The tajno ultramafic-alkaline-carbonatite massif, ne poland: A review. geophysics, petrology, geochronology and isotopic signature

Abstract

This paper reviews all avail able geo logical data on the Tajno Mas sif that in truded the Paleoproterozoic crys tal line base ment of NE Po land (Mazowsze Do main) north of the Teisseyre-Tornquist Zone, on the East Eu ro pean Craton. This mas sif (and the nearby E³k and Pisz in tru sions) oc curs be neath a thick Me so zoic-Ce no zoic sed i men tary cover. It has first been rec og nized by geophys i cal (mag netic and grav ity) in ves ti ga tions, then by drill ing (12 bore holes down to 1800 m). The main rock types iden ti fied (clinopyroxenites, syenites, carbonatites cut by later multiphase vol ca nic/subvolcanic dykes) al low char ac ter iz ing this mas sif as a dif fer en ti ated ultra mafic, al ka line and carbonatite com plex, quite com pa ra ble to the nu mer ous mas sifs of the Late De vo nian Kola Prov ince of NW Rus sia. Re cent geo chron ol ogi cal data (U-Pb on zir con from an albitite and Re-Os on pyrrhotite from a carbonatite) in di cate that the mas sif was emplaced at ~348 Ma (Early Carbon if er ous). All the rocks, but more spe cif i cally the carbonatites, are en riched in Sr, Ba and LREE, like many carbonatites world wide, but de pleted in high field strength el e ments (Ti, Nb, Ta, Zr). The ini tial87 Sr/86 Sr (0.70370 to 0.70380) and Nd(t) (+3.3 to +0.7) iso to pic com po si-tions of carbonatites plot in the de pleted quad rant of the Nd-Sr di a gram, close to the “FO cal ZOne” deep man tle do main. The Pb iso to pic data (206 Pb/204 Pb <18.50) do not point to an HIMU (high U/Pb) source. The ranges of C and O sta ble iso to pic com-po si tions of the carbonatites are quite large; some data plot in (or close to) the “Pri mary Ig ne ous Carbonatite” box, while oth-ers ex tend to much higher, typ i cally crustal 18 O and 13 C val ues.