Publication Date:
2022-05-25
Description:
© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Volcanology and Geothermal Research 323 (2016): 80-96, doi:10.1016/j.jvolgeores.2016.04.041.
Description:
North Su is a double-peaked active andesite submarine volcano located in the eastern
Manus Basin of the Bismarck Sea that reaches a depth of 1154 m. It hosts a vigorous
and varied hydrothermal system with black and white smoker vents along with several
areas of diffuse venting and deposits of native sulfur. Geologic mapping based on ROV
observations from 2006 and 2011 combined with morphologic features identified from
repeated bathymetric surveys in 2002 and 2011 document the emplacement of a
volcanic cryptodome between 2006 and 2011. We use our observations and rock
analyses to interpret an eruption scenario where highly viscous, crystal-rich andesitic
magma erupted slowly into the water-saturated, gravel-dominated slope of North Su. An
intense fragmentation process produced abundant blocky clasts of a heterogeneous
magma (olivine crystals within a rhyolitic groundmass) that only rarely breached through
the clastic cover onto the seafloor. Phreatic and phreatomagmatic explosions beneath
the seafloor cause mixing of juvenile and pre-existing lithic clasts and produce a
volcaniclastic deposit. This volcaniclastic deposit consists of blocky, non-altered clasts
next, variably (1-100 %) altered clasts, hydrothermal precipitates and crystal fragments.
The usually applied parameters to identify juvenile subaqueous lava fragments, i.e.
fluidal shape or chilled margin, were not applicable to distinguish between pre-existing
non-altered clasts and juvenile clasts. This deposit is updomed during further injection of
magma and mechanical disruption. Gas-propelled turbulent clast-recycling causes clasts
to develop variably rounded shapes. An abundance of blocky clasts and the lack of
clasts typical for the contact of liquid lava with water is interpreted to be the result of a
cooled, high-viscosity, crystal-rich magma that failed as a brittle solid upon stress. The
high viscosity allows the lava to form blocky and short lobes. The pervasive volcaniclastic cover on North Su is partly cemented by hydrothermal precipitates. These
hydrothermally-cemented breccias, crusts and single pillars show that hydrothermal
circulation through a thick layer of volcaniclastic deposits can temporarily increase slope
stability through precipitation and cementation.
Description:
The RV Melville work was funded by a combination of
the US National Science Foundation grant OCE-0327448 and a collaborative research
funding grant from Nautilus Minerals for the ABE surveys. The RV Sonne research
cruise was funded through the BMBF (Grant G03216a). Additional funding, including
salary support for JT, was provided by the German DFG Research Centre/Excellence
Cluster ―The Ocean in the Earth System‖. WB acknowledges support from DFG
research grant BA1605/4-1.
Description:
2018-05-10
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
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