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1 2011

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Pliocene age of the oldest basaltic rocks of Penguin Island (South Shetland Islands, northern Antarctic Peninsula)

Pańczyk M., Nawrocki J.

Geological Quarterly

2011

Vol. 55, No. 4

335-344

The Penguin Island volcano is located on the southern shelf of King George Island (South Shetland Islands, West Antarctica). Its activity is regarded as connected with the opening of the Bransfield Strait. Penguin Island is dominated by a 180 m high basaltic stratocone (Deacon Peak) with a 350 m wide crater containing a small basaltic plug inside and radial dykes, and it has a second principal vent – the Petrel Crater maar – that was formed during a phreatomagmatic eruption about 100 years ago. A low-potassium, calc-alkaline sequence of basaltic lava flows with intercalations of beach deposits (Marr Point Formation) forms the basement of the stratocone. The Marr Point Formation lava flows have never been dated before. Combined whole rock 40Ar-39Ar isotopic dating and magnetostratigraphy were applied for this purpose. We obtained an isotopic 40Ar-39Ar plateau age of 2.7 š0.2 Ma, and together with the palaeomagnetic data, middle Pliocene age (Piacenzian) is implied for the basaltic plateau of Penguin Island.