October 2021 Archives

v17n6 From the Editors

By Jodi J. Rosso, John M. Eiler, Richard Harrison and Becky Lange |

There are many individuals and organizations who we want to recognize for their participation in and support of Elements in 2021.

Reflecting on the Colonial Legacy of Geoscience in Africa

By Kathryn Goodenough and Keely Mills |

Although carbonatites are now known worldwide, much of the early work to identify them was done in Africa, particularly around Oldoinyo Lengai (Tanzania) led by the late John Barry Dawson (1932–2013). Barry was a professor at the University of Edinburgh (UK) when one of us (KG) was there during the 1990s doing a PhD on alkaline igneous rocks and carbonatites; his interest and enthusiasm for the subject was infectious. Barry’s initial work on Oldoinyo Lengai, and his recognition of it as a carbonatite volcano, was done when he was a geologist for the Geological Survey of Tanganyika, around the time of Tanzanian independence. This was a time when colonial attitudes still strongly governed the way geological work was done in Africa, and the early papers on carbonatites abound with names of former colonies such as Rhodesia, Nyasaland, and South-West Africa.

Evolution and Involution of Carbonatite Thoughts

By Francesco Stoppa |

During my doctoral studies, in the late 1980s, I realised that the Italian kamafugites (kalsilite melilitites) had to be related to carbonatite magmatism. I started a detailed study of the kamafugitic sites, and I explored remote areas deep in Italy’s Apennine mountains. When I found the Polino carbonatite, I put a few drops of acid on it, and the rock reacted. I have a vivid memory of my heart beating faster. I had found it! My fellow geologists were somewhat sceptical, but the late Professor Giorgio Marinelli (1922–1993) encouraged me and predicted many new carbonatite discoveries. He was right. Overcoming my Latin temperament, I focused on the concept that carbonatites, however unusual as rocks, cannot be dismissed as simple geological oddities but require detailed and comprehensive study. I am fond of all the history that marked my latest 40 years of life, and it reminds me of the many friends and mentors that I have had, especially when I was a young researcher. Sadly, some of them are no longer with us. I am so grateful to them, and I consider it a life-changing experience to have met them.

Ending 30 Years of Hurt: The Winchcombe Meteorite Fall

By Luke Daly, Ashley J. King, Katherine H. Joy and Jim Rowe |

Meteorite hunting is a lot like football (soccer) … just run with us on this. Success requires skill, a cracking team, a whole lot of luck … and, historically, England (and the UK) are not very good at it … we were just unlucky … the (fire)ball always seems to miss the goal! Meanwhile, around the world, meteorite fall recoveries are becoming more and more frequent; but in the UK, to put it in the style of the famous English football anthem by the band the Lightning Seeds, it’s been “30 years of hurt” since our last meteorite fall.

Remembrance of Carbonatites Past

By Alan R. Woolley |

The Oxford English Dictionary defines ‘vector’ as a quantity having direction as well as magnitude, and ‘scalar’ as a quantity having only magnitude, not direction. Much geological research starts with fieldwork, manifestly a vector activity. In Figure 1A, the geologists are exploring the intersection of a complex, 3-D body, the layered Klokken syenite, a 4 × 3 km igneous intrusion in the Gardar alkaline province of SW Greenland, with a mountainous 3-D land-surface. I described the unusual layering in Elements v10n1 (Parsons 2014). The igneous rocks were emplaced 1,166.3 ± 1.2 million years ago, and the 650 m of 3-D topography, which reveals the inner workings of the magma chamber, was carved by the advance and retreat of the mighty Greenland ice sheet in the last few thousand years. Only the age (a U–Pb age from baddelyite, ZrO2) is a scalar quantity.

The Power of Mysterious Words

By John M. Eiler |

One of the joys of growing up in a little-remarked-upon corner of the upper Midwest USA is that it came with its own secret words and rituals—cricks and bubblers, hotdishes and euchre. The Wisconsin patois served as a daily reminder that humans have a passion for using mysterious languages to express the numinous: cants and glossolalia that describe new things or express new ideas or emotions, and that draw lines, intentionally or otherwise, between the community of “insiders” and everyone else.

v17n5 From the Editors

By John M. Eiler, Richard Harrison, Becky Lange and Jodi J. Rosso |

Elements is published through the collaboration of 18 participating scientific societies. The Elements editorial team is responsible for the content and the day-to-day management of the magazine. The Elements Executive Committee is responsible for the management of the magazine through financial oversight, approval of editorial appointments, and facilitating a close working relationship between the editorial team and the participating societies.

Carbonatites and Global Tectonics

By Emma R. Humphreys-Williams and Sabin Zahirovic |

Carbonatites have formed for at least the past three billion years. But over the past 700 My the incidence of carbonatites have significantly increased. We compile an updated list of 609 carbonatite occurrences and plot 387 of known age on plate tectonic reconstructions. Plate reconstructions from Devonian to present show that 75% of carbonatites are emplaced within 600 km of craton edges. Carbonatites are also associated with large igneous provinces, orogenies, and rift zones, suggesting that carbonatite magmatism is restricted to discrete geotectonic environments that can overlap in space and time. Temporal constraints indicate carbonatites and related magmas may form an ephemeral but significant flux of carbon between the mantle and atmosphere.

The Distinctive Mineralogy of Carbonatites

By Andrew G. Christy, Igor V. Pekov and Sergey V. Krivovichev |

The mineralogy of carbonatites reflects both the diversity of the sources of their parent magmas and their unusual chemistry. Carbonatites contain diverse suites of both primary magmatic minerals and later hydrothermal products. We present a summary of the variety of minerals found in carbonatites, and note the economic importance of some of them, particularly those that are major sources of “critical elements”, such as Nb and rare earth elements (REEs), which are essential for modern technological applications. Selected mineral groups are then discussed in detail: the REE carbonates, the alkali-rich ephemeral minerals that are rarely preserved but that may be important in the petrogenesis of carbonatites and their metasomatic haloes in adjacent rocks, and the Nb-rich oxides of the pyrochlore supergroup.

Formation of Rare Earth Deposits in Carbonatites

By Michael Anenburg, Sam Broom-Fendley and Wei Chen |

Carbonatites and related rocks are the premier source for light rare earth element (LREE) deposits. Here, we outline an ore formation model for LREE-mineralised carbonatites, reconciling field and petrological observations with recent experimental and isotopic advances. The LREEs can strongly partition to carbonatite melts, which are either directly mantle-derived or immiscible from silicate melts. As carbonatite melts evolve, alkalis and LREEs concentrate in the residual melt due to their incompatibility in early crystallising minerals. In most carbonatites, additional fractionation of calcite or ferroan dolomite leads to evolution of the residual liquid into a mobile alkaline “brine-melt” from which primary alkali REE carbonates can form. These primary carbonates are rarely preserved owing to dissolution by later fluids, and are replaced in-situ by monazite and alkali-free REE-(fluor)carbonates.