Lamprophyres

Following their recognition by Gumbel (1874), lamprophyres were treated for an entire century as little more than obscure curiosities. Although this situation has changed recently, with a flowering of publications and active workers, lamprophyres remain almost the only group of igneous rocks which have not yet received attention in a dedicated monograph. In five exploratory reviews (1977-1987), the writer aimed to set out what was known about these rocks. The lUGS Subcommission on igneous rock systematics had meanwhile presented its nomenclatural framework (Streckeisen 1979). All this has now been overtaken by a recent explosion of interest, epitomized not least by lamprophyres' greater prominence in the 4th International Kimberlite Conference Proceedings. More data have become available since 1985 than over the entire previous century, and it is obviously impossible for such an extraordinary outpouring to be fully reviewed in this first, preliminary book. At the risk of dissatisfying some readers, therefore, this book concentrates on factual matters, and on a broad overview rather than minutiae. Because not even a world map of known lamprophyres was previously available, almost half the book is deliberately taken up by the first global lamprophyre compilation, and its commensurately extensive Bibliography. Such a compendium of largely objective information is believed to be of more immediate interest and lasting value than a premature pottage of petrogenetic polemic. Chapters 1-7 bring previous studies up to date, and concentrate on factual information.

1 What are Lamprophyres? ― History, Definitions, Classification.- 1.1 A brief history of lamprophyre research.- 1.1.1 The 19th and early 20th centuries: lamprophyres are characterized.- 1.1.2 1940–1960: the wilderness period.- 1.1.3 The late 1960s to the present: lamprophyres come of age.- 1.2 Classification and nomenclature: the Lamprophyre Clan.- 1.3 In defence of the Lamprophyre Clan.- 1.3.1 Further arguments for including lamproites within the lamprophyre clan.- 1.3.2 A brief note on lamproite nomenclature.- 1.3.3 Further arguments for including kimberlites within the lamprophyre clan.- 1.4 Summary of criteria for identifying lamprophyres as a clan.- 1.4.1 Mineral assemblage.- 1.4.2 Texture.- 1.4.3 Mode of occurrence.- 1.4.4 Whole-rock composition.- 1.4.5 Tectono-magmatic association.- 1.4.6 Miscellaneous features.- 1.5 Identification and nomenclature of closely related rock-types.- 1.5.1 Volatile-poor lamprophyre relatives.- 1.5.2 Ultramafic (cumulate) and felsic (differentiated) lamprophyre relatives.- 1.5.3 Plutonic and volcanic lamprophyre equivalents.- 1.6 Distinctions between some petrographically similar rock-types.- 1.6.1 Coexisting lamprophyres from different branches.- 1.6.2 Calc-alkaline lamprophyres versus shoshonites and common calc-alkaline rocks.- 1.6.3 Ultramafic lamprophyres versus melilitites and related rocks.- 1.6.4 Ultramafic lamprophyres versus leucite-bearing ultramafic rocks.- 1.6.5 Alnöites versus aillikites and carbonatites.- 1.6.6 Ultramafic lamprophyres versus Group II kimberlites.- 1.7 Genetic connotations for lamprophyre names: are they reasonable?.- 1.8 A new definition of the term ‘lamprophyre’.- 2 When and Where? ― Global Distribution, Igneous Associations.- 2.1 A preliminary caveat: metamorphism and lamprophyres.- 2.2 A compilation of worldwide lamprophyre occurrences.- 2.3 Global distribution and abundance of lamprophyres.- 2.3.1 Overall distribution through geological time.- 2.3.2 Overall volumetric abundance.- 2.3.3 Geographical distribution.- 2.4 Tectono-magmatic associations.- 2.4.1 Association A: with calc-alkaline granitoid plutons.- 2.4.2 Association B: with shoshonitic suites.- 2.4.3 Association C: with appinite-breccia pipe-complexes.- 2.4.4 Inter-relationships between Associations A, B and C.- 2.4.5 Association L: lamprophyres with each other alone.- 2.4.6 Association M (mildy alkaline): with alkaline syenite-gabbro plutons.- 2.4.7 Association R: regional lamprophyric magmatism unrelated to other igneous activity.- 2.4.8 Association S (strongly alkaline): with carbonatite-ijolite-nephelinite complexes.- 2.4.9 Some spurious or equivocal associations.- 2.5 Repeated lamprophyre injection in one area over geological time.- 3 Field Geology and Petrography ― Macroscopy and Microscopy.- 3.1 Field geology of lamprophyres: diagnostic forms of occurrence.- 3.1.1 Small-scale characteristics of lamprophyre intrusions.- 3.1.2 Composite intrusions of lamprophyres with felsic rock-types.- 3.1.3 Differentiated lamprophyre intrusions.- 3.1.4 Contact metamorphism and metasomatism around lamprophyre intrusions.- 3.1.5 Larger-scale groupings of lamprophyre intrusions.- 3.1.6 Inferred intrusion mechanisms.- 3.1.7 Volcanic lamprophyres: lavas, pyroclastics and tuffs.- 3.2 Petrographical (thin section) characteristics of lamprophyres.- 3.2.1 Modal composition and paragenetic sequence.- 3.2.2 Lamprophyric (panidiomorphic) and related textures.- 3.2.3 Autometasomatic alteration.- 3.2.4 Globular structures.- 3.2.5 Autoliths, lapilli, pellets and related structures.- 4 Cognate Mineralogy.- 4.1 Mineralogical features diagnostic of the whole lamprophyre clan.- 4.2 Minerals and parageneses diagnostic of each lamprophyre branch.- 4.3 Olivines.- 4.4 Monticellites.- 4.5 Garnets.- 4.6 Clinopyroxenes.- 4.7 Amphiboles.- 4.8 Biotite-phlogopites.- 4.9 Feldspars.- 4.9.1 Plagioclases.- 4.9.2 Na-K-Ba feldspars.- 4.9.3 A further note on feldspar assemblages and structural states.- 4.10 Feldspathoids.- 4.10.1 Analcimes.- 4.10.2 Nephelines, cancrinites and sodalite group minerals.- 4.10.3 Leucites.- 4.11 Melilites.- 4.12 Carbonates.- 4.13 Spinels.- 4.14 Ilmenites.- 4.15 Perovskites.- 4.16 Other oxides and sulphides.- 4.17 Miscellaneous primary minerals.- 4.18 Secondary minerals.- 4.19 Glass.- 5 Whole-rock Geochemistry.- 5.1 Major and minor oxides.- 5.1.1 Discrimination between the 5 lamprophyre branches based on major elements.- 5.1.2 Overlap between branches: the effects of accumulation, fractionation and alteration.- 5.1.3 Discrimination between aillikites and kimberlites based on major oxides.- 5.2 CIPW normative composition.- 5.3 Trace elements.- 5.4 Rare-earth elements (REE).- 5.5 Precious metals (PGE, Au).- 5.6 Radiogenic isotopes.- 5.7 Stable isotopes.- 6 Inclusion Suites ― Macrocrysts, Xenocrysts, Xenoliths, etc.- 6.1 Type B (largely cognate): inclusions derived from host melt at high-P.- 6.2 Type C (semi-cognate): inclusions derived from evolved melt.- 6.3 Type D (partly cognate): inclusions derived for related melts.- 6.4 Type E (related or foreign): mantle-type mafic-ultramafic inclusions.- 6.5 Type F: True xenocrysts and xenoliths of unrelated crustal rocks.- 6.6 The discrete nodule (macrocryst, megacryst) suite.- 6.6.1 Megacrysts of one mafic mineral.- 6.6.2 “Megacrystalline rocks” and intergrowths of two or more mafic minerals.- 6.6.3 Feldspar megacrysts and feldspar intergrowths.- 6.7 Abundance of different inclusion types in different lamprophyres.- 6.8 P-T significance of inclusion suites.- 7 Plutonic and Volcanic Equivalents of Lamprophyres.- 7.1 Plutonic and volcanic equivalents of calc-alkaline lamprophyres.- 7.1.1 The appinite suite: plutonic spessartites and vogesites.- 7.1.2 The vaugnérite series: plutonic minettes and kersantites.- 7.1.3 Calc-alkaline lamprophyres versus plutonic and volcanic shoshonitic rocks.- 7.1.4 Calc-alkaline lamprophyres versus volcanic boninites.- 7.1.5 Minettes versus volcanic olivine-leucitites (ugandites).- 7.1.6 Minettes versus volcanic selagites.- 7.2 Plutonic and volcanic equivalents of alkaline lamprophyres.- 7.3 Plutonic and volcanic equivalents of ultramafic lamprophyres.- 7.3.1 Ultramafic lamprophyres versus volcanic melilitites.- 7.3.2 Ultramafic lamprophyres versus plutonic melilitolites.- 7.3.3 Ultramafic lamprophyres versus volcanic meimechites.- 7.3.4 Ultramafic lamprophyres versus volcanic ankaratrites.- 7.3.5 Ultramafic lamprophyres versus volcanic katungites.- 8 Nature, Origin and Evolution of Lamprophyre Melts.- 8.1 Do ‘lamprophyre magmas’ exist?.- 8.2 How many distinct lamprophyre magma-types are there?.- 8.2.1 Calc-alkaline lamprophyres.- 8.2.2 Alkaline lamprophyres.- 8.2.3 Ultramafic lamprophyres.- 8.2.4 Kimberlites.- 8.2.5 Lamproites.- 8.2.6 Seven lamprophyre magma-types.- 8.3 What parameters can we use to deduce lamprophyres’ origins?.- 8.3.1 Indications of primary magmatic status from whole-rock geochemistry.- 8.3.2 High LILE and HFSE enrichments.- 8.3.3 Coupled negative Ta-Nb-Ti (TNT) anomalies.- 8.3.4 Radiogenic isotopes ― crust v. mantle, contamination v. metasomatism.- 8.3.5 Experimental petrology.- 8.3.6 Mantle-type inclusions.- 8.3.7 Oceanic versus continental settings.- 8.3.8 Lamprophyre mineral assemblages ― what do they represent?.- 8.4 Petrogenesis of individual lamprophyre magma-types.- 8.4.1 M1 magma-type (AL/UML): volatile-enriched alkali basaltic to melilititic melts?.- 8.4.2 M2 magma-type (UML): primary carbonatite affiliates?.- 8.4.3 M3 and M4 magma-types (KIL and olivine-lamproites): deep mantle melts?.- 8.4.4 M5 magma-type (LL): multi-reservoir, multi-stage mantle melts?.- 8.4.5 M6 magma-type (Navajo minettes, etc.): slightly contaminated mantle melts?.- 8.4.6 M7 magma-type (CAL): heavily contaminated mantle melts?.- 8.5 Evolution (differentiation) of lamprophyre melts.- 8.5.1 Evidence of evolution within single lamprophyre bodies.- 8.5.2 Evidence of evolution within regional dyke-suites.- 8.5.3 Role of liquid immiscibility in the evolution of lamprophyre melts.- 8.6 Lamprophyres as parental melts to other igneous rock-suites.- 8.6.1 M7 (CAL) magma-type and calc-alkaline suites.- 8.6.2 M2 (AL) magma-type and alkaline gabbro-syenite plutons.- 8.6.3 M3 (UML) magma-type and carbonatite-ijolite-nephelinite complexes.- 8.7 Petrogenetic overview.- 9 Economic Geology.- 9.1 Lamprophyres and diamond.- 9.2 Calc-alkaline lamprophyres and gold.- 9.3 Lamprophyres and miscellaneous mineral deposits.- 10 A Selective Lamprophyre Bibliography.- Appendix A Abbreviations and Symbols.- Appendix B Glossary of lamprophyres and ambiguous petrological terms.- Appendix C Global Compilation of Lamprophyre Occurrences.- Table C1 Confirmed occurrences of calc-alkaline lamprophyres.- Table C2 Confirmed occurrences of alkaline lamprophyres.- Table C3 Confirmed occurrences of ultramafic lamprophyres.- Table C4 Confirmed occurrences of lamproites.- Table C5 Additional documentation for the appinite suite and vaugnérite series.- Table C6 Confirmed mixed or transitional occurrences (covering two or more branches).- Table C7 Unconfirmed occurrences of “lamprophyres”.- Table C8 Apocryphal occurrences of ”lamprophyres”.- Appendix D The computerized lamprophyre database LAMPDA.