Geochemical features of dike rocks of the Argentine islands and the near area of the antarctic peninsula (Western Antarctica)

Abstract

The block of the Antarctic Peninsula is part of a magmatic arc formed along the southwestern part of the paleo-Pacific margin of the Gondwana supercontinent. Currently, subduction processes continue only in its northwestern part — in the region of the South Shetland islands, and to the southwest of it — there is a passive segment of the continental margin, within which the Argentine islands are located. Here, subduction was completed in the late Miocene-Early Pliocene. In the geological structure of the Argentine islands archipelago, the rocks of the Upper Jurassic volcanic group (AP Volcanic Group) and intrusive batholiths of the batholiths (AP batholiths) are distinguished. In them, there are numerous dikes of basic, medium and acidic compositions. The activation of dyke magmatism on the passive margin of the Antarctic Peninsula was probably connected with subduction processes in its northwestern part.

The age sequence of dike formation in the rocks of the Antarctic Peninsula (AP) volcanic Group and intrusions of the gabbroids and granitoids of the Andean complex in the Argentine Islands and the near area of the Antarctic Peninsula is determined. The early dikes of the dacites in the volcanogenic stratum of the AP volcanic Group and the gabbrodiabases in the gabbroids of the Andean complex have a submeridional and northwestern strike. After the introduction of the granitoids of the Andean complex, dikes predominantly of the sublatitudinal and northeasterly strike are formed. The early dikes in the gabbroids of the Andean complex are Fe-Ti cumulates, and in granodiorite intrusions they are represented by aplites, probably formed from the residual magma of these intrusions. Later dikes were formed, probably due to the melting of the metasomatized mantle source at moderate depths under the influence of plumes. To their primitive (initial) melts, the composition of high-magnesian dike rocks is probably close. Products of deep mantle (plume) sources in the sample of selected samples were not detected. The dike rocks of this region according to their geochemical characteristics correspond to the mature island-arc formations of the calc-alkaline series.