Date File Created Name of Creator 3/29/2011 Josh Rosera (UNC) GeoRef Data 2010-029009 DN GeoRef TI "New (super 40) Ar/ (super 39) Ar ages reveal contemporaneous mafic and silicic eruptions during the past 160,000 years at Mammoth Mountain and Long Valley Caldera, California" AU "Mahood, Gail A; Ring, Joshua H; Manganelli, Simone; McWilliams, Michael O" AF "Stanford University, Department of Geological and Environmental Sciences, Stanford, CA, United States (USA)" SO Geological Society of America Bulletin122.3-4 (March 2010): 396-407 IS 0016-7606 CD BUGMAF DE "absolute age, acidic composition, Ar/Ar, basaltic composition, calderas, California, Caso Diablo Till, Cenozoic, clastic sediments, dacites, dates, eruptions, glaciation, igneous rocks, lava, Long Valley Caldera, mafic composition, magma chambers, magmas, Mammoth Mountain, Mono County California, periodicity, Pleistocene, Quaternary, sediments, till, trachytes, United States, upper Quaternary, volcanic features, volcanic rocks, volcanism, volcanoe" AB "We undertook a (super 40) Ar/ (super 39) Ar study of young mafic and silicic lavas at Mammoth Mountain and the Long Valley caldera (east-central California) to better understand the frequency of these eruptions and the magmatic plumbing system that drives them. Our results show that most of Mammoth Mountain, a lava-dome complex straddling the southwestern topographic rim of the caldera, consists of trachydacite lavas erupted at ca. 68 ka. These ages and new 29- and 41 ka ages for trachydacite lavas in the northwest quadrant of the caldera indicate that these silicic lavas are considerably younger than previously thought. Mafic lavas vented widely in the western third of the caldera in the past 190,000 years, suggesting that this area has not been underlain by large bodies of silicic magma during this interval, as such magma would have prevented the rise of the denser basaltic magma. We identify four eruptive sequences over the past 190,000 years: the western moat sequence ( approximately 190-160 ka), the Mammoth sequence ( approximately 120-58 ka), the northwest caldera sequence ( approximately 41-29 ka), and the Inyo chain sequence ( approximately 9 ka-present). In each eruptive sequence mafic and silicic lavas erupted contemporaneously from spatially associated vents. This suggests that intrusion of alkali basalt into the shallow crust led to the silicic eruptions. If the seismic unrest and deformation of the past three decades is a result of basalt injected beneath Mammoth Mountain and perhaps the western third of the caldera, then there is the possibility of spatially associated small-volume silicic eruptions, which would typically be considerably more explosive. In the past 40,000 years, eruptions have occurred along a N-S linear trend less than 10 km wide, limiting the zone subject to volcanic hazards. Our data bear on Pleistocene glaciation in the region. Ages of 162+ or -2 ka and 99+ or -1 ka for bracketing mafic lava flows better constrain the age of the Casa Diablo till. Our results provide equivocal support for a suggested anticorrelation between volcanism and glaciation for the past 800,000 years in eastern California (Glazner et al., 1999)." LA English FE "References: 45, illus. incl. 1 table, geol. sketch map" PY 2010 PT Serial; Analytic CP United States (USA) CL "24: Quaternary geology, 03: Geochronology" CY "GeoRef, Copyright 2008, American Geological Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States | Reference includes data supplied by the Geological Society of America, Boulder, CO, USA, United States" AN 2010-029009 Sample Data Item Age Max_age Min_age Age Max_age Min_age Age Max_age Min_age LatDD LongDD Loc_prec Location_Name Rock_Type Material Rock_Class State Units ma ma ma ma ma ma ma ma ma dd dd Method 1 1 1 2 2 2 3 3 3 4 4 Sample Name M-17 0.042 0.045 0.039 37.728 -118.994 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Biotite Trachydacite California M-14 0.096 0.098 0.094 37.629 -119.031 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Biotite Trachydacite California M-15 0.119 0.123 0.115 37.64 -119.034 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Biotite Trachydacite California M-7 0.143 0.145 0.141 37.675 -118.984 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Biotite Rhyolite California M-34 0.098 0.099 0.097 37.604 -119.08 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachydacite California M-30 0.031 0.033 0.029 37.747 -118.979 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-31 0.066 0.068 0.064 37.725 -118.963 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-35 0.081 0.082 0.08 37.613 -119.024 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-33 0.082 0.083 0.081 37.639 -119.083 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-141 0.087 0.094 0.08 37.661 -119.042 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-137 0.088 0.093 0.083 37.661 -119.031 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-139 0.094 0.103 0.085 37.666 -119.046 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-39 0.099 0.1 0.098 37.636 -118.928 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-37 0.1 0.102 0.098 37.637 -118.919 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-101 0.105 0.112 0.098 37.592 -119.022 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-32 0.121 0.124 0.118 37.665 -119.014 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-126 0.148 0.162 0.134 37.65 -118.967 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-38 0.162 0.164 0.16 37.637 -118.921 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-124A 0.193 0.2 0.186 37.714 -118.947 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-124B 0.19 0.199 0.181 37.714 -118.947 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Groundmass Trachybasalt California M-20 0.065 0.067 0.063 37.637 -119.015 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Na-sanidine Rhyolite California M-11 0.067 0.068 0.066 37.646 -119.027 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Na-sanidine Trachydacite California M-14 0.068 0.069 0.067 37.629 -119.031 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Na-sanidine Trachydacite California M-15 0.068 0.069 0.067 37.64 -119.034 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Na-sanidine Trachydacite California M-9 0.081 0.082 0.08 37.643 -119.022 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Na-sanidine Rhyolite California M-3#1 0.088 0.094 0.082 37.652 -118.995 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Na-sanidine Rhyolite California M-3#2 0.091 0.093 0.089 37.652 -118.995 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Na-sanidine Rhyolite California M-22 0.058 0.06 0.056 37.616 -119.013 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Plagioclase Trachydacite California M-6 0.087 0.089 0.085 37.659 -118.995 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Plagioclase Trachydacite California M-27 0.113 0.115 0.111 37.657 -119.013 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Plagioclase Trachydacite California M-16 0.027 0.028 0.026 37.728 -118.991 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Sanidine Trachydacite California M-17 0.03 0.031 0.029 37.728 -118.994 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Sanidine Trachydacite California M-18 0.04 0.041 0.039 37.736 -119.012 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Sanidine Trachydacite California M-19 0.041 0.042 0.04 37.737 -119.002 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Sanidine Trachydacite California M-5 0.113 0.114 0.112 37.657 -118.984 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Sanidine Rhyolite California M-8 0.163 0.165 0.161 37.672 -118.971 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Sanidine Rhyolite California M-26 0.161 0.163 0.159 37.693 -118.969 0.001 Mammoth Mtn. and Long Valley caldera Volcanic Sanidine Rhyolite California Method Data 1 AR-AR:BIO 180 2 AR-AR:GM 180 3 AR-AR:SAN 180 4 SCAN 2010-029009