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An excellent petrologist who opened up the field of alkaline volcanism and carbonatite research.

Michael John Le Bas graduated in geology with chemistry and mathematics at University College London in 1952. He then completed his doctorate at the University of Cambridge, where he studied the Tertiary central complex of Carlingford, Northern Ireland, supervised by C.E. Tilley and S.R. Nockolds. After his 2-year military service abroad, Michael returned to Cambridge and published his work on the layered basic rocks of Carlingford in the Transactions of the Royal Society of Edinburgh in 1960. In 1961, Michael was appointed as igneous petrologist in the geology department at the University of Leicester. 

Left: Michael Le Bas. Photo courtesy of Diana Milne.

Methodical investigator 

Michael then investigated the igneous rocks of Leicestershire, including the Precambrian volcanic outcrops of Charnwood Forest and the Caledonian intrusive rocks that lie unevenly buried beneath Triassic sediments. He contributed a chapter to The Geology of the East Midlands by P.C. Sylvester-Bradley and T.D. Ford (1968), and, in 1972, Michael’s paper, titled “Caledonian Igneous Rocks Beneath Central and Eastern England”, was published by The Yorkshire Geological Society. Michael was an excellent petrologist; he was well-read and methodical, and he trained generations of students at the University of Leicester. 

Alkaline volcanism 

Michael’s research opened a new field in 1963, when he had the opportunity to study peralkaline volcanic rocks and carbonatites An excellent petrologist who opened up the field of alkaline volcanism and carbonatite research.in western Kenya with Professor B.C. King of Bedford College, London. King had published a Memoir (1949) for the Geological Survey of Uganda on Napak, a nephelinite volcano in eastern Uganda where the central conduit is composed of carbonatite. The study was planned as a team effort, with graduate students mapping the Kisingiri volcanic area adjacent to Lake Victoria, away from the Kenyan rift zone. 

In 1963, the University of Leicester was undergoing expansion, with the construction of a new building for the geology and geography departments, including proposed geochemistry facilities. Michael recruited five new graduate students for fieldwork with him in western Kenya, with one from Bedford College, London. A Natural Environment Research Council grant was awarded from 1963 to 1969. 

The team’s work led to the publication of the remarkably well-informed book, Carbonatite-Nephelinite Volcanism, in 1977. Recognising the unique association of these rocks, Michael then considered liquid immiscibility. Michael published widely, contributing a chapter, “Nephelinites and carbonatites”, to Alkaline Igneous Rocks, edited by J.G. Fitton and B.G.J. Upton (1987), and another to Carbonatites, edited by K. Bell (1989). 

Michael was Chief Editor of the Journal of the Geological Society for 13 years. In 1997, he was awarded a Coke Medal, recognising his major contribution to studies of alkaline volcanism and his services to the geological community. 

Local geologist

Michael retired in 1992 with his wife Pam to Blandford Forum, Dorset. Here, he became curator of the Town Museum, producing popular booklets including Building Stones of Blandford. He was awarded the Freedom of Blandford Forum in 2019. Michael was well-known locally as a geologist and historian, a Trustee of Dorset Natural History and Archaeological Society (Dorset Museum), and supporter of the Etches Museum in Kimmeridge. 

Michael is especially remembered at the University of Leicester. 

By Diana Milne (D.S. Sutherland), Tim Le Bas, Brian Windley, John Hudson and David Siveter

The full version of this obituary appears below. Editor.

An excellent petrologist who opened up the field of alkaline volcanism and carbonatite research.

Michael John Le Bas graduated in geology with chemistry and mathematics at University College London in 1952. He then completed a doctorate at the University of Cambridge, where he studied the Tertiary central complex of Carlingford, Northern Ireland, supervised by C.E. Tilley and S.R. Nockolds. After his 2-year military service abroad, Michael returned to Cambridge and published his work on the layered basic rocks of Carlingford in the Transactions of the Royal Society of Edinburgh in 1960. In 1961, Michael was appointed as igneous petrologist in the geology department at the University of Leicester.

Michael then investigated the igneous rocks of Leicestershire, including the Precambrian volcanic outcrops of Charnwood Forest and the Caledonian intrusive rocks that lie unevenly buried beneath Triassic sediments. The buried landscape of igneous intrusions continued to interest him, including borehole evidence across the Midlands. He contributed a chapter to The Geology of the East Midlands by P.C. Sylvester-Bradley and T.D. Ford (1968), and, in 1972, Michael’s paper, titled “Caledonian Igneous Rocks Beneath Central and Eastern England”, was published by The Yorkshire Geological Society.

Michael became a member of the Leicester Literary and Philosophical Society (1963), and Chair of their geology group, Section C, before he retired. His last publication in their Transactions (1996) covered the Precambrian volcanic rocks of Bardon quarry, recognising the brecciation and prominent dome structures of dacite porphyry, similar to those he had seen actively forming in Kyushu, Japan, in 1982. Michael was an International Union of Geological Sciences expert in normative petrology. He was well-read and methodical, and he trained generations of students at the University of Leicester.

Michael’s research opened a new field in 1963, when he had the opportunity to study peralkaline volcanic rocks and carbonatites in western Kenya with Professor B.C. King of Bedford College, London. King had published a Memoir (1949) for the Geological Survey of Uganda on Napak, a nephelinite volcano in eastern Uganda where the central conduit is composed of carbonatite.

In 1963, the University of Leicester was undergoing expansion, with the construction of a new building for the geology and geography departments, including proposed geochemistry facilities. A Natural Environment Research Council grant was awarded from 1963 to 1969. The study of western Kenya was planned as a team effort, with five newly recruited graduate students mapping the Kisingiri volcanic and Homa Mountain areas adjacent to Lake Victoria, away from the Kenyan rift zone. The Tertiary volcano of Kisingiri is very much eroded, exposing the underlying Precambrian basement, together with early alkaline silicate intrusions and a central carbonatite complex (Rangwa). Thirty miles to the northeast is Homa Mountain, with early ijolitic intrusions, fenitisation, and high ramparts formed of multiple carbonatite cone-sheets. Late veins of brown ferrocarbonatites (with iron oxide) contain rare minerals such as monazite, baryte, fluorite, and dahlite. Between Rangwa and Homa are several alkaline, carbonatite complexes and many phonolite plugs.

In October 1965, at a colloquium of the Volcanic Studies Group of the Geological Society on African volcanoes, King spoke on volcanism in eastern Africa and its structural setting; Michael described the intrusive and volcanic centres of the Wasaki area, Homa Bay; and other members of the team introduced their areas. The team also presented at another Volcanic Studies Group meeting in Leicester in 1970, before Michael, King, and Sutherland published an overview of the project in 1972. The team’s work led to the publication of Michael’s comprehensive book, Carbonatite-Nephelinite Volcanism, in 1977.

In 1960, carbonatite lava had been reported erupting from Ol Doinyo Lengai volcano, Tanzania. Using the work of Koster van Groos and Wyllie, who were investigating liquid immiscibility between carbonate and alkali silicate melts, Michael realised that this process was relevant to the development of the west Kenyan volcanic complexes. Interest in fluid inclusions in apatite crystals was also growing, and, in 1981, Le Bas and Aspden identified fluid inclusions comparable with the natrocarbonatite lava from Ol Doinyo Lengai.

Michael published widely, contributing a chapter, “Nephelinites and carbonatites”, to Alkaline Igneous Rocks, edited by J.G. Fitton and B.G.J. Upton (1987). In this chapter, Michael contrasted the western zone of melanephelinites without olivine, and nephelinites with olivine in the Kenyan rift zone.

In 1987, Michael conducted a 2-week long workshop on carbonatites in west Kenya, studying outcrops from Homa Mountain to Rangwa, assisted by M.C.G. Clarke (former Leicester team-member, before investigating geothermics in Kenya). International participants included K. Bell (Carleton University, Canada), who subsequently edited the book, Carbonatites (1989), which contained Michael’s chapter, “Diversification of Carbonatite”.

Besides teaching Leicester undergraduate students, Michael supervised 23 postgraduate students, including some from Pakistan, India, and South Africa; he also travelled widely, to China, the Canary Islands, and Cape Verde islands.

Michael was Chief Editor of the Journal of the Geological Society for 13 years. In 1997, he was awarded a Coke Medal, recognising his major contribution to studies of alkaline volcanism and his services to the geological community.

Michael retired in 1992 with his wife Pam to Blandford Forum, Dorset. Here, he became curator of the Town Museum, producing popular booklets including The Building Stones of Blandford. He was awarded the Freedom of Blandford Forum in 2019. Michael was well-known locally as a geologist and historian, a Trustee of Dorset Natural History and Archaeological Society (Dorset Museum), and supporter of the Etches Museum in Kimmeridge. Michael Le Bas was a quietly knowledgeable man. Pam pre-deceased him (2010); he leaves three sons and seven grandchildren.

Michael is especially remembered by the University of Leicester and those who knew him.

By Diana Milne (D.S. Sutherland), Dr Tim Le Bas, Brian Windley, John Hudson, David Siveter, and Aftab Khan