HR: 1330h
AN: V32A-0994    [PDF]
TI: East Molokai Volcano, Hawaii: Petrogenesis of Shield-, Postshield- and Rejuvenated Stage Lavas
AU: * XU, G
EM: gpxu@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massuchusetts Avenue, 54-1210, Cambridge, MA 02139 United States
AU: Frey, F A
EM: fafrey@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massuchusetts Avenue, 54-1210, Cambridge, MA 02139 United States
AU: Clague, D A
EM: clague@mbari.org
AF: Monerey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AU: Weis, D
EM: dweis@eos.ubc.ca
AF: Pacific Centre for Isotope and Geochemical Research, Department of Earth Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AB: The results of the Hawaii Scientific Drilling Project have led to renewed interest in the existence of Kea and Loa trends defined by recent Hawaiian volcanoes, that is correlations between geochemical characteristics and volcano location along the recent hotspot track (Lassiter et al., 1996). Mauna Kea and Haleakala are well studied, relatively young but inactive Hawaiian volcanoes belonging to the Kea trend. East Molokai is an older Kea-trend volcano (shield and postshield volcanism from $\sim$1.5 to 1.75 Ma). We have analyzed major and trace element abundances and isotopic ratios of Sr, Nd and Pb in lavas from the 305 m Kalaupapa section that exposes lavas erupted at the end of shield building and during the transition to the alkalic postshield stage at East Molokai volcano (Beeson, 1976). In addition, our study includes older shield-stage lavas from below the Kalaupapa section and samples from the overlying rejuvenated-stage basalt, including submarine rejuvenated-stage lavas recovered by submersible (Clague et al., 2002). The major and trace element abundances and trends of East Molokai lavas are similar to lavas from Haleakala. At both volcanoes there is a long-term trend for $^{87}$Sr/$^{86}$Sr to decrease and $^{143}$Nd/$^{144}$Nd to increase with decreasing eruption age. However, over short time intervals these trends show scatter and, especially at East Molokai, there is considerable range in $^{87}$Sr/$^{86}$Sr at a given $^{143}$Nd/$^{144}$Nd, even after acid leaching. The late shield and early post-shield lavas of East Molokai also define a positive $^{87}$Sr/$^{86}$Sr vs $^{206}$Pb/$^{204}$Pb trend, a distinctive feature of postshield Hawaiian lavas. The rejuvenated-stage East Molokai lavas are not as silica-undersaturated as the well known rejuvenated lavas forming the Honolulu Volcanics and Koloa Volcanics, and they range to higher $^{143}$Nd/$^{144}$Nd. We evaluate the relative importance of source heterogeneity, which is clearly indicated by temporal changes in isotopic ratios and correlated abundance ratios and processes, such as the extent and depth of melting which control the change from tholeiitic to alkalic volcanism.
DE: 3640 Igneous petrology
DE: 4825 Geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting