Wed 26th July @ noon, Rm 312.222

Abstract:

The giga-annum periodicity in global radiogenic Hf and Sr isotopic trends is investigated by integrating data from tectonics, geodynamics, and palaeomagnetism, in order to build a holistic geodynamic model linking modes of mantle convection to plate tectonic motions over the last 2,500 Myr. The gigacycle reflects an alternating dominance between degree-2 and degree-1 mantle convective flow, manifest as the presence and absence of a hemispheric subduction girdle, respectively. The girdle is currently represented by the circum-Pacific subduction system and is geologically recorded by Phanerozoic circum-Pacific accretionary orogens. Degree-1 convection resulted in the amalgamation of Columbia ca. 2,000 Myr ago and Gondwana ca. 550 Myr ago accompanied by peaks in crustal reworking (-εHf), whereas degree-2 convection produced Nuna ca. 1,600 Myr ago and Pangaea 200 Myr ago accompanied by peaks in mantle input (+εHf). The change from degree-2 to degree-1 coincided with Rodinia amalgamation ca. 1,100 Myr ago, when the circum-Nuna subduction girdle collapsed. The gigacycles are rhymthic oscillations of mantle circulation patterns that control plate motion trajectories and contrasting styles of supercontinent amalgamation.

Short bio:

Professor WJ Collins began his work on A-type granites at ANU with Bruce Chappell, before moving to La Trobe University for a PhD on Archean granites with Prof Allan White. A post-doc on high-grade Proterozoic terranes in central Australia ensued with Prof. Ron Vernon at Macquarie  University before moving to the University of Newcastle as a lecturer. He moved to James Cook University as a Professor before returning to Newcastle as Director of the NSW Institute for Frontiers Geoscience. He became a Curtin Professorial Fellow last year.