Late Precambrian to Late Devonian mafic magmatism in the Antigonish Highlands of Nova Scotia: multistage melting of a hydrated mantle
Five suites of alkalic basalt ranging in age from Late Precambrian to Late Devonian are found in the Antigonish Highlands of Nova Scotia. In contrast, on neighbouring Cape Breton Island, alkalic basalts are rare even in suites that are contemporaneous with those in the Antigonish Highlands. Late Precambrian alkalic basalts in the Antigonish Highlands are genetically associated with calc-alkalic rocks and are probably subduction related, whereas the younger suites are continental, rift related, and within plate. Major and compatible trace-element abundances can be explained by crystal fractionation of olivine ± clinopyroxene ± orthopyroxene ± spinel ± garnet. However, incompatible trace-element concentrations are strongly influenced by mantle metasomatism that occurred prior to, or synchronously with, the oldest alkalic rocks. The metasomatic event enriched the mantle in Fe, Ti, P, Zr, and light rare-earth elements. The trace-element composition of the younger suites is similar to that of the oldest alkali...