Abstract:

Volcanic rocks in the South Shetland Islands belong to the basalt andesite decite association and have lower 87 Sr/ 86 Sr ratios, 0.703297-0.703507, and higher 143 Nd/ 144 Nd ratios, 0.512835 -0.513779, both being negative correlative. Also, in the εNd 87 Sr/ 86 Sr diagram their samples fall in the depleted mantle domain. All of these indicate that these volcanic rocks came from a depleted mantle. Their formation ages are mainly 96Ma, 91Ma, 78Ma, 60Ma and 35Ma. The time space distribution and petrochemical characteristics of volcanic rocks suggest that the South Shetland Islands have been in a geological environment of island arc. At the early stage the South Shetland Islands were connected with the Antarctic Peninsula. Owing to the subduction of the Drake plate, the islands were separated from the peninsula. Then with back arc spreading and rifting, the islands were further far away from the peninsula, bringing about new volcanism. There was a long quiet period of volcanism from 35Ma to 8-6 Ma. It is in this long period that continental ice sheets were gradually formed in Antarctica. Although relationships between volcanic activity and climatic change need further study, such a relationship has existed indeed: volcanic activity weakens or stops in a cold epoch but revives and increases in a warm epoch.