The Theresabjerg complex of about 8x4 km cross-cuts, partly domes and metamorphoses its sedimentary cover. It is composed principally of peralkaline syenites but there are also extensive volcanic breccias and an early gabbro-diorite stock. The syenites are leucocratic rocks of alkali feldspar with minor quartz or feldspathoid sometimes present, and minor aegirine/aegirine-augite and biotite. The gabbros contain biotite and hornblende. A few km north of Theresabjerg, and largely covered by ice, is the Pictet Bjerge stock of peralkaline granite. The granite is homogeneous, has a granophyric texture, and consists of alkali feldspar, quartz, 5-20% aegirine and 1-8% sodic amphibole. Breccias are abundant within the confines of the Theresabjerg complex and as small vents cutting the sediments, particularly around Pictet Bjerge. In some syenite blocks are dominant, while others contain a broad range of igneous and sedimentary blocks. Rock analyses of all the main types are available in Kapp (1960).
KAPP, H. 1960. Zur Petrologie der Subvulkane Zwischen Mesters Vig und Antarctic Havn (Ost-Gronland). Meddelelser om Gronland, 153(2): 1-203.