ROSS OROGENY MAGMATISM IN NORTHERN VICTORIA LAND, ANTARCTICA: INSIGHT INTO ALONG-STRIKE ARC VARIATION AND COMPARISON TO THE DETRITAL ZIRCON RECORD

The Wilson Terrane, the inboard-most terrane in Northern Victoria Land, Antarctica, consists of Neoproterozoic to Ordovician continental arc rocks of the paleo-Pacific Gondwana margin. These rocks are thought to be syn-tectonic mid-crustal granitoid to mafic plutons emplaced near the final stages of northward-younging, oblique subduction. Sparse existing bedrock crystallization ages suggest igneous activity between c. 545 to 481 Ma. Detrital zircons from the region suggest metamorphic and igneous activity between c. 626 to 490 Ma. Here, we present zircon U-Pb geochronology, Hf isotope, and trace element geochemistry, as well as whole rock major and trace element data from ~100 granitoids from NVL to further determine the extent of along-strike variation in the timing and nature of magmatism, as well as compare ages of exposed basement rocks to detrital zircons from overlying units. Our new age data indicate long-lived, dominantly peraluminous magmatism from c. 622 to 473 Ma, with evidence for several cyclic magmatic “flare-up” events separated by lulls. Hf isotope data indicate the rocks were sourced from an enriched region(s) of the lithospheric mantle throughout the history of the arc. Our data reveal an igneous crystalline basement for the Wilson Terrane younger than recorded by detrital zircon and concurrent to deformed zircon in the outboard terranes, further supporting the tectonic model placing the outboard terranes within the Gondwana realm prior to Ross contraction. This study provides support for multiple, short-lived subduction zones along the Antarctic sector of the Gondwana margin, similar in geometry but pre-dating the Delamerian-Lachlan system in SE Australia. Our data also reveal a step-like transition in magmatic pulses between NVL and the Delamerian in Australia. The forcing mechanism for the transition from a passive to an active subduction margin remains uncertain due to significant overlap of collisional tectonic events in Eastern Antarctica. However, the results can provide insight for prediction of end-convergence dynamics for modern active margins.