Monday, November 23, 2009
Uplift Pulsing of the Hurricane Fault, Hf, at Hurricane Town
Pulsing of the Hurricane Fault, Hf
An introduction to this phenomenon is shown by the below photo, looking eastward towards Zion National Park and the town of Virgin, UT, which shows three levels of erosion:
a. The present Hurricane Valley level has dropped about 100 meters from the present rim of the scarp, leaving a fairly sharp basaltic edge. This tough rock allows erosion to remain small, so that a good view of the basalts can be seen. The approximate age is 200 k.years, since this is the age of the start of the Pleistocene volcanic craters nearby. This area is anomalous, because of the rotation of both Hf and the 20 km Coriolis cell (from Laverkin to the AZ border). Hence, the 100 meters is not representative of scarp heights found away from the cell. And it is not eroded as slowly either, because the Laverkin graben and sink have accelerated loosening of the Crust.
b. At higher elevations above the youngest scarp is another, which is somewhat more eroded. Notice the rounding of the limestone outcrops, and the wider drainage features.
c. The last one which is obvious is the oldest scarp, but it may be preceded by others which are older and fainter. Age dating of the oldest scarp may be approximated by the occurrence of Pine Valley Monzonite boulders north of the Virgin town, where there is a basalt-covered mesa which has been measured to be about 1 million years age. Below this basalt is a conglomerate containing the granite-like rocks which could only derive from PVM. These boulders rolled down from the Mountains when there was no scarp in their path- sometime before the million year basalt. This then was the start of the present series of scarps at Hf. Although this age of 1 m.y. is a minimum age (they may have rolled there at any time between Mesozoic and the age of the overlying basalt- but not before the age of PVM, which is 21 m.y.). We will use the minimum age as a precursor to the age of the oldest scarp shown at Hf at present. Consequently, the pulsing recurs near the time of 300 k.years, assuming that the creek through which the PVM boulders flowed was the same one which allowed the lava to flow in its most recent configuration. ABOVE PHOTO SHOWS THE MULTI-SHEARING TERRACES OCCURRING NEAR THE TOWN OF VIRGIN, ABOVE KOLOB CANYON-IN THIS CASE 5 PARALLEL FEATURES WHICH HAVE SLUMPED OFF THE MESA, AS IT ROSE. THIS BASALT OF 1 M.Y. AGE ELUDES THE GEOLOGISTS AS TO SOURCE, SINCE IT HAS RISEN ABOVE THE OBVIOUS BASALT FLOW LOWER IN THE CANYON (THE KOLOB ROAD RIDES ON THIS FLOW TO THE NORTH- WHICH IS THE SAME FLOW ELEVATED FURTHER SOUTH).
Using all of these highly tentative ages and scarp developments, we can conjecture that vulcanism and Hf scarp renewals are simultaneously occurring- acting as pulses to a movement which is otherwise extremely slow. I have measured the rate of movement of Hf laterally, along with down drop of the local graben and find that the outer extremity of the shear along lateral striations in local canyons is about 5 mm/year, while Hf is forming on the edge of the Colorado Plateau, CP (which is moving CCW at a rate of 1/3 the vertical drop in a nearby graben). Vulcanism proceeds CW around CP- having moved from the Rio Grande rift since Oligocene time, to the St. George area now.
I anticipate that the pulsing is that of the magnetic reversal of the Earth’s field, creating vulcanism along the Mid-Atlantic Ridge at fairly regular time intervals. The pulsing must create a renewal of magma emergence sufficient to shove the two parts of the Atlantic Ocean basin apart at intervals. This is all highly speculative, but I see the same pulsing occurring at intervals of less than a million years at a newly-forming transform found SE of the big island of Hawaii.
Grid lines are formed parallel to each other and deviating regularly at intervals, about 8 nautical miles apart. This at the measured rate of movement of the apparent positioning of extrusion sites (volcanic islands) of 8.6 cm/year, yields a cyclicity of something less than a million years. This CONJECTURE is tying together Magnetic pulsing or striping, vulcanism at Hf, gridlines SE of Hawaii, uplift at Hf, and whatever institutes magnetic reversal.