Implications of the emplacement age of the Kläppsjö gabbro; a mafic layered intrusion in the Bothnian basin, north central Sweden

Abstract

The 6X3.5 km large Kläppsjö gabbro in the county of Västernorrland is a tholeiitic mafic layered intrusion that was emplaced into metaturbidites of the Bothnian basin, and is partly bordered by early- and late-orogenic Svecofennian granitoids. The intrusion consists of ultramafic, gabbroic, leucogabbroic and ferrogabbroic mega-units, tens to hundreds of metres thick forming a c. 3 km thick layered sequence. The gabbro is exposed in cross section, with a sub-vertical igneous layering that is sub-parallel to the bedding in the surrounding metasediments. U-Pb SIMS zircon dating yields an emplacement age of 1877±5 Ma, and the gabbro is thus contemporaneous with 1.88–1.86 Ga early-orogenic Svecofennian magmatism in the Bothnian basin. This includes a tonalite bordering on the gabbro here dated to 1870±10 Ma. Extension related magmatism of this age characterises major parts of the Svecofennian domain, and the emplacement of the Kläppsjö gabbro was probably related to extension in the Bothnian basin.