Morphological Characteristics of Detrital Zircon Grains from Source to Sink (Western Australia)

Abstract:

Detrital zircon studies have become the tool of choice to address a wide range of geological questions including basin evolution, geodynamic setting, paleogeographic reconstructions, and determining source-sink relationships. However, grain destruction during transportation may be critical in understanding the detrital zircon record, yet it has not been explored in detail. In the magmatic crystallization environment zircon crystal shape is effectively a function of the magma chemistry and temperature.

We address to what extent the zircon population represents an artefact of preservation, or a meaningful record of the magmatic events within the source terrain. We use image analysis of previously SIMS U-Pb dated zircon crystals to quantify how zircon grain shapes relate to the chemical composition of magmatic and detrital zircon crystals. We achieve this by testing the correlation between shape factors and the uranium, thorium content, apparent alpha dose, and isotopic signature of individual zircons with statistical methods.

We focus our investigation on two different areas of Western Australia: (1) the Archean of the Yilgarn Craton and (2) the Proterozoic of the Musgrave Province, and their associated Proterozoic basin sediments:

(1) The Yilgarn craton represents a Neoarchean amalgamation of c. 3.8 Ga and 2.6 Ga granite-greenstone belts including a variety of gneisses, metasedimentary and metavolcanic rock formations, and granites. Along the northern edge of the craton a series of four Proterozoic basins, with variable tectonic and metamorphic overprinting overlay this basement.

(2) The West Musgrave Province consists of an east-west trending Meso- to Neoproterozoic belt dominated by granites and volcanics deformed by several major orogenic events between c. 1.35 Ga and 350 Ma. Based on age and Hf isotopic relationships the bedrock of the Musgrave Province is the source for the Neoproterozoic to Early Carboniferous Amadeus Basin to its north.

Using rigorous statistical techniques in a coherent approach across all samples, we show quantitatively whether the zircon shape distribution in sediments is similar to the magmatic population of the inferred basement. We propose that by taking into account grain shape distributions we have a better control on the representativeness of the detrital zircon record.