Early extension and associated mafic alkalic volcanism from the southern Basin and Range Province: Geology and petrology of the Rodeo and Nazas volcanic fields, Durango, Mexico

摘要

East-northeast extension ca. 24 Ma at Rodeo and Nazas, México, was accompanied by eruption of hawaiites, marking some of the earliest intraplate-type mafic alkalic volcanism associated with development of the southern Basin and Range Province. An earlier extensional pulse, 32.3–30.6 Ma, concurrent with subduction- related rhyolitic volcanism of the Sierra Madre Occidental, is the earliest established extension in the southern Basin and Range Province. The Rodeo hawaiites are mostly along or just west of the north- northwest–striking, west-dipping Rodeo fault, a major breakaway fault that separates moderately extended terrane to the west from less extended terrane to the east. Hawaiites and interbedded conglomerates in the Rodeo half graben are flat lying to gently tilted and cut by the Rodeo fault. Underlying Eocene–Oligocene ash-flow tuffs to the west are cut by numerous west- dipping faults and tilted as much as 40°. Nazas hawaiites are also along north-northwest–striking faults but are generally unfaulted.