Environments Past and Present
We look at the changes in Earth’s ocean-climate system recorded in inorganic and biological archives, and in the modern environment. We use geochemical proxies in foraminifera, speleothems and corals as paleoenvironmental archives, Antarctic ice core records, ferromanganese nodules and crusts as archives of ocean chemistry through time, and trace heavy metals in soils and plants.
Current projects investigate the dynamic changes that take place in the Earth's crust as a result of tectonic plate interactions.
We investigate what the rock record tells us about changing conditions as well as the processes that operate in the Earth's crust during events such as mountain building. Topics include interpreting metamorphic pressure-temperature-time (P-T-t) histories, and investigating the causes and potential effects of metamorphic fluid generation.
Methods used include microscope work and compositional studies of minerals and mineral assemblages, along with geochronology studies and forward modeling methods such as construction of P-T pseudosections.
An ongoing project is the examination of the metamorphic evolution of the Alpine Schist in the Southern Alps of New Zealand. The continuing oblique collision of the Pacific Plate against the Australia Plate at the Alpine Fault is forming the Southern Alps along the south eastern side of the Alpine Fault and bringing mid crustal rocks to the surface.
Another project looks at amphibolite-facies metamorphism and gold mineralisation of ancient mafic rocks at the Plutonic Mine, Western Australia.
Previous work has included studies of Proterozoic high temperature, low pressure metamorphic rocks in central Australia and Archaean high temperature, medium pressure metamorphic rocks in Canada.
Low temperature thermochronology: Fission-track analysis, (U-Th-Sm)/He analysis with applications in tectonics, structural geology, basin analysis and landscape evolution.
Current projects include:
- landscape evolution of North Island, New Zealand
- timing of the re-routing of the Yangtze River – basin studies through to Eocene time U/Pb zircon ages, heavy mineral analysis, FT analysis from the Yangtze River
- source to sink landscape and tectonic evolution in Sri Lanka related to Gondwana break-up
- thermo-tectonic history of various regions of the Himalayas
- Evolution of the Kohistan Arc, Pakistan
- Synthesis of world apatite fission track data (with Frederic Herman, ETH Zurich)
Our volcanology research centres around identifying and quantifying the processes involved in crustal magmatism, explosive volcanism and the impacts and aftermaths of explosive eruptions.
This work embraces a wide range of igneous processes concerned with the generation, storage and eruption of magmas (molten rock), together with the ways in which volcanoes erupt and pyroclastic rocks are generated and eroded.
We mainly use interrelated case studies which involve considerable amounts of fieldwork.
An ongoing multidisciplinary study of the eruptive history and structure of the Taupo Volcanic Zone (TVZ). Both surface and subsurface mapping and dating techniques are used to better establish the dynamics of the most frequently active and productive Quaternary silicic system on Earth.
Other research projects include:
- Using multidisciplinary techniques to understand the structure, eruptive frequency and hazards of volcanoes, particularly those that are large and erupt silicic magmas.
- Understanding when, how and why volcanoes erupt. We study historic eruptions such as Tarawera in 1886, Novarupta in 1912 and Raoul Island in 2006, as well as prehistoric eruptions such as Bishop, Taupo, Oruanui and Huckleberry Ridge. The events enable us to calibrate methods of determining eruption durations, document how eruptions begin, evolve and terminate, and explore what intrinsic or external factors control the eruptive styles and hazards.
- Quantifying the physics of processes that operate during explosive eruptions, as magma vesiculates and fragments emerge from the vent, forming a high plume. We are working towards quantifying the processes involved and the deposits generated where magma:water interactions occurs. Work involves reconstructing pyroclastic deposition processes, focussing on fundamental physical controls on the nature and genesis of pyroclastic deposits in general, and the chronology, 3D anatomy and emplacement history of ignimbrites in particular.
- Understanding the physics of volcaniclastic sedimentary processes. This work investigates the timing, processes and products of catastrophic flooding and sedimentation that follows large pyroclastic eruptions, including the curious transport properties of pumice.
Supervolcanoes and the tephra record, subaerial and submarine felsic eruptives in the Kermadec Arc, and microanalytical investigations of intermediate magmas in arc settings.
The supervolcanoes project seeks to infer the processes involved in generation and storage of magmas, principally rhyolites at Taupo (New Zealand), Long Valley (California) and Yellowstone. We use detailed field, geochemical and isotopic studies to look at the physical volcanology and eruption dynamics of the eruption products and the chemical and physical natures of the pre-eruptive magma bodies.
Investigations into arc magmatism, both onshore and offshore New Zealand, are carried out collaboratively with colleagues at NIWA and GNS Science. We combine mapping, petrographic and geochemical techniques to investigate the origins and growth of volcanoes such as Tauhara Volcano, Mt Ruapehu, and the seamounts of the southern Kermadec arc, through to the recycling of materials at subduction zones into the mantle, the overlying crust, and into the oceans and atmosphere.
Geothermal Geology and Geochemistry
We take a geological approach to studies of geothermal topics.
This research is carried out collaboratively with colleagues at GNS Science and the Universities of Auckland and Canterbury, and supported by grants from the New Zealand Foundation for Research, Science and Technology.
Modelling for Geothermal Exploration
We are building comprehensive models for the overall history of the central Taupo Volcanic Zone (TVZ) that will guide the drilling programmes and exploration strategies for New Zealand’s geothermal industry.
This is being accomplished through field mapping projects to establish geological histories and tectonic patterns from the surface geology, coupled with examination of sub-surface material from past and ongoing drilling programmes. Most of the rock units encountered at depth in geothermal drillholes have never been correlated or dated, yet understanding the histories of eruption, faulting and subsidence in the TVZ are critical to guiding exploration for future resources and management of existing resources.
Dating Eruption Products
We use an ion probe to date the products of past silicic eruptions in hydrothermally altered drillhole material, by U-Pb dating of zircon crystals. This work is providing first-order age constraints on major stratigraphic units encountered in geothermal fields, and allowing us to measure natural rates of subsidence in the rifted-arc setting. Fault offsets can be measured and the rates inferred to provide new insights into the development of faults as pathways or barriers to fluid flow in the shallow crust.
Work in high-temperature aqueous geochemistry and metal speciation.
Development of Non-traditional Stable Isotope Systems
Magnesium, platinum and gallium stable isotopes, and their application to topics in cosmochemistry and igneous, geothermal and environmental geochemistry.
Recent projects include measuring the magnesium and platinum stable isotopic composition of Earth's mantle and chondrite meteorites.