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International Research
R/V Celtic Explorer cruise to survey and sample the V-shaped ridges, south of
Iceland: testing the heartbeat of the Iceland Plume
Bramley Murton 1 , Stephen Jones 2 , Gavin Elliot 1 , Stephanie Ingles 1 , Godfrey Fitton 3 , and Nicholas White 4
V-Shaped Ridges (VSRs), developed in oceanic crust to the
south of Iceland (Fig. 1), are the world’s best window into the
time-dependent dynamics of mantle convection (Vogt 1971,
1974, 1979; Vogt and Avery 1974). It is generally agreed that
VSRs result from melting anomalies that propagate outward
from Iceland, but the cause of the melting anomalies and what
drives the mantle flow that carries them are debated. From
their geometry, the VSRs appear to derive from perturbations
in mantle melting that advect away from Iceland at a rate of
20 cm per year (Murton and Parson 1993; Jones et al. 2002).
This astonishing velocity is 10 times faster than the adjacent
mid-ocean ridge spreading rate, and the fluctuations in melting
have affected the adjacent continental margins and deep
ocean circulation throughout the Eocene. Previous work in
this region, which acquired detailed bathymetry and collected
and analysed basalt samples from the Reykjanes Ridge, concluded
that the VSRs were the result of anomalous regions of
southward advecting asthenosphere that yield higher degrees of
mantle melting (Taylor et al. 1995, 1997; Murton et al. 2002).
The new survey, on board the Irish research ship R/V Celtic Explorer
with PIs SJ and BM, acquired essential bathymetric data
and volcanic samples of the VSRs. These will be used to answer
questions about temporal variation in mantle convection. They
will also contribute to site survey data in support of IODP proposal
646-Full (lead PI BM; proposal summary available at:
http://www.interridge.org/files/interridge/646-Full_Cover[1].
pdf). The survey, on cruise CE008 from 20 April - 16 May
2008, covered one of the VSRs (VSR2W) developed in oceanic
crust south of Iceland.
We collected a total of 80 new samples from 33 dredge stations
and bathymetrically surveyed the entire strike of VSR2W
using the portable multibeam echosounder system ‘RESON
SeaBat 8160’ (Fig. 2). These new data are the first to have been
collected from the off-axis VSRs since the first reflection seismic
survey that lead to discovery of the VSRs in the 1960s.
Initial results show that the VSRs are the result of thermal and
compositional fluctuations that propagate out from Iceland at a
rate of up to 20 cm per year over a distance of 1000 km. These
fluctuations are wholly compatible with an origin within an
upwelling mantle plume beneath Iceland, where composition
and temperature appear to be intrinsically linked, and which
is deflected southwards along the Reykjanes Ridge. Further
isotopic and trace element analyses are underway which, by
comparison with the Reykjanes Ridge geochemical data, will
be used to test hypotheses for the geometry of the wedge of
asthenospheric mantle as it advects away from Iceland.
Acknowledgements
Other seagoing scientists and students involved with cruise
CE008 include: Garath Roberts and Sarah Nixon (Cambridge),
Janine Guinan, (Marine Institute, Ireland), Samantha
Unsworth (NOCS), Cora McKenna (University College,
Cork), and Zara Archibald and Catherine Breheny (National
University of Ireland, Galway). The work was only possible due
to the dedication of the crew and officers of the R/V Celtic
Explorer who managed to cope with adverse and, at times, extreme
North Atlantic weather conditions (Fig. 3). We are also
indebted to John Davis and Tim LeBas (NOC) and Danny
Wake (Reson Offshore Ltd.) for assistance in the initial Reson
set-up. Ship time and logistical support was granted to SJ
by the Science Foundation, Ireland and the Marine Institute,
Ireland. Support for the Reson multibeam echosounder
and dredging was granted to BM and GE from a UK-IODP
grant (NE/G001251/1), titled “Site Survey for IODP Proposal
646-Full: Icelandic V-Shaped-Ridges.”
References
Jones, S.M., N. White, & J. Maclennan, V-shaped ridges
around Iceland: implications for spatial and temporal pat-
Figure 1: V-shaped ridges southwest of Iceland are revealed by
the free air gravity field. White dots are the locations of samples
taken in the 1990’s (Murton et al. 2002). The blue, green and red
dots are the locations of the R/V Celtic Explorer samples on the
southern Reykjanes Ridge, VSR2W, and VSR1W respectively.
1
National Oceanography Centre (NOC), Southampton, UK; 2 Trinity College, Dublin, Ireland; 3 University of Edinburgh, UK; 4 University
of Cambridge, UK
InterRidge News 10 Vol. 17, 2008