Thursday, January 7, 2010
Virgin Anticline, UT Coriolis rotation through Time
Above is a photo of the Virgin anticline in the distance, taken from the Hurricane fault, Hf, and below is a Google photo looking from space, for orientation:
Below can be seen the Virgin River and the bend in the trend of the anticline:
During the compressional forces of the Laramide Revolution, several large N-S anticlines formed due to the E-W compression.
These include the Cockscomb of east Utah, the East Kaibab monocline, AZ, and ones more distant in New Mexico. The generalized push was from the west, with a resultant orientation of the anticlines perpendicular to the principal stress. This is not the case for the Virgin Anticline, which trends almost parallel to the Pine Valley Mountains (laccolith or intrusion) in SW Utah- orienting NE-SW.
This region of SE Utah is near the great lateral fault system, which runs from the Wasatch Line (Hurricane fault) southward, then SW-ward on to the Valley of Fire, NV to create a zone of sheared earth, with documenting slickensides and circular Crustal features reacting to this CW movement around SW Utah and south NV. Generally the crust immediately adjacent to the rotation rotates CW on the north side and CCW on the south side. The Virgin anticline occurs on both sides of the river which is formed by this shear zone, and is an interesting case study for determining movements made since the Laramide incipience.
Below is a photo of the anticline, taken from the WA County landfill road, looking to the east. Both limbs of the anticline may be seen, and there is an inflection at the Quail Lake Dam, which is shown below in a Google photo, as a space or plan view:
My analysis of the movements made (since the supposed original N-S orientation) is shown below. You can see several circular presentations, and RULES MUST BE USED TO DETERMINE THE ROTATION DIRECTION:
1. WHEN THE RIVER TRACE IS ROTATING CW, AS IN A SINKING CELL (THIS CASE), THE IMMEDIATE ADJOINING CELL WILL ROTATE IN REACTION TO THIS MOVEMENT (CCW). You can see that the Anticline NW limb has been rotated CCW at the inflection.
2. When 2 circular displays are adjacent, they must rotate in harmony, OR ELSE THERE WILL BE HOT SPRINGS OR VULCANISM! THE QUAIL LAKE PRESENTS 2 ROTATIONS, AND THE RESULT OF ALL THIS IS THAT THE ANTICLINE HAS MOVED FROM ITS ORIGINAL ORIENTATION.
3. DETERMINING THE ORIGINAL ORIENTATION BEFORE ROTATION REQUIRES THE ANALYSIS OF RATE OF MOVEMENT OF DOMINANT FAULTING. GEOLOGISTS GENERALLY FIND THE FASTEST MOVEMENT-IN THIS CASE THE WA FAULT TO THE WEST- AND THIS HAS LATERAL MOVEMENT ON THE EAST SIDE TO THE NORTH (LEFT LATERAL FAULT). AS A RESULT, THE ANTICLINE HAS BEEN ROTATED TO A MORE NE-SW ORIENTATION.
Below are shown slickensides on the east side of the lake, by a shear rim of 40 meters drop, and these parallel the lake, orienting N20E to 200 degrees:
AFTER RE-HIKING THE ANTICLINE NEAR HIWAY 9, AT THE VIRGIN RIVER, THERE IS ADDITIONAL EVIDENCE FOR UPLIFT, SHEARING AND ROTATION:
TO BE CONTINUED, WHEN MORE FIELD WORK HAS BEEN DONE, UP ON THE ANTICLINE!