Cordilleran Section - 108th Annual Meeting (29–31 March 2012)

Paper No. 6
Presentation Time: 10:40


LAWTON, Timothy F.1, GILBERT, John C.1 and AMATO, Jeffrey M.2, (1)Geological Sciences/MSC 3AB, New Mexico State University, P.O. Box 30001, Las Cruces, NM 88003, (2)Geological Sciences, New Mexico State University, P.O. Box 30001/MSC 3AB, Las Cruces, NM 88003,

New LA-ICP-MS and SHRIMP U-Pb ages from zircons in tuffs of the Huachuca Mountains, Mustang Mountains and Canelo Hills of southeastern Arizona indicate Early to Middle Jurassic ages for stratigraphic sections previously identified as Canelo Hills Volcanics and Glance Conglomerate. Ages in the Canelo Hills conform to stratigraphic order of the samples. The upper part of a thick caldera-fill tuff of the Canelo Hills Volcanics yielded an age of 178.4 ± 1.1 Ma (n = 36; MSWD = 1.3) and a thin outflow tuff at the top of the volcanic section yielded a statistically indistinguishable age of 178.1 ± 0.8 Ma (n = 31; MSWD =1.07). Two eutaxitic outflow tuffs interbedded with overlying rhyolite- and limestone-clast conglomerate, assigned to the Canelo Pass member of the Glance Conglomerate by Bilodeau et al. (1987), have ages of 174.8 ± 1.0 Ma (n = 29; MSWD = 1.06) and 172.7 ± 0.9 Ma (n = 36; MSWD = 1.11). These rocks were formerly considered Late Jurassic on the basis of a whole-rock Rb-Sr isochron age (151 ± 2 Ma; Kluth et al., 1982). In the Huachuca Mountains, a 30-m welded tuff in Garden Canyon that overlies Permian carbonate strata and underlies limestone-clast Glance Conglomerate yielded an age of 171.6 ± 1.3 Ma (n = 25; MSWD = 1.0). In the Mustang Mountains, the basal welded tuff filling a paleocanyon eroded in Permian carbonate strata yielded a SHRIMP U-Pb age of 175.6 ± 1.9 Ma (n = 12; MSWD = 0.75), indicating correlation with the Canelo Pass member of the Glance Conglomerate. A detrital zircon sample from volcanic-clast facies of the Glance Conglomerate in the SW Huachuca Mountains contains Jurassic zircon grains in the range 200-176 Ma (81 of 96 grains). These ages indicate that the volcanic and sedimentary succession interbedded with and overlain by the Glance Conglomerate ranges in age from approximately 200 to 170 Ma and correlates with rocks of the Nazas volcanic arc of Mexico.