Abstract :
[en] 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 Os-188/Os-187 ratios for sulphide-oxide isochrons and negative epsilon(Nd) values are best accounted for by melting a similar to 2.0 Ga mafic crust.
Disciplines :
Physical, chemical, mathematical & earth Sciences: Multidisciplinary, general & others
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