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Geochemistry of Mesoproterozoic Hongshuizhuang Formation Shales in Northern North China: Implications for Provenance and Source Weathering
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摘要


     The Hongshuizhuang Formation shales from the northern part of North China are Mesoproterozoic organic-rich sediments which may carry important information at that time. Major and trace elements contents of the Hongshuizhuang Formation shales were analyzed in order to research the provenance and source weathering. The high ratios of Th/Sc, Al2O3/TiO2, La/Sc, La/Cr, La/Co, Th/Cr and Th/Co, the low value of Cr/Zr and TiO2/Zr, and Euan, Co/Y-Ti/Zr diagram and La-Th-Sc Ternary indicate that the provenance of the Hongshuizhuang Formation shales is mainly granodiorites from the upper crust. A1, Ca, Na and K contents of the studied samples indicate they have moderate Chemical Index of Alteration CIA. On the ternary plot of A1203-CaO 4-NazO-K20A-CN-K, the chemical weathering trend suggests that the composition of the Hongshuizhuang Formation shales was affected by the K- metasomatism which leads to underestimate the value of Chemical Index of Alteration CIA. The original CIA is higher than 90. The high original CIA, Chemical Index of Weathering CIW and Plagioclase Index of Alteration PIA illustrate that the provenance of the Hongshuizhuang Formation shales had experienced intense chemical weathering. Intense chemical weathering and trace element indicate the paleoclimate was warm and wet during the deposition of the Hongshuizhuang Formation, consistent with the high CO2 concentration in the atmosphere during the Mesoproterozoic and its place in Columbia supercontinent.

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