The Limestone Assimilation Hypothesis

In a recent communication describing the synthesis of feldspathoids by feldspar-carbonate reactions, R. D. Schuiling discussed the limestone-syntexis hypothesis, which proposes that rock-types under-saturated in silica can form from silica-over-saturated magmas by assimilation of limestone, and he stated that, from a physico-chemcial point of view, there was no essential difference between this process and one involving the assimilation of sialic material by a carbonatite magma. He remarked that: "Nobody, however, seems to have tried to verify experimentally such proposed processes". The purposes of this communication are: (1) to direct attention to an extensive series of experiments by Stansfield which were aimed directly at testing assimilation hypotheses, and which included investigation of the extent and products of assimilation of limestone by various igneous melts; (2) to outline some of our own experiments which are concerned with the origin of carbonatites and associated alkalic rocks and, inevitably therefore, with the limestone assimilation hypothesis as well; (3) to comment on some points of Schuiling's communication.