HR: 09:15h
AN: GP41A-06    [Abstracts]
TI: Secular Variation and Paleomagnetic Studies of Southern Patagonian Plateau Lavas, 46S to 52S, Argentina
AU: * Brown, L
EM: lbrown@geo.umass.edu
AF: Dept Geosciences, University of Massachusetts, Amherst, MA 01003-9297, United States
AU: Gorring, M
EM: gorringm@mail.montclair.edu
AF: Dept Earth and Env. Studies, Montclair State University, Montclair, NJ 07043, United States
AU: Mason, D
EM: dmason@geo.umass.edu
AF: Dept Geosciences, University of Massachusetts, Amherst, MA 01003-9297, United States
AU: Condit, C
EM: ccondit@geo.umass.edu
AF: Dept Geosciences, University of Massachusetts, Amherst, MA 01003-9297, United States
AU: Lillydahl-Schroeder, H
AF: Dept Geosciences, University of Massachusetts, Amherst, MA 01003-9297, United States
AB: Regional studies of paleosecular variation of the Earth's magnetic field can provide us with information beyond that available from one location. Southern Patagonia, Argentina (46S to 52S latitude and 68W to 72W longitude) is a place where numerous Plio-Pleistocene lava flows are available for such a study. Volcanic activity in this area is related to back arc volcanism due to slab window activity as the South Chile Ridge is subducted beneath western South America, producing Neogene volcanic centers capping Mesozoic basement extending far to the east of the active plate boundary. Published studies on young lavas from both the northern (Meseta del Lago Buenos Aires, Brown et al, 2004) and southern (Pali Aike Volcanic Field, Mejia et al, 2004) portions provide stable paleomagnetic data on nearly 70 lava flows. Paleosecular variation values for the two studies differ, with 17.1 degrees obtained from the Pali Aike field and 20.0 degrees from the Lago Buenos Aires field. Recent fieldwork in the plateau lavas between these two locations has provided some 80 new sites allowing us to better investigate secular variation and the time-averaged field over this entire region during the past 5 myr. Rock magnetic studies on selected new samples (isothermal remanent magnetization and hysteresis measurements) as well as optical observations indicate low titanium magnetite as the primary carrier of remanence. Hysteresis properties range from 0.1 to 0.4 for Mr/Ms and 1.4 to 3.0 for Hcr/Hc indicating psuedo-single domain behavior. Mean destructive fields for AF demagnetization average 40 to 60 mT. Thirty-three new sites, mostly from Gran Meseta Central (48°S), yield a mean direction of inclination –61.8, declination of 356.6 with an alpha-95 of 5.7 degrees. These directions, with additional sites recently collected from Meseta de la Muerte south to Rio Santa Cruz, will allow us to further investigate paleosecular variation over this wide region.
DE: 1522 Paleomagnetic secular variation
DE: 1540 Rock and mineral magnetism
DE: 1560 Time variations: secular and longer
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting