锆石中表面结构检测方案(电镜部件)

SPARC SPARC application note Zircons delmc application noteZircons Zircon (ZrSiO4) is a ubiquitous mineral in the earth’s crust. Because the material ischemically inert and hard， it is very resilient to weathering processes and can persistfor a long time in a large variety of sedimentary， igneous， and metamorphic rocks.When zircon crystals are formed from a melt， conditions can vary over time whichaffects the zircon growth. Such changes in conditions lead to zonation in the zircon(zones of zircon which contain different amounts of trace elements， for instance).Similar to the growth rings in trees， these zones contain chronological informationabout the geological formation of the zircons. Typically the zonation is subtle and does not， for instance， lead to large densitydifferences， thus rendering it difficult to observe with regular scanning electronmicroscopy (SEM). Cathodoluminescence (CL) imaging， on the other hand， is highlysensitive to small concentration variations in trace elements such as rare-earth ions， asthey have a strong and spectrally distinct CL response [1]. Interestingly， zircons oftenhave high uranium and thorium content which can be used for radiometric dating CL can be used as a prescreening tool for high-resolution secondary-ion-mass spec-trometry (SIMS) to image the zonation pattern and identify regions of interest forisotope analysis. These can then be interrogated with the more expensive and time-consuming SIMS technique. Such a combined analysis has been used to date zirconsthat are over 4.3 billion years old， which is the oldest native crustal rock from earthever to be dated [21. In Figure 1 we show a secondary electron image (a) and a panchromatic CL imagecollected with a photomultiplier tube (PMT) in the SPARC CL system (b). In bothcases the zircon grains can clearly be distinguished from the background but the CLimage shows significantly more structure within the grains. In (c) we show another CLimage in which there is strong CL contrast within a single grain and the zonation isclearly visible. These results illustrate that the SPARC CL system provides anexcellent platform to quickly reveal zonation patterns in such minerals and that it canalso be used as an effective screening tool for advanced geological characterizationtechniques. Max (b) (c c 25 um Min Figure 1 (a) SEM image of some zircon grains. (b) Panchromatic PMT intensity image (grayscale) ofthe same area. (c) Close-up panchromaticPMT image ofa single zircon grain. These measurements were taken at 10 kV acceleration voltage and I nA current with a 100 us dwell time. CLimages took ~1.5 minutes to collect. Samples courtesy of Prof. Jens Jahren (University ofOslo). References 1Zircon，J.M. Hanchar and P.W.O Hoskin， Rev. Mineral. Geochem. 53 (2003) 2 S. A. Wilde et al.， Nature 409 (2001) 175-178. delncDELMIC BV|+()nfo@delmic.comwww.delmic.com These results illustrate that the SPARC CL system provides an excellent platform to quickly reveal zonation patterns in such minerals and that it can also be used as an effective screening tool for ad.