Subglacial morphology and structural geology in the southern Transantarctic Mountains from airborne geophysics




Davis, Marcy B.

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The Transantarctic Mountains (TAM) form the high western rift flank of the West Antarctic Rift System (WARS), a region of extended crust that separates East and West Antarctica. Little is known about the structural geology in the southern TAM due to limited accessibility and more ice cover than in the central and northern TAM. The objectives of this study are to characterize the subglacial bedrock morphology interior of the southern TAM and to define the structural geology along the southern TAM Front through analysis of airborne ice-penetrating radar data. The airborne survey extended from the Ross Ice Shelf, southward over the TAM along the 150°W meridian and between the Scott and Reedy Glaciers then over the high plateau and through the South Pole. Approximately 15,000 line km were flown and processed using finite difference migration techniques in a seismic processing software package. Subsequently, the ice and bed surfaces were picked along each line and known geology was interpreted on the radar records where it exists. Ice-penetrating radar sounding coupled with a compilation of field geologic studies has proven to be a powerful technique for examining the architecture and structural geological relationships of the southern TAM. Four distinct morphological provinces are identified along the length of the survey, these include: 1) the South Pole Basin and Plateau Province, with low relief features and up to 4 km of ice; 2) the Alpine Glaciated Province, with well-preserved U-shaped valleys that show a glaciation network that flowed opposite of contemporary glaciers; 3) the TAM Massif, which includes three subglacial blocks and the outcropping portion of the TAM; and 4) the TAM Front, a normal fault zone north of the TAM to Ice Stream A. The southern TAM have a southward tilted block structure with the area of maximum uplift in a region 30-50 km wide from the Watson Escarpment, the highest part of the TAM in this area, southward and is bounded by NW-SE-trending normal faults on both the north and south sides. Down-to-the-north normal faults north of the Watson Escarpment topographically downdrop the TAM from >3000 m to sea level over ~50 km and facilitate the development of the Leverett Glacier and Ice Stream A. The primary structural trend between the Scott and Reedy Glaciers is NW-SE, parallel to the TAM. Faults oriented obliquely to the TAM break the area of maximum uplift into three NNW-SSE trending blocks that appear offset ~10 km in a left-lateral sense relative to each other with range-parallel horst and graben features superimposed. One of these faults may control the eastern side of Scott Glacier. Structural relationships across the Watson Escarpment suggest that the southern TAM are a result of upward block faulting along the TAM Front rather than a result of regional upwarping.