Calderas and ash flow tuffs of the Mogollon Mountains, southwestern New Mexico

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Abstract
The Mogollon Mountains are a major volcanic source area in the southwestern Mogollon‐Datil volcanic field, where about 2000 m of middle‐Tertiary rocks are exposed. The volcanic sequence includes eight major (>100 km3) ash flow units, believed to represent four caldera‐related, compositionally zoned ash flow sequences. Each caldera‐related sequence shows normal compositional zonation from high‐silica rhyolite to rhyolite and dacite. The Mogollon caldera (34 Ma) is preserved only as a fragment in the wall of the Bursum caldera. The Emory caldera (34 Ma) is about 50 km east of the Mogollon Mountains, and only the high‐silica facies of its presumed outflow sheet (Fall Canyon Tuff) reaches the Mogollons. The Gila Cliff Dwellings caldera (30 Ma), earlier interpreted as the source of the Bloodgood Canyon Tuff, probably is a large remnant of a caldera or pair of calderas that were the source of the Davis Canyon and Shelley Peak Tuffs. The Bloodgood Canyon Tuff was most likely erupted from the Bursum caldera (29–28 Ma), but ponded in the Gila Cliff Dwellings caldera. The resurgent dome of the approximately 40‐km‐diameter Bursum caldera is the predominant topographic and structural feature of the Mogollon Mountains. The caldera probably collapsed initially in response to eruption of the Bloodgood Canyon Tuff, then was largely filled with Apache Spring Tuff prior to resurgent doming. The cyclical eruption, beginning about 34 Ma, of similar compositionally zoned ash flows from separate shallow magma chambers, suggests derivation from a common parent magma of batholithic proportions. A regional Bouguer gravity low of about 40 mGals has been interpreted to reflect the presence of such a batholith. Major ash flow eruptions in the Mogollon‐Datil field were followed 26–25 Ma by fundamentally basaltic volcanism, characterized mainly by andesite. About 22–21 Ma, high‐silica rhyolite, tholeiitic basalt, and alkali basalt were erupted as a bimodal suite roughly coincident with the beginning of basin‐range extensional faulting. Alkali olivine basalt as young as 5.5 Ma is interlayered with basin fill (Gila Conglomerate) adjacent to the Mogollon Mountains.