Timing and Petrogenesis of the Permo-Carboniferous Larvik Plutonic Complex, Oslo Rift, Norway: New Insights from U-Pb, Lu-Hf and O Isotopes in Zircon

Abstract The Permo-Carboniferous Oslo Rift is a narrow, aborted continental rift with comparatively little extension but voluminous magmatism, developed at Proterozoic lithospheric discontinuity. On the southern flank of onshore part rift, multiple intrusive phase Larvik plutonic complex (LPC) encompasses almost width conspicuous over- to undersaturated assemblage monzonite (larvikite, tønsbergite) and nepheline syenite (lardalite, foyaite). We present new single-crystal U–Pb–, Lu–Hf–, O–in–zircon isotope data for centers complex. U–Pb ages slightly monzonites show shift in igneous activity from 299 Ma on eastern edge 289 west. western built two consanguineous magmatic systems northward locus 296 (undersaturated monzonite) ~288 (nepheline syenite). Moreover, an early oversaturated was emplaced ~302 Ma. Hf O composition syenites shows variation zircon εHf (295 Ma) values +5.5 +8 δ18Ο +4.79‰ +5.49‰. No change observed varying alkalinity compositions are interpreted as mantle source values. precursors monzonitic syenitic magmas probably mildly depleted, sublithospheric peridotite lithosphere-asthenosphere boundary zone (at 3–4 GPa). Rhyolite–MELTS modeling implies polybaric fractionation weakly alkaline basaltic melts having led oversaturated/saturated liquid line descent ~0.5 GPa one ~1 GPa. Magmatism had imperative role evolution by localizing strain weakening lithosphere along A fractionating crustal melt column tapped depths course advancing rupturing no significant mixing melts, magma batches were sequential nested plutons response differential opening rift. Among saturated-undersaturated complexes, LPC may be unique emplacement successive across direction opening, tapping increasingly deeper parts rifting, intrusion contemporaneous, contrasting lineages end activity. marked step Precambrian basement southeastern Norway driving force inception system.