Magmatic history and evolution of continental lithosphere of the Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica

The Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica, are situated within the Pan-African suture zone, between West and East Gondwana, and the timing of collision event is regarded as the late Neoproterozoic to early Cambrian. In order to understand the tectonothermal history and evolution of the continental lithosphere, geochemical studies were conducted and zircon U–Pb SHRIMP dating was performed on intrusive rocks with basaltic compositions and associated metamorphic rocks. The metamorphosed tonalite complex exposed in the southwestern part of the mountains comprises tonalite associated with microgabbros, occurring as magmatic enclaves and later dikes that have intruded both the host and magmatic enclaves. Geochemically, the microgabbros are classified as low-Ti and high-Ti types, corresponding to the magmatic enclaves and dikes, respectively. Moreover, the geochemical features of the low-Ti microgabbro resemble those of an oceanic-arc tholeiite, whereas the high-Ti microgabbro has features of a back-arc basalt. The apparent zircon U–Pb ages show c. 990 Ma for the low-Ti microgabbro and c. 950 Ma for the high-Ti microgabbro. The high-grade metamorphic rocks situated in the northern part of tonalite complex were metamorphosed between 640 and 620 Ma, as constrained by zircon overgrowth rims of a migmatite leucosome (620 ± 2 Ma) and the previously reported age data. The timing of peak metamorphism corresponds to the early stage of the Pan-African suture event. Postdating the suturing event, unmetamorphosed minette dikes, dated 564 ± 2 Ma, intrude the tonalite complex and high-grade gneisses. On the basis of geochemical investigation, including Sr and Nd isotopic systematics, the microgabbros are considered to have originated from a depleted mantle source, whereas the minette magma is derived from an enriched mantle source. Consequently, the source mantles of the mafic magmas in the Sør Rondane Mountains have fundamentally changed from a depleted source in the early Neoproterozoic to a more enriched source in the late Neoproterozoic. Geochemical and isotopic evidence suggest that this compositional change of source mantle would reflect the interaction between the depleted mantle and the enriched crustal materials, such as subducted crustal rocks, caused by the Pan-African suture event.

► Proterozoic (990–950 Ma) microgabbros were derived from depleted sources. ► Pan-African (∼560 Ma) minettes having enriched-Nd isotopic signatures. ► The lithospheric mantle changed from a depleted source to a more enriched source. ► The evolution of the lithospheric mantle resulted from the continental collision.