Cross-Orogen Granite Migration as an Indicator of Slab Rollback Along Eastern Gondwana

Abstract

Slab rollback during subduction plays a key role in controlling continental growth at convergent plate boundaries. The dynamics of currently subducting slabs can be precisely constrained using geophysical techniques. In contrast, ancient episodes of slab rollback can be difficult to constrain, yet are critical to unlocking the tectonic evolution of long-lived orogens such as the Phanerozoic Australian Tasmanides of eastern Gondwana. Recognition of ancient slab rollback relies on the identification of the progressive migration of magmatic arcs. Here, we investigate the timing and isotopic variation of ∼90 km of the trans-orogen migration of the Carboniferous Bathurst Batholith as a potential indicator of slab rollback. U-Pb-Hf isotopes, combined with a regional zircon Hf isotope data set, suggest that the eastward migration of the batholith over ∼18 Myr−1 , from 340.1 to 322.4 Ma, records a maximum slab steepening rate of ∼0.6-1.2° Myr−1 in a relatively stable trench setting. These results provide a magmatic record of Carboniferous slab rollback and establish a missing link between the long-lived Lachlan and New England orogens of the eastern Gondwanan Tasmanides.