Abstract:

The isotopic age of the volcanic rocks of the Mount Bowles Formation (MBF) outcropped on the eastern part of Livingston Island, South Shetland Islands, Antarctica have been remeasured by 40 Ar/ 39 Ar and laser microarea isochron age dating techniques. The results indicate that the isochron ages of 45D andesitic lava and 262 basaltic andesite are (105.62±2.11) Ma and (111.48±2.23)Ma respectively. The two good fit isochron lines give the 40 Ar/ 36 Ar initial ratio of 295.3 and 294.6, which are almost the same as the ratio of atmospheric argon (Neir value=295.5). That images no excess argon in the rocks and the isochron age being the real forming age. The 40 Ar/ 39 Ar plateau age of A9352 aplite is (96.7±1.6) Ma and the calculated isochron age is 96.6Ma, which suggests that the aplite occurred after lava eruption. These new ages further verify that the MBF volcanic rocks were formed during Cretaceous. Therefore, Cretaceous volcanic activity should have created a great impression on the whole Livingston Island and the MBF volcanic rocks, which had been covered by younger overburden, were influenced by the thermal event of Tertiary intrusives.