Polskie badania geologiczne na Wyspie Króla Jerzego (Antarktyka Zachodnia) w sezonie 1985-1986

Abstract

POLISH GEOLOGICAL INVESTIGATIONS ON THE KING GEORGE ISLAND, WEST ANTARCTICA IN THE AUSTRAL SUMMER 1985-1986 Summary Field work has been carried . out on Barton Peninsula and at Low Head (King George Island, West Antarctica), (Figs 1, 3, 6). At Barton Peninsula a calc-alkaline, volcanic-arc, stratified sequence, pierced by three intrusions, is divided by subhorizontal decollements (Fig. 4) into three tectonic units. The middle unit, which consists mostly of detrital rocks, is tightly folded, in contrast to the upper unit, which contains thick lava flows and is deformed only by open f olds. Both units are folded around a NW-SE-oriented axis (parallel to the extension of the Noel Hill intrusion) where the rocks conform with the shapes of the latter. A recently found fossil flora, considered to be Eocene-Oligocene in age (14), occurs near the base of the upper unit. The flora is however older than the 60 Ma K-Ar date obtained from the Noel Hill intrusion (10), which post-date the plant-bearing strata. Pillow lavas (Fig. 7) have been found in breccias underlying glacio-marine deposits of the Polonez Cove Formation (Fig. 5) between Low Head and Chopin Dyke (Fig. 6). These breccias, here interpreted as hyaloclastites, were formed contemporaneously with deposition of the lower part of the Polonez Cove Formation. Numerous neptunian dykes occur in deposits of the Low Head Member (see Fig. 5) as well as in the uppermost part of the breccias which underlie them. The dykes in the breccias fill an irregular net of thermal cracks, while in the deposits of the Lowe Head Member they occur in two sets of tectonic tension gashes. One of the sets is older than the Oberek Cliff Member (see Fig. 5), while the age of the second is not known.