Electron microprobe dating of lunar zirconolite

Journal of Analytical Science and Technology

Table 3 Blank-corrected U, Th, and Pb concentrations from 20 analyses and their recalculated values and ages with different percentages of interference on Pb Mα and U Mβ

Blank-corrected with 91500 zircon								6.8^a	2.5^b		7.5^b		12.5^b
U (ppm)	2σ	Th (ppm)	2σ	Pb (ppm)	2σ	Age (Ma)	2σ	Pb (ppm)	U (ppm)	Age (Ma)	U (ppm)	Age (Ma)	U (ppm)	Age (Ma)
5199	50	13,463	75	9628	71	4372	58	9081	5072	4282	4836	4353	4621	4420
3754	48	14,495	77	7999	68	4375	71	7618	3663	4298	3492	4363	3337	4424
3652	47	12,472	73	7053	66	4259	73	6717	3563	4183	3397	4250	3246	4313
3864	48	13,896	76	7921	68	4350	70	7544	3770	4274	3594	4340	3435	4403
3628	48	12,390	74	7029	66	4266	73	6694	3539	4190	3375	4257	3225	4320
3702	47	11,377	72	7125	66	4335	74	6785	3612	4263	3444	4331	3291	4396
5210	50	13,820	76	9647	72	4356	58	9188	5083	4287	4846	4357	4631	4424
5721	50	14,313	77	10,496	73	4374	54	9997	5582	4306	5322	4377	5086	4445
3265	46	11,757	72	6748	65	4367	79	6427	3185	4291	3037	4357	2902	4420
3413	47	12,069	73	6931	65	4343	77	6601	3330	4267	3175	4333	3034	4396
3285	47	12,223	73	6830	65	4352	79	6505	3205	4275	3056	4341	2920	4403
3630	47	12,174	73	7043	66	4284	73	6708	3541	4209	3377	4276	3227	4340
7668	53	14,978	78	12,765	78	4311	45	12,157	7481	4247	7133	4321	6816	4391
6377	51	14,004	76	11,023	74	4326	51	10,498	6221	4260	5932	4333	5668	4402
4321	48	10,720	71	7638	67	4299	67	7274	4215	4231	4019	4302	3841	4370
3963	48	10,265	70	7083	66	4295	72	6746	3867	4226	3687	4296	3523	4363
6491	51	14,370	77	11,347	75	4345	50	10,807	6333	4279	6038	4352	5770	4421
6530	51	14,629	77	11,541	75	4361	50	10,991	6370	4295	6074	4368	5804	4436
5676	50	14,135	76	10,296	73	4353	54	9806	5537	4285	5280	4356	5045	4423
3132	47	11,169	72	6133	64	4251	82	5841	3056	4176	2914	4242	2784	4305
				Weighted mean		4333	14			4262		4332		4398

^a Interference percentage on Pb. The uncorrected value is greater than the actual (corrected) value by the percentage shown. The total interference % on Pb in zirconolite is dominated by the interference of Y Mγ2,3 on Pb Mα (~ 6.8%). The interference of Th Mζ on Pb Mα is very small (~ 0.03%) with the correction factor estimated as a function of Th content (Jercinovic and Williams 2005)
^b Estimated interference percentages on U. The interference percentage of Th on U is estimated to be ~ 2.5% using the correction factor of 0.008 for Th (Jercinovic and Williams 2005). Since the K content influenced by K-feldspar was not measured in this study, the K interference percentages of 0, 5, and 10 on Pb are considered, in addition to the ~ 2.5% interference of Th on U