Mid-Ocean Ridge Magma Chambers

We have performed Full waveform inversion on multi-channel seismic reflection data collected along the northern and southern East Pacific Rise. The accurate velocity structure obtained showed the presence of a thin (<50 m thick) molten sill, with a solid roof and solid floor, beneath the ridge axis. This body is significantly smaller than had been predicted from studies of ophiolites (pieces of oceanic crust that are now on land).

Fig.1 Data (left, fk filtered gathers) and AVO models (right) at two locations with a mushy (top) and pure melt (bottom) magma in the chamber. (From Singh et al., 1998).

We also detected a mode-conversion (known as PmeltS) which travelled to the top of the magma chamber as a P-wave and back to the surface as a S-wave. The strength of the S-wave conversion is directly controlled by the S-wave velocity of the magma - with pure melt giving a stronger return than a mushy melt (a partially crystallised melt), Fig.1.

Along axis variations of the molten state of the magma on a few-tens of kilometre scale were detected by using the strength of the PmeltS phase (Fig.2). These results help our understanding of how melt is delivered from the mantle, the eruption history of mid-ocean ridges and the process of oceanic crustal accretion.

Magma chambers
Fig.2 Cartoon of along-axis segmentation of magma chamber beneath the southern East Pacific Rise (above) from partial-aperture stacks of large-offset seismic reflection data (below). (From Singh et al., 1998)






  • "Melt to mush variations in crustal magma properties along the ridge crest at the southern East Pacific Rise" (1998) S.C. Singh, G.M. Kent, J S Collier, A.J. Harding, J.A. Orcutt.  Nature,  Vol.394, No.6696, pp.874-878 PDF
  • "Detailed structure of the top of the melt body beneath the East Pacific Rise at 9 40´N from waveform inversion of seismic reflection data" (1997) J S Collier, S.C. Singh.  J. Geophys. Res., 1997, Vol.102, No.B9, pp.20287-20304 PDF
  • "A seismic inversion study of the axial magma chamber reflector beneath the East Pacific Rise near 10 degrees N" (1998) Collier, J. S. and S. C. Singh. Modern Ocean Floor Processes and the Geological Record. R. Mills and K. Harrison, Geol Soc. London Special Publication. 148: 17-28. PDF


External Collaborators

  • Graham Kent (SIO, USA)
  • Alistair Harding (SIO, USA)