HR: 14:40h
AN: V23C-05    [Abstracts]
TI: Buried Rift Zones and Seamounts in Hawaii: Implications for Volcano Tectonics
AU: * Park, J
EM: samabar@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St., Houston, TX 77005 United States
AU: Morgan, J K
EM: morganj@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St., Houston, TX 77005 United States
AU: Zelt, C A
EM: czelt@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St., Houston, TX 77005 United States
AU: Okubo, P G
EM: pokubo@usgs.gov
AF: U.S. Geological Survey, Hawaiian Volcano Observatory, P.O. Box 51, Hawaii National Park, HI 96718 United States
AB: As volcanoes grow, they deform due to their own weight and ongoing magmatic intrusions. For example, Kilauea's south flank is moving seaward ~10 cm/yr, apparently pushed by dike injection along rift zones and/or gravitational spreading. Offshore, Kilauea's south flank has developed a broad bench, attributed to overthrusting at the toe of the mobile flank. Mauna Loa's southeastern flank is much less mobile today, and exhibits no offshore bench. The great variability in present-day surface motions and deformation of these two volcanoes is not well explained by the distribution of surface structures, which might influence the driving and resisting forces acting on the flanks. Using first-arrival seismic tomography of a unique onshore-offshore airgun dataset, we have developed a 3-D P-wave velocity model of the southeastern part of the Island of Hawaii. This model provides an unprecedented view into both the submarine and subaerial portions of Kilauea, Mauna Loa, and Loihi volcanoes, helping to resolve some outstanding puzzles. The preferred velocity model shows that the known summits and rift zones of Kilauea, Mauna Loa and Loihi volcanoes are underlain by high velocity anomalies (6.5-7.0 km/s), indicating the presence of intrusive magma cumulates and dike complexes. In addition, we observe an anomalously high velocity feature (7.0-7.5 km/s) within the southeastern flank of Mauna Loa that extends ~40 km south of the volcano's summit. Our model also shows anomalously high velocity materials (6.3-6.8 km/s) in the oceanic crust beneath Kilauea's outer bench. Based on the geometry of their high velocities, we propose that these features represent previously unrecognized intrusive complexes that have influenced the evolution of the two volcanoes. The high velocity feature within Mauna Loa's southeastern flank appears to represent a buried rift zone, either of ancient Mauna Loa, or an older volcano perhaps related to the Ninole Hills. Curiously, at shallow depths (5-9 km below sea level), the high velocities are sharply truncated to the south. However, at greater depths, the anomalously high velocities extend another 20 km into the submarine flank, distinguishing this feature as a once extensive rift zone. The presence of dense, coherent intrusive rock may have anchored Mauna Loa's southeastern flank, such that much of the volcano's recent deformation has occurred along the west flank of Mauna Loa. This massive rift zone may also impede the propagation of Kilauea's southwest rift zone, accounting for its lesser development relative to Kilauea's east rift zone. The velocity highs beneath Kilauea's submarine flank likely represent buried seamounts that might obstruct the seaward migration of volcano's south flank, causing the bench uplift at the toe of flank. These new observations lead us to propose that previously unrecognized intrusive complexes within Mauna Loa and Kilauea have significantly affected the past evolution of these volcanoes in the Island of Hawaii, and are likely responsible for the present patterns of deformation on these active volcanoes.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 8000 STRUCTURAL GEOLOGY
DE: 8145 Physics of magma and magma bodies
DE: 8400 VOLCANOLOGY
DE: 8434 Magma migration and fragmentation
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005