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Isle of Rum

Isle of Rum

The Isle of Rum is fascinating from a geological standpoint for four reasons:

  • It’s a classic layered intrusion… one of the world’s best examples of a replenished mafic magma chamber.
  • It arguably offers the opportunity to see the ‘guts’ of a volcano. Could it be that the magma chambers of the
    Hawaiian volcanoes look much like this?
  • It allows us to try and understand the processes that
    go on inside a 1000 km3 ultramafic magma chamber.
  • It’s one of the important volcanoes of the British Tertiary Volcanic Province (BTVP).

Dr. Mike Cheadle and Dr. Bobbie John from the University of Wyoming accompanied
our MIT/WHOI group into the field, providing expert discussions
on the different aspects of Rum geology. Rum is one of the oldest
volcanoes in the west of Scotland, pre-dating the centers in
Skye and Mull. Ages close to 63 Ma link this closely to the
initation of the Icelandic hotspot, still active today. The
gabbros that form the core of the exposed volcano are divided
into three sections, two layered series in the East and West
and a chaotic central zone, which is inferred to be the feeder
zone where new melt was delivered into the chamber from the
underlying mantle.

The gabbros are inferred to represent a 1000 km3
magma chamber and are famous for their rhythmic, layered appearance
whose origin has been hotly debated by geologists. One viewpoint
holds that these represent precipitation of crystals in a liquid
magma chamber, with each layer representing the arrival of new
batch of melt. Others have argued that the chamber was originally
semi-solid and relatively homogeneous, with the banding the
result of the late stage injection of a series of gabbroic sills.
Click here
to read Joint Program student Cara Santelli’s series of three
haikus composed in honor of Rum’s volcanic past.

On the first day, the group hiked to see the chaotic folding
and slumping of the central zone, with time to see the famous
long olivine crystals of the Harrisites. More Harrisites were
viewed by an elite and dedicated minority on the second day
in the face of an unrelenting north Atlantic downpour. On the
third day, the heavens smiled on the party enough to allow an
inspection of the classic eastern layered series on the slopes
of Mt. Hallival.

The accompanying slide shows provide a glimpse at the geology and scenery we encountered on the Isle of Rum.