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Extremely enrichment of 7Li in highly weathered saprolites developed on granite from Huizhou, southern China
Applied Geochemistry ( IF 3.1 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.apgeochem.2020.104825 Jun-Wen Zhang , Zhi-Qi Zhao , Xiao-Dong Li , Ya-Ni Yan , Yun-Chao Lang , Hu Ding , Li-Feng Cui , Jun-Lun Meng , Cong-Qiang Liu
Applied Geochemistry ( IF 3.1 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.apgeochem.2020.104825 Jun-Wen Zhang , Zhi-Qi Zhao , Xiao-Dong Li , Ya-Ni Yan , Yun-Chao Lang , Hu Ding , Li-Feng Cui , Jun-Lun Meng , Cong-Qiang Liu
Abstract Lithium isotope is potentially useful tracer of continental weathering. However, the factors affecting Li isotope composition in highly weathered saprolites are still largely unclear. In the present study, Li and Nd isotope compositions in saprolites developed on granite from Huizhou, southern China, were analyzed and Li isotope composition in quartz samples separated from the saprolites was determined. The Nd isotope composition of saprolites (eNd = −6.1 ± 0.4, 1σ) was almost identical to that of parent granite (eNd = −5.7), suggesting the eolian deposition in this profile is negligible. The δ7Li value in saprolites varied greatly from −7.7‰ to +14.0‰. Below a depth of 3 m, almost all saprolites were isotopically lighter than the parent granite (+1.0‰). However, above 3 m, δ7Li values were higher in saprolites (+2.2‰ to +14.0‰, average + 7.6‰) than in the parent granite and showed a significant increasing trend toward the surface. Moreover, the δ7Li value showed a negative correlation with the CIA value below 3 m, but a positive correlation above 3 m. Compared with the parent granite, quartz separates had a higher Li concentration (1.1–28.9 mg/kg, average 9.5 mg/kg) and δ7Li value (+12.1‰ to +13.9‰). As weathering progressed, the formation of secondary minerals (such as kaolinite) led to the incorporation of lighter 6Li, which may have contributed significantly to the low δ7Li value in saprolites below 3 m. However, this mechanism could not explain the relative enrichment of heavy 7Li in the upper layer saprolites. The relative enrichment of quartz may contribute significantly to the increase of δ7Li in saprolites. The direct evidence was that Li was abundant and distinctly isotopically heavier in quartz separates. Moreover, quartz content correlated positively with Li concentration (R2 = 0.90, p
更新日期：2021-02-01
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