Melting reactions and trace element relationships in selected specimens of migmatitic pelites from New Hampshire and Maine |
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| Authors: | Thomas W Dougan |
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| Institution: | (1) Department of Geology, Allegheny College, 16335 Meadville, PA, USA |
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| Abstract: | Leucosomes and melanosomes in selected specimens of migmatitic, sillimanite-zone, pelitic schists are modal and chemical complements formed by segregation within originally homogeneous paleosomes. Systematic bulk chemical and modal variations in melanosomes can be used to infer the reactions by which leucosomes were generated.Trace element variations and relationships in melanosomes and leucosomes indicate that the migmatites behaved as closed systems during leucosome formation. Mass-balance evaluation of trace element relationships in the context of inferred leucosome-forming reactions suggest that trace elements essentially followed the melanosome phases initially containing them, as these phases reacted in leucosome generation. The trace element composition of a leucosome is given by the sum of those of the melanosome phases reacted, minus the trace element contents of any new solid melanosome phases produced by the reactions.Trace element relations are consistent with metamorphic equilibrium during leucosome generation, but suggest that once leucosome was segregated, equilibrium was not maintained between leucosome and melanosome. |
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