INSIGHTS ON THE AGE AND EVOLUTION OF PRECAMBRIAN BASEMENT COMPRISING THE LOPPA HIGH, BARENTS SEA, FROM DETRITAL ZIRCONS AND FELDSPARS

The Loppa High is situated on the western margin of the Barents Shelf between Svalbard and northern Norway. The region is an important piercing point for Arctic tectonic evolution because the Caledonian, Timanian and Grenville orogens are all inferred to traverse the Barents Shelf and affect the Loppa High. Moreover, it is unclear whether the crystalline basement comprising the Loppa High was originally part of Baltica or Laurentia because the trace of the Caledonian suture from north Norway to Svalbard is contentious. The consensus from geophysical data is that it is part of Baltica, specifically the c. 1.65 Ga phase of the Transscandinavian Igneous Belt. In order to test this affinity for the Loppa High, we have carried out U-Pb geochronology on detrital zircons and Pb isotope measurements on detrital feldspars from Carboniferous sedimentary rocks from the Barents Sea adjacent to the basement high. These are thought to have been deposited in small rift basins and locally sourced. Both zircons and feldspars yield compatible results and indicate that the zircons were not recycled from sedimentary or metasedimentary rocks. Zircons form a single age peak and indicate that the basement crystallised some 400 Ma earlier than the Transscandinavian Igneous Belt. Feldspar Pb isotopic signatures form isochrons indistinguishable from the zircon ages and they are less radiogenic than is typical for the Fennoscandian Shield. However, these patterns can be reconciled as a consequence of relatively recent Pb isotopic re-equilibration. This event may also have affected the zircons, which record variable but significant late Devonian Pb loss. These results will be discussed in context of Caledonian and Columbia Supercontinent paleogeographies.