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Title: Puhahonu: Earth’s biggest and hottest shield volcano
New bathymetric and gravity mapping, refined volume calculations and petrologic analyses show that the Hawaiian volcano P¯uh¯ahonu is the largest and hottest shield volcano on Earth. This ∼12.5-14.1 Ma volcano in the northwest Hawaiian Ridge (NWHR) is twice the size of Mauna Loa volcano (148 ±29 vs. 74.0 ×103km3), which was assumed to be not only the largest Hawaiian volcano but also the largest known shield volcano. We considered four testable mechanisms to increase magma production, including 1) thinner lithosphere, 2) slower propagation rate, 3) more fertile source, and 4) hotter mantle. The first three of these have been ruled out. The lithosphere was old (∼88 Myrs) when P¯uh¯ahonu was formed, and thus, too thick and cold to allow for greater extents of partial melting. The propagation rate was relatively fast when it erupted (87 km/Myr), so this is another unlikely reason. Source fertility was Kea-like and no more fertile than for other much smaller NWHR volcanoes. A hotter mantle remains the best mechanism to produce the large magma volumes and is consistent with the high forsteritic olivine phenocryst compositions (up to 91.8%) and the calculated high percent of melting (24%). Thus, the gargantuan size of P¯uh¯ahonu reflects its high more » melting temperature, the highest reported for any Cenozoic basalt. A solitary wave within the Hawaiian plume is the probable cause of P¯uh¯ahonu’s higher melting temperature and the resulting increased volume flux given the absence of a more fertile source for P¯uh¯ahonu basalts, as found for many basalts from the Hawaiian Islands. « less
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Chemical geology
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National Science Foundation
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