Late Proterozoic juvenile arc metatonalite and adakitic intrusions in the Sør Rondane Mountains, eastern Dronning Maud Land, Antarctica

This study is a detailed investigation of the petrology and geochronology of the Late Proterozoic metatonalite in the Sør Rondane Mountains, eastern Dronning Maud Land, Antarctica. Metatonalite is dominant over roughly 100 × 20 km2 area in the southwestern end of the mountain range and is classified into five lithologies: gneissose Bt–Hbl metatonalite, weak gneissose Hbl–Bt metatonalite, Hbl metagabbro, Hbl–Bt tonalitic gneiss, and Bt metatonalite. The gneissose Bt–Hbl metatonalite is the main lithotype widely distributed over this area, which is geochemically categorized as low-K tholeiitic granitoid. Petrological studies suggest that the tholeiitic magma was derived from low-K basalt melting at the crustal depth, and the most plausible tectonic setting is a juvenile oceanic arc. The other four metaplutonic rocks are scattered as stocks or small intrusions in this area. They are geochemically regarded as calc-alkaline adakites related to oceanic slab melting. U–Pb SHRIMP zircon ages of the tholeiitic metatonalite are concentrated at 998–995 Ma, whereas the calc-alkaline adakitic rocks are younger and divided between ages 945–920 Ma and 772 Ma. We believe that the tholeiitic metatonalite was formed first as a juvenile arc component between 998 and 995 Ma, followed by adakitic magmatism and oceanic slab melting at 945–920 Ma and 772 Ma. Magmatism during this stage is not recorded in the western to central Dronning Maud Land. Moreover, the exposure of an adakitic equivalent continues at the farther eastern side of the Sør Rondane Mountains. This suggests that the tectonic framework of the Sør Rondane Mountains, eastern Dronning Maud Land, is different from the western to central Dronning Maud Land.

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► Finding of tholeiitic and calc-alkaline (adakitic) metatonalites association from Antarctica.
► Timing of tholeiitic plutonism constrained as 998–995 Ma from U–Pb zircon chronology.
► Younger calc-alkaline adakites intruded 945–920 Ma and 772 Ma.
► The most plausible tectonic setting for the magmatisms is a juvenile oceanic arc.
► Tectonic framework of Sør Rondane Mountains is different from the western to central Dronning Maud Land.