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Geology of tertiary volcanic rocks at Turred Point and Mersey Spit, King George Island (South Shetland Islands, West Antarctica)

Birkenmajer K.

Bulletin of the Polish Academy of Sciences. Earth Sciences

1998

Vol. 46, nr 3-4

223-234

Three Lower Tertiary volcanic complexes occur at the Turred Point-Mersey Spit promotory on King George Island (South Shetland Islands, West Antarctica. The first complexis represented by a pile of thick andesitic-basaltic lava flows attributed to the Mazurek Point Formation. The second complex consist of andesite breccias which from vertical cutting the lavas. The third complex is represented by vertical andesite plugs and dykes cutting the lavas and the vent braccias.

Geological structure of Barton Peninsula and Weaver Peninsula, Maxwell bay King George Island (south Shetland Islands, west Antarctica)

Birkenmajer K.

Bulletin of the Polish Academy of Sciences. Earth Sciences

1998

Vol. 46, nr 3-4

191-209

The rock-units of group rank occur at Barton and Weaver penisulas, King George Island (South Shetland Islands, West Antarctica): the Cardozo Cove GRoup (the oldest), the Wegger Peak Group, and the Admiralty Bay Group. The Cardozo Cove Group (CCG) represents a stratiform volcanic-volcaniclastic complex, predominantly andesite and basaltic-andesite lavas, alernating with tuffs and volcanic agglomerates. The rocks are strongly altered due to widespread propylitic and argillic alterations. Hovever, Plant-imprints are locally preservatived in terrestrial-type sediment interlayers. The CCG rocks were strongly folded, locally also low-angle thrust, before the WPG plutonic intrusion wich reset their radiametric ages. The Wegger Peak Group (WPG) is represented by two moderate-scale, and one small-scale, calc-alkaline plutonic intrusions of granodiorite to diorite to quartz-gabbro composition. The Noel Hill pluton (vertical dyke or sill) and the North Spit pluton (vertical sill) probably represent the same intrusive body, displaced by a left-lateral strike-slip fault running along Marian Cove. Radiometric dates plot in two groups: the older one, 63.4-60.6 Ma (Paleocene), probably represents true geological age of the pluton; the younger group, 53-42.1 Ma (Eocene), could be an effect of resetting of older radiometric ages by successive thermal events, mainly at 44 Ma (Middle Eocene). The admiralty Bay Group (ABG) is represented by uncommon hypabyssal intrusions (basalt and andesite): a moderate-size plug, several small dykes and sills. They all post-ddate the CCG and the WPG rocks,thus they are late Middle Eocene or younger in age.