The Mazury complex of northeastern Poland forms a 200 km long, E Á/W trending anorthosite Á/mangerite Á/ charnockite Á/granite belt derived from bimodal, multiphase anorogenic magmatism and is similar to the classic anorogenic complexes of the Fennoscandian Shield (e.g. Wiborg, Salmi and Ragunda).

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Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic features of some massif‐type anorthosites (polybarism, jotunitic parent magma), diapirically emplaced in the mid crust together with the rapakivi granites of the EW‐trending Mazury complex, intruded along a major crustal discontinuity. Geochemical modelling and isotope data corroborate recent experimental work on the basaltic system in dry conditions: the source rock of the parental magma is a gabbronorite, necessarily lying in the lower crust. Since no Archaean crust is known in the region, high initial 188Os/187Os ratios for sulphide‐oxide isochrons and negative εNd values are best accounted for by melting a ∼ 2.0 Ga mafic crust.

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