Precise U-Pb zircon dating at a scale of ＜5 micron by the CAMECA 1280 SIMS using a Gaussian illumination probe
会议名称：《中国科学院地质与地球物理研究所第11届（2011年度）学术年会》
会议日期：2012年
学科分类：070902[理学-地球化学] 0709[理学-地质学] 07[理学]
基 金：supported by the State Key Laboratory of Lithospheric Evolution IGG-CAS(Grants Z201003 and Z0908)
摘 要：Zircon is arguably the best,certainly the most commonly used mineral for U-Pb geochronology. Modern large-geometry secondary ion mass spectrometry(SIMS) has been routinely utilized for precise U-Pb zircon age determination at a lateral resolution of 10-30μ***,in situ U-Pb dating at a scale of ca.5μm scale or less for fine-grained zircons and/or zircon crystals with complex structural and chemical features is still a challenge to the geoscience *** we describe a method of precise U-Pb dating for zircons as young as the Jurassic age at a scale of up to5μm using the CAMECA ims-1280 *** mode primary O and O probes of ca 5.2μm and ca.4.5μm in diameter with beam intensities of～100 pA were obtained,respectively,by optimizing the primary *** ion optics was optimized to ensure a high Pb sensitivity in zircons,producing～21 cps/ppm/nA using O and～13 cps/ppm/nA using O(with oxygen flooding technique).As a demonstration of this method,three well-characterized zircon standards with a range of ages,AS3 (1099 Ma),Plesovice(377 Ma) and Qinghu(159.5 Ma),were *** demonstrate with these zircon standards that their ages could be determined with precision and accuracy of 1-2%using a spot5 *** O primary beam is preferred over the O beam for small-spot U-Pb zircon geochronology,because it has higher density and produces smaller craters on the target surface,with insignificant trade off in precision and accuracy of the final U-Pb *** U-poor minerals of younger ages,O might be preferred in order to generate sufficient Pb ions for measurement with minimal loss of spatial resolution.