Hi,
There is probably another parameter involved in all this discussion about
nomenclature. Some people like to follow strict rules about the
nomenclature of a rock, which is good up to a certain point but sometimes
has disadvantages. I think the idea is not to just give 'labels' to ALL
rocks and rock-types. Reality shows that there is such a variety of rock
types (regarding their mineralogical composition, conditions of formation,
bulk composition) that sometimes it is impossible to find a generally
accepted term. I think that in such cases, when we are dealing with
'uncommon' rocks like the one in question, we should give ourselves the
freedom to decide how to name them, as long as we can transmit to the
people what we mean exactly.
Now, more concretely about the rock in question, which was a regional
metamorphic rock (amphibolite) that has later undergone contact
metamorphism, a convenient name should include 1) the actual mineralogical
composition, 2) the metamorphic conditions under which this rock formed.
Under this aspect I would suggest 'cpx-opx-hbl-plag hornfels' formed by
contact metamorphism of regional metamorphic amphibolite. Some people may
argue it's too long but at least this descriptive term does not cause any
misunderstanding neither about the min. composition nor about how it
formed. In addition, the term 'amphibolite' is informative about the bulk
composition.Somebody else may want to name the same rock differently, e.g.
'amph-2prx hornfels' as suggested by Christian Nicolet. I wouldn't object
to this at all and I wouldn't insist that he has to follow my nomenclature
because I understand what he means.
cheers
Anthi
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Dr Anthi Liati
Institute of Isotope Geology and Mineral Resources
Department of Earth Sciences
ETH-Zentrum
Sonneggstr. 5, 8092 Zürich
Tel. ++41 1 632 6607
++41 1 632 3764 (secretary Mrs. Britt Meyer)
Fax ++ 41 1 632 1827
