Sediment Fusion In the Palisades Sill and Karroo Dolerite: A Comparison

Sediment Fusion is present in both the Palisades Sill NY/NJ and the Karroo Dolerites of South Africa. Palisades and Karroo dolerites are petrologically and geochemically similar.

Benimoff and Sclar (1978, 1984) reported on a xenolith of Na-rich Lockatong argillite that fused around its margins when immersed in the magma of the Palisades Sill. Walker and Poldervaart(1942, 1949) studied what can only be interpreted as a fused xenolith of siltstone immersed in the magma of the Karroo Dolerite. Surrounding this xenolith is a granophyre and a pegmatite. The above is surrounded by Karroo dolerite.

The occurrences described above represent the arrested state. Benimoff and Puffer (2005), reported on additional sediment fusion occurrences in the Newark Basin, NJ and NY. They showed that there was tri-modal fusion of meta-argillites along margins of early Jurassic diabase intrusions generating trondhjemites, granites and syenites. As shown by Benimoff and Puffer (2005) there are 4 factors that control the chemical composition and nature of the tri-modal fusion products. They are (1) variations in the chemical composition of the host rock;(2) heat driven metasomatism;(3) degree of partial melting; and (4) the degree of mixing. In this study, granophyre and pegmatite compositions of Walker and Poldervaart (1942, 1949) were plotted in the Quartz - Albite – Orthoclase System of Luth et al. 1964. The results indicate that granites were generated instead of syenites or trondhjemites. In the case of the Palisades Sill, the most common fusion products are syenites and trondhjemites. However, granite fusion products seem to be the most common fusion products within the Karroo. It is suggested that partial fusion of potassic rich sediments resulted in the formation of these granophyres and pegmatites. These results have important applications considering the role that contamination has had on the chemistry of both dolerites.