HR: 1330h
AN: B12A-0729    [PDF]
TI: Geomorphology of the East Lau Spreading Center
AU: * Martinez, F
EM: fernando@hawaii.edu
AF: University of Hawaii/SOEST, 1680 East-West Rd., Honolulu, HI 96822 United States
AB: The East Lau Spreading Center (ELSC) is a 390 km-long first-order ridge segment accommodating opening behind the Tonga subduction zone. The axial morphology of the ELSC changes in a way similar to the variation seen at fast- to intermediate-rate mid-ocean ridges (MORs) but with an opposite sense of spreading rate variation. The axis is comprised of en-echelon segments with non-transform overlapping offsets. From south to north the ELSC separates from the Tofua Arc volcanic front by 40 to 100 km as spreading rates increase from 40 to 85 mm/yr. At its southern end (22 45'S-21 25'S) the ELSC forms a narrow axial high with depths of about 1700-2000 m. Between 21 25'N and 20 43'N the ELSC axis deepens from 2000-2300 m and forms shallow and narrow valleys within a broader flanking high. North of 20 30'N the axis abruptly deepens again by 200-300 m. The axial depression continues to deepen and broaden to the north approaching 3000 m water depths. The deepening is not dynamically maintained as at slow spreading MORs, but rather reflects thinner crust near the axis than on the shallower flanks as indicated by local seismic measurements, by northward increasing mantle Bouguer anomalies, and by less volcanic and more tectonic morphology. The axial variations are mirrored on the flanks. They indicate systematically changing melting conditions in the mantle wedge as the spreading center propagated southward with its tip near the arc volcanic front and diverged northward from the arc. The axial variations imply that: The local proximity of the spreading axis to the volcanic front not only controls the degree of melting and crustal thickness and composition, but also in controls the occurrence and depth of magma chambers, crustal vesicularity, brecciation and faulting styles. In turn these effects should influence the style, intensity, and composition of hydrothermal circulation and the crustal mineralizations produced. Changes in morphology from a peaked shallow axial high to a broad deep axial valley may also influence near-bottom water circulation patterns, the dispersal of hydrothermal plumes and of vent biota. A planned survey of the ELSC Integrated Study Site will investigate the variations and interrelationships between crustal structure, volcanism and hydrothermal circulation along the length of the ELSC.
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
SC: Biogeosciences [B]
MN: 2003 Fall Meeting