Precambrian basement geology of the Permian basin region of west Texas and eastern New Mexico: A geophysical perspective

Because most of the Permian basin region of west Texas and southern New Mexico is covered by Phanerozoic rocks, other means must be found to examine the Precambrian upper crustal geology of the region. We have combined geologic information on the Precambrian from outcrops and wells with geophysical information from gravity and magnetic surveys in an integrated analysis of the history and structure of basement rocks in the region. Geophysical anomalies can be related to six Precambrian events: formation of the Early Proterozoic outer tectonic belt, igneous activity in the southern Granite-Rhyolite province, an episode of pre-Grenville extension, the Grenville orogeny, rifting to form the Delaware aulacogen, and Eocambrian rifting to form the early Paleozoic continental margin. Two geophysical features were studied in detail: the Abilene gravity minimum and the Central Basin platform gravity high. The Abilene gravity minimum is shown to extend from the Delaware basin across north-central Texas and is interpreted to be caused by a granitic batholith similar in size to the Sierra Nevada batholith in California and Nevada. This batholith appears to be related to formation of the southern Granite-Rhyolite province, possibly as a continental margin are batholith. Because of this interpretation, we have located the Grenville tectonic front southward from its commonly quoted position, closer to the Llano uplift. Middle Proterozoic mafic intrusions are found to core the Central Basin platform and the Roosevelt uplift. These intrusions formed at about 1.1 Ga and are related in time to both the Mid-Continent rift system and the Grenville orogeny in Texas. Because these features are likely to be rift related, they suggest that the concept of a Delaware aulacogen needs to be revised only to the extent that the rifting is Proterozoic in age, not Eocambrian. Precambrian basement structures and changes in Lithology have influenced the structure and stratigraphy in the overlying Permian basin, and thus have potential exploration significance. Interpretation of the gravity and magnetic data with geologic information also leads us to suggest the existence of pre-Ellenburger basins, which may be extensive and of potential exploration interest.