IUGS Task Group to integrate and revise the classification and nomenclature of igneous rocks


Società Geologica Italiana

The IUGS Subcommission on the Systematics of Igneous Rocks began its work in 1970 and reached its first conclusions almost two decades later, with the publication of the book edited by Roger Le Maitre in 1989. This volume soon became the reference standard for all geoscientists concerned with magmatic rocks and in particular those working in the field of igneous petrology. The interest in the correct classification of igneous rocks is beyond just the relatively restricted group of igneous petrologists, because mapping geologists, structural geologists and geodynamicists all use such nomenclature when they encounter and describe igneous rocks. The second edition of the IUGS classification scheme, published in 2002, helped to resolve in part some outstanding issues, particularly relating to the classification of pyroclastic rocks, carbonatites, kalsilite-bearing lithologies, lamproites and high-MgO volcanic rocks. Since its publication, the second edition has been quoted in scientific articles 6,700 times, i.e. roughly one citation each single day in the last 18 years. This emphasizes the extreme importance of this book for the scientific community. The preface of the 2002 edition makes the following statement: "The work of the Subcommission continues, not only to resolve these problematic areas but also to tackle new issues as they arise".

After almost twenty years, there has been little substantive work to address these problems and, as will be detailed below, a further revision of the IUGS classification of igneous rocks was urgently required. The last October 2020 a task force group made up of 17 researchers from 11 nations of the 5 continents submitted a proposal to IUGS to update the classification and nomenclature scheme of igneous rocks. The Executive Committee of IUGS approved the project in just one week, considering highly urgent such an activity.

This revision will integrate new field evidence as well as the results of improved analytical techniques and experimental petrology to infer genetic links between different rock types and rock groups. Through the years, IUGS has played a fundamental role in clarifying essential topics related to igneous rock classification and it is anticipated that this role will continue during future revisions. The publication of the new version of the book is scheduled no later than 2024 (hopefully before the end of 2022).

The proposal considers relatively minor but necessary revisions, leaving unchanged the overall structure of the original nomenclature and classification. The most important points that require at least some modification (e.g., modal vs mineralogical vs whole-rock chemical vs genetic classification) regards: 1) plutonic and rocks in general; 2) specific aspects on ultramafic rocks and their connection with metamorphic variants; 3) the use of the TAS diagram; 4) the concept of silica saturation; 5) the definition of sodic vs potassic vs ultrapotassic magmas; 6) the definition of tholeiitic vs calc-alkaline compositions; 7) the classification of kimberlites, lamprophyres, lamproites, kamafugites, carbonatites, boninites komatiites, meimechites and hybrid compositions among these terms; 8) the inclusion of a section on meteorites; 9) the possibility to correlate the book with an iconographic section (to be decided if reported in the book or as a link to the IUGS website). Additional arguments to be discussed will be certainly taken into consideration once the effective work will start. The entire geological community is strongly invited to participate to this huge effort, and the help of tends of additional researchers is indispensable to reach the most widespread consensus.

The researchers involved in the task force group as voting members are, in alphabetical order:

Bernard Bonin (France),
Anna Doroshkevich (Russia),
Zhengfu Guo (China), Andrew Kerr (UK),
Monica Heilborn (Brazil),
Tony Irving (USA),
Alexei Ivanov (Russia),
Michele Lustrino (Italy; Chair and Treasurer),
Roger Mitchell (Canada; Vice Chair),
Mitsuhito Nakagawa (Japan),
James H. Natland (USA),
Julian A. Pearce (UK),
Barbara Scott Smith (Canada),
Rajesh K. Srivastava (India),
Sebastian Tappe (South Africa),
Marjorie Wilson (UK),
Georg Zellmer (New Zealand; Secretary General).

Task Group on Igneous Rocks (TGIR)
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