微區原位Nd同位素比值測試在武漢上譜分析科技有限責任公司利用激光剝蝕多接收杯電感耦合等離子體質譜（LA-MC-ICP-MS）完成。激光剝蝕系統為Geolas HD（Coherent，德國），MC-ICP-MS為Neptune Plus（Thermo Fisher Scientific，德國）。激光剝蝕系統使用氦氣作為載氣。少量的氮氣被加入到ICP以提高Nd同位素的測試信號（Xu et al. 2015）。分析采用單點模式，激光的束斑大小和剝蝕頻率根據樣品的Nd信號強度調節，一般為32-90 μm和4-10 Hz。激光能量密度固定在~8.0 J/cm2。分析過程配備了信號平滑裝置，可以提高信號穩定性和同位素比值測試精密度（Hu et al. 2015）。質譜儀Neptune Plus配備9個法拉第杯，可同時靜態接收142Nd, 143Nd, 144Nd, 145Nd, 146Nd, 147Sm, 148Nd和149Sm信號。143Nd/144Nd同位素儀器質量分餾校正通過指數法則校正，校正因子利用146Nd/144Nd = 0.7219估算獲得。144Sm對144Nd的干擾校正通過監控149Sm的信號，并選擇144Sm/149Sm = 0.2301。144Sm/149Sm的儀器質量分餾校正通過歸一化到無干擾的147Sm/149Sm，并選擇147Sm/149Sm = 1.08680。詳細的分析方法校正描述請參考（Xu et al. 2015）。全部分析數據采用專業同位素數據處理軟件“Iso-Compass”進行數據處理（Zhang et al., 2020）。
兩個天然磷灰石標樣，Durango和MAD作為未知樣品監控微區原位磷灰石Nd同位素校正方法的可靠性。Durango和MAD的化學組成和Nd同位素組成參見Xu et al.（2015）。
兩個天然榍石標樣，MKED1和SP-Ttn-01作為未知樣品監控微區原位榍石Nd同位素校正方法的可靠性。MKED1的化學組成和Nd同位素組成參見Spandler et al.(2016)。
一個天然獨居石標樣GBW44069和一個天然榍石標樣MKED1作為未知樣品監控微區原位獨居石Nd同位素校正方法的可靠性。GBW4409的化學組成和Nd同位素組成參見Xu et al.（2015）。
23.2 In-situ Nd isotope analysis by LA-MC-ICP-MS
In situ Nd isotope analysis was performed on a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Bremen, Germany) equipped with a Geolas HD excimer ArF laser ablation system (Coherent, Göttingen, Germany) at the Wuhan Sample Solution Analytical Technology Co., Ltd, Hubei, China. In the laser ablation system, helium was used as the carrier gas within the ablation cell and was merged with argon (makeup gas) after the ablation cell. Small amounts of nitrogen were added to the argon makeup gas flow for the improvement of sensitivity of Nd isotopes (Xu et al. 2015). The spot diameter ranged from 32 to 90 μm dependent on Nd signal intensity. The pulse frequency was from 4 to 10 Hz, but the laser fluence was kept constant at ~8 J/cm2. A new signal-smoothing device was used downstream from the sample cell to efficiently eliminate the short-term variation of the signal and remove the mercury from the background and sample aerosol particles (Hu et al. 2015). The Neptune Plus was equipped with nine Faraday cups fitted with 1011Ω resistors. Isotopes 142Nd, 143Nd, 144Nd, 145Nd, 146Nd, 147Sm, 148Nd and 149Sm were collected in Faraday cups using static mode. The mass discrimination factor for 143Nd/144Nd was determined using 146Nd/144Nd (0.7219) with the exponential law. The 149Sm signal was used to correct the remaining 144Sm interference on 144Nd, using the 144Sm/149Sm ratio of 0.2301. The mass fractionation of 147Sm/149Sm was corrected by the 147Sm/149Sm normalization, using the 147Sm/149Sm ratio of 1.08680 and exponential law. All data reduction for the MC-ICP-MS analysis of Nd isotope ratios was conducted using “Iso-Compass” software (Zhang et al. 2020).
Two natural apatite megacrysts, Durango and MAD, were used as the unknown samples to verify the accuracy of the calibration method for in situ Nd isotope analysis of apatites. The chemical and Nd isotopic compositions of Durango and MAD have been reported by Xu et al. (2015).
Two natural titanite megacrysts, MKED1 and SP-Ttn-01, were used as the unknown samples to verify the accuracy of the calibration method for in situ Nd isotope analysis of titanite. The chemical and Nd isotopic compositions of MKED1 have been reported by Spandler et al.(2016).
One natural monazite megacrysts GBW44069 and another natural titanite megacrysts MKED1 were used as the unknown samples to verify the accuracy of the calibration method for in situ Nd isotope analysis of monazite. The chemical and Nd isotopic compositions of GBW44069 have been reported by Xu et al. (2015).
Xu, L., Hu, Z.C, Zhang, W., Yang, L., Liu, Y.S., Gao, S., In situ Nd isotope analyses in geological materials with signal enhancement and non-linear mass dependent fractionation reduction using laser ablation MC-ICP-MS. Journal of Analytical Atomic Spectrometry, 2015, 30(1), 232-244.
Hu, Z.C., Zhang, W., Liu, Y.S., Gao, S., Li, M., Zong, K.Q., Chen, H.H., Hu, S.H., 2015. “Wave” signal-smoothing and mercury-removing device for laser ablation quadrupole and multiple collector ICPMS analysis: application to lead isotope analysis. Analytical Chemistry, 87(2), 1152–1157.
Carl Spandler,Johannes Hammerli. MKED1:A new titanite standard for in situ analysis of Sm-Nd isotopes and U-Pb geochronology[J].Chemical Geology,2016,425(1):110-126.
Zhang W., Hu Z.C., Liu Y.S. (2020). Iso-Compass: new freeware software for isotopic data reduction of LA-MC-ICP-MS. J. Anal. At. Spectrom., 2020, 35, 1087–1096.