The north-eastern Polish anorthosite massifs: petrological, geochemical and isotopic evidence for a crustal derivation |
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| Authors: | Janina Wiszniewska Stefan Claesson Holly Stein Jacqueline Vander Auwera Jean-Clair Duchesne |
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| Affiliation: | Polish Geological Institute, Warsaw, Poland;;Swedish Museum of Natural Sciences, Stockholm, Sweden;;AIRIE Program, Colorado State University, Fort Collins, USA;;Géologie, Pétrologie et Géochime, University of Liège, Belgium |
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| Abstract: | ABSTRACT 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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