Early Mesoproterozoic magmatism in northwestern Lithuania: a new U-Pb zircon dating

Vara-Mesoproterosoikumi magmatismi ilmingud Loode-Leedus: uued tsirkoonide U-Pb isotoopdateeringud

10.3176/earth.2015.26

Irma Vejelyte；Svetlana Bogdanova；Grazina Skridlaite

U-Pb zircon dating ； LA-ICP-MS ； granodiorite ； Lithuania ； East European Craton

Estonian Journal of Earth Sciences

64卷3期（2015 / 09 / 20）

189 - 198

英文

On esitatud uus isotoopvanune andmestik Vara-Mesoproterosoikumi magmatismi kohta Loode-Leedu Telsiai tektoonilises vööndis. Kasutades induktiivseotud plasma massispektromeetriat (ICP-MS), on näidatud, et varem 1850-1820 Ma vanuseks peetud Kursiai tšarnokiitse batoliidi granodioriit on tegelikult kivimis olevate tsirkooniterade U–Pb vanuse järgi 1620 Ma vanusega. Kaheksa tsirkooniproovi Pb^(207)/Pb^(206) vanuse kaalutud keskmine on 1625 ± 6 Ma ja määrangute ülemine lõikepunkt on 1619 ± 27 Ma. Kuna ka Eesti aluskord sisaldab lähedase vanusega intrusioone, viitab sellise vanusega magmatismi olemasolu Leedus laiaulatuslikule ülessulamisele. Nii 1620 Ma magmatism kui ka 1580 Ma vanusega Riia anortosiidi, rabakivi ja graniitse batoliidi teke on Ida-Euroopa kraatoni loodeservas toimunud Gooti mäetekkeprotsesside kraatonisisesed ilmingud.

We present new geochronological evidence of latest Palaeoproterozoic-earliest Mesoproterozoic magmatism in the Telsiai Deformation Zone, NW Lithuania. Employing the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at the University of Tasmania, Australia, we demonstrate that a granodiorite, which had previously been considered to belong to the 1850-1820 Ma Kursiai charnockitic batholith, has a U-Pb zircon age of ca 1.62 Ga. The weighted mean Pb^(207)/Pb^(206) age obtained from eight concordant zircon grains is 1625 ± 6 Ma (MSWD = 0.6), while the upper-intercept concordia age is 1619 ± 27 Ma (MSWD = 0.56). Like similar ages of granitoids from several small intrusions in Estonia, this once more indicates extensive melting of the crust at that time. We suggest that both the 1.62 Ga magmatism and the emplacement and crystallization of the large Riga anorthosite-mangerite-charnockite-rapakivi batholith in Latvia and western Estonia at 1580 Ma were far-field feedback effects of the formation of the new Palaeoproterozoic continental crust during the Gothian orogeny at the present SW margin of the East European Craton.