Changing magmatic and tectonic styles along the paleo-Pacific margin of Gondwana and the onset of early Paleozoic magmatism in Antarctica

Basement rocks of the Transantarctic Mountains are believed to record a change in the paleo-Pacific margin of Gondwana from a passive to a tectonically active margin. Widespread emplacement of calc-alkaline batholiths (Granite Harbor intrusives) occurred during the active margin phase. We present new concordant zircon and titanite U-Pb ages for these magmatic rocks in southern Victoria Land and the Scott Glacier area. Most magmatic rocks previously associated with a pre-late Early Cambrian (>530 Ma) deformational event(s) (Beardmore orogeny) have yielded younger crystallization ages. The lack of definite are magmatism prior to similar to 530 Ma suggests that deformation may have been associated with a strike or oblique-slip regime, although shallow subduction without significant are magmatism cannot be ruled out. Local transpressional and transtensional domains may account for compressional deformation and rare alkaline and carbonatite magmatism during this early period. The oldest and most voluminous magmatic rocks were emplaced after similar to 530 Ma. This magmatism has been associated with active subduction, and suggests a fundamental change in the plate boundary at similar to 530 Ma. Ductile shearing of plutons and contractional deformation of supracrustal rocks after similar to 530 Ma (Ross orogeny) may have been due to transpressional tectonics in an oblique subduction setting and/or a collision. Compressional deformation associated with the Ross orogeny may have ceased by similar to 500 Ma along the southern Victoria Land-Scott Glacier segment of the Antarctic margin, as indicated by undeformed magmatic rocks of this age, although magmatic activity continued to at least similar to 485 Ma.