AGE AND CHARACTERISITICS OF DEBACA TERRANE, EAST-CENTRAL NEW MEXICO

The well Mescalero 1, drilled by Labrador Oil Company in 1996 in the Tucumcari Basin of east-central New Mexico, penetrated 2652 m of basement rocks. Three main rock packages were encountered in this well: granite and quartz syenite associated with the Panhandle terrane, weakly metamorphosed volcaniclastic, sedimentary, and volcanic rocks of the Debaca terrane, and gabbroic dikes. The gabbro, which yields a biotite 40Ar/39Ar age of 1090 ± 4 Ma, is most likely the youngest rock unit because the gabbro caused contact metamorphism in the other Mesoproterozoic rocks. The quartz syenite, which underlies the Debaca sequence, has a SHRIMP U-Pb zircon age of 1334 ± 52 Ma. On the basis of the ages of the gabbro and quartz syenite, the age of the Debaca terrane can be reasonably constrained to be between 1.09 and 1.33 Ga. The Debaca sequence includes volcaniclastic sediment, tuffaceous sandstone, arkose, rhyolite, dolomite, and dolomitic quartzite. Here, the Debaca sequence rests on weathered quartz syenite of the underlying Panhandle terrane. This nonconformity can be easily identified and traced on a seismic reflection line located near Mescalero 1. The seismic data show that the Debaca basin thins to the north of the drillhole.