SILL EMPLACEMENT IN WET SEDIMENTS - FLUID INCLUSION AND CATHODOLUMINESCENCE STUDIES AT GRUNEHOGNA, WESTERN DRONNING-MAUD-LAND, ANTARCTICA

The Grunehogna and Kullen sills of western Dronning Maud Land were emp laced into water-saturated, partially lithified sediments of the mid-P roterozoic Ritscherflya Supergroup. Fluid inclusion and optical and sc anning electron microscope cathodoluminescence studies of quartz grain s within and adjacent to the sills (the 'sill-sediment interactive zon e', referred to as the 'interactive zone') showed that only a single g eneration of later fluid inclusions is present. The fluids are Na-K-Ca -Cl aqueous solutions with temperatures of homogenization between 95 a nd 105 degrees C. Individual quartz particles in the sedimentary rocks above the interactive zone have unique fluid inclusion populations. P etrographic and cathodoluminescence evidence indicated that there are three types of quartz grains in the interactive zone. These consist of (i) a xenocrystic type, (ii) a high-temperature quartz that crystalli zed either from the magma or as a result of anatectic melting of xenol ithic (and/or xenocrystic) material, and (iii) euhedral quartz crystal s that have grown in vugs in the peripheral zone. Cathodoluminescence of xenocrystic grains indicated the existence of healed microfractures along which fluid inclusions were concentrated and secondary and auth igenic overgrowths on older generation quartz grains had developed. Th e presence of zonal luminescence patterns of detrital particles, coupl ed with evidence for equilibrium polygonization in the sedimentary roc ks adjacent to the peripheral zone up to about 8 m above the upper con tact of the Grunehogna sill suggested local thermal tempering or sinte ring and recrystallization. Luminescence of detrital quartz particles in the overlying Hogfonna Formation reflected variation in the charact eristics of their source terrains, and showed limited evidence of heat ing by the magma. The interactive zone fluid inclusions are formation waters which penetrated microfractures during diagenesis. We show that no large-scale hydrothermal circulation system is likely to develop f ollowing intrusion into a water-saturated environment.