The Big Bend region is an igneous paradise!
Here one can find an intense concentration and variety of both intrusive and extrusive, Tertiary igneous rocks. From about 48 million years ago until about twenty million years ago the Big Bend was intruded time and again by widespread magmatic activity. At the surface, numerous calderas erupted great thicknesses of domes, ash falls, ash flows, and lava flows over vast areas of southwest Texas and northeastern Mexico. Igneous intrusions took the form of plugs, stocks, dikes, sills, and laccoliths. Indeed, this is one of the most intensely intruded areas one can find anywhere in North America.
 |
This northwest-trending dike is one of a series of such dikes standing out in relief along the west flank of the Chisos Mountains along the east side of Ross Maxwell Drive in Big Bend National Park. Here the dike intrudes strata of the Tertiary Chisos formation. |
 |
Three Dike Hill. Any guess where the name came from? These trachyte dikes are common throughout the Bofecillos Mountains. Here they intrude the Santana Tuff along Highway 170 in Big Bend Ranch State Park. |
A beautiful example of a peralkaline quartz trachyte forming a sill by intruding between limestone layers of the Boquillos formation. Karen Waggoner checks the strike and dip of the layers with her trusty Brunton Compass. Photo by Eric Murphy.
Photo of the Cretaceous rocks uplifted by the Black Mesa laccolith forming a flat-topped structure northeast of Lajitas, Texas.
Digital Elevation Model (DEM) of the Black Mesa laccolith located on the Terlingua uplift.
The south half of the laccolith is completely covered with Cretaceous limestones whereas the north half is eroded through exposing the rhyolitic rocks forming the laccolith which intruded 34 million years ago. Note that the laccolith sits on the southeast edge of a northeast-trending graben.
4901 E. University . Odessa, Texas 79762 . (432) 552-2020