Bulletin 135 — Paleomagnetism and ⁴⁰Ar/³⁹Ar ages of ignimbrites, Mogollon–Datil volcanic fields, southwestern New Mexico

By W. C. McIntosh, L. L. Kedzie, and J. F. Sutter, 1991, 79 pp., 3 tables, 32 figs., 3 appendices.

This report presents ⁴⁰Ar/³⁹Ar sanidine ages and paleomagnetite data for 36 ignimbrites and associated lavas in the Eocene-Oligocene Mogollon-Datil volcanic field of southwestern NM.

⁴⁰Ar/³⁹Ar age spectra from the ignimbrites yield plateau ages that range from 36.2 to 24.3 Ma and show within-sample and within-unit 1s precision of ±0.5% or better. These ages agree closely with independently established stratigraphic order and indicate that Mogollon-Datil ignimbrite activity was highly episodic, being confined to four brief (<2.6 Ma) eruptive intervals separated by 1.5–3 Ma long hiatuses.

Ignimbrite outflow sheets show stable paleomagnetic remanence directions that are uniform over most of their areal extents, including facies ranging from thick, densely welded proximal ignimbrites to unwelded distal fringes as thin as 1.5 m.

Used in concert with lithologic and stratigraphic position data, ⁴⁰Ar/³⁹Ar ages and paleomagnetic directions allow accurate long-range ignimbrite correlations that provide reliable ties between previously established subregional stratigraphic sequences. These correlations have helped to establish an integrated time-stratigraphic framework for the Mogollon-Datil volcanic field.