Metamorfica

BRITISH GEOLOGICAL SURVEY

RESEARCH REPORT NUMBER RR 99–02 BGS Rock Classification Scheme Volume 2 Classification of metamorphic rocks

S Robertson

Subject index Bibliographical Reference

Rock classification, metamorphic rocks Robertson, S. 1999. BGS Rock Classification Scheme Volume 2 Classification of metamorphic rocks. British Geological Survey Research Report, RR 99–02.

© NERCCopyright 1999

British Geological Survey Keyworth Nottingham NG12 5GG UK

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Contents
1 Introduction 1.1 Definition of metamorphism 1.2 Basic principles Metamorphic rock nomenclature 2.1 Construction of rock names. 2.2 How to use the classification scheme Sedimentary protolith: metasedimentary rocks 3.1 Protolith name 3.2 Modal composition 3.2.1 Rocks composed largely of quartz ± feldspar ±mica with less than 10% carbonate and/or calcsilicate minerals 3.2.2 Rocks composed of 10 to 50% carbonate and/or calcsilicate minerals and at least 50% quartz ± feldspar ± mica 3.2.3 Rocks composed of more than 50% calcsilicate and carbonate minerals 3.3 Textural attributes Volcaniclastic rock protolith: metavolcaniclastic rocks Igneous protolith: meta-igneous rocks 5.1 Protolith name 5.2 Modalcomposition 5.2.1 Metafelsic rocks 5.2.2 Metamafic rocks 5.2.3 Meta-ultramafic rocks 5.3 Textural attributes Unknown or undefined protolith and preliminary field classification 6.1 Textural attributes 6.2 Modal features 6.2.1 Amphibolite 6.2.2 Eclogite 6.2.3 Marble Mechanically broken and reconstituted rocks 7.1 Rocks without primary cohesion 7.2 Unfoliated rocks with primary cohesion: cataclasticrocks 7.3 Foliated rocks with primary cohesion: mylonitic rocks 7.4 Glassy rocks Metasomatic and hydrothermal rocks Figure 7 Figure 8 Figure 9 10.3 10.4 References Appendix List of approved rock names Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Flow diagram for assigning root names to metamorphic rocks Temperature and pressure fields of various metamorphic facies and examples ofdiagnostic minerals and assemblages Classification scheme for metamorphic rocks Changing nomenclature with increasing metamorphism and deformation of a mudrock protolith Subdivision of rocks composed largely of quartz ± feldspar ± mica Subdivision of rocks composed of up to 50% carbonate and/or calcsilicate minerals and at least 50% quartz ± feldspar ± mica Subdivision of rocks containing more than50% carbonate and calcsilicate minerals Meta-igneous rocks classified by modal composition British Geological Survey grain size scheme Colour qualifiers Qualifiers based on protolith structures

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Tables Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Classification of rocks composed largely of quartz, feldspar and mica Subdivision of metavolcaniclastic-rocks basedon primary grain size Classification of fault rocks without primary cohesion Classification of cataclastic rocks Classification of mylonitic rocks Examples of protolith structure qualifiers Colour index qualifiers 3.2.1 4. 7.1 7.2 7.3 10.4 10.4

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ACKNOWLEDGEMENTS I would like to thank the review panel and other members of BGS staff together with Dr K Brodie and Dr N Fry for comments...