Magmatic dyke systems of the South Shetland Islands volcanic arc (West Antarctica): reflections of the geodynamic history

摘要: The Antarctic Peninsula forms part of a magmatic arc at least since Jurassic times. Magmatic dykes are essential elements such arcs and intrude along zones instability. In contrast to other hypabyssal intrusions the effusive products activity, do not only reflect geochemical characteristics their magma source but also tectonic parameters time emplacement. The South Shetland Islands form an archipelago located northern tip belong this arc. Areas up 100,000 m2 have been mapped several locations these islands, mainly on King George Livingston Island. A structural analysis and the host rocks was carried out, about 250 dykes were sampled for further studies. As deduced from field relationships, Island six different intrusive events could be distinguished, seven. This subdivision into is well reflected by data. Analysis data shows, that stress very similar throughout archipelago, moreover minor changes occurred during dyke emplacement. holds all investigated areas in Islands. The (ICP-MS) reveal, most calc-alkaline, arc-related suite, ranging basalts highly differentiated rhyolites. However, especially early stages activity respective areas, tholeiites occur. Isotopic (Sr, Nd, Pb) prove strong crustal component initial Hurd (Livingston Island). decreased with time, accompanied increase sedimentary input subduction zone. The high amount contamination probably due still unstretched continental crust. Besides crust underlying Islands, partial melts subducted sediments, fluids derived subducting plate depleted, heterogeneous mantle wedge contributed genesis. According Ar-Ar datings plagioclase separates K-Ar (WR) age determinations, intrusion restricted Paleocene Eocene. started around Cretaceous/Paleogene boundary Only Thanetian/Ypresian boundary, commenced NE Nelson Island, culminating Lutetian 47-45 Ma areas. Dyke then ceased latter continued until Priabonian. Combining information given datasets, interval covered obviously marks period geodynamic stability. includes stable geometry zone corresponding (subduction direction velocity) as sources. contribution sources (sediments, slab, mantle, crust) varied, themselves remained same. Very primitive, olivine tholeiitic Penguin by-product work yielded unexpectedly (Tortonian), thus questioning onset rifting Bransfield Strait Pliocene, believed so far.