HR: 0800h
AN: V41B-1385    [Abstracts]
TI: Volcanology and Petrochemistry of West Rota Caldera, Southern Mariana Arc
AU: * Basu, N K
EM: neil.basu@student.utdallas.edu
AF: Geosciences Department, University of Texas at Dallas, Box 830688, Richardson, TX 75083-0688 United States
AU: Stern, R J
EM: rjstern@utdallas.edu
AF: Geosciences Department, University of Texas at Dallas, Box 830688, Richardson, TX 75083-0688 United States
AU: Leybourne, M I
EM: mleybo@utdallas.edu
AF: Geosciences Department, University of Texas at Dallas, Box 830688, Richardson, TX 75083-0688 United States
AU: Manton, W I
EM: manton@utdallas.edu
AF: Geosciences Department, University of Texas at Dallas, Box 830688, Richardson, TX 75083-0688 United States
AU: Chadwick, W W
EM: bill.chadwick@noaa.gov
AF: CIMRS, Oregon State University, 2115 SE OSU Drive, Newport, OR 97365-5258 United States
AU: Embley, R W
EM: robert.w.embley@noaa.gov
AF: Pacific Marine Environmental Laboratory, NOAA, Newport, OR 97365-5258 United States
AB: West Rota volcano is a large dormant submarine volcano with a well-developed caldera in the southern Mariana Arc. West Rota was surveyed and dredged during the 2001 Cook 7 expedition and later explored and sampled with the ROV ROPOS, during the Submarine Ring of Fire 2004 expedition. The caldera floor lies approximately 1500 m below sea level and extends 5 km E-W and 8 km N-S. The eastern caldera rim reaches to within 400 m of the sea surface and slope reconstructions indicate that the volcano was subaerial prior to the caldera-forming eruption. Twenty samples collected by dredging, from three locations and eight samples obtained by ROV sampling were studied petrographically and geochemically. In addition to sampling, the ROPOS dive examined the succession of flows in the caldera wall, which record the magmatic evolution of this volcano. The dredged samples, which vary from fresh to intensely altered, range from 50 to 81 weight % SiO$_{2}$. The fresh samples are basalts to rhyolite. Samples from two dredges on the slopes of the volcano consist of fresh basalts, basaltic-andesites and andesites, along with rare rhyolite pumice. Mafic lavas contain olivine and plagioclase and, rare orthopyroxene. Five of the twelve samples dredged from the base of the eastern wall of the caldera contain sanidine and tridymite, which are a result of high temperature hydrothermal alteration. Three of the altered samples are enriched in K$_{2}$O (7 to 8.5 weight %) and the remaining two have 3 weight % K$_{2}$O. The samples collected during the ROV dive were all taken from the caldera floor and the lower eastern wall along a dredge path from the 2001 expedition. The 2004 samples range from 56 to 70 weight % SiO$_{2}$ and are porphyritic basaltic andesites, porphyritic andesites and pyroxene-bearing dacitic pumices. The upper 400 m of the eastern wall of the caldera consists of an uninterrupted vertical sequence of eruptive products. These include andesite flows, pyroclastic flows and finely laminated ash-fall deposits all on the order of 10s of meters thick capped by the final eruptive unit consisting of dacite and rhyolite pumice boulders up to 3 meters in diameter. Work in progress includes Sr isotope and trace element analyses, which will help in the understanding of an apparent increase of SiO$_{2}$ in the eruptives over time.
DE: 8400 VOLCANOLOGY
DE: 5480 Volcanism (8450)
DE: 1749 Volcanology, geochemistry, and petrology
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting