15 November 1972 Volcanic Studies Group Meeting
Current vulcanological research. Chairman: Professor I. G. Gass
1. Magmatic evolution of Mauritius. A. N. Baxter, Sir John Cass College, London.
Mauritius is entirely volcanic with three distinct series.
(1) Older Series. Early activity constructed a shield volcano with alternating lavas and agglomerates. The lavas form oceanites, arrkaramites, olivine basalts, basalts, hawaiites, mugearites and feldsparphyric basalts, with ultramafic and anorthositic inclusions and a related radial dyke swarm. A slight erosional unconformity within the series, separates the shield phase from a later group of feldsparphyric basalts, hawaiites, mugearites and trachytic endogenous domes. The basic lavas show a marked transitional character and the differentiated nature of the series is reflected in well defined chemical trends controlled by fractionation of observed phenocryst phases. The shield was highly incised by erosion, following cessation of activity.
(2) Intermediate Series. Activity renewed with the eruption of small volumes of alkali olivine basalts and basanitoids, in the SW of the island. Major element and some trace element trends are poorly defined, but the ‘incompatible’ elements K, P, Ti, Ba, Rb, Sr, Zr, show pronounced enrichment trends clearly unrelated to any likely low pressure fractionation scheme, and attributed here to eclogite fractionation at elevated pressures.
(3) Younger Series. A further pause was termin- ated by eruption of a voluminous alkaline olivine basalt from a median NNE-SSW line of 21 very low angled shield volcanoes. Major and trace elements show trends compatible with the fractionation of olivine, the dominant phenocryst phase in