A genetic link between the Lauterbrunnen migmatites (LM) of the
Innertkirchen-lauterbrunnen Crystalline Zone (ILC) in the Aar massif and
the nearby 303 +/- 4-Ma Gastern granite is indicated by chemical
similarities as well as spatial proximity. The new U-Pb zircon ages of
289 +/- 9 Ma (igneous zircon, nearly concordant) and 303.4 +/- 1.2 Ma
(metamorphic zircon, concordant) for the LM in this study indicate that
the LM and Gastern granite are also coeval. The relatively mafic
composition of the LM sample that yielded the nearly concordant U/Pb
ages is interpreted to reflect intrusion of a parental magma into the
LM, which would have been too mafic to reflect in situ partial melting
of the mid-level crust at geologically reasonable temperatures. Highly
discordant U-Pb zircon ages for other LM samples are interpreted to
reflect mixing of the intruded ma,nma and country rocks. The new U/Pb
age data provide the evidence for a temporal link of the LM to the
Gastern granite, which is interpreted to belong to thr same Variscan-age
magmatic event that formed the LM.