West Texas and Eastern New Mexico Precambrian Basement Revealed

Melanie Barnes¹

¹Texas Tech University

Abstract

Seismic interpretations, U-Pb zircon ages, and geochemical and isotopic analysis from the last decade combined with earlier information, provides a geologic framework for the Precambrian basement of west Texas and eastern New Mexico. Much of the crystalline basement documents voluminous, episodic magmatism that is a key component in the development of southern Laurentia. This complex history involves at least four major magmatic events and at least two periods of basin development from 1.49 to 1.07 Ga. The Texas Panhandle Precambrian basement consists of quartz monzonite, granite, rhyolite, and quartz syenite that can be divided into separate periods of magmatism at ~1.47 and ~1.37 Ga and may extend as far south as the Carrizo Mountain Group near Van Horn (1.33 Ga). Sm-Nd isotopic signatures indicate that these magmas had similar source regions.

From 1.28 to 1.22 Ga, a broad, carbonate-dominated shelf, known locally as the Debaca sequence, extended throughout the region from the Llano Uplift in the southeast to the western Grand Canyon regions. Well log data coupled with seismic data and deep crustal reflection data image large basins with cross-cutting sills. Outcrop and well data support the presence of associated mafic magmatism, along with episodic rhyolite ash falls which may be sourced in the Burro Mountains of southwestern New Mexico.

About 1150 Ma, after the deposition of quartz-rich sandstone of the Lanoria Formation, renewed bimodal magmatism began and lasted until ~1070 Ma. This magmatic episode was characterized by tholeiitic basalt and alkaline ("A-type") rhyolite/granite, all typical of extensional settings. U-Pb (zircon) dating provides evidence of widespread, Grenville-age (1070-1110 Ma) plutonic rocks in the Texas/New Mexico basement. Dated samples include alkali feldspar granite of the Abilene gravity minimum, monzonitic xenoliths from Patrillo maar west of El Paso, a differentiated sill from the Texas Panhandle and 40Ar/39Ar age from a gabbroic sill in the basement of eastern New Mexico. In addition, evidence of the northwest directed Grenville collisional event is apparent in the deformed nature of rocks located in the southern most part of the Laurentian continent.

AAPG Datapages/Search and Discovery Article #90190©AAPG Southwest Section Annual Convention, Midland, Texas, May 11-14, 2014