Late Proterozoic juvenile arc metatonalite and adakitic intrusions in the S?rRondane Mountains, eastern Dronning Maud Land, Antarctica

摘要

This study is a detailed investigation of the petrology and geochronology of the Late Proterozoicmetatonalite in the S?r Rondane Mountains, eastern Dronning Maud Land, Antarctica. Metatonalite isdominant over roughly 100 × 20 km~2area in the southwestern end of the mountain range and is classifiedinto five lithologies: gneissose Bt-Hbl metatonalite, weak gneissose Hbl-Bt metatonalite, Hbl metagab-bro, Hbl-Bt tonalitic gneiss, and Bt metatonalite. The gneissose Bt-Hbl metatonalite is the main lithotypewidely distributed over this area, which is geochemically categorized as low-K tholeiitic granitoid. Petro-logical studies suggest that the tholeiitic magma was derived from low-K basalt melting at the crustaldepth, and the most plausible tectonic setting is a juvenile oceanic arc. The other four metaplutonic rocksare scattered as stocks or small intrusions in this area. They are geochemically regarded as calc-alkalineadakites related to oceanic slab melting. U-Pb SHRIMP zircon ages of the tholeiitic metatonalite areconcentrated at 998-995 Ma, whereas the calc-alkaline adakitic rocks are younger and divided betweenages 945-920 Ma and 772 Ma. We believe that the tholeiitic metatonalite was formed first as a juvenilearc component between 998 and 995 Ma, followed by adakitic magmatism and oceanic slab melting at945-920 Ma and 772 Ma. Magmatism during this stage is not recorded in the western to central Dron-ning Maud Land. Moreover, the exposure of an adakitic equivalent continues at the farther eastern sideof the S?r Rondane Mountains. This suggests that the tectonic framework of the S?r Rondane Mountains,eastern Dronning Maud Land, is different from the western to central Dronning Maud Land.