Geology and geologic structure of the northern Ongul Islands and surroundings, East Antarctica

Abstract

The outline of geology and geologic structure of the northern Ongul Islands and surroundings of Lutzow-Holm Bay, East Antarctica is herein described. In this region is distributed the Ongul Group of the Lutzow-Holm Bay System. The Ongul Group is characterized by alternating layers of gneissic rocks of late Precambrian age. The crystalline rocks exposed in this region are classified as follows : (1) metabasite, (2) charnockitic rock, (3) hornblende gneiss, (4) garnet-biotite gneiss, (5) potassium feldspar porphyroblastic gneiss, (6) garnet gneiss, (7) garnet-bearing granitic gneiss and (8) pegmatite. Tectonically two principal deformational stages are discriminated in this region; the first deformational stage : inclined isoclinal folds with the axial trace trending north-south, the second deformational stage : close to open folds with the axial trace of an east-west trend. The third deformational stage which is distinguished in the Langhovde and Skarvsnes regions adjacent to this region is not so clearly recognized, but the conjugate sets of fractures which occurred during a later deformational stage are well developed throughout this region