HR: 1330h
AN: V22C-0596    [PDF]
TI: Hawaiian Shield Stage Submarine Volcaniclastics: Insights From HSDP Core
AU: * Bridges, K P
EM: kbridges@hawaii.edu
AF: SOEST, University of Hawai'i, 1680 East-West Road, POST 813, Honolulu, HI 96822 United States
AU: Garcia, M
EM: garcia@soest.hawaii.edu
AF: SOEST, University of Hawai'i, 1680 East-West Road, POST 813, Honolulu, HI 96822 United States
AU: Houghton, B
EM: bhought@soest.hawaii.edu
AF: SOEST, University of Hawai'i, 1680 East-West Road, POST 813, Honolulu, HI 96822 United States
AU: Thordarson, T
EM: moinui@soest.hawaii.edu
AF: SOEST, University of Hawai'i, 1680 East-West Road, POST 813, Honolulu, HI 96822 United States
AB: Ocean island volcanoes are traditionally associated with the non-explosive eruption of fluid lavas, but volcaniclastic rocks comprise a significant portion of many submarine shield volcanoes. Deep drilling (3,098 m) by the Hawaiian Scientific Drilling Project (HSDP) into the flank of Mauna Kea volcano has exposed the volcaniclastics within the pedestals of a Hawaiian volcano that were previously poorly known. The HSDP continuously cored 2,019 m of submarine Mauna Kea deposits with $\sim$95% recovery and revealed that volcaniclastics comprise $\sim$55% of this section. The shallow submarine section consists of $\sim$80% volcaniclastics interbedded with thin ($\sim$3 m) massive lava flows and the deep section is $\sim$35% volcaniclastics interbedded with packages of pillow lavas up to 180 m thick. Throughout the submarine section, the volcaniclastics can occur in thick packages up to $\sim$100 m. The emplacement of submarine volcaniclastics is not well understood. Possible origins include primary fragmentation of lava via magmatic explosivity and magma-water interactions, and secondary fragmentation via erosion. Secondary transport of material down the steep submarine flanks by gravity flows is expected to be common, as is reworking by currents. Emplacement processes are predicted to evolve as the volcano shoals. In this study major element analyses of glassy clasts in the volcaniclastics are used to distinguish monomict and polymict assemblages, which can indicate primary versus secondary fragmentation. Clast shapes reflect fragmentation mechanisms and secondary processes and this study attempts to improve on this approach with quantitative analysis of clast shapes for the HSDP volcaniclastics and for samples of known origin. The first documentation of the textures of the Mauna Kea volcaniclastics, integrated with geochemistry, petrography, and quantitative clast shape analysis and inferences about their origins and modes of transport and deposition will be presented to better understand the shoaling of Hawaiian volcanoes.
DE: 3022 Marine sediments--processes and transport
DE: 8400 VOLCANOLOGY
DE: 9355 Pacific Ocean
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting