Abajo Mountain Structure, Blanding, Utah

The La Sal 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

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

The Abajo Mountains also known as the Blue Mountains are located approximately 45 miles south southwest of the La Sal Mountains, west of Monticello, Utah and North of Blanding, Utah. Along with the Henry Mountains and the La Sal Mountains they have been mapped as Mid-Tertiary laccolithic structures, but I have found the following evidence that each of them may be the central uplift of a peak-ring impact crater or the result of simultaneous impact of multiple bolides.

Shatter Cones

The following three photos in increasing detail of what appears to be a shatter cone developed on a joint in the Dakota-Morrison sandstone at the 8300 foot level of the Abajo Mountains on Johnson Ridge near Johnson Creek.

The following three photos in increasing detail of what appears to be a shatter cone development in a green shale in the Dakota-Morrison Formation at the 8300 foot level on Johnson Ridge near Johnson Creek and adjacent to the shatter cones illustrated above.

Microscopic Evidence of Shock metamorphism

Photomicrograph of a quartz grain with one primary and possibly a second set of planar microstructures (PM’s) that fit the scale of planar deformation features (PDF’s).

Photomicrograph of toasted, melted and plastically deformed quartz grains with multiple sets of remnant PM’s that fit the scale of PDF’s.

Photomicrograph of a toasted, partially melted and plastically deformed quartz grain with multiple sets of what appear to be remnant PM’s that fit the scale of PDF’s.

Burro Canyon Formation apparent forceful contact with Dakota Sandstone.

Boulder of Burro Canyon Formation, pea sized conglomerate in which some og the pea sized clasts seem to have have been meltd and quenched. See following photos and photomicrographs.

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Burro Canyon Formation pea sized conglomerate intruding a Dakota-Morrison sand stringer, in this and the following photo the notice the turbulent nature of the contact caused by rapid forceful injection of the conglomerate.

The following photomicrographs are made from thin sections of the Cretaceous Dakota-Morrison sandstone from a sample taken of the above boulder.

The above photomicrograph illustrates the shocked nature of the Dakota – Morrison sandstone in the vicinity of the injected Burro Canyon Formation clasts. The quartz grains have been fractured, accelerated into one another, and plastically deformed.

The above photomicrograph of a quartz grain illuminate by plane polarized light has 2 sets of  planar microstructures (PM’s), has been fractured by another grain that was accelerated in to it, and may have been plastically deformed.

The following photomicrographs are made from thin sections of the Burro Canyon Formation pea conglomerate in which some of the clasts appear to have been melted and quenched from a sample taken of the above boulder.

The above two photomicrographs, the first illuminated by plane polarized light and the second by cross polarized light, are of a melted and quenched quartz spherule withen the Burro Canyon Formation.

The above two photomicrographs are fractured, and plastically deformed quartz grains with 2 sets of PM’s

The above two photomicrographs, the first illuminated by plane polarized light and the second by cross polarized light, illustrate the nature of the pea sized suevite clasts.

The above photgraph is of a clast of Dakota-Morrison clay caught up and incased in the Burro Canyon conglomerate.

The followinf photomicrographs illustrate more examples of the nature of the suevite clasts.

Photomicrograph of a clast in the suevite conglomerate that has been melted and quenched with what appear to be planar features, possibly remnant PM’s that fit the scale of PDF’s, see the detailed photomicrograph below of the same clast.

Photomicrograph of a melted portion of one of the suevite clasts that appears to have formed quenched crystals that exhibit flow structure, see the more detailed view below of the same melt in the photomicrograph.

Photomicrograph of high definition melt in one of the clasts in the suevite, see same view below illuminated by cross polarized light.

Inner ring of the Abajo Mountain Impact Crater

Photo of a cross section in a road cut of the impact craters inner ring, a pressure ridge where some of the Dakota-Morrison Formation's green clay has been squeezed up through one of the same formations sandstone stringers.