AMARANTE, J. F. A., and SHARI A. KELLEY, Dept. of Earth and Environmental Science, New Mexico Institute of Mining and Tech., Socorro, NM 87801; and KATE C. MILLER, Dept. of Geological Sciences, University of Texas at El Paso, El Paso, TX 79968

ABSTRACT: Characterization of the Precambrian Basement in Mescalero #1, Guadalupe County, New Mexico

Labrador Oil Company drilled a deep petroleum exploration well, Mescalero No. 1, in the Tucumcari Basin, Guadalupe County, east central New Mexico in 1996. This well penetrated of 2650 m of Precambrian basement consisting of gabbro at the top of the section, followed by a metavolcanic-sedimentary sequence, syenite, and finally granite at the bottom of the section. Petrographic examination of cuttings and analysis of geophysical logs from this well provide a unique opportunity to correlate lithology with basement reflectors on seismic lines in the Tucumcari Basin.

Gabbro is the most abundant rock type in the basement section, and characteristically occurs as sill-like bodies, although some gabbro dikes are also inferred. The two largest sills are at depths of 1759-1859 m and 1905-2155 m and are strong reflectors on seismic lines in the Tucumcari Basin. The gabbro appears to be the youngest rock unit within the basement since it intrudes the other Precambrian rock units. The metavolcanic-sedimentary sequence (depth of 2155-2664 m) consists of rhyolitic tuff, dacite, gneissic metasediment and meta-arkose. The meta-arkose is fine to medium grained and cemented by carbonate. The lower portion of the meta-arkose contains abundant fragments of underlying syenite. The syenite (2664-3740 m) exhibits some variation in composition, passing from syenite to quartz syenite downhole. Near its top, the syenite is brick-red and strongly altered. This zone may represent an erosional contact between the arkosic unit and the syenite. The granite (3740 to 4100 m) has a porphyritic texture; the age relationship between the granite and the other basement units is not known.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico