Abstract
AbstractThe flow of high‐temperature and compositionally enriched material between mantle plumes and nearby spreading centers influences up to 30% of the global mid‐ocean ridge system and represents a significant, but currently unconstrained, flux of volatiles out of the mantle. Here, we present new analyses of H2O, F, Cl, and S in basaltic glass chips from an archetypal region of plume‐ridge interaction, the Galápagos Spreading Center (GSC). Our data set includes samples from the eastern GSC, on ridge segments that are strongly influenced by the adjacent Galápagos mantle plume, and complements published analyses of volatiles largely from the western GSC. We use forward models of mantle melting to investigate the role of solid and melt‐phase transport from a lithologically heterogeneous (peridotite‐pyroxenite) mantle in plume‐ridge interaction along approximately 1,000 km of the GSC. Our results indicate that the observed geochemical and geophysical variations cannot be recreated by models that only involve solid‐state transfer of material between the Galápagos mantle plume and the GSC. Instead, we show that the geochemical and geophysical data from the GSC are well‐matched by models that incorporate channelized flow of volatile‐rich melts formed at high‐pressures (>3 GPa) in the Galápagos plume stem to the GSC. In addition, our new models demonstrate that channelized flow of enriched, plume‐derived melt can account for up to ∼60% of the H2O outgassed from regions of the GSC, which are most strongly influenced by the Galápagos mantle plume.
Highlights
The majority of ocean island basalts (OIBs) are believed to form as a consequence of adiabatic decompression melting in high-temperature, and potentially lithologically heterogeneous, mantle plumes (Asimow & Langmuir, 2003; Herzberg & Asimow, 2008; Ito & Mahoney, 2005; Métrich et al, 2014; Morgan, 1971; Sobolev et al, 2007)
Higher concentrations of volatiles in OIBs compared to midocean ridge basalts (MORBs) reflect the volatile-rich nature of deep-sourced plume material, relative to the MORB source, and are evidence of small-fraction decompression melting at higher pressures than the anhydrous peridotite solidus (Dixon et al, 2017; Gibson & Richards, 2018; Ingle et al, 2010; Jackson et al, 2015; Koleszar et al, 2009; Métrich et al, 2014)
Our new Secondary Ion Mass Spectrometry (SIMS) and EPMA data represent the first systematic analyses of H2O, F, S, and Cl for well-characterized D, N, and E-MORB erupted on the eastern Galápagos Spreading Center (GSC) and, expand the published volatile data set to cover the entire section of the Galápagos plume-influenced ridge (Cushman et al, 2004; Ingle et al, 2010; Le Voyer et al, 2018; Michael, 1995)
Summary
The majority of ocean island basalts (OIBs) are believed to form as a consequence of adiabatic decompression melting in high-temperature, and potentially lithologically heterogeneous, mantle plumes (Asimow & Langmuir, 2003; Herzberg & Asimow, 2008; Ito & Mahoney, 2005; Métrich et al, 2014; Morgan, 1971; Sobolev et al, 2007). Higher concentrations of volatiles (such as H2O, F, or Cl) in OIBs compared to midocean ridge basalts (MORBs) reflect the volatile-rich nature of deep-sourced plume material, relative to the MORB source, and are evidence of small-fraction decompression melting at higher pressures than the anhydrous peridotite solidus (Dixon et al, 2017; Gibson & Richards, 2018; Ingle et al, 2010; Jackson et al, 2015; Koleszar et al, 2009; Métrich et al, 2014). Approximately 30% of the global midocean ridge (MOR) system is influenced by the lateral transfer of deep-sourced mantle plume material (Ito & Lin, 1995) and potentially represent sites of substantial volatile outgassing from the Earth’s mantle (Gibson & Richards, 2018; Le Voyer et al, 2018). M. Gleeson Writing – review & editing: Matthew L. Gibson to the role of melt channelization in the transfer of geochemically enriched plume material between mantle plume stems and nearby spreading centers
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