Ashton Flinders

Widespread Secondary Volcanism Near Northern Hawaiian Islands

Hot spot theory provides a key framework for understanding the motion of the tectonic plates, mantle convection and composition, and magma genesis. The age-progressive volcanism that constructs many chains of islands throughout the worlds ocean basins is essential to hot spot theory. In contrast, secondary volcanism, which follows the main edifice building stage of volcanism in many chains including the Hawaii, Samoa, Canary, Mauritius, and Kerguelen islands, is not predicted by hot spot theory. Hawaiian secondary volcanism occurs hundreds of kilometers away from, and more than 1 million years after, the end of the main shield volcanism, which has generated more than 99% of the volume of the volcanos mass [Macdonald et al., 1983; Ozawa et al., 2005]. Diamond Head, in Honolulu, is the first and classic example of secondary volcanism.

Seismic evidence for a possible deep crustal hot zone beneath Southwest Washington

Crustal pathways connecting deep sources of melt and the active volcanoes they supply are poorly understood. Beneath Mounts St. Helens, Adams, and Rainier these pathways connect subduction-induced ascending melts to shallow magma reservoirs. Petrogenetic modeling predicts that when these melts are emplaced as a succession of sills into the lower crust they generate deep crustal hot zones. While these zones are increasingly recognized as a primary site for silicic differentiation at a range of volcanic settings globally, imaging them remains challenging. Near Mount Rainier, ascending melt has previously been imaged ~28 km northwest of the volcano, while to the south, the volcano lies on the margin of a broad conductive region in the deep crust. Using 3D full-waveform tomography, we reveal an expansive low-velocity zone, which we interpret as a possible hot zone, linking ascending melts and shallow reservoirs. This hot zone may supply evolved magmas to Mounts St. Helens and Adams, and possibly Rainier, and could contain approximately twice the melt volume as the total eruptive products of all three volcanoes combined. Hot zones like this may be the primary reservoirs for arc volcanism, influencing compositional variations and spatial-segmentation along the entire 1100 km-long Cascades Arc.

Publisher Correction: Seismic evidence for a possible deep crustal hot zone beneath Southwest Washington

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