Far East Avalonia: its chronostratigraphic structure revealed by SHRIMP zircon ages from Upper Carboniferous to Lower Permian volcanic rocks (drill cores from Germany, Poland and Denmark).

Abstract

Sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages have been obtained from zircons separated from Upper Carboniferous to Lower Permian SiO2-rich volcanic and subvolcanic rocks of eleven drill sites. The volcanic rocks belong to a large volcanic province that formed during the initial stage of the Central European Basin System. Two drill sites are located in Denmark (North Sea and Lolland), five in northern Germany, and four in western Poland.Apart from establishing the emplacement age of the volcanic units, the focus of the present study was the dating of inherited zircons. They give information about the chronostratigraphic structure of the anatectic component of the hybrid intraplate magmas, that is, the crust below the Central European Basin System. The Central European Basin System substrate consists mainly of a little known, covered terrane called Far Eastern Avalonia. The northern margin of the Central European Basin System rests on the collisional suture of Avalonia with Laurentia and Baltica. The southern margin is superposed on the Variscan orogen, which formed as a result of the Carboniferous collision of the Armorican Terrane Assemblage with Laurussia/Old Red continent.Where possible, a minimum of ten analyses has been used to calculate the emplacement age for each sample, which range between 290 and 303 Ma. The two Danish samples yielded only a small zircon population with a similar, but poorly constrained emplacement age. These results, together with the data of a precursor project (Breitkreuz and Kennedy, 1999) indicate a remarkable synchronicity of the magmatic activity focused between 295 and 299 Ma throughout the Central European Basin System.Most zircon separates contain inherited grains or old cores. About seventy analyses, including data from the precursor study, are presumed to represent Avalonia and subordinately southern Baltica crust. The ages range from 320 to 2614 Ma. Paleozoic ages fall within the range of the Caledonian and Variscan orogenies. The Precambrian ages show two maxima, one between 1400 and 1600 Ma with a peak at 1450 Ma, and one between 750 and 1200 Ma with a peak at 1050 Ma. This age distribution strongly indicates an affiliation of the sub-Central European Basin System crust to Avalonia and an original position adjacent to the Amazonian craton.