U-PB ISOTOPE GEOCHRONOLOGY OF ZIRCON - EVALUATION OF THE LASER PROBE-INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY TECHNIQUE

被引：270

作者：

HIRATA, T ^{[1
]}

NESBITT, RW ^{[1
]}

机构：

[1] UNIV SOUTHAMPTON,DEPT GEOL,SOUTHAMPTON SO17 1BJ,HANTS,ENGLAND

来源：

GEOCHIMICA ET COSMOCHIMICA ACTA | 1995年 / 59卷 / 12期

关键词：

D O I：

10.1016/0016-7037(95)00144-1

中图分类号：

P3 [地球物理学]; P59 [地球化学];

学科分类号：

0708 ; 070902 ;

摘要：

Using a laser ablation microprobe-inductively coupled plasma mass spectrometer( LP-ICPMS) we have determined U-238, Pb-207, Pb-206, and Pb-204 abundances of several zircon populations whose ages have previously been measured by other techniques (principally ion microprobe). Ages of the samples range from 360-2800 Ma. A frequency quadrupled Nd-YAG UV laser (266 nm) which produces pit sizes of 10-15 mu m was used to ablate the zircon samples. Prolonged measurements of the Pb-206/U-238 isotope ratio using ablation techniques show a serious fractionation effect because of nonconstant focusing of the laser. This ablation fractionation dramatically increases the Pb/U isotopic ratio because of the greater volatility of Pb. If the beam is constantly refocussed during ablation (active focusing), the effect of fractionation is minimised and the duration of the signal intensity increased. Pb-207/Pb-206 isotopic ratio measurements on zircons with ages greater than 2400 Ma previously measured by SHRIMP give an excellent agreement. Typical precision of the measurement for Pb-207/Pb-206 isotopic and Pb/U elemental ratios determined on single zircon grains is about 0.6-5% and 3-20%, respectively. In the case of Phanerozoic zircons (c. < 500 Ma), the LP-ICPMS allows the use of Pb-206/U-238 ratios and this provides more accurate data than the comparable Pb-207/Pb-206 system. The data presented here demonstrate clearly that the LP-ICPMS has a potential to become a significant and cost-effective tool for use in U-Pb zircon geochronology.

引用

页码：2491 / 2500

页数：10

共 23 条

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