New Mexico Geological Society Annual Spring Meeting — Abstracts

Two general hypotheses have been proposed to describe the tectonic evolution of the southeastern boundary of the Colorado Plateau. One hypothesis suggests that the geophysical boundary of the Plateau of migrating toward the Plateau interior as a result of crustal/lithospheric thinning, for example as is thought to be occurring along the northwestern Plateau boundary. Another hypothesis, however, suggests that much of the volcanic activity along the southwestern Plateau boundary reflects the presence of a pre-existing zone of weakness in the lothosphere, the Jemes lineament, which has leaked magma to the surface. Several observations derived from this study tend to favor the latter hypothesis. First, profound regional trends in heat fIow are not observed in the study area (although deeper heat-flow data are surely needed). The data present a heat-flow pattern consisting of local anomalies of relatively high heat flow superimposed on a regional low to intermediate heat-flow setting, rather than a gradual increase of heat flow from the Plateau interior across the transition zone to the Rio Grande rift/Basin and Range Province. Sites with relatively high heat flow located towards the Plateau interior and away from recent volcanic activity may reflect magma intrusion and/or ground-water movement along crustal zones of weakness associated with Laramide deformation (monoclines). Second, the lack of profound regional trends in coal maturation across the study area suggests that any post-cretaceous thermal events which may be associated with the southern Plateau boundary of Jemez lineament have been initiated relatively recently and/or are occurring at relatively great depths; or the thermal events are in the form of relatively small, widely spaced intrusions.