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Many geologists have an equivocal attitude to fluid movements
within the crust and the associated changes in the chemical and
physical properties of crustal rocks. The controversies earlier
this centuary between the "soaks" and the "pontiffs" memorably
summarised by H. H. Read (1957) in The Granite Controversy have
largely been resolved. Few would now advocate the formation of
large granitic bodies by in situ transformation of pre-existing
crust as the result of the passage of ichors without the formation
of a granitic melt. To many geochemists fluid transport and
metasomatism have become slightly suspect processes which at the
most locally disturb the primary geochemical and isotopic
signatures. While there is common agreement that there are marked
differences in the composition of the lower and upper crust, the
role of fluid movement as one of the controls of this
differentiation is often neglected in favour of suggested primary
differences in the composition of igneous rocks emplaced at
different depths. Selective fluid transport however provides many
geologists with their livelyhood. Without the secondary
concentration of commercially important elements by fluids within
the crust the mining industry, geological science and human
activities based on their products would be very different.
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