Jurassic (159 Ma), ultrapotassic, mica-rich dykes of Kjakebeinet represent the youngest magmatic rock type observed in western Dronning Maud Land, Antarctica; abundant xenoliths are enclosed by the dykes.
A petrographical description of the xenoliths and one of the dykes was made to distinguish the rock types and to gain information of the unknown basement below Kjakebeinet, situated on the southern edge of Vestfjella mountainrange. The mineral chemistry and petrography of the xenoliths and one of the lamproite dykes were studied using petrographic microscope and electron microprobe (EDS-mode). Rb-Sr and Sm-Nd isotopic determinations were made on metagabbroic and carbonatite xenoliths.
Most of the xenoliths record evidence of granulite facies metamorphosis and they represent several crustal rock types. Tonalite, alkali feldspar granite, and augen gneisses, metagabbros and metasedimentary xenoliths were observed. Two of the xenoliths, carbonatite, and phlogopite rock, are cognate.
This thesis shows that the crust below the southern Vestfjella is heterogenic, and contains differentiated metaigneous rock types. The xenoliths include Proterozoic basement gneisses, and possibly also Permian sedimentary rocks and Mesozoic igneous rocks. The studied lamproite dyke is phlogopite-sanidinediopside-olivine lamproite which shows affinity to madupitic lamproites and group II kimberlites.
