looking southwest of the Henry Mountains, Mt. Pennell to the left and the North and South Summit Ridge consisting of Kimble, Turner, Mt. Ellen and Mt. Ellen Peak.

View looking west of the North and South Summit Ridge.

Map of the Henry Mountains with my waypoints plotted on it and marking the area where I found the Shatter Cones(?) illustrated below.

Planar Microstructures

The following photomicrographs of quartz grains with planar microstructures, PM's, were made from samples of sandstone collected at the southern end of the Henry Mountains to the east of Mt. Hillers, and between Mt. Pennell and Mt. Hillers. The scale of the PM's fit the scale of  planar deformation structures, PDF's, which I believe they are but they have not been verified by the experts in the field of impact structure geology. If they prove to be PDF's they would be diagnostic of an impact structure.

Photomicrograph of a quartz grain with two sets of PM's illuminated with cross polarized light.

Photomicrograph of a quartz grain with three sets of PM's illuminated with cross polarized light.

Photomicrograph of a quartz grain with three possibly five sets of PM's illuminated with cross polarized light.

Photomicrograph of a cataclastic, micro-clastic dike in the same sandstone as the above photomicrographs of planar microstructures.

Photomicrograph of a quartz grain collected from waypoint 02075 located to the east of Mt. Hillers.

Shatter Cones

The following photos of possible shatter cones were taken in the area indicated on the above map. The proposed shatter cones are not classic shatter cones, nor are they slickensides. The horsetail striations are on a curved surface but not on a conical surface. Some of the shatter cones at the Santa Fe Impact Structure are similar; however, at Santa Fe the surfaces have more curviture than at this location (08020) in the Henry Mountains.

The above photo of horsetail striations on a curved surface are even more bazaar,

The above photo of horsetail striations is also very interesting, but does not fit any photo of a classical shatter cone that I have ever seen.

Another illustration of strange horsetail striations on rather flat joint surfaces, also notice the horsetail striations below the pen on another joint surface.

The above proposed shatter cone (08016) in the above photo is a clast of a shatter cone within another shatter cone represented by the convex surface at the bottom or outside edge of the sample.

The above photo is a closeup of the same shatter cone cast  (08016) with rather faint horsetail striations.

The following photomicrographs of quartz grains with planar microstructures were made of grains of quartz taken from the orthoquartzite making up shatter cone 08016.

The above photomicrograph of a quartz grain that has one set of planar microstructures (PM's) and a set of planar fractures (PF's).