|Dandahra Creek Leucogranite|
Not all of the zircon crystals in rocks show the same age. In the case of the Dandahra Creek Leucogranite some seemingly having much older ages. These crystals are actually inherited from the parent rock. The stability of the zircons means that they have not fully melted in the magma chamber. Often a good way to determine if a zircon is older than the magma chamber is to look at the shape and determine whether there has been any melting of the edges of the crystal. However, sometimes it is very hard to tell because the zircon often builds itself up again with an old core and a new crystal face.
To overcome the problem of age zoning in zircon crystals an alternative method was developed measure the ratio of lead and uranium. A high accuracy ion beam is aimed at the different portions of crystal. The ion beam vaporises the elements in that tiny area. The vapour is then measured for the abundance of each element and then the ratio of elements can be calculated. This is called the Sensitive High Resolution Ion Micro Probe or SHRIMP.
SHRIMP was a method developed right here in Australia. It is regarded as one of the most reliable ways to analyse microscopic crystals to determine when and how they formed. The need for the special machine came from dating the Rocks that make up the oldest parts of Western Australia which are the oldest in the world. It has no become a recognised tool around the world (Ireland et al 2008). There are 20 SHRIMP analysers around the world with four built in the last couple of years in Japan, China and Poland. Like Wi-Fi, the Hills-Hoist and Pavlova it is another example of Australian scientific ingenuity.
*Chisholm, E.I., Blevin, P.L. and Simpson, C.J. 2014. New SHRIMP U–Pb zircon ages from the New England Orogen, New South Wales: July 2012–June 2014. Record 2014/52. Geoscience Australia
*Clarke, Peter J. & Myerscough, Peter J. 2006. Introduction to the Biology and Ecology of Gibraltar Range National Park and Adjacent areas: Patterns, Processes and Prospects. Proceedings of the Linnean Society of New South Wales
*New South Wales National Parks and Wildlife Service 2005. Gibraltar Range Group of National Parks (Incorporating Barool, Capoompeta, Gibraltar Range, Nymboida and Washpool National Parks and Nymboida and Washpool State Conservation Areas) Plan of Management. February 2005. ISBN 0 7313 6861 4
*Ireland, T.R., Clement, S., Compston, W., Foster, J. J., Holden, P., Jenkins, B., Lanc, P., Schram, N. & Williams, I. S. (2008), "Development of SHRIMP", Australian Journal of Earth Sciences V55 p937–954