| The study groups, in addition to Subcommission members, also
drew membership from appropriate specialists worldwide. The main consultative
work of the Subcommission was done initially by correspondence and during
annual working meetings. Also, questionnaires were sent to members of the
working group to improve prepared definitions and test international acceptance.
The provisional recommendations were published on the SCMR website and
critical comment encouraged. The final results and recommedations were
then drawn up. The Subcommission’s work was conducted in English and all
its recommendations and definitions are designed only for English language
Scope of the SCMR
The SCMR has dealt with all metamorphic rocks. This was taken to include
rocks which are quenched melts produced by, or closely associated with
metamorphic processes and which are not defined by the Igneous Subcommission.
In addition the SCMR has defined a number of structural terms and processes
closely associated with metamorphic processes.
The SCMR also includes the systematics of impactites. Although many impactite
products and processes are not strictly metamorphic it was considered
expedient to deal with the group as an entity, especially as no part
of the subject was being considered elsewhere by the CSP.
Basis of the recommendations
A prime objective is to provide a scheme for naming and describing metamorphic
rocks, no attempt has been made to cover the terminology relating to
the detail or theory behind metamorphic processes, mineral chemistry,
graphical presentations, etc. It was agreed that rock names should,
as far as possible be applicable at the hand-specimen scale, that they
should be based on non-genetic criteria and that these criteria should
be measurable in the field or under the microscope. Nomenclature based
on criteria such as rock chemistry or metamorphic grade was obviously
unsuitable and a systematic scheme was devised based on compound names
with structural root terms and mineral qualifiers. This scheme allows
a systematic name to be given to any rock. However, it was accepted
that there were many well-established specific names, such as marble, amphibolite and eclogite,
that would have to remain and could potentially be used as alternative
names. In addition many metamorphic rocks can be named by reference
to their protolith. Thus, metamorphic rocks may potentially have up
to three acceptable names, that is a systematic name, a specific name
and a protolith-based name, for example, carbonate granofels – marble – metalimestone or hornblende-plagioclase
schist – amphibolite – metabasalt. The nomenclature
scheme has taken account of this situation.