Monday, November 5, 2007
Slickensides in the Hurricane fault zone (scarp)
These Slickensides are more extensive on hiway 9 cliffs, east of the shoulder, on the north part of hte Graben
This is the most massive Slickensides found- you should study it to use as an
Example for Future Finds; notice the Linear Striations and Grooves of hardened surface (probably silicates) precipitated from warm water flowing along the previous Subsurface Fault Face (original composition was Limestone, CaCO3)
The South view of Graben shows where it started (Water tank sits on Graben Downthrown Block)
Westward, the Upthrown Block shows a 15 Degree departure from Vertical (West Edge of Graben wall moved northward, as well as Vertically)
Eastward, the Upthrown Block Has Almost-Vertical Striations, indicating that the Plunge to north has little influence on the orientation
Graben Slickensides show Direction of Crustal Movement
Shown above and below are photos of “Skid Marks” or slickensides in the walls and Scarps above the town of Hurricane, in the Hurricane Fault, Hf to the east. These are the result of the rasping of one block of the Crust, as it moved relative to another block which is more stationary. These are primarily the work of normal faulting, which is unknown as to origin, but they give details of the movement in one local area. They may yield understanding of the larger underlying event which has Hf as a final result. The movement which produced the slickensides is very deliberate and slow, so that the final product is slick and contains regular lines and a glassy portrait of the direction and type of movement.
First, notice that the surface of the slickensides is so well-polished that it shines in the sunlight. The two blocks which slid relative to each other are of similar composition, and therefore of similar hardness. This causes the honed surface to appear extremely fine-grained.
Secondly, the surface is discolored in the millimeter or so thickness which is preserved. This is caused by the heat which is generated by the friction of rubbing, which changes the solubility of compounds in the water which has found the fractured and faulted space. The drop-out of iron compounds and other solutes in the water makes the surface harder than it was originally- initially calcite or limestone, which is soft (3 on Moh’s hardness scale).
Thirdly, small grains of hard material entrained in the moving block remain un-dissolved long enough to leave a line or trough, which indicates the direction of the movement. For a graben, this movement should be vertical, since this is a normal fault, happening under extension. However, the deviation from vertical is striking and regular for the west wall of the graben, which is the upthrown block (the downthrown block cannot be seen, because it has fallen into the earth).
1. The west wall of the graben has slickensides with striations dipping down into the earth- Down-to-the-South. Since the graben plunges down to the north, part of this 15 degree angle is due to rotation of the graben as it plunges down to the north (look at the larger photo of the whole graben, where the incipience or start of the graben is shown to be less than a kilometer to the south).
A Closeup of east wall of the Graben shows Striations resulting from "Drag" of Downthrown Block hard pebble inclusions- which leave parallel grooves.
2. The east wall of the graben (again the upthrown block) has a few degrees dip down to the north. This is not significant, and may be approximated as vertical, but the importance is that it shows that the plunge of the graben to the north is not a significant contribution to the deviation from vertical.
The Detailed Closeup of Striations (East Wall) show the angle of deviation as less than 5 Degrees, indicating that Plunge of Graben is not the Primary Factor causing the movement away from Verticality in the West Graben Wall
3. Since the graben west wall is the one showing deviation from vertical of the drop of the downthrown block, this indicates that we are looking a phenomenon which is occurring closer to Hf proper. Although the entire graben is part of Hf, and there is transfer of stress to form the graben, the entire result can be interpreted as part of the total movement of Hf. In this case, generalizing, the rim of the graben is moving north with the time of fall of the graben relative to the downthrown block. This would be a right-lateral fault, with movement laterally caused by something other than gravity (a weight of rock simply falling- due to gravitational attraction- as the earth is pulled apart). The lateral movement would be due to a compressive force, such as rotation of the Colorado Plateau, CP.
4. This right-lateral faulting is representative only of the graben where it is found but could be an indication of further investigation to determine whether it is representative of CP as a whole (at least on the western side, near the Pine Valley Mountains and local volcanism which bear on it- all Post-Laramide features).
The Massiveness of the Slicks shows that they were the Result of a continuous Sliding, and the Regularity indicates a slow movement which was heated by the Friction- allowing Water to Rearrange its Chemical Contents over significant time (NOT lurching)
A Rare image shows that there was occasionally a Disruption in the Graben Sliding- an interference