THE TECTONIC EVOLUTION OF WEST TEXAS

West Texas has been located close to what is now the southern boundary of the North American plate for at least the last 1.3 Ga. The earliest recorded deformation associated with an island-arc environment is recorded in the Grenville-aged rocks of the Van Horn area. In general, the rocks have a WNW orientation and increase in metamorphic grade to the SSW. The Mica Mines area hosts somewhat enigmatic granite pegmatites.

Subsequent Ouachita deformation is apparent in the rocks of the Marathon Basin, Persimmon Gap and Solitario areas. The rocks having a NE to SW alignment and increase in the extent of deformation to the SE. Unfortunately, apart from roadcuts and State and Federal land, very little is available for examination. The Ouachita deformation does not extend sufficiently far north to overprint the Grenville deformation.

With the termination of Ouachita deformation (early Permian), the western North American plate boundary assumes a greater significance in the tectonic orientation of west Texas structural elements. The Laramide Orogeny (late Cretaceous-early Tertiary) is aligned approximately north- south and it, like the younger basin-and-range deformation, is superimposed on both the Grenville and Ouachita deformed rocks. Deformation continues, as is evidenced by the April 13th earthquake of 1995.