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PRISE Annual Report 2005

The Prise Group operates as a unique entity within the Research School, with the principal charter to provide external access to the Research School’s specialised equipment and expertise in the areas of geochronology, isotope geochemistry and major and trace element geochemistry. Members of the Prise Group seek support from a wide range of external funding sources; projects undertaken range from collaborative research projects supported by research grants through to fully commercial projects. The level of expertise is internationally recognised with high acclaim. Areas of current personal research activity undertaken by members of the Prise Group include:

The rock record from 2600 to 2000 million years ago preserves evidence for dramatically fluctuating greenhouse and icehouse climates at the same time as, and possibly caused by, change from an oxygen-deficient to an oxygen-rich atmosphere. Although the global changes are well-documented, correlation of their timing and duration between continents is poorly constrained. This project aims to redress that problem by producing a precise calibration of the global time scale for the oxidation of Earth's atmosphere between 2.6 and 2.0 billion years ago through the analysis of the rock records in Australia, Canada and South Africa. It will provide a much needed time framework within which long-term feedback between atmospheric composition and climate can be understood

Geochemical studies of the early solar system are being conducted to investigate physical conditions leading to assembly of the terrestrial planets and the chronology of events that shaped the Earth and Moon. Primitive objects from the solar nebula and samples from the Earth, Moon, Mars, and differentiated asteroids are being analysed. This research aims to(1) understand the astrophysical environment of the inner solar system, (2) establish high-resolution absolute timescales for early geological events including planetary differentiation and impact histories, and (3) identify the characteristics and provenance of small bodies present during the early stages of planetary development.

Recycling of oceanic lithosphere into the mantle at subduction zones is a fundamental part of the earth’s plate tectonics. Isotopic characteristics of many lavas indicate that this recycled material is present in upper mantle melting zones. This suggests that these lavas derive from partial melting of complex, mixed sources composed of ancient recycled oceanic crust with low melting temperatures, and normal peridotite with much higher melting temperatures. There is little understanding of how such heterogeneous material melts and the sorts of liquids it produces. This project is using high-pressure-temperature experiments and major, minor and trace element analysis of experimental run products to investigate the melting behaviour of mixed mantle sources.

The concept of a Snowball Earth has stimulated much discussion and ongoing research. A fundamental criterion is the absolute timing of the glaciogene events on a global scale. This project involves the study of stratigraphically well-constrained rocks in North America, Africa, Australia and South America with the principal aim being to place absolute age constraints on the glaciogene events and so enable one to draw comparisons and contrasts with other correlated horizons. Preliminary results from this and other studies show that some glaciogene events are globally coincident, whilst others are clearly outside the bounds of a single coeval, coincident Snowball Earth event.

Research Highlights from

Mark Fanning - Constraining depositional ages for Neoproterozoic siliciclastic sequences through detrital zircon ages: a ca.770 Ma maximum age for the lower Uinta Mountain Group

Richard Armstrong - Constraints on the Mesoarchaean crustal development of the central Kaapvaal Craton, South Africa

Marc Norman - Trace element distribution coefficients for pyroxenes, plagioclase, and olivine in evolved tholeiites from the 1955 eruption of Kilauea Volcano, Hawai`i, and petrogenesis of differentiated rift zone lavas

Greg Yaxley - The oxidation state of Fe in mantle garnets: implications for diamond stability during metasomatic events

Greg Yaxley - Detrital apatite geochemistry and its application in provenance studies