HR: 10:50h
AN: T12A-03 INVITED    [Abstracts]
TI: Gravity, Bathymetry and Submarine Volcanism in the Mesozoic Pacific Ocean
AU: * Watts, A B
EM: tony@earth.ox.ac.uk
AF: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX13PR, United Kingdom
AU: Kalnins, L M
AF: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX13PR, United Kingdom
AB: Submarine volcano loading studies suggest that the effective elastic thickness, T_e, of oceanic lithosphere increases with age at the time of loading. Therefore, a seamount formed on a ridge crest will be characterised by a lower T_e than a similar size feature that formed off-ridge. Compilations of data where both crustal and sample ages are known show that T_e is given approximately by the depth to the 450° oceanic isotherm, based on plate cooling models. By comparing observed bathymetry and gravity anomalies to predictions based on simple elastic plate models it is possible to estimate T_e and hence the age of oceanic lithosphere at the time of loading at bathymetric features of unknown tectonic setting. Early results based on ~100 features suggested that Hess Rise, Necker ridge, Line Islands, and Manihiki Plateaus formed on-ridge and, hence, that there was a major period of volcanism in the central Pacific ~90- 120 Ma. This ‘event' appears to have been accompanied by deep-water volcanism, as shown by the pioneering work of Roger L. Larson in the Nauru Basin. Recently, Watts et al. (2006) used a bathymetric prediction technique to estimate the T_e at >9000 seamounts in the Wessel (2001) database. Plots of T_e Vs. age at features of known age, however, revealed considerable scatter with many lower values at old ages than expected. T_e maps show that these low values form a broad swath from East Pacific Rise crest in the SE, through the Tuamotu Plateau region, to the Line and Marshall Islands and Mid-Pacific Mountains in the NW. The SE end of the swath includes the region dubbed the South Pacific Isotopic and Thermal Anomaly (SOPITA) and some features (e.g. Marcus Wake Guyots, Lines Islands) at the NW end backtrack into the SOPITA. Therefore, some of the scatter maybe caused by a regional shallowing of the controlling isotherm. This has been verified using a moving window admittance technique which suggest controlling isotherms of <~350° as the SOPITA region is approached. These new constraints on the controlling isotherms are used here to estimate the distribution of submarine volcanism in the Mesozoic Pacific Ocean through time.
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 3010 Gravity and isostasy (1218, 1222)
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8138 Lithospheric flexure
SC: Tectonophysics [T]
MN: 2007 Fall Meeting