U-Pb ages of plutonic and volcanic rocks in the Svecofennian Bothnian Basin, central Sweden, and their implications for the Palaeoproterozoic evolution of the Basin

New U-Pb age data on two early orogenic granodiorites (ca. 1930 Ma) and one felsic metavolcanite (1870 Ma) from the Svecofennian Bothnian Basin area o f central Sweden are presented. Combined with literature data they suggest an extended, at least ca. 80 m.y. long, evolution of this part of the Bothn ian Basin. Sedimentation started before 1950 Ma, and continued up to at lea st 1870 Ma. Early-orogenic plutonic activity started at ca. 1950 Ma, perhap s even earlier, and continued up to ca. 1850-1840 Ma. Detrital zircons foun d in low-grade greywackes of the region range in age from ca. 1880 to 2020 Ma. According to the tentative model suggested here, these zircons may eman ate from granitoids intruded into the greywacke sequence of the Bothnian Ba sin. They were subsequently exposed to erosion and included in upper parts of the sedimentary column. These upper parts could (statistically) be of a lower metamorphic grade than older greywackes, which are generally migmatiz ed.