VOLCANIC CONE ALIGNMENTS AND THE INTRAPLATE STRESS FIELD IN THE MOUNT MORNING REGION, SOUTH VICTORIA LAND, ANTARCTICA

Unlike most continents on earth, there is virtually no data on the intraplate stress field within Antarctica. Recent results of the Cape Roberts Drilling Project have provided the first in situ stress data within Antarctica, along the Transantarctic Mountain rift flank uplift and West Antarctic rift system boundary. In order to define SHmax orientation elsewhere in the Antarctic interior, we have been examining young volcanic cones found within Cenozoic volcanic provinces. Volcanic cone alignments are considered to form along natural hydrofractures induced by pressurized magma; if magmatic pressures exceed the sum of the tensile strength of the surrounding rock and the least external compressive stress, a tensile fracture develops. Eruptions along such stress-controlled fissures produce linear arrays of volcanic vents and cones, elongated cones, and dikes. These volcanic features can be mapped to determine the neotectonic stress directions in an area. Around the Mount Morning stratovolcano within the Erebus Volcanic Province, we measured the orientation of Quaternary volcanic cone alignments and the long-axis trend of elongated cones using SPOT 3 panchromatic satellite imagery, RADARSAT and JERS radar imagery, aerial photography, and available geologic maps. We found that the trends of cone alignments and the long axes of elongated cones form an hourglass pattern in map-view, suggesting that fissures radiate from the central crater, but assume a northeast trend at a greater distance. The northeast-trending hourglass pattern implies that the Antarctic intraplate stress field is anisotropic with SHmax NE-SW and Shmin NW-SE. The interpreted NE SHmax trend is oblique to regional structural boundaries and to the Cape Roberts in situ contemporary stress direction.