Geological structures inferred from airborne geophysical surveys around Lützow-Holm Bay, East Antarctica

The area around Syowa Station, the Japanese Antarctic wintering station in Lützow-Holm Bay, is widely considered as a junction of the continents of Africa, India, Madagascar, and Antarctica, according to a reconstruction model of Gondwana that considers the suture between East and West Gondwana. This area is therefore key for investigating the formation of Gondwana. To reveal the tectonic evolution that contributed to Gondwana's formation in this area, joint Japanese-German airborne geophysical surveys were conducted around Syowa Station in January 2006 during the 47th Japanese Antarctic Research Expedition, from 67° S to 73° S latitude and from 35° E to 45° E longitude. Ice radar, magnetic, and gravity data were obtained from onshore areas. Several characteristic features that are possibly related to the tectonic evolution of Gondwana were inferred, primarily from magnetic anomalies, as well as from gravity anomalies and bedrock topography. The boundaries of the Lützow-Holm Complex, the Yamato-Belgica Complex, and the Western Rayner Complex are defined, but the inland extension of the boundary between the Lützow-Holm and the Yamato-Belgica Complexes is unknown south of 71° S. The main geological structural trends of the Lützow-Holm Complex derived from magnetic anomalies are NW–SE and are concordant with the geological results in the coastal region. However, nearly NE–SW-trending magnetic anomalies cut across the NW–SW magnetic anomaly trends, and NE–SW right lateral strike-slip faults were deduced from the magnetic and the gravity anomaly data of the Lützow-Holm Complex. The Lützow-Holm Complex was sub-divided into four blocks based on the estimated strike-slip faults. These strike-slip faults may have been generated during a younger stage of Pan-African orogeny, after the formation of NW–SE-striking geological structures. Cape Hinode, which is considered an allochthonous unit in the Lützow-Holm Complex according to its surface geology, may have originated from the Rayner Complex and been displaced by right lateral strike-slip motions. These results provide new constraints on the tectonic evolution of Gondwana during the Pan-African orogeny.

► Newly obtained magnetic and gravity anomalies and bedrock topography from airborne surveys around the Lützow-Holm bay are presented.
► The boundaries of major complexes were delineated.
► The Lützow-Holm Complex is divided into four blocks based on the newly identified strike-slip faults.
► Plausible explanation on the allochthonus nature of Cape Hinode in the Lützow-Holm Complex is presented.