Rapid passage of a small-scale mantle heterogeneity through the melting regions of Kilauea and Mauna Loa Volcanoes
Jared P. Marskee , Aaron J. Pietruszkaa, Dominique Weisb,c, Michael O. Garciad and J. Michael Rhodese
aDepartment of Geological Sciences, San Diego State University, 5500 Campanile Dr., San Diego, CA 92182-1020, USA
bFNRS Research Director, Department of Earth and Environmental Sciences, CP 160/02-Université Libre de Bruxelles, Avenue F. D. Roosevelt, 50, B-1050 Brussels, Belgium
cPacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Rd., Vancouver, Canada BC V6T-1Z4
dDepartment of Geology and Geophysics, University of Hawaii, 1680 East West Rd., Honolulu, HI 96822, USA
eDepartment of Geosciences, Morrill Science Center, University of Massachusetts, 611 North Pleasant St., Amherst, MA 01003-9297, USA Received 27 September 2006; revised 12 April 2007; accepted 16 April 2007. Editor: R.W. Carlson. Available online 22 April 2007.
Abstract
Recent Kilauea and Mauna Loa lavas provide a snapshot of the size, shape, and distribution of compositional heterogeneities within the Hawaiian mantle plume. Here we present a study of the Pb, Sr, and Nd isotope ratios of two suites of young prehistoric lavas from these volcanoes: (1) Kilauea summit lavas erupted from AD 900 to 1400, and (2) 14C-dated Mauna Loa flows erupted from 2580–140 yr before present (relative to AD 1950). These lavas display systematic isotopic fluctuations, and the Kilauea lavas span the Pb isotopic divide that was previously thought to exist between these two volcanoes. For a brief period from AD 250 to 1400, the 206Pb/204Pb and 87Sr/86Sr isotope ratios and εNd values of Kilauea and Mauna Loa lavas departed from values typical for each volcano (based on historical and other young prehistoric lavas), moved towards an intermediate composition, and subsequently returned to typical values. This is the only known period in the eruptive history of these volcanoes when such a simultaneous convergence of Pb, Sr, and Nd isotope ratios has occurred. The common isotopic composition of lavas erupted from both Kilauea and Mauna Loa during this transient magmatic event was probably caused by the rapid passage of a small-scale compositional heterogeneity through the melting regions of both volcanoes. This heterogeneity is thought to have been either a single body ( 35 km long based on the distance between the summits of these volcanoes) or the plume matrix itself (which would be expected to be present beneath both volcanoes). The time scale of this event (centuries) is much shorter than previously noted for variations in the isotopic composition of Hawaiian lavas due to the upwelling of heterogeneities within the plume (thousands to tens of thousands of years). Calculations based on the timing of the isotopic convergence suggest a maximum thickness for the melting region (and thus, the heterogeneity) of 5–10 km. The small size of the heterogeneity indicates that melt can be extracted from small regions within the Hawaiian plume with minimal subsequent chemical modification (beyond the effects of crystal fractionation). This would be most effective if melt transport in the mantle beneath Hawaiian shield volcanoes occurs mostly in chemically isolated channels.
Earth and Planetary Science Letters Volume 259, Issues 1-2, 15 July 2007, Pages 34-50
Dr. Peterson has been a Professor of Geological Sciences here at San Diego State University since 1963. Gary started his career here as a stratigrapher / sedimentologist providing thousands of geology students with a sound basis in geology. During his career Peterson has published more than 40 articles and advised numerous thesis projects. Over the last 15 years, Peterson has used his extensive knowledge and field experience to develop his early interests in extraterrestrial geology. He began the Department's general education planetary geology course and the very popular "Independant Planetologist" lecture service, sharing his passion for for the planets throughout the local science community. Dr. Gary Peterson will be taking part in the Faculty Early Retirment Program starting Fall 2007.
