Submarine Rejuvenated-Stage Lavas Offshore Molokai, Oahu, Kauai, and Niihau, Hawaii
Abstract
Rejuvenated-stage lavas from the Hawaiian Islands form many distinctive landmarks, such as Diamond Head. They have been relatively well studied due to their primitive, strongly alkaline compositions (alkalic basalt, basanite, nephelinite, melilitite, phonolite). More recently, compositionally similar lavas have been mapped and sampled on the deep seafloor around the islands. Rejuvenated-stage cones also occur on the submarine flanks of the islands. A Pisces V submersible dive collected samples from the only submarine cone on the north slope of East Molokai. The alkalic basalt to basanite composition lava is similar to the subaerial Kalaupapa basalt (Clague and Moore, 2003). MBARI Tiburon ROV dives recovered nephelinite from a lone steep cone on the northeast slope of Oahu, alkalic basalt from two shallow steep cones just west of the Koko Rift, and alkalic basalt from the submarine flank of Diamond Head on Oahu's south flank. These lavas are generally similar to subaerial Honolulu Volcanics, although the isotopic data extend to higher Sr isotopic values. Other MBARI Tiburon ROV dives recovered alkalic basalt and basanite from 8 separate steep cones on the south flank of Kauai. Once again, these lavas are chemically similar to those from the subaerial Koloa Volcanics. Samples from one of these cones contained common xenoliths of upper mantle lherzolite and harzburgite. Seven MBARI Tiburon ROV dives on the northwest flank of Niihau sampled 6 flat-topped cones and 5 pointed cones. The lavas from the flat-topped cones are alkalic basalt similar to rejuvenated Kiekie Basalt on Niihau Island whereas the lavas from the pointed cones are basanite, hawaiite, and tephrophonolite that are chemically distinct from the Kiekie Basalt, but similar to rejuvenated-stage lavas on Kauai and Oahu. Volcaniclastic deposits were observed and sampled at many of the sites offshore Niihau, Kauai, and Oahu, as well as the North Arch. Breadcrust and spindle bombs and spatter were found offshore Kauai as deep as 1500 m, in addition to finer volcaniclastic deposits consisting of vesicular angular glass fragments, which also occur offshore Oahu and in the North Arch as deep as 4100 m (Davis and Clague, submitted). The glass data from all these deposits as well as on pillow and sheet flow rinds from Oahu, Molokai, Niihau, Kauai, North Arch, South Arch, Southwest Oahu volcanic field, and some of the cones between Oahu and Kauai demonstrate that rejuvenated stage lavas did not erupt as near-primary melts, but rather as crystal-rich magmas whose bulk compositions approach primary magma compositions. The low-MgO contents of almost all the glasses indicate that these magmas cooled and crystallized significantly during transit through the cool lithosphere. The distribution of these lavas on the islands, on the flanks of some islands, and on the deep seafloor suggest that the melting region around the Hawaiian hot-spot is at least 400 km across.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.V11B..01C
- Keywords:
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- 3640 Igneous petrology;
- 8400 VOLCANOLOGY;
- 8429 Lava rheology and morphology;
- 8450 Planetary volcanism (5480)