Friday, April 3, 2009

Formation of Basins with Coriolis Rotation

Avery Island salt dome, Louisiana

Basin Formation from Coriolis cell rotation
Coriolis force, rotating portions of the Earth’s crust, forms circular cells in the crust of continents, and simultaneously creates basins and uplifts on opposite sides of those cells.
The mechanism is as follows:

ong>This is an interpreted version of the Hurricane fault, near the town of Hurricane, UT. See the following photo for the unedited Google Earth map.

In the case of a rising magma (or salt domes), in the northern hemisphere, the tendency to move to the right results in a CW spin to the crust. This affects the cover rock, causing it to rotate CW also, and the process creates shear zones on the perimeter of the circular configuration. When there is a crustal thickness difference on one side of the shear circle, compared to the other side, the thicker crust rotates faster (greater mass over the Asthenosphere results in increased forced rotation rate) and compresses the slower-moving portion. This creates an uplift or mountain range, while the lagging portion results in a basin or depression (graben) on the opposite of the shearing circle.

A photo of the Grass Valley basaltic flow is shown above. This flow originated above Hf, falling down the slope created by Hf and the monocline to the west. This action resulted from the compression of CW rotation from the east overtaking the slower rotation of the thinner crust to the west (with the continujous CW movenent).

Slickensides, which yield a record of relative movements of rocks sliding along a shear zone face, show that a portion of Hf fell while being dragged westward. The result is a slanting trace or groove on the south-facing scarp- which shows the direction of movement laterally (as well as downwardly).
The cases of larger rotating cells- as with the Colorado Plateau, CP- show that the same thing happens, whenever the base is heated. Then the shearing circumference effects vulcanism from the excess heat (from both the basal heat and friction from shear). For CP, the result is a clockwise advance of volcanoes, relative to the CCW rotation of the perimeter. CP has had vulcanism commence at the Rio Grande rift and proceed westward at the southern edge, CW, since the Oligocene- resulting in a geothermal anomaly under St. George, UT now.

Relatively flat terrain such as in the Texas oil country, exhibits a Coriolis rotating cell also. The result for this large cell is uplift at Round Mountain, near Austin, and the Atchafalaya Basin in SW Louisiana. In between lie many oil basins, which sink to varying degrees according to the thickness of the crust beneath. The ratio of the length of the basins, which parallel the rotating cell, to the diameter of the cell is about 1:10; that is, for a 30 mile basin, the diameter of the cell is about 300 miles.
This feature was discovered for a volcanic magma chamber near the Hurricane fault, and subsequently searched in other volcanic areas of the west. When these rotating cells were noticed in all part of the various continents, as evidenced by areas where I had some geological experience- Turkey, AZ, NM, and the Puget Sound, WA- I began to categorize them. Mountainous country where there was considerable difference in crustal thickness exhibited easily found cells, while flatter country exhibited more subtle cells. The cells are easily found by searching for arcuate-shaped river valleys. Further substantiation is found by looking on either side of the cell to find the resulting graben, or basin-depression, and uplift.