Contact Metamorphic Rocks

10. Contact Metamorphic Rocks
Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: Web version 01.02.07
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E. Callegari and 2N.N. Pertsev
E. Callegari, Department of Science, Mineralogy and Petrology, University of Torino, Italy N. Pertsev, IGEM, Moscow, Russia

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Introduction
A Study Group under the leadership of E. Callegari was set up to look atdefinitions concerning contact metamorphism and contact metamorphic rocks. The Study Group was also asked to consider metamorphism associated with other localised heat sources, such as combustion metamorphism and ligthning strikes. This paper presents the report of the Study Group.
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Brief historical notes on contact metamorphism

Les roches de ces derniers terrains (Vosges) ont souvent subi, àproximité du granite, des modifications si variées que leur nomenclature précise devient un sujet d’embarras pour le géologue. Daubrée, 1857. The first mention of contact metamorphic phenomena dates back to the end of eighteenth century when James Hutton observed that the rocks surrounding a granitic body at Glen Tilt (Perthshire, Scotland) had suffered marked changes in either colour or structureespecially in zones crossed by granitic veins (Playfair, 1822). At that time Neptunists and Plutonists were still debating the sedimentary vs igneous origin of granitic rocks, and the terms ‘metamorphism’ (Boué, 1820; Lyell, 1833) and ‘contact metamorphism’ (Delesse, 1857) had still to enter the geological vocabulary. In the first decades of the nineteenth century rock alterations close tocontacts with granitic rocks were increasingly discovered in other localities of England and Scotland (MacCulloch, 1819) as well as in other European countries. They were observed in a variety of settings (plutonic and volcanic) involving a wide spectrum of rock types. Many names appeared for this particular and localised type of metamorphism and its varietie. Eventually Delesse (1857) proposed the termcontact metamorphism which found general acceptance and is still widely used today. Most names for contact metamorphic rocks (see Appendix) entered geological literature between the end of the eighteenth and the first two thirds of the nineteenth century. Many of these names were coined before the study of thin sections developed and the subsequent widespread use of microscope techniques,particularly in the last quarter of the nineteenth century, did much to improve the existing definitions removing most of the uncertainties and ambiguities. At the same time unnecessary rock names were gradually abandoned or superseded by more appropriate synonyms. The pioneering works of the early petrographers also provided a general framework for many aspects of contact metamorphism includingwww.bgs.ac.uk/scmr/home.html

definitions or basic concepts of contact aureole (von Buch, in Humboldt, 1831), endo- and exomorphism (Fournet, 1847), contact metasomatism (Durocher, 1846) and many other terms which are still current. Unfortunately, most of the original definitions were in languages other than English, and in some cases the original name was lost in translation. At the onset of thetwentieth century, there was, in many countries, a renewed interest in the study of contact aureoles. However, the interest of metamorphic petrologists was mainly directed towards the interpretation of the relationships between rock microstructures, mineral assemblages, rock chemistry and metamorphic conditions. It was the time when the concepts of metamorphic zones (Becke, 1903b; Grubenmann, 1904,1906; Barrow, 1912) and metamorphic facies (Eskola, 1920) opened new horizons in the field of metamorphic petrology and Golschmidt (1911) discovered very simple and fixed relations between rock chemistry and mineral assemblages in the contact metamorphic rocks of the Christiania (Oslo) region, Norway. Only a restricted number of new contact metamorphic rock names appeared at this time including...