Abstract This study presents high precision Zn stable isotope analyses for lower crustal rocks (9 granulites from Archean terrains and 30 lower crustal xenoliths) from the north margin of the North China Craton (NCC) to understand the behavior of Zn isotopes during deep crustal processes and the Zn isotopic composition of the lower continental crust (LCC). The lower crustal xenoliths range in composition from mafic to felsic with MgO contents of between 0.4 to 20.2 wt.%. The δ66Zn (the permil deviation of the 66Zn/64Zn ratio from the JMC-Lyon standard) values of lower crustal xenoliths range from −0.17‰ to 0.38‰. The lack of clear correlation of δ66Zn with geochemical indicators (e.g., Al2O3, Cr, Ba/La, 87Sr/86Sr and 143Nd/144Nd) indicates that assimilation of Precambrian lower crust, fluid metasomatism, and accumulation of pyroxene and plagioclase had a limited effect on Zn isotopic compositions of these lower crustal xenoliths. The δ66Zn values (0.18‰ to 0.34‰) of garnet-bearing mafic granulites decrease with increasing FeO(T) and V contents, which are likely results of the accumulation of Fe-Ti oxides. The average δ66Zn of the lower continental crust is estimated to be 0.29 ± 0.02‰ (95% SE) using lower crustal xenoliths from the Neogene Hannuoba basalts. This δ66Zn value is similar to the estimated value (0.28 ± 0.04‰, 95% SE) obtained from the granulites from Archean terrains, suggesting that there is no significant difference in the Zn isotopic composition between the Archean and present-day lower continental crust. Combining the δ66Zn data of the lower crustal xenoliths and granulite terrains and different weighting methods, the Zn isotopic composition of the lower continental crust is estimated to be 0.28 ± 0.04‰ (95% SE).

中文翻译：

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从下地壳捕虏体和麻粒岩地形估计下大陆地壳的锌同位素组成

摘要 本研究对华北克拉通 (NCC) 北缘的下地壳岩石（9 个来自太古代地形的麻粒岩和 30 个下地壳捕虏体）进行了高精度 Zn 稳定同位素分析，以了解深部地壳过程中 Zn 同位素的行为和下大陆地壳 (LCC) 的 Zn 同位素组成。下地壳捕虏体的组成范围从镁铁质到长英质，MgO 含量在 0.4 至 20.2 重量％之间。下地壳捕虏体的δ66Zn（66Zn/64Zn 比值与JMC-Lyon 标准的千分之一偏差）值范围从-0.17‰ 到0.38‰。δ66Zn 与地球化学指标（如 Al2O3、Cr、Ba/La、87Sr/86Sr 和 143Nd/144Nd）缺乏明确的相关性，表明前寒武纪下地壳同化、流体交代、辉石和斜长石的积累对这些下地壳捕虏体的锌同位素组成影响有限。含石榴石的镁铁质麻粒岩的δ66Zn值（0.18‰至0.34‰）随着FeO（T）和V含量的增加而降低，这可能是Fe-Ti氧化物积累的结果。使用来自新近系汉诺巴玄武岩的下地壳捕虏体估计下陆地壳的平均δ66Zn为0.29±0.02‰（95% SE）。该δ66Zn值与太古代地壳麻粒岩的估计值(0.28±0.04‰, 95% SE)相似，表明太古代与现今下陆壳的Zn同位素组成没有显着差异。结合下地壳捕虏体和麻粒岩地形的δ66Zn数据和不同的加权方法，