Deep roots for mid-ocean-ridge volcanoes revealed by plagioclase-hosted melt inclusions

Abstract

The global mid-ocean ridge system is the most significant magmatic system on our planet and is the site of 75% of Earth volcanism 1. The vertical extent of mid-ocean ridge magmatic systems has been considered to be restricted: even at the ultraslowspreading Gakkel Ridge, where the lithosphere is thickest, crystallisation depths of magmas feeding eruptions are thought to be <9 km 2. These depths have been determined using the volatile contents of melt inclusions, which are small volumes of magma that become trapped within crystallising minerals. In studies of basaltic magmatic systems, olivine is the mineral of choice for this approach 2-6. However, pressures derived from olivine-hosted melt inclusions are at odds with pressures derived from basalt major element barometers 7 and geophysical measurements of lithospheric thickness 8. Here, we present a comparative study of olivine-and plagioclase-hosted melt inclusions from the ultraslow-spreading Gakkel mid-ocean ridge (Arctic Ocean). We show that the volatile contents of (complexly zoned) plagioclase-hosted melt inclusions correspond to significantly higher crystallisation pressures (mean 270 MPa) than (simply zoned) olivine-hosted melt inclusions (mean 145 MPa). The highest recorded pressure we find equates to 16.4 km depth below the seafloor. These higher depths are consistent with both the thickness of the Gakkel

Reconstructing Magma Storage Depths for the 2018 Kı̄lauean Eruption From Melt Inclusion CO2 Contents: The Importance of Vapor Bubbles

“…Unfortunately, the vast majority of published volatile contents in melt inclusions globally, and at Kı̄lauea, only measured CO 2 in the glass phase, using techniques such as secondary‐ion mass spectrometry (SIMS), or Fourier‐transform infrared spectroscopy (FTIR; Bennett et al., 2019; Ruth et al., 2018; Sides, Edmonds, Maclennan, Houghton et al., 2014; Sides, Edmonds, Maclennan, Swanson et al., 2014). Given that recent work has shown that ∼40%–90% of the total CO 2 budget of melt inclusions may be held within the vapor bubble (Hartley et al., 2014; Moore et al., 2015; Rasmussen et al., 2020; Wallace et al., 2015), entrapment pressures from studies neglecting vapor bubble carbon must be viewed as minimum estimates (Anderson & Brown, 1993; Ruth et al., 2018).…”

Reconstructing Magma Storage Depths for the 2018 Kīlauean Eruption from Melt inclusion CO2 Contents: The Importance of Vapor Bubbles

“…Unfortunately, the vast majority of published volatile contents in melt inclusions globally, and at Kīlauea, only measured CO 2 in the glass phase, using techniques such as secondary-ion mass spectrometry (SIMS), or Fourier transform infrared spectroscopy (FTIR;Bennett et al, 2019;Ruth et al, 2018;. Given that recent work has shown that ∼40-90% of the total CO 2 budget of melt inclusions may be held within the vapor bubble (Hartley et al, 2014;Wallace et al, 2015;Moore et al, 2015;Rasmussen et al, 2020), entrapment pressures from studies neglecting vapor bubble carbon must be viewed as minimum estimates (Anderson & Brown, 1993;Ruth et al, 2018).…”

Magma Reservoir Formation and Evolution at a Slow-Spreading Center (Atlantis Bank, Southwest Indian Ridge)

“…Most of this heterogeneity can be linked to uneven distribution of melt generation within the mantle below the ridge axis (e.g., Tucholke and Lin, 1994;Dunn et al, 2005;Rubin and Sinton, 2007;Dunn, 2015 and references therein). Uneven melt supply results in the formation of intermittent and discontinuous magma reservoirs within the crust (e.g., Dick et al, 2003;Carbotte et al, 2015), contrasted reservoir geometry (axial magma chamber or sill intrusions; Jian et al, 2016;Canales et al, 2017), and variable depth of melt emplacement which can range between 2 and 16 km depth below seafloor (Dunn et al, 2005;Singh et al, 2006;Canales et al, 2017;Bennett et al, 2019). The common thread running through all processes that potentially govern magma accretion at spreading ridges is the importance of melt migration mechanisms involved.…”