Chilwa Province

The group of alkaline intrusions located west and south of Lake Chilwa were first described in detail by Dixey et al. (1937) who referred to them as the Chilwa Series, but later writers (e.g. Garson, 1966) have used the term ‘Chilwa Alkaline Province’. The province is of considerable interest for two main reasons: firstly, it lies at the extreme southern end of the East African Rift system and is the only province along the rift which is essentially intrusive. Secondly, the province is characterised by the great diversity of rocks present ranging from carbonatites, through nephelinites, ijolites and nepheline syenites, to syenites, quartz syenites and granites. The carbonatites were the first to be recognised in Africa and in fact Dixey and Smith (Dixey et al., 1937) described 11 carbonatite centres, the importance of which may be gauged from the fact that only about half-a-dozen carbonatites had been recognised worldwide at that time. Very full reviews of the carbonatites in the province have been published by Garson (1965a and 1966) and a general account of the province emphasising the tectonics and petrochemistry, and taking into account adjacent areas of Mozambique, is that of Woolley and Garson (1970). A further review (Woolley,1991) considers research on the province in terms of progress over recent decades. Geochronological data are compiled in Eby et al. (1995). It should be pointed out that there are numerous intrusions in the adjacent areas of Mozambique that are coeval with those of the Chilwa Alkaline Province: these are described under the entries for that country.