Zircon U-Pb Dating of the Irizar Granite in the Central Victoria Land, Antarctica: Insights into the Tectonic Evolution along the Ross Orogen

Abstract

It has been accepted that granitoids of the Irizar unit in the Central Victoria Land (Antarctica), as an important part of the Granite Harbour Intrusives, were formed in a post-collisional setting during the Ross orogeny along the margin of east Gondwana. However, the emplacement ages of the Irizar unit remain poorly constrained, making it difficult to form a more complete picture of the geodynamic evolution of the Ross orogen and its counterpart (Delamerian orogen) in southeast Australia. In this work, four syenogranite samples from the Irizar unit were chosen for SHRIMP zircon U-Pb dating, which yielded ages of 507.8–489.7 Ma. The new geochronological data indicate that the post-collisional extension in the Central Victoria Land had begun by ~508 Ma, much earlier than previously thought (i.e., 490–480 Ma). Integrated with U-Pb ages for Early Paleozoic granitoids from the literature, the Ross–Delamerian orogen shows that the post-collisional granitic magmatism initiated at ~515 Ma in the Central Transantarctic Mountains and northward systematically decreased to ~508 Ma in the Victoria Land, and then to ~487 Ma in southeast Australia. This can be explained well by the propagating northward transition from pre- and syn-collisional compression to post-collisional extension.