Airborne Geophysical Study in the Pensacola Mountains of Antarctica

Abstract

A seismic reflection, gravity, and aeromagnetic reconnaissance was made in the Pensacola Mountains, Antarctica, during the 1965-66 austral summer. Prominent ice streams located between the Neptune and Patuxent Ranges and east of the Forrestal Range overlie channels in the rock surface 2000 meters below sea level which are probably of glacial origin. Seismic reflections show that the Filchner Ice Shelf is 1270 meters thick near its southern margin. Along the boundary between West and East Antarctica, Bouguer anomalies decrease from +60 milligals in West Antarctica to -80 milligals in East Antarctica. An abrupt change in crustal structure across this boundary is required to explainl the 2 milligals per kilometer gradient. This may indicate a fault extending through the crust into the mantle. Aeromagnetic profiles delineate anomalies up to 1800 gamma associated with the basic stratiform intrusion which comprises the Dufek and Forrestal ranges. A probable minimum area of 9500 square kilometers is calculated for the intrusive body on the basis of the magnetic anomalies, making it one of the largest bodies of its type. The extension of this magnetic anominaly across a fault forming the north border of the Pensacola Mountains probably precludes transcurrent movement.

Aeromagnetic and Radio Echo Ice-Sounding Measurements Show Much Greater Area of the Dufek Intrusion, Antarctica

“…The Dufek intrusion has been under study since 1957 by U.S. geologists (2) and geophysicists (3)(4)(5), and a geological-geophysical team from the Soviet Union investigated the area in 1978 (6). The intrusion extends across the transition from West to East Antarctica along the Transantarctic Mountains, of which the Dufek Massif and Forrestal Range are a part (Fig.…”

Geophysical investigations of the Pensacola Mountains and adjacent glacierized areas of Antarctica

“…A significant feature of model 3 is the vertical step at the crustmantle interface required to fit the observed steep gradient. This step-like effect suggests a steeply dipping fault separating East and West Antarctica and has been postulated previously by Behrendt, Meister, and Henderson (1966) and Robinson (1964). Plate 1 indicates that the steep gravity gradient fitted by the models calculated for line A-A' extends northeast; that gradient is coincident with a mapped fault separating the Schmidt Hills from the Neptune Range, as discussed in an earlier section.…”

“…Scattered data to the east of the Pensacola Mountains at seismic reflection stations suggest that the Bouguer anomaly values increase somewhat in this area. Behrendt, Meister, and Henderson (1966) discussed this regional anomaly and suggested that it was a result of crustal thickening across the transition from West to East Antarctica. In the present report we discuss this interpretation and present some computed models.…”

The Dufek intrusion of Antarctica

“…Geophysical studies [e.g., Behrendt, 1962Behrendt, , 1971Behrendt et al, 1966Behrendt et al, , 1979 show that the exposures of the intrusion in the Dufek Massif and Forrestal Range near the body's southern end comprise only a few percent of its extent (Figure 1) [Behrendt et al, 1973a], where the lowest-exposed, magnetite-poor rocks of the intrusion crop out. Aeromagnetic intensities increase to about 4007 over the eastern end of the massif in the Davis Valley area and to more than 1000y over the Forrestal Range [Behrendt et al, 1973a, b].…”