V53H-05
New Radiometric Age Constraints for the Matuyama-Bruhnes Reversal and Santa Rosa Excursion
Friday, 18 December 2015: 14:40
310 (Moscone South)
Andrea Balbas1, Anthony A P Koppers1, Dennis V Kent2, Robert S Coe3, Kevin Konrad4 and Peter U Clark5, (1)Oregon State University, Corvallis, OR, United States, (2)Rutgers University New Brunswick, EPS, New Brunswick, NJ, United States, (3)University of California Santa Cruz, Santa Cruz, CA, United States, (4)Oregon State University, College of Earth, Ocean, and Atmospheric Science, Corvallis, OR, United States, (5)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States
Abstract:
The coupling of the timing of the virtual geomagnetic pole (VGP) position and the absolute paleointensities for geomagnetic events is vital for understanding the Earth’s geodynamo. Here we present new high-precision 40Ar/39Ar age determinations using an ARGUS-VI multi-collector mass spectrometer for lava flows on Floreana Island, Galapagos, and Tahiti Nui, Society Islands. New Galapagos ages (n=6) place the GA-79 lava flow on Floreana Island, which records an excursional VGP from an equatorial region (Cox and Dalrymple, 1966), within the Santa Rosa excursion. This flow contains extremely low paleointesity values of 1.1 x 1022 Am2 (n=11; Wang and Kent, 2013). We also present 52 new ages on 18 lava flows from the Punaruu valley, Tahiti, which record the Matuyama-Bruhnes reversal. The new ages confirm that the lavas record this reversal, but the ages differ from the original stratigraphy presented in Mochizuki et al. (2011). Our new ages using the Kuiper et al. (2008) fish canyon sanidine ages for Punaruu valley lava flows are concordant with previous astronomically tuned ages (Channell et al. 2002, 2009) and represent the highest precision radiometric ages for the most recent reversal. Here we show that paleointensity lows associated with excursional events can be comparable to or less than those associated with reversals. In addition, such field strength reductions can occur in time intervals as short as 3 thousand years.
