The age of the Lødingen granite and its possible regional significance

A new 11 point Rb-Sr whole rock isochron age from the foliated Lødingen granite has yielded an age of 1644 + 36 Ma (MSWD = 3.4) and an initial 87Sr/86Sr ratio of 0.70780. The age is interpreted as the crystallisation age of the pluton. This age is higher than previously published ages and links the Lødingen granite to the emplacement of the mangerite-charnockite suite of the Lofoten-Vesterålen-Tysfjord
Province. The initial 87Srf!6sr ratio for the Lødingen granite differs significantly from the initial ratios obtained on the non-mangeritic Tysfjord and Rombak granites. The boundary between the granulite facies rocks in the Lofoten-Vesterålen-Hamarøy area and the normal granites further east, including the
Lødingen granite, is interpreted as a fossil isothermal surface now dipping eastwards.