HR: 1330h
AN: V12B-0578    [PDF]
TI: Crustal Structure Beneath the Gravity Lineations in the South Pacific from Seismic Refraction Data
AU: * Holmes, R
EM: cholmes@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Webb, S C
EM: scw@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Forsyth, D W
EM: Donald_Forsyth@brown.edu
AF: Department of Geological Sciences, Brown University, Providence, RI 02912 United States
AB: The GLIMPSE (Gravity Lineations, Intraplate Melting, Petrologic and Seismic Expedition) Experiment explores the origin of cross grain gravity lineations and associated volcanic ridges in the central South Pacific. The active-source seismic refraction component of GLIMPSE Experiment investigated the crustal thickness and velocity structure beneath the Sojourn Ridge and Hotu Matua Ridge systems (~116.5-115.5 W, 16.0-12.5 S). The SSE trending ~450 km long refraction line crossed over sixteen three-component ocean bottom seismometers (OBSs) sampling at a rate of 128 Hz . Throughout the survey, shots were triggered every two minutes for the 5-gun, 3625 cubic inch airgun array, while the R/V Melville maintained a ship speed between 4-5.5 knots to obtain a shot spacing of approximately 250 m. We will report on the crustal thickness, velocity structure, and upper mantle velocity determined from picks of the primary crustal and mantle phases (Pg, PmP, and Pn) recorded on the thirteen OBSs that returned viable data. Seabeam2000 sidescan measurements suggest fresh lava flows in the vicinity of the Matua ridge, possibly indicative of a robust and active magma system underlying the Hotu Matua volcanic system. High reflectivity along the eastern section of the Sojourn Ridge also suggests a recent eruptive history. The resultant velocity model will help to clarify the extent to which these ridges overlie partially molten material. In addition, the results of this investigation will provide evidence to aid in distinguishing between the competing hypotheses on the origins of the Sojourn, Hotu Matua, and similar anomalous ridge systems. In particular, the lithospheric boudinage and convective roll models predict opposing crustal thickness trends beneath the intraplate ridges, which will be resolvable in the results from the current study.
DE: 7220 Oceanic crust
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting