Structure and tectonics of the Marlborough and Rockhampton ultramafic massifs

This PhD project will focus on ultramafic rocks from the area of Marlborough and Rockhampton. The project aims to characterise ultramafic rocks and evaluate the hypothesis that they originated from a ‘lost ocean’.

Work will involve mapping ultramafic massifs and understanding field relations between serpentinites and other lithologies, such as peridotite, gabbro, plagiogranite, dolerite, and high-pressure metamorphic rocks. Samples from these lithologies will be used to constrain the nature of the ophiolitic material and its mantle sources. Samples will be studied using petrographic microscopy, XRD, SEM, Raman and Hylogger analyses for mineral recognition. Serpentinite mineralogy (e.g., antigorite, lizardite) will be used to characterise protolith lithologies and to help constrain the temperature and pressure conditions during serpentinisation and test tectonic models. To determine the protolith of the serpentinites, whole-rock major- and trace-element geochemistry including immobile elements such as rare-earth elements (REE), and high-field strength elements (HFSE). Relict primary mineral compositions (major- and trace-element analyses and mineral maps) in serpentinised ultramafic rocks (e.g., Cr-spinel, pyroxene, and olivine) will be used to obtain information on the tectonic setting of the mantle protoliths and potential metasomatic overprints.

To constrain the age and origin of the ophiolitic material, multiple approaches will be used. The age of this mantle material will be constrained by in situ Re-Os on base metal sulphides and/or whole-rock Re-Os and Sm-Nd geochronology. Crustal ophiolitic material will be constrained by dating plagiogranite, using U-Pb zircon and baddeleyite geochronology (LA-ICP-MS), complemented by zircon trace-element and Hf and O isotope analyses (SHRIMP and MC-ICP-MS). A further constraint on the timing of mafic magmatism will be obtained using Ar-Ar geochronology on hornblende.

The project will benefit from world-class laboratories at UQ SENV, including sample preparation laboratories, Ar-Ar lab, Radiogenic Isotope Facility (laser ablation ICP-MS and MC-ICP-MS), and the analytical facilities at the UQ’s Centre for Microscopy and Microanalysis (electron microprobe, XRD, SEM, and Raman).

The principal advisor, Prof Rosenbaum, has an outstanding record in research supervision and was nominated twice for the UQ’s Awards for Excellence in Research Higher Degree Supervision. He has supervised 17 PhD students (principal advisor = 11), 1 MPhil student, 5 coursework Masters, 16 Honours students, and 6 postdoctoral researchers.