New Mexico Geological Society Annual Spring Meeting — Abstracts

⁴⁰Ar/³⁹Ar age spectra and paleomagnetic analyses tightly constrain the history of ignimbrite volcanism in the 36-24 Ma Mogollon-Datil volcanic field. High-precision (±.15 Ma) sanidine plateau ages have been obtained from most of the 30+ voluminous (100-1200 km²) regional ignimbrites. Age and paleomagnetic data allow reliable correlation of ignimbrites among isolated ranges, providing an integrated time-stratigraphic framework for the entire field.

Mogollon-Datil ignimbrite activity was strongly episodic, being confined to 4 brief (<2 Ma) eruptive episodes separated by 1-3 Ma gaps during which no caldera-forming eruptions occurred. Ignimbrite activity generally tended to migrate from the southeast towards the north and west.

Episode 1 (36-33.3 Ma): Rhyolitic ignimbrite activity, dominantly low-silica, commenced at the southeast edge of the field with eruption of the Organ Mountains caldera and associated outflow sheets at 36.1 and 36.5 Ma, closely followed by eruption of the nearby Dona Ana caldera at 35.4 Ma. Activity shifted 100 km northwest with eruption of the Kneeling Nun Tuff (>900 km³) at 34.8 Ma, followed by several less voluminous ignimbrite eruptions from 34.8 to 33.4 Ma.

Episode 2 (32.0-31.3 Ma): After a 1.5 Ma hiatus, low-silica rhyolitic ignimbrite activity shifted north and west, producing the Hells Mesa (32.0 Ma, 1200 km³), Caballo Blanco (31.6 Ma, a.k.a. Fall Canyon), and Tadpola Ridge (31.1 Ma) Tuffs.

Episode .3 (29.0-27.3 Ma): Following a 2.7 Ma hiatus, the "ignimbrite flare-up" occurred, producing within a span of 1.7 Ma more than 15 regional units, primarily high-silica rhyolites, totaling >6000 km³. Well-dated units withln this interval include Davis Canyon (29.0 Ma), La Jencia (28.8 Ma), vicks Peak (28.5 Ma), Shelley Peak (28.0 Ma), Bloodgood Canyon (28.0 Ma), Lemitar (28.0 Ma), and South Canyon (27.3 Ma) Tuffs. Calderas for these units were located near the western and northern margins of the volcanic field.

Episode 4 (24.3 Ma): After a 3.0 Ma hiatus, Mogollon-Datil ignimbrite activity ended near the northern edge of the field with the eruption of the high-silica rhyolite tuff of Turkey Springs at 24.3 Ma. Mogollon-Datil ignimbrite episodes 1, 3, and 4 closely parallel the timing of ignimbrite activity in the San Juan volcanic field of Colorado, indicating regional tectonic control of caldera-forming rhyolitic eruptions.