Download - Abajo Mountain Structure
-
8/4/2019 Abajo Mountain Structure
1/30
Abajo Mountain Structure, Blanding, Utah
Tim McElvain
The La Sal Mountains are conventionally described
as Mid-Tertiary, shallow emplacement, laccolithic
structures and are more particularly described in the
following publication:
Geology of the Tertiary Intrusive Centers of the La SalMountains, UtahInfluence of
Preexisting Structural Features on Emplacement and Morphology
By Michael L. Ross
http://pubs.usgs.gov/bul/b2158/B2158-9.pd
http://pubs.usgs.gov/bul/b2158/B2158-9.pdfhttp://pubs.usgs.gov/bul/b2158/B2158-9.pdf -
8/4/2019 Abajo Mountain Structure
2/30
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 theresult of simultaneous impact of multiple bolides.
Shatter Cones
-
8/4/2019 Abajo Mountain Structure
3/30
The following three photos in increasing detail are 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.
-
8/4/2019 Abajo Mountain Structure
4/30
-
8/4/2019 Abajo Mountain Structure
5/30
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.
-
8/4/2019 Abajo Mountain Structure
6/30
-
8/4/2019 Abajo Mountain Structure
7/30
-
8/4/2019 Abajo Mountain Structure
8/30
Microscopic Evidence of Shock Metamorphism
-
8/4/2019 Abajo Mountain Structure
9/30
The above photomicrograph is of a quartz grain with one primary and
possibly a second set of planar microstructures (PMs) that fit thescale of planar deformation features (PDFs).
-
8/4/2019 Abajo Mountain Structure
10/30
The above photomicrograph of toasted, melted and plastically deformed
quartz grains with multiple sets of remnant PMs that fit the scale of PDFs.
-
8/4/2019 Abajo Mountain Structure
11/30
The above photomicrograph is of a toasted, partially melted and
plastically deformed quartz grain with multiple sets of what appear
to be remnant PMs that fit the scale of PDFs.
Burro Canyon Formation apparent forceful contact
with Dakota Sandstone
-
8/4/2019 Abajo Mountain Structure
12/30
The above photograph is of a boulder of Burro Canyon
Formation, pea sized conglomerate in which some of the
pea sized clasts seem to have been melted and quenched.
See following photos and photomicrographs.
-
8/4/2019 Abajo Mountain Structure
13/30
Burro Canyon Formation pea sized conglomerate intruding
or coming in contact with a Dakota-Morrison sand stringer,
in this and the following photo notice the turbulent nature
of the contact possibly caused by rapid forceful injection of
the conglomerate.
-
8/4/2019 Abajo Mountain Structure
14/30
THE FOLLOWING
PHOTOMICROGRAPHS ARE MADE
FROM THIN SECTIONS OF THE
CRETACEOUS DAKOTA-MORRISON
SANDSTONE FROM A SAMPLE
TAKEN OF THE ABOVE BOULDER.
-
8/4/2019 Abajo Mountain Structure
15/30
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.
-
8/4/2019 Abajo Mountain Structure
16/30
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.
-
8/4/2019 Abajo Mountain Structure
17/30
-
8/4/2019 Abajo Mountain Structure
18/30
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 within the Burro Canyon Formation.
-
8/4/2019 Abajo Mountain Structure
19/30
-
8/4/2019 Abajo Mountain Structure
20/30
The above two photomicrographs are of fractured and
plastically deformed quartz grains with 2 sets of PMs
-
8/4/2019 Abajo Mountain Structure
21/30
-
8/4/2019 Abajo Mountain Structure
22/30
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 melt clasts.
-
8/4/2019 Abajo Mountain Structure
23/30
The above photograph is of a clast of Dakota-Morrison clay caught up and
incased in the Burro Canyon conglomerate.
THE FOLLOWINF PHOTOMICROGRAPHSILLUSTRATE MORE EXAMPLES OF THENATURE OF THE SUEVITE CLASTS
-
8/4/2019 Abajo Mountain Structure
24/30
Photomicrograph of a clast in the melt clast in the Burro Canyon
conglomerate that has been melted and quenched with what appear to beplanar features, possibly remnant PMs that fit the scale ofPDFs, see the
detailed photomicrograph below of the same clast.
-
8/4/2019 Abajo Mountain Structure
25/30
-
8/4/2019 Abajo Mountain Structure
26/30
Photomicrograph of a melted portion of one of the melt 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.
-
8/4/2019 Abajo Mountain Structure
27/30
-
8/4/2019 Abajo Mountain Structure
28/30
The above photomicrograph is of high definition melt in one of the melt
clasts in the Burro Canyon Formation, the following photomicrograph is of
the same view below illuminated by cross polarized light.
-
8/4/2019 Abajo Mountain Structure
29/30
Inner ring of the Abajo Mountain Impact Crater
-
8/4/2019 Abajo Mountain Structure
30/30
The above photograph is 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.
Summary
All of the above evidence I believe confirms that the Abajo Mountains,
Blanding Utah are the central uplift of an impact crater.