Geological evolution of western H.U. Sverdrupfjella, Dronning Maud land, Antarctica.

Abstract

The oldest rocks of western H.U. Sverdrupfjella, the Jutulrora Formation, consist of interlayered mafic to felsic ortho- and paragneisses thought to represent calc-alkaline volcanic and clastic sedimentary rocks. These rocks are structurally overlain by the largely paragneissic, carbonate- dominated Fuglefjellet Formation which may represent a miogeosynclinal shelf facies. This sequence is structurally overlain by the dominantly para-gneissic Sveabreen Formation which may comprise a eugeosynclinal facies. Three granitic bodies, the Roerkulten, Jutulrora and Brekkerista Granites intrude the Jutulrora Formation. The trace element chemistry of these granites suggest that accessory minerals played significant roles during their generation and crystallization. Various mafic intrusions, now discordant amphibolites, and a phase of diorite veining are present. The Dalmatian Granite was emplaced syntectonically with the 470Ma Pan-African (or Ross) orogeny during D3. This granite was generated by crustal anatexis at >5kb. Jurassic age intrusions include alkaline complexes at Straumsvola and Tvora and numerous dolerite dykes, some of which postdate the alkali intrusions. Five episodes of deformation are recognised. The first two resulted in folds (F1 and F2) which are co-planar and coaxial resulting in type 3 interference structures. Low angle thrust faulting occurred during D2. Fold vergence and associated lineations suggest tectonic transport from the southeast during D1 and D2, D3 involved folding and reverse faulting. The orientations of the fault and axial planes of these structures suggest transport from the west and north-west. D4 involved open dome and basin folding. D6 involved normal faulting and jointing, adjacent and parallel to the Jutulstraumen Glacier in the west. The joints affect the Tvora Alkaline Complex. Three phases of metamorphism, related to the deformation, are recognised. The dominant mineral assemblages are typical of medium to high grade metamorphism and define S1 and S2 planar fabrics. Discordant mafic intrusions provide evidence of a long history of metamorphism. M3 mineral development, commonly represented by biotite, is oriented axial planar to D3 folds. Comparison of the geology of the area with that of southern Mozambique reveals many similarities. These support reconstructions based on geophysical data which juxtapose Dronning Maud Land and southern Africa prior to the break up of Gondwanaland.