DEFORMATION IN THE CHRISTMAS MOUNTAIN LACCOCALDERA AND ITS ASSOCIATION WITH THE TASCOTAL MESA FAULT

Deformation in the Christmas Mountain Laccocaldera and its association with the Tascotal Mesa Fault

The Christmas Mountains area has gone through several tectonic and volcanic events over the last 42 million years that has led to the laccocaldera complex we see today. The geology of the area consists of Tertiary volcanics which includes various tuffs and igneous intrusions that are interbedded with tilted Cretaceous limestones. Also in the area you can find evidence for the Ouachita Orogeny, Laramide Orogeny, Basin and Range and the Rio Grande rifting. The complex is different from most calderas because it developed over a rather thin laccolith as opposed to developing over a deep pluton of magma. Various fractures show horizontal and vertical synthetic shear components. The structures are aligned with the Texas Lineament Corridor and the Texas-Chihuahua intracontinental transform zone. In a recent trip to the complex, we were able to collect structure data that we interpret as evidence as deformation associated with the Tascotal Mesa fault. Orientation data of lineaments from previous work shows a general trend of N10˚-20 ˚W in the northern corner of the dome. Theses fractures occur in weathered volcanic units that show variations of compositions. Previous remote sensing and field work documented eighty- two fractures that have a mean vector of 347.5 ˚ ± 18.5˚, five faults with an orientation of a mean vector of 348˚ ± 60.8˚, and two dikes ≈1.6 km long that are oriented ~020˚. Using Google Earth I was able to detect more evidence of faulting by noticing 90 degree turns in creek beds. I was also able to confirm these observations in the field. These data are consistent with a NW trend for structures associated with transtensional deformation along the southern Rio Grande Rift.