New data on net-veined complexes in the Oslo Rift, southeastern Norway.

Abstract

Bodies of basaltic trachyandesite occur in the endocontact zone of the Mykle granite against the large Skrim larvikite massif in the southern part of the Oslo igneous province.\rNew Sr and Nd isotope data indicate that the 87Sr\/86Sr(0.704023-0.70544) and End (0.7-2.8) at 272 Ma of the basaltic trachyandesite are within the corresponding ranges of larvikite and the Vestfold basalts, but different from the Skien basalts. The isotopic data support a model for the origin of the trachyandestite by mixing if basic and granitic or syenitic melts, which is also in accordance with trace element data and petrographic observations. Black and emulsified trachyandesites have uniform End (+2.2+-0.5), but variable 87 Sr\/86Sr, which indicate that the melts were heterogeneous in Sr isotopes at the time of emplacement, most probably because of selective introduction of radiogenic Sr from older rocks by fluid phase before or during emplacement. Globular bodies of granite in the basaltic trachyandesite are surrounded by biotite haloes in the trachyandesite and are thought to be lumps of pratially consolidated granite or of the already consolidated granite picked up by the hot trachyandesitic magma.