Pervasive Neoarchean melting of subducted sediments generating sanukitoid and associated magmatism in the North China Craton, with implications for the operation of plate tectonics

Measurements of U-Pb isotopes were carried out by an inductively coupled plasma-mass spectrometer (ICP-MS) coupled with a NewWave 193UC excimer laser ablation system at the China University of Geosciences, Beijing (CUGB). Detailed procedures were described by Zhang et al. (2019). Data off-line analysis was conducted following Ludwig (2003), Andersen (2002), and Liu et al. (2010).

In situ zircon Hf isotopes were collected using a Neptune plus multicollector (MC)-ICP-MS system equipped with a NewWave 193UC excimer laser ablation system at CUGB. Instrumental conditions and analytical procedures were described by Wu et al. (2006). During these analyses, the 176Hf/177Hf ratio of standard zircon Plešovice was 0.282481 ± 22 (2σ), which is consistent within error with the recommended value in Sláma et al. (2008).

Major element oxides were determined with an X-ray fluorescence spectrometer at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS). Analytical accuracies are better than 1%. Trace elements were determined by a high-resolution ICP-MS (Element-XR) at CUGB. Based on the USGS standards GPS-2 and BHVO-2, the analytical accuracy of most trace elements is better than 5%.

Samples for the whole-rock Sr-Nd isotope analysis were performed using a Neptune Plus MC-ICP-MS at CUGB, following the analytical procedures described by those of Li et al. (2022). Measured 87Sr/86Sr and 143Nd/144Nd ratios were normalized to 86Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219, respectively, in exponential law. The measured average 87Sr/86Sr ratio for the SRM 987 standard and 143Nd/144Nd ratio for the Alfa Nd standard during the analytical process were 0.710246 ± 14 (2SD, n=15) and 0.512420 ± 14 (2SD, n=15), respectively. Measured values for the rock standard BHVO-2 were 87Sr/86Sr = 0.703473 ± 15 and 143Nd/144Nd = 0.512990 ± 9, respectively, both of which are consistent with the recommended ratios (http://georem.mpch-mainz.gwdg.de).

Zinc (Zn) isotopes were measured with a Neptune Plus MC-ICP-MS at CGUB, following the detailed analytical methodology described by Liu et al. (2016). The instrumental mass fractionation effects were calibrated using the sample-standard bracketing method. About 2 V signals for 66Zn were collected for a 200 ppb Zn solution using high-sensitivity (X) cones in low-resolution mode. All samples were analyzed over three blocks for 40 cycles with ~8 s integration. The measured Zn isotope ratios are presented in δ-notation form in per mil relative to JMC 3-0749L:

δ66, 68Zn (‰) = ((δ66, 68Zn/δ64Zn) sample / (δ66, 68Zn/δ64Zn) JMC 3-0749L-1) *1000

Measured values for the GSP-2 and BHVO-2 Zn standards were δ66Zn GSP-2 = 1.02 ± 0.01 ‰ (n = 9) and δ66Zn BHVO-2 = 0.31 ± 0.03 ‰ (n = 12), respectively, both of which are consistent with previously reported values within uncertainty (Liu et al., 2016; Wang et al., 2017b; Sossi et al., 2018; Chen et al., 2021).