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 Earth and Planetary Science Letters 453 (2016): 152-160, doi:10.1016/j.epsl.2016.08.007.
Description:
Eruption rates at the mid–ocean ridges (MORs) are believed to strongly
control the morphology and length of lava flows emplaced along the ridge axis, and thus
the structure and porosity of the upper oceanic crust. Eruption rate also represents one of
the few tools to gain insight into the driving pressures within sub-ridge magmatic
systems. As eruption rate is inferred to vary systematically along the global mid-ocean
ridge, understanding of how to assess eruption rate in submarine systems and how it
maps to observable features of the ridge axis would provide a powerful tool to understand
Earth's largest magmatic system. Eruption rates at MORs are poorly constrained,
however, because of a lack of direct observations, preventing the duration of an eruption
to be quantified. This study uses decompression experiments of MORB samples and
numerical modeling of CO2 degassing to reconstruct the timescales for magma ascent and
lava emplacement during the 2005–06 eruption of the East Pacific Rise at ca. 9°51’N.
Samples collected from the lava flow are all supersaturated in dissolved CO2 contents,
but CO2 decreases with distance from the vent, presumably as a consequence of
progressive CO2 diffusion into growing bubbles. Samples collected at the vent contain
~105 vesicles per cm3. Pieces of these samples were experimentally heated to 1225°C at
high pressure and then decompressed at controlled rates. Results, plus those from
numerical modeling of diffusive bubble growth, indicate that magma rose from the axial
magma chamber to the seafloor in ≤1 hour and at a rate of ≥2–3 km hr-1. Our modeling,
as validated by experimental decompression of MORB samples with ~106 vesicles cm-3,
also suggests that CO2 degassed from the melt within ~10–100 minutes as the vesicular
lava traveled ~ 1.7 km along the seafloor, implying a volumetric flow rate on order of
103–4 m3 s-1. Given an ascent rate of ≥0.2 m s-1, the width of a rectangular dike feeding
the lava would have been ~1–2 meters wide. MORB samples from the Pacific ridge are
generally more supersaturated in dissolved CO2 than those from slower spreading
Atlantic and Indian ridges. Our results suggest that Pacific MORBs ascend to the
seafloor faster than Atlantic or Indian MORBs
Description:
This project was partially
funded by a grant to J.E.G. from the U.S. National Science Foundation (OCE-1333882).
Description:
2017-08-27
Keywords:
Mid-ocean ridge
;
Basalt
;
Eruption rate
;
Bubble
;
H2O
;
CO2
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
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