The granites of the Mykle region in the southern part of the Oslo igneous province, Norway

Abstract

The granites exposed around lake Mykle constitute two discrete massifs. The western granite massif, the subject of the present paper, is an intrusive complex, with larvikite as country rocks making up the topographic highs and occurring as stoped blocks within the granite. Two types of granite were identified: a marginal, fine- to medium grained, reddish granite and a central, younger, coarse-grained, white to grey granite akin to ekerite. The reddish granite displays chilled margins at the contacts with with larvikite and locally contains mafic rocks as net-veined complexes. It is metaluminous to weakly peraluminous and yields the highest contents of incompatible elements. Though later than syenite and the reddish granite, the ekerite displays sharp contacts only, with no chilled margins, indicating that no significant temperature gradients were created during its emplacement. Miarolitic cavities, abundant in all rock types, are evidence of fluid exsolution from volatile-rich magmas. The present surface level corresponds to the poorly exposed roof near part of a larger intrusion, emplaced within larvikite and rhomb porphyry lavas by magmatic stoping and perhaps cauldron subsidence.