HR: 1330h
AN: V12B-0582 INVITED     [PDF]
TI: Distribution of Recent Volcanism and Morphology of Volcanic Features in the GLIMPSE Study Area west of the East Pacific Rise
AU: * Scheirer, D
EM: daniel_scheirer@brown.edu
AF: Brown University Geological Sciences, 324 Brook St. Box 1846, Providence, RI 02912
AU: Forsyth, D
AF: Brown University Geological Sciences, 324 Brook St. Box 1846, Providence, RI 02912
AU: Harmon, N
AF: Brown University Geological Sciences, 324 Brook St. Box 1846, Providence, RI 02912
AU: Duncan, R
AF: COAS, Oregon State University 104 Ocean Admin Bldg, Corvallis, OR 97331-5503
AB: The existence of seamounts and volcanic ridges west of the East Pacific Rise (EPR), perhaps associated with cross-grain gravity lineations, was initially revealed by detailed satellite altimetry. Multibeam bathymetry and sidescan reflectivity measurements made on board the R/V Melville in 2001 and 2002 as part of the GLIMPSE Experiment, plus additional data gathered on other cruises including those of the MELT Experiment, have allowed us to map the distribution of recent, off-axis volcanic activity west of the EPR and south of the Garrett Fracture Zone and to more precisely define the form of the volcanic features. The Southern Cross Seamount, Sojourn Ridge and Brown Ridge combine to form a linear feature nearly 500 km long, oriented perpendicular to the EPR about 80 km south of the Garrett FZ. Both the Sojourn and Brown ridges comprise several en echelon segments, each about 30 km long, linked together to form continuous topographic highs standing 2000 m or more above the surrounding seafloor. Side-scan data reveal reflective patches along the Brown Ridge at the eastern end of this feature that appear to be recent lava flows. Dredging of fresh basalts dated by Ar/Ar methods at about 0.3 Ma confirm this interpretation. The Southern Cross Seamount, at the western end of the chain, is the largest individual feature, standing more than 3.5 km above the surrounding seafloor and shoaling to depths less than 200 m below sealevel. The Hotu-Matua volcanic complex also extends for several hundred km, but is much more varied in its morphology. The western end has some very small, very linear ridges, flanked on the south by an extensive region of resurfaced, hummocky seafloor. This area is more reflective and presumably younger than the surrounding seafloor, but less reflective than the areas interpreted as recent flows. Roughly midway along this complex are the Hotu and Matua seamounts. Surrounding Matua is an extensive region of highly reflective, recent lava flows, some of which seem to have been dammed against pre-existing, small seamounts. Age dates in this area are highly variable, ranging from $<$0.6 to about 6 Ma, also suggesting a mixture of pre-existing and resurfaced seafloor. Reflective flows are scattered over a roughly linear region extending another 150 km to the east of Matua, sometimes associated with very small seamounts and sometimes appearing just to fill topographic lows. We find no evidence in the detailed bathymetry or sidescan in this region for any pre-existing tectonic features or cracks extending along the line of volcanic activity.
DE: 3010 Gravity
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 9355 Pacific Ocean
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting